Berkelium

<h2 id="characteristics">Characteristics</h2>
<h3>Physical</h3>

Berkelium is a soft, silvery-white, radioactive <a href="/facts/Actinide/kHC4lxJV">actinide</a> metal. In the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>, it is located to the right of the actinide <a href="/facts/Curium/LMyWXg8l">curium</a>, to the left of the actinide <a href="/facts/Californium/AJVjoVut">californium</a> and below the lanthanide <a href="/facts/Terbium/ICF3PMED">terbium</a> with which it shares many similarities in physical and chemical properties. Its density of 14.78 g/cm3 lies between those of curium (13.52 g/cm3) and californium (15.1 g/cm3), as does its melting point of 986 °C, below that of curium (1340 °C) but higher than that of californium (900 °C).<a class="footnote-ref" id="fnref:1" href="#fn:1">1</a> Berkelium is relatively soft and has one of the lowest <a href="/facts/Bulk_modulus/yCRFQonn">bulk moduli</a> among the actinides, at about 20 <a href="/facts/Pascal_(unit)/Am1To2Qm">GPa</a> (2×1010 Pa).<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a>
Berkelium(III) ions shows two sharp <a href="/facts/Fluorescence/qsJVT2qP">fluorescence</a> peaks at 652 <a href="/facts/Nanometre/a98sjHyu">nanometers</a> (red light) and 742 nanometers (deep red – <a href="/facts/Infrared/44XdJNcc">near-infrared</a>) due to internal transitions at the <a href="/facts/Electron_configuration/TQjRr22P">f-electron shell</a>. The relative intensity of these peaks depends on the excitation power and temperature of the sample. This emission can be observed, for example, after dispersing berkelium ions in a silicate glass, by melting the glass in presence of berkelium oxide or halide.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a><a class="footnote-ref" id="fnref:4" href="#fn:4">4</a>
Between 70 K and room temperature, berkelium behaves as a <a href="/facts/Curie%E2%80%93Weiss_law/w4h6zNqb">Curie–Weiss</a> paramagnetic material with an effective magnetic moment of 9.69 <a href="/facts/Bohr_magneton/sK2YxXAk">Bohr magnetons</a> (μB) and a <a href="/facts/Curie_temperature/ygotSuMg">Curie temperature</a> of 101 K. This magnetic moment is almost equal to the theoretical value of 9.72 μB calculated within the simple atomic <a href="/facts/Angular_momentum_coupling/xsfw1hBG">L-S coupling model</a>. Upon cooling to about 34 K, berkelium undergoes a transition to an <a href="/facts/Antiferromagnetism/aQ124Kh7">antiferromagnetic</a> state.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> The <a href="/facts/Enthalpy_change_of_solution/wuVVEDDs">enthalpy of dissolution</a> in <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric acid</a> at standard conditions is −600 kJ/mol, from which the <a href="/facts/Standard_enthalpy_of_formation/UFgGC7UQ">standard enthalpy of formation</a> (ΔfH°) of aqueous Bk3+ ions is obtained as −601 kJ/mol. The <a href="/facts/Standard_electrode_potential/YQUhbI6K">standard electrode potential</a> Bk3+/Bk is −2.01 V.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The <a href="/facts/Ionization_energy/lezUajfA">ionization potential</a> of a neutral berkelium atom is 6.23 eV.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>

<h3>Allotropes</h3>
At ambient conditions, berkelium assumes its most stable α form which has a <a href="/facts/Hexagonal_crystal_family/sSSok8wo">hexagonal</a> symmetry, <a href="/facts/Space_group/2XQx0J7M">space group</a> P63/mmc, lattice parameters of 341 <a href="/facts/Picometre/Cb54mVBX">pm</a> and 1107 pm. The crystal has a double-<a href="/facts/Close-packing_of_equal_spheres/AqL1HUxe">hexagonal close packing</a> structure with the layer sequence ABAC and so is <a href="/facts/Isostructural/xWlgsQ95">isotypic</a> (having a similar structure) with α-lanthanum and α-forms of actinides beyond curium.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> This crystal structure changes with pressure and temperature. When compressed at room temperature to 7 GPa, α-berkelium transforms to the β modification, which has a <a href="/facts/Cubic_crystal_system/92Co7BKM">face-centered cubic</a> (fcc) symmetry and space group Fm3m. This transition occurs without change in volume, but the <a href="/facts/Enthalpy/bBou8lCE">enthalpy</a> increases by 3.66 kJ/mol.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> Upon further compression to 25 GPa, berkelium transforms to an <a href="/facts/Orthorhombic_crystal_system/3zo4F8P0">orthorhombic</a> γ-berkelium structure similar to that of α-uranium. This transition is accompanied by a 12% volume decrease and delocalization of the electrons at the <a href="/facts/Electron_shell/QxI30eh9">5f electron shell</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> No further phase transitions are observed up to 57 GPa.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
Upon heating, α-berkelium transforms into another phase with an fcc lattice (but slightly different from β-berkelium), space group Fm3m and the lattice constant of 500 pm; this fcc structure is equivalent to the closest packing with the sequence ABC. This phase is metastable and will gradually revert to the original α-berkelium phase at <a href="/facts/Room_temperature/YHwUIUTE">room temperature</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> The temperature of the phase transition is believed to be quite close to the melting point.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a><a class="footnote-ref" id="fnref:15" href="#fn:15">15</a><a class="footnote-ref" id="fnref:16" href="#fn:16">16</a>

<h3>Chemical</h3>
Like all <a href="/facts/Actinide/kHC4lxJV">actinides</a>, berkelium dissolves in various aqueous inorganic acids, liberating gaseous <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> and converting into the berkelium(III) state. This <a href="/facts/Valence_(chemistry)/ck7cHByj">trivalent</a> <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> (+3) is the most stable, especially in aqueous solutions,<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a><a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> but <a href="/facts/Valence_(chemistry)/ck7cHByj">tetravalent</a> (+4),<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a> <a href="/facts/Valence_(chemistry)/ck7cHByj">pentavalent</a> (+5),[22] and possibly <a href="/facts/Valence_(chemistry)/ck7cHByj">divalent</a> (+2) berkelium compounds are also known. The existence of divalent berkelium salts is uncertain and has only been reported in mixed <a href="/facts/Lanthanum(III)_chloride/IrfXFC7Y">lanthanum(III) chloride</a>-<a href="/facts/Strontium_chloride/ekDUxqhm">strontium chloride</a> melts.<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a><a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> A similar behavior is observed for the lanthanide analogue of berkelium, <a href="/facts/Terbium/ICF3PMED">terbium</a>.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> Aqueous solutions of Bk3+ ions are green in most acids. The color of Bk4+ ions is yellow in <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric acid</a> and orange-yellow in <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a><a class="footnote-ref" id="fnref:24" href="#fn:24">24</a><a class="footnote-ref" id="fnref:25" href="#fn:25">25</a> Berkelium does not react rapidly with <a href="/facts/Oxygen/acyn6o8r">oxygen</a> at room temperature, possibly due to the formation of a protective oxide layer surface. However, it reacts with molten metals, <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, <a href="/facts/Halogen/YeFgWHeA">halogens</a>, <a href="/facts/Chalcogen/nXLGmnqL">chalcogens</a> and <a href="/facts/Pnictogen/jX4hvCkK">pnictogens</a> to form various binary compounds.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a>
In 2025 an <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic</a> compound containing berkelium was synthesized from 0.3 mg of berkelium and named berkelocene.<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a>

<h3>Isotopes</h3>
Main article: <a href="/facts/Isotopes_of_berkelium/RnvnlKK4">Isotopes of berkelium</a>
Nineteen isotopes and six <a href="/facts/Nuclear_isomer/L8DHcqnk">nuclear isomers</a> (excited states of an isotope) of berkelium have been characterized, with mass numbers ranging from 233 to 253 (except 235 and 237).<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a> All of them are radioactive. The longest <a href="/facts/Half-life/kGVH8BAB">half-lives</a> are observed for 247Bk (1,380 years), 248Bk (over 300 years), and 249Bk (330 days); the half-lives of the other isotopes range from microseconds to several days. The isotope which is the easiest to synthesize is berkelium-249. This emits mostly soft <a href="/facts/Beta_decay/vxTBlckp">β-particles</a> which are inconvenient for detection. Its <a href="/facts/Alpha_decay/rCsHNIUE">alpha radiation</a> is rather weak (1.45×10−3%) with respect to the β-radiation, but is sometimes used to detect this isotope. The second important berkelium isotope, berkelium-247, is an alpha-emitter, as are most actinide isotopes.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a><a class="footnote-ref" id="fnref:30" href="#fn:30">30</a>

<h3>Occurrence</h3>
All berkelium isotopes have a half-life far too short to be <a href="/facts/Primordial_nuclide/lFAUqHDv">primordial</a>. Therefore, any primordial berkelium − that is, berkelium present on the Earth during its formation − has decayed by now.
On Earth, berkelium is mostly concentrated in certain areas, which were used for the atmospheric <a href="/facts/Nuclear_weapons_testing/s2srGDFP">nuclear weapons tests</a> between 1945 and 1980, as well as at the sites of nuclear incidents, such as the <a href="/facts/Chernobyl_disaster/mNj9JHyf">Chernobyl disaster</a>, <a href="/facts/Three_Mile_Island_accident/TWPp30Iq">Three Mile Island accident</a> and <a href="/facts/1968_Thule_Air_Base_B-52_crash/lhwwoDVf">1968 Thule Air Base B-52 crash</a>. Analysis of the debris at the testing site of the first <a href="/facts/United_States/P0sCdLe5">United States</a>' first <a href="/facts/Thermonuclear_weapon/T9zFe3H0">thermonuclear weapon</a>, <a href="/facts/Ivy_Mike/yFqF9H72">Ivy Mike</a>, (1 November 1952, <a href="/facts/Enewetak_Atoll/Mj0yc3W3">Enewetak Atoll</a>), revealed high concentrations of various actinides, including berkelium. For reasons of military secrecy, this result was not published until 1956.<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a>
Nuclear reactors produce mostly, among the berkelium isotopes, berkelium-249. During the storage and before the fuel disposal, most of it <a href="/facts/Beta_decay/vxTBlckp">beta decays</a> to californium-249. The latter has a half-life of 351 years, which is relatively long compared to the half-lives of other isotopes produced in the reactor,<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> and is therefore undesirable in the disposal products.
The <a href="/facts/Transuranium_element/a12PwdAw">transuranium elements</a> from <a href="/facts/Americium/rxL9Yc64">americium</a> to <a href="/facts/Fermium/Us3rnvG5">fermium</a>, including berkelium, occurred naturally in the <a href="/facts/Natural_nuclear_fission_reactor/G7FIGsEV">natural nuclear fission reactor</a> at <a href="/facts/Oklo/p2jg2BuS">Oklo</a>, but no longer do so.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a>
Berkelium is also one of the elements that have theoretically been detected in <a href="/facts/Przybylski%27s_Star/1unV7g8C">Przybylski's Star</a>.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a>

<h2 id="history">History</h2>

Although very small amounts of berkelium were possibly produced in previous nuclear experiments, it was <a href="/facts/Timeline_of_chemical_element_discoveries/QY4X2RP3">first intentionally synthesized</a>, isolated and identified in December 1949 by <a href="/facts/Glenn_T._Seaborg/w1a3mume">Glenn T. Seaborg</a>, <a href="/facts/Albert_Ghiorso/jP5gHCwp">Albert Ghiorso</a>, <a href="/facts/Stanley_Gerald_Thompson/aBYmwxMd">Stanley Gerald Thompson</a>, and <a href="/facts/Kenneth_Street_Jr./EnRWbFMU">Kenneth Street Jr.</a> They used the 60-inch <a href="/facts/Cyclotron/Q8APwhWm">cyclotron</a> at the <a href="/facts/University_of_California,_Berkeley/MXVEjklr">University of California, Berkeley</a>. Similar to the nearly simultaneous discovery of <a href="/facts/Americium/rxL9Yc64">americium</a> (element 95) and <a href="/facts/Curium/LMyWXg8l">curium</a> (element 96) in 1944, the new elements berkelium and <a href="/facts/Californium/AJVjoVut">californium</a> (element 98) were both produced in 1949–1950.<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a><a class="footnote-ref" id="fnref:36" href="#fn:36">36</a><a class="footnote-ref" id="fnref:37" href="#fn:37">37</a><a class="footnote-ref" id="fnref:38" href="#fn:38">38</a><a class="footnote-ref" id="fnref:39" href="#fn:39">39</a>
The name choice for element 97 followed the previous tradition of the Californian group to draw an analogy between the newly discovered <a href="/facts/Actinide/kHC4lxJV">actinide</a> and the <a href="/facts/Lanthanide/rt3XIRCl">lanthanide</a> element positioned above it in the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>. Previously, americium was named after a continent as its analogue <a href="/facts/Europium/dqmBm1vr">europium</a>, and curium honored scientists <a href="/facts/Marie_Curie/EGjeuJ14">Marie</a> and <a href="/facts/Pierre_Curie/Sbtlw2xj">Pierre Curie</a> as the lanthanide above it, <a href="/facts/Gadolinium/eLYUeScu">gadolinium</a>, was named after the explorer of the <a href="/facts/Rare-earth_element/PQSUQumk">rare-earth elements</a> <a href="/facts/Johan_Gadolin/dMFU1Lna">Johan Gadolin</a>. Thus, the discovery report by the Berkeley group reads: "It is suggested that element 97 be given the name berkelium (symbol Bk) after the city of Berkeley in a manner similar to that used in naming its chemical homologue <a href="/facts/Terbium/ICF3PMED">terbium</a> (atomic number 65) whose name was derived from the town of <a href="/facts/Ytterby/6CaEoUjc">Ytterby</a>, <a href="/facts/Sweden/u3qC7lyj">Sweden</a>, where the rare earth minerals were first found."<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a> This tradition ended with berkelium, though, as the naming of the next discovered actinide, <a href="/facts/Californium/AJVjoVut">californium</a>, was not related to its lanthanide analogue <a href="/facts/Dysprosium/eMev6zGS">dysprosium</a>, but after the discovery place.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a>
The most difficult steps in synthesising berkelium were its separation from the final products and the production of sufficient quantities of americium for the target material. First, americium (<a href="/facts/Americium-241/HnXXm1nx">241Am</a>) <a href="/facts/Nitrate/5AnVlYnL">nitrate</a> solution was coated on a <a href="/facts/Platinum/qJC6lQf7">platinum</a> foil, the solution was evaporated and the residue converted by annealing to <a href="/facts/Americium_dioxide/8jrEHRKM">americium dioxide</a> (AmO2). This target was irradiated with 35 MeV <a href="/facts/Alpha_particle/dzNMs9WP">alpha particles</a> for 6 hours in the 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley. The (α,2n) reaction induced by the irradiation yielded the 243Bk isotope and two free <a href="/facts/Neutron/oRCM1geb">neutrons</a>:<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a>

24195Am + 42He → 24397Bk + 2 10n
After the irradiation, the coating was dissolved with <a href="/facts/Nitric_acid/UDbwGp6s">nitric acid</a> and then precipitated as the <a href="/facts/Hydroxide/zW0wxpWD">hydroxide</a> using concentrated aqueous <a href="/facts/Ammonia_solution/pRg1m03X">ammonia solution</a>. The product was <a href="/facts/Centrifugation/q9WkB8T4">centrifugated</a> and re-dissolved in nitric acid. To separate berkelium from the unreacted americium, this solution was added to a mixture of aqueous <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> and <a href="/facts/Ammonium_sulfate/9vtbmLww">ammonium sulfate</a> and heated in the presence of atmospheric oxygen to convert all the dissolved americium into the <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> +6. Unoxidized residual americium was precipitated by the addition of <a href="/facts/Hydrofluoric_acid/wdXqu4bE">hydrofluoric acid</a> as americium(III) <a href="/facts/Fluoride/LpqNMzwa">fluoride</a> (AmF3). This step yielded a mixture of the accompanying product curium and the expected element 97 in form of trifluorides. The mixture was converted to the corresponding hydroxides by treating it with <a href="/facts/Potassium_hydroxide/NBhPBuXc">potassium hydroxide</a>, and after centrifugation, was dissolved in <a href="/facts/Perchloric_acid/gjhK386J">perchloric acid</a>.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a>

Further separation was carried out in the presence of a <a href="/facts/Citric_acid/EgKGQBdl">citric acid</a>/<a href="/facts/Ammonium/jYm8wc1n">ammonium</a> <a href="/facts/Buffer_solution/zrLz9eaa">buffer solution</a> in a weakly acidic medium (<a href="/facts/PH/RnSv8D7y">pH</a> ≈ 3.5), using <a href="/facts/Ion_exchange/C2DPoGqg">ion exchange</a> at elevated temperature. The <a href="/facts/Chromatography/2FrvPjNV">chromatographic</a> separation behavior was unknown for element 97 at the time but was anticipated by analogy with terbium. The first results were disappointing because no alpha-particle emission signature could be detected from the elution product. With further analysis, searching for <a href="/facts/K-alpha/FYk5MPEn">characteristic X-rays</a> and <a href="/facts/Internal_conversion/mVkoudEe">conversion electron</a> signals, a berkelium isotope was eventually detected. Its <a href="/facts/Mass_number/VyBbJ1oI">mass number</a> was uncertain between 243 and 244 in the initial report,<a class="footnote-ref" id="fnref:44" href="#fn:44">44</a> but was later established as 243.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a>

<h2 id="synthesis-and-extraction">Synthesis and extraction</h2>
<h3>Preparation of isotopes</h3>
Berkelium is produced by bombarding lighter actinides <a href="/facts/Uranium/n2sGWBzU">uranium</a> (238U) or <a href="/facts/Plutonium/4bUw9zH3">plutonium</a> (239Pu) with <a href="/facts/Neutron/oRCM1geb">neutrons</a> in a <a href="/facts/Nuclear_reactor/8xqjIbge">nuclear reactor</a>. In a more common case of uranium fuel, plutonium is produced first by <a href="/facts/Neutron_capture/elsFpM12">neutron capture</a> (the so-called (n,γ) reaction or neutron fusion) followed by beta-decay:<a class="footnote-ref" id="fnref:46" href="#fn:46">46</a>

U
 
 
 
 92
 238
 
 
 
 →
 
 
 
 (
 n
 ,
 γ
 )
 
 
 
 
 
 
 U
 
 
 
 92
 239
 
 
 
 →
 
 23.5
  
 
 min
 
 
 
 
 β
 −
 
 
 
 
 
 Np
 
 
 
 93
 239
 
 
 
 →
 
 2.3565
  
 
 d
 
 
 
 
 β
 −
 
 
 
 
 
 Pu
 
 
 
 94
 239
 
 
 
 
 {\displaystyle {\ce {^{238}_{92}U ->[{\ce {(n,\gamma)}}] ^{239}_{92}U ->[\beta^-][23.5 \ {\ce {min}}] ^{239}_{93}Np ->[\beta^-][2.3565 \ {\ce {d}}] ^{239}_{94}Pu}}}
 
 (the times are <a href="/facts/Half-life/kGVH8BAB">half-lives</a>)
Plutonium-239 is further irradiated by a source that has a high <a href="/facts/Neutron_flux/nDE9Nlrx">neutron flux</a>, several times higher than a conventional nuclear reactor, such as the 85-megawatt <a href="/facts/High_Flux_Isotope_Reactor/BmAqsqgq">High Flux Isotope Reactor</a> (HFIR) at the <a href="/facts/Oak_Ridge_National_Laboratory/Elq84HKF">Oak Ridge National Laboratory</a> in Tennessee, US. The higher flux promotes fusion reactions involving not one but several neutrons, converting 239Pu to 244Cm and then to 249Cm:

Pu
                    
                    
                    
                    94
                    239
                  
                  
                    
                      →
                      
                        
                          4
                          
                          
                            (
                            n
                            ,
                            γ
                            )
                          
                        
                      
                    
                  
                  
                    Pu
                    
                    
                    
                    94
                    243
                  
                  
                    
                      →
                      
                        4.956
                         
                        
                          h
                        
                      
                      
                        
                          β
                          −
                        
                      
                    
                  
                  
                    Am
                    
                    
                    
                    95
                    243
                  
                  
                    
                      →
                      
                        
                          
                            (
                            n
                            ,
                            γ
                            )
                          
                        
                      
                    
                  
                  
                    Am
                    
                    
                    
                    95
                    244
                  
                  
                    
                      →
                      
                        10.1
                         
                        
                          h
                        
                      
                      
                        
                          β
                          −
                        
                      
                    
                  
                
              
              
                
                  
                    Cm
                    
                    
                    
                    96
                    244
                  
                
              
            
            
              
              
                
                  
                    Cm
                    
                    
                    
                    96
                    244
                  
                  
                    
                      →
                      
                        
                          5
                          
                          
                            (
                            n
                            ,
                            γ
                            )
                          
                        
                      
                    
                  
                  
                    Cm
                    
                    
                    
                    96
                    249
                  
                
              
            
          
        
      
    
    {\displaystyle {\begin{aligned}{\ce {^{239}_{94}Pu ->[{\ce {4(n,\gamma)}}] ^{243}_{94}Pu ->[\beta^-][4.956 \ {\ce {h}}] ^{243}_{95}Am ->[{\ce {(n,\gamma)}}] ^{244}_{95}Am ->[\beta^-][10.1 \ {\ce {h}}]}}&{\ce {^{244}_{96}Cm}}\\&{\ce {^{244}_{96}Cm ->[{\ce {5(n,\gamma)}}] ^{249}_{96}Cm}}\end{aligned}}}

Curium-249 has a short half-life of 64 minutes, and thus its further conversion to 250Cm has a low probability. Instead, it transforms by beta-decay into 249Bk:<a class="footnote-ref" id="fnref:47" href="#fn:47">47</a>

Cm
            
            
            
            96
            249
          
          
            
              
                →
                
                  64.15
                   
                  
                    min
                  
                
                
                  
                    
                      β
                      
                        −
                      
                    
                  
                
              
            
            
              97
            
            
              249
            
          
          Bk
          
            
              
                →
                
                  330
                   
                  
                    d
                  
                
                
                  
                    β
                    
                      −
                    
                  
                
              
            
            
              98
            
            
              249
            
          
          Cf
        
      
    
    {\displaystyle {\ce {^{249}_{96}Cm->[{\beta ^{-}}][64.15\ {\ce {min}}]_{97}^{249}Bk->[\beta ^{-}][330\ {\ce {d}}]_{98}^{249}Cf}}}

The thus-produced 249Bk has a long half-life of 330 days and thus can capture another neutron. However, the product, 250Bk, again has a relatively short half-life of 3.212 hours and thus does not yield any heavier berkelium isotopes. It instead decays to the californium isotope 250Cf:<a class="footnote-ref" id="fnref:48" href="#fn:48">48</a><a class="footnote-ref" id="fnref:49" href="#fn:49">49</a>

Bk
            
            
            
            97
            249
          
          
            
              →
              
                
                  
                    (
                    n
                    ,
                    γ
                    )
                  
                
              
            
          
          
            Bk
            
            
            
            97
            250
          
          
            
              →
              
                3.212
                 
                
                  h
                
              
              
                
                  β
                  −
                
              
            
          
          
            Cf
            
            
            
            98
            250
          
        
      
    
    {\displaystyle {\ce {^{249}_{97}Bk ->[{\ce {(n,\gamma)}}] ^{250}_{97}Bk ->[\beta^-][3.212 \ {\ce {h}}] ^{250}_{98}Cf}}}

Although 247Bk is the most stable isotope of berkelium, its production in nuclear reactors is very difficult because its potential progenitor 247Cm has never been observed to undergo beta decay.<a class="footnote-ref" id="fnref:50" href="#fn:50">50</a> Thus, 249Bk is the most accessible isotope of berkelium, which still is available only in small quantities (only 0.66 grams have been produced in the US over the period 1967–1983<a class="footnote-ref" id="fnref:51" href="#fn:51">51</a>) at a high price of the order 185 <a href="/facts/United_States_dollar/naEEDUhC">USD</a> per microgram.<a class="footnote-ref" id="fnref:52" href="#fn:52">52</a> It is the only berkelium isotope available in bulk quantities, and thus the only berkelium isotope whose properties can be extensively studied.<a class="footnote-ref" id="fnref:53" href="#fn:53">53</a>
The isotope 248Bk was first obtained in 1956 by bombarding a mixture of curium isotopes with 25 MeV α-particles. Although its direct detection was hindered by strong signal interference with 245Bk, the existence of a new isotope was proven by the growth of the decay product 248Cf which had been previously characterized. The half-life of 248Bk was estimated as 23±5 hours,<a class="footnote-ref" id="fnref:54" href="#fn:54">54</a> though later 1965 work gave a half-life in excess of 300 years (which may be due to an isomeric state).<a class="footnote-ref" id="fnref:55" href="#fn:55">55</a> Berkelium-247 was produced during the same year by irradiating 244Cm with alpha-particles:<a class="footnote-ref" id="fnref:56" href="#fn:56">56</a>

{
            
              
                
                  
                    
                      Cm
                      
                      
                      
                      96
                      244
                    
                    
                      
                        →
                        
                          
                            
                              (
                              α
                              ,
                              n
                              )
                            
                          
                        
                      
                    
                    
                      Cf
                      
                      
                      
                      98
                      247
                    
                    
                      
                        →
                        
                          3.11
                           
                          
                            h
                          
                        
                        
                          ϵ
                        
                      
                    
                    
                      Bk
                      
                      
                      
                      97
                      247
                    
                  
                
              
              
                
                  
                    
                      Cm
                      
                      
                      
                      96
                      244
                    
                    
                      
                        →
                        
                          
                            
                              (
                              α
                              ,
                              p
                              )
                            
                          
                        
                      
                    
                    
                      Bk
                      
                      
                      
                      97
                      247
                    
                  
                
              
            
            
          
        
      
    
    {\displaystyle {\begin{cases}{\ce {^{244}_{96}Cm ->[{\ce {(\alpha,n)}}] ^{247}_{98}Cf ->[\epsilon][3.11 \ {\ce {h}}] ^{247}_{97}Bk}}\\{\ce {^{244}_{96}Cm ->[{\ce {(\alpha,p)}}] ^{247}_{97}Bk}}\end{cases}}}

Berkelium-242 was synthesized in 1979 by bombarding 235U with 11B, 238U with 10B, 232Th with 14N or 232Th with 15N. It converts by <a href="/facts/Electron_capture/EIccoV1u">electron capture</a> to 242Cm with a half-life of 7.0±1.3 minutes. A search for an initially suspected isotope 241Bk was then unsuccessful;<a class="footnote-ref" id="fnref:57" href="#fn:57">57</a> 241Bk has since been synthesized.<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a>

{
            
              
                
                  
                    
                      U
                      
                      
                      
                      92
                      235
                    
                    +
                    
                      B
                      
                      
                      
                      5
                      11
                    
                    ⟶
                    
                      Bk
                      
                      
                      
                      97
                      242
                    
                    +
                    4
                    
                      
                      
                        0
                      
                      
                        1
                      
                    
                    n
                  
                
                
                  
                    
                      Th
                      
                      
                      
                      90
                      232
                    
                    +
                    
                      N
                      
                      
                      
                      7
                      14
                    
                    ⟶
                    
                      Bk
                      
                      
                      
                      97
                      242
                    
                    +
                    4
                    
                      
                      
                        0
                      
                      
                        1
                      
                    
                    n
                  
                
              
              
                
                  
                    
                      U
                      
                      
                      
                      92
                      238
                    
                    +
                    
                      B
                      
                      
                      
                      5
                      10
                    
                    ⟶
                    
                      Bk
                      
                      
                      
                      97
                      242
                    
                    +
                    6
                    
                      
                      
                        0
                      
                      
                        1
                      
                    
                    n
                  
                
                
                  
                    
                      Th
                      
                      
                      
                      90
                      232
                    
                    +
                    
                      N
                      
                      
                      
                      7
                      15
                    
                    ⟶
                    
                      Bk
                      
                      
                      
                      97
                      242
                    
                    +
                    5
                    
                      
                      
                        0
                      
                      
                        1
                      
                    
                    n
                  
                
              
            
            
          
        
      
    
    {\displaystyle {\begin{cases}{\ce {^{235}_{92}U + ^{11}_{5}B -> ^{242}_{97}Bk + 4^{1}_{0}n}}&{\ce {^{232}_{90}Th + ^{14}_{7}N -> ^{242}_{97}Bk + 4^{1}_{0}n}}\\{\ce {^{238}_{92}U + ^{10}_{5}B -> ^{242}_{97}Bk + 6^{1}_{0}n}}&{\ce {^{232}_{90}Th + ^{15}_{7}N -> ^{242}_{97}Bk + 5^{1}_{0}n}}\end{cases}}}

<h3>Separation</h3>
The fact that berkelium readily assumes <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> +4 in solids, and is relatively stable in this state in liquids greatly assists separation of berkelium away from many other actinides. These are inevitably produced in relatively large amounts during the nuclear synthesis and often favor the +3 state. This fact was not yet known in the initial experiments, which used a more complex separation procedure. Various inorganic oxidation agents can be applied to the berkelium(III) solutions to convert it to the +4 state, such as <a href="/facts/Bromate/UH4DoPFT">bromates</a> (BrO−3), <a href="/facts/Bismuthate/znSGlItd">bismuthates</a> (BiO−3), <a href="/facts/Chromate_and_dichromate/6xkFLIJw">chromates</a> (CrO2−4 and Cr2O2−7), silver(I) thiolate (Ag2S2O8), lead(IV) oxide (PbO2), <a href="/facts/Ozone/o0E5gn2p">ozone</a> (O3), or photochemical oxidation procedures. More recently, it has been discovered that some organic and bio-inspired molecules, such as the chelator called 3,4,3-LI(1,2-HOPO), can also oxidize Bk(III) and stabilize Bk(IV) under mild conditions.<a class="footnote-ref" id="fnref:59" href="#fn:59">59</a> Berkelium(IV) is then extracted with <a href="/facts/Ion_exchange/C2DPoGqg">ion exchange</a>, extraction <a href="/facts/Chromatography/2FrvPjNV">chromatography</a> or liquid-liquid extraction using HDEHP (bis-(2-ethylhexyl) phosphoric acid), <a href="/facts/Amine/JvfYJfP6">amines</a>, <a href="/facts/Tributyl_phosphate/lze1seSK">tributyl phosphate</a> or various other reagents. These procedures separate berkelium from most trivalent actinides and <a href="/facts/Lanthanide/rt3XIRCl">lanthanides</a>, except for the lanthanide <a href="/facts/Cerium/a7UjMBQ6">cerium</a> (lanthanides are absent in the irradiation target but are created in various <a href="/facts/Nuclear_fission/LfkIylvm">nuclear fission</a> decay chains).<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a>
A more detailed procedure adopted at the <a href="/facts/Oak_Ridge_National_Laboratory/Elq84HKF">Oak Ridge National Laboratory</a> was as follows: the initial mixture of actinides is processed with ion exchange using <a href="/facts/Lithium_chloride/mNbthJx2">lithium chloride</a> reagent, then precipitated as <a href="/facts/Hydroxide/zW0wxpWD">hydroxides</a>, filtered and dissolved in nitric acid. It is then treated with high-pressure <a href="/facts/Elution/ns3pIr7e">elution</a> from <a href="/facts/Ion_exchange/C2DPoGqg">cation exchange</a> resins, and the berkelium phase is oxidized and extracted using one of the procedures described above.<a class="footnote-ref" id="fnref:61" href="#fn:61">61</a> Reduction of the thus-obtained berkelium(IV) to the +3 oxidation state yields a solution, which is nearly free from other actinides (but contains cerium). Berkelium and cerium are then separated with another round of ion-exchange treatment.<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a>

<h3>Bulk metal preparation</h3>
In order to characterize chemical and physical properties of solid berkelium and its compounds, a program was initiated in 1952 at the <a href="/facts/Idaho_National_Laboratory/HGyEyBxn">Material Testing Reactor</a>, <a href="/facts/Arco,_Idaho/8W22FAL3">Arco, Idaho</a>, US. It resulted in preparation of an eight-gram plutonium-239 target and in the first production of macroscopic quantities (0.6 micrograms) of berkelium by Burris B. Cunningham and <a href="/facts/Stanley_Gerald_Thompson/aBYmwxMd">Stanley Gerald Thompson</a> in 1958, after a continuous reactor irradiation of this target for six years.<a class="footnote-ref" id="fnref:63" href="#fn:63">63</a><a class="footnote-ref" id="fnref:64" href="#fn:64">64</a> This irradiation method was and still is the only way of producing weighable amounts of the element, and most solid-state studies of berkelium have been conducted on microgram or submicrogram-sized samples.<a class="footnote-ref" id="fnref:65" href="#fn:65">65</a><a class="footnote-ref" id="fnref:66" href="#fn:66">66</a>
The world's major irradiation sources are the 85-megawatt High Flux Isotope Reactor at the <a href="/facts/Oak_Ridge_National_Laboratory/Elq84HKF">Oak Ridge National Laboratory</a> in Tennessee, USA,<a class="footnote-ref" id="fnref:67" href="#fn:67">67</a> and the SM-2 loop reactor at the <a href="/facts/Research_Institute_of_Atomic_Reactors/NMa2AJF0">Research Institute of Atomic Reactors</a> (NIIAR) in <a href="/facts/Dimitrovgrad,_Russia/26R1F29h">Dimitrovgrad, Russia</a>,<a class="footnote-ref" id="fnref:68" href="#fn:68">68</a> which are both dedicated to the production of transcurium elements (atomic number greater than 96). These facilities have similar power and flux levels, and are expected to have comparable production capacities for transcurium elements,<a class="footnote-ref" id="fnref:69" href="#fn:69">69</a> although the quantities produced at NIIAR are not publicly reported. In a "typical processing campaign" at Oak Ridge, tens of grams of <a href="/facts/Curium/LMyWXg8l">curium</a> are irradiated to produce <a href="/facts/Kilogram/lU2zbPk8">decigram</a> quantities of <a href="/facts/Californium/AJVjoVut">californium</a>, <a href="/facts/Kilogram/lU2zbPk8">milligram</a> quantities of berkelium-249 and <a href="/facts/Einsteinium/RePoIVN9">einsteinium</a>, and <a href="/facts/Kilogram/lU2zbPk8">picogram</a> quantities of <a href="/facts/Fermium/Us3rnvG5">fermium</a>.<a class="footnote-ref" id="fnref:70" href="#fn:70">70</a><a class="footnote-ref" id="fnref:71" href="#fn:71">71</a> In total, just over one gram of berkelium-249 has been produced at Oak Ridge since 1967.<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a>
The first berkelium metal sample weighing 1.7 micrograms was prepared in 1971 by the reduction of berkelium(III) fluoride with <a href="/facts/Lithium/7vXX6BWA">lithium</a> vapor at 1000 °C; the fluoride was suspended on a tungsten wire above a <a href="/facts/Tantalum/VwaxMm33">tantalum</a> crucible containing molten lithium. Later, metal samples weighing up to 0.5 milligrams were obtained with this method.<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a><a class="footnote-ref" id="fnref:74" href="#fn:74">74</a>

BkF3 + 3 Li → Bk + 3 LiF
Similar results are obtained with berkelium(IV) fluoride.<a class="footnote-ref" id="fnref:75" href="#fn:75">75</a> Berkelium metal can also be produced by the reduction of berkelium(IV) oxide with <a href="/facts/Thorium/ysdWH470">thorium</a> or <a href="/facts/Lanthanum/Uhmmy1sB">lanthanum</a>.<a class="footnote-ref" id="fnref:76" href="#fn:76">76</a><a class="footnote-ref" id="fnref:77" href="#fn:77">77</a>

<h2 id="compounds">Compounds</h2>
Main article: <a href="/facts/Berkelium_compounds/yqb6vdvX">Berkelium compounds</a>
<h3>Oxides</h3>
Two oxides of berkelium are known, with the berkelium <a href="/facts/Redox/Pyd5RVcj">oxidation</a> state of +3 (Bk2O3) and +4 (<a href="/facts/Berkelium(IV)_oxide/fjqKwLF8">BkO2</a>).<a class="footnote-ref" id="fnref:78" href="#fn:78">78</a> Berkelium(IV) oxide is a brown solid,<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a> while berkelium(III) oxide is a yellow-green solid with a melting point of 1920 °C<a class="footnote-ref" id="fnref:80" href="#fn:80">80</a><a class="footnote-ref" id="fnref:81" href="#fn:81">81</a> and is formed from BkO2 by <a href="/facts/Redox/Pyd5RVcj">reduction</a> with molecular <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>:

2 BkO2 + H2 → Bk2O3 + H2O
Upon heating to 1200 °C, the oxide Bk2O3 undergoes a phase change; it undergoes another phase change at 1750 °C. Such three-phase behavior is typical for the actinide <a href="/facts/Sesquioxide/KbfWnDuI">sesquioxides</a>. Berkelium(II) oxide, BkO, has been reported as a brittle gray solid but its exact chemical composition remains uncertain.<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a>

<h3>Halides</h3>
In <a href="/facts/Halide/ujYu8kGD">halides</a>, berkelium assumes the oxidation states +3 and +4.<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a> The +3 state is the most stable, especially in solutions, while the tetravalent halides BkF4 and Cs2BkCl6 are only known in the solid phase.<a class="footnote-ref" id="fnref:84" href="#fn:84">84</a> The coordination of berkelium atom in its trivalent fluoride and chloride is tricapped <a href="/facts/Octahedral_molecular_geometry/bNXLVvks">trigonal prismatic</a>, with the <a href="/facts/Coordination_number/mf48hsoX">coordination number</a> of 9. In trivalent bromide, it is bicapped trigonal prismatic (coordination 8) or <a href="/facts/Octahedral_molecular_geometry/bNXLVvks">octahedral</a> (coordination 6),<a class="footnote-ref" id="fnref:85" href="#fn:85">85</a> and in the iodide it is octahedral.<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a>

<table><tbody><tr><th>Oxidation number</th><th>F</th><th>Cl</th><th>Br</th><th>I</th></tr><tr><th>+4</th><td>BkF4 (yellow<a class="footnote-ref" id="fnref:87" href="#fn:87">87</a>)</td><td>Cs2BkCl6(orange<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a>)</td><td></td><td></td></tr><tr><th>+3</th><td>BkF3 (yellow<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a>)</td><td>BkCl3 (green<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a>)Cs2NaBkCl6<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a></td><td>BkBr3<a class="footnote-ref" id="fnref:92" href="#fn:92">92</a><a class="footnote-ref" id="fnref:93" href="#fn:93">93</a>(yellow-green<a class="footnote-ref" id="fnref:94" href="#fn:94">94</a>)</td><td>BkI3 (yellow<a class="footnote-ref" id="fnref:95" href="#fn:95">95</a>)</td></tr></tbody></table>
Berkelium(IV) fluoride (BkF4) is a yellow-green ionic solid and is isotypic with <a href="/facts/Uranium_tetrafluoride/AtKs4Sal">uranium tetrafluoride</a> or <a href="/facts/Zirconium_tetrafluoride/gXqCVEzb">zirconium tetrafluoride</a>.<a class="footnote-ref" id="fnref:96" href="#fn:96">96</a><a class="footnote-ref" id="fnref:97" href="#fn:97">97</a><a class="footnote-ref" id="fnref:98" href="#fn:98">98</a> Berkelium(III) fluoride (BkF3) is also a yellow-green solid, but it has two crystalline structures. The most stable phase at low temperatures is isotypic with <a href="/facts/Yttrium(III)_fluoride/uFDheGgH">yttrium(III) fluoride</a>, while upon heating to between 350 and 600 °C, it transforms to the structure found in <a href="/facts/Lanthanum_trifluoride/uYAvd936">lanthanum trifluoride</a>.<a class="footnote-ref" id="fnref:99" href="#fn:99">99</a><a class="footnote-ref" id="fnref:100" href="#fn:100">100</a><a class="footnote-ref" id="fnref:101" href="#fn:101">101</a>
Visible amounts of <a href="/facts/Berkelium(III)_chloride/2Irmh7M9">berkelium(III) chloride</a> (BkCl3) were first isolated and characterized in 1962, and weighed only 3 billionths of a <a href="/facts/Gram/sRSW5RJb">gram</a>. It can be prepared by introducing <a href="/facts/Hydrogen_chloride/7Wzkhomd">hydrogen chloride</a> vapors into an evacuated quartz tube containing berkelium oxide at a temperature about 500 °C.<a class="footnote-ref" id="fnref:102" href="#fn:102">102</a> This green solid has a melting point of 600 °C,<a class="footnote-ref" id="fnref:103" href="#fn:103">103</a> and is isotypic with <a href="/facts/Uranium(III)_chloride/vNtL0fPQ">uranium(III) chloride</a>.<a class="footnote-ref" id="fnref:104" href="#fn:104">104</a><a class="footnote-ref" id="fnref:105" href="#fn:105">105</a> Upon heating to nearly melting point, BkCl3 converts into an orthorhombic phase.<a class="footnote-ref" id="fnref:106" href="#fn:106">106</a>
Two forms of berkelium(III) bromide are known: one with berkelium having coordination 6, and one with coordination 8.<a class="footnote-ref" id="fnref:107" href="#fn:107">107</a> The latter is less stable and transforms to the former phase upon heating to about 350 °C. An important phenomenon for radioactive solids has been studied on these two crystal forms: the structure of fresh and aged 249BkBr3 samples was probed by <a href="/facts/X-ray_crystallography/WtI0F5DN">X-ray diffraction</a> over a period longer than 3 years, so that various fractions of berkelium-249 had <a href="/facts/Beta_decay/vxTBlckp">beta decayed</a> to californium-249. No change in structure was observed upon the 249BkBr3—249CfBr3 transformation. However, other differences were noted for 249BkBr3 and 249CfBr3. For example, the latter could be reduced with hydrogen to 249CfBr2, but the former could not – this result was reproduced on individual 249BkBr3 and 249CfBr3 samples, as well on the samples containing both bromides.<a class="footnote-ref" id="fnref:108" href="#fn:108">108</a> The intergrowth of californium in berkelium occurs at a rate of 0.22% per day and is an intrinsic obstacle in studying berkelium properties. Beside a chemical contamination, 249Cf, being an alpha emitter, brings undesirable self-damage of the crystal lattice and the resulting self-heating. The chemical effect however can be avoided by performing measurements as a function of time and extrapolating the obtained results.<a class="footnote-ref" id="fnref:109" href="#fn:109">109</a>

<h3>Other inorganic compounds</h3>
The <a href="/facts/Pnictogen/jX4hvCkK">pnictides</a> of berkelium-249 of the type BkX are known for the elements <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>,<a class="footnote-ref" id="fnref:110" href="#fn:110">110</a> <a href="/facts/Phosphorus/27xCeIqs">phosphorus</a>, <a href="/facts/Arsenic/k1c4f44D">arsenic</a> and <a href="/facts/Antimony/YsA7lVgT">antimony</a>. They crystallize in the <a href="/facts/Cubic_crystal_system/92Co7BKM">rock-salt structure</a> and are prepared by the reaction of either berkelium(III) hydride (BkH3) or metallic berkelium with these elements at elevated temperature (about 600 °C) under high vacuum.<a class="footnote-ref" id="fnref:111" href="#fn:111">111</a>
Berkelium(III) sulfide, Bk2S3, is prepared by either treating berkelium oxide with a mixture of <a href="/facts/Hydrogen_sulfide/UbCqjMMk">hydrogen sulfide</a> and <a href="/facts/Carbon_disulfide/b04Tadmy">carbon disulfide</a> vapors at 1130 °C, or by directly reacting metallic berkelium with elemental sulfur. These procedures yield brownish-black crystals.<a class="footnote-ref" id="fnref:112" href="#fn:112">112</a>
Berkelium(III) and berkelium(IV) hydroxides are both stable in 1 <a href="/facts/Molar_concentration/P2WL5b9q">molar</a> solutions of <a href="/facts/Sodium_hydroxide/xjtdYtq7">sodium hydroxide</a>. Berkelium(III) <a href="/facts/Phosphate/FDGVCxUG">phosphate</a> (BkPO4) has been prepared as a solid, which shows strong <a href="/facts/Fluorescence/qsJVT2qP">fluorescence</a> under excitation with a green light.<a class="footnote-ref" id="fnref:113" href="#fn:113">113</a> Berkelium hydrides are produced by reacting metal with hydrogen gas at temperatures about 250 °C.<a class="footnote-ref" id="fnref:114" href="#fn:114">114</a> They are non-stoichiometric with the nominal formula BkH2+x (0 < x < 1).<a class="footnote-ref" id="fnref:115" href="#fn:115">115</a> Several other salts of berkelium are known, including an oxysulfide (Bk2O2S), and hydrated <a href="/facts/Berkelium(III)_nitrate/0vuXnKlF">nitrate</a> (Bk(NO3)3·4H2O), chloride (BkCl3·6H2O), <a href="/facts/Sulfate/yuWVxsUf">sulfate</a> (Bk2(SO4)3·12H2O) and <a href="/facts/Oxalate/u0Gdem0A">oxalate</a> (Bk2(C2O4)3·4H2O).<a class="footnote-ref" id="fnref:116" href="#fn:116">116</a> Thermal decomposition at about 600 °C in an <a href="/facts/Argon/QX6NRH6d">argon</a> atmosphere (to avoid oxidation to BkO2) of Bk2(SO4)3·12H2O yields the crystals of berkelium(III) oxysulfate (Bk2O2SO4). This compound is thermally stable to at least 1000 °C in inert atmosphere.<a class="footnote-ref" id="fnref:117" href="#fn:117">117</a>

<h3>Organoberkelium compounds</h3>
Berkelium forms a trigonal (η5–C5H5)3Bk <a href="/facts/Metallocene/AecA5Qrk">metallocene</a> complex with three <a href="/facts/Cyclopentadienyl_complex/rezSmzLI">cyclopentadienyl</a> rings, which can be synthesized by reacting berkelium(III) chloride with the molten <a href="/facts/Beryllocene/3x53VSly">beryllocene</a> (Be(C5H5)2) at about 70 °C. It has an amber color and a density of 2.47 g/cm3. The complex is stable to heating to at least 250 °C, and sublimates without melting at about 350 °C. The high radioactivity of berkelium gradually destroys the compound (within a period of weeks).<a class="footnote-ref" id="fnref:118" href="#fn:118">118</a><a class="footnote-ref" id="fnref:119" href="#fn:119">119</a> One cyclopentadienyl ring in (η5–C5H5)3Bk can be substituted by chlorine to yield [Bk(C5H5)2Cl]2. The optical absorption spectra of this compound are very similar to those of (η5–C5H5)3Bk.<a class="footnote-ref" id="fnref:120" href="#fn:120">120</a>
Berkelium also forms Berkelocene, an <a href="/facts/Actinocene/tG8phIFL">actinocene</a> complex, with substituted cyclooctatetraenides.<a class="footnote-ref" id="fnref:121" href="#fn:121">121</a>

<h2 id="applications">Applications</h2>

There is currently no use for any isotope of berkelium outside basic scientific research.<a class="footnote-ref" id="fnref:122" href="#fn:122">122</a> Berkelium-249 is a common target nuclide to prepare still heavier <a href="/facts/Transuranium_element/a12PwdAw">transuranium elements</a> and <a href="/facts/Superheavy_element/9PjYvCc3">superheavy elements</a>,<a class="footnote-ref" id="fnref:123" href="#fn:123">123</a> such as <a href="/facts/Lawrencium/HVw2LVlx">lawrencium</a>, <a href="/facts/Rutherfordium/44LSnv9p">rutherfordium</a> and <a href="/facts/Bohrium/epvp3GWM">bohrium</a>.<a class="footnote-ref" id="fnref:124" href="#fn:124">124</a> It is also useful as a source of the isotope californium-249, which is used for studies on the chemistry of <a href="/facts/Californium/AJVjoVut">californium</a> in preference to the more radioactive californium-252 that is produced in neutron bombardment facilities such as the HFIR.<a class="footnote-ref" id="fnref:125" href="#fn:125">125</a><a class="footnote-ref" id="fnref:126" href="#fn:126">126</a>
A 22 milligram batch of berkelium-249 was prepared in a 250-day irradiation and then purified for 90 days at Oak Ridge in 2009. This target yielded the first 6 atoms of <a href="/facts/Tennessine/eGCBDvEr">tennessine</a> at the <a href="/facts/Joint_Institute_for_Nuclear_Research/JrSF8sQQ">Joint Institute for Nuclear Research</a> (JINR), <a href="/facts/Dubna/mn37rc4l">Dubna</a>, Russia, after bombarding it with calcium ions in the U400 cyclotron for 150 days. This synthesis was a culmination of the Russia-US collaboration between JINR and <a href="/facts/Lawrence_Livermore_National_Laboratory/WuXIbIKz">Lawrence Livermore National Laboratory</a> on the synthesis of elements 113 to 118 which was initiated in 1989.<a class="footnote-ref" id="fnref:127" href="#fn:127">127</a><a class="footnote-ref" id="fnref:128" href="#fn:128">128</a>

<h2 id="nuclear-fuel-cycle">Nuclear fuel cycle</h2>
The <a href="/facts/Nuclear_fission/LfkIylvm">nuclear fission</a> properties of berkelium are different from those of the neighboring actinides curium and californium, and they suggest berkelium to perform poorly as a fuel in a nuclear reactor. Specifically, berkelium-249 has a moderately large neutron capture <a href="/facts/Neutron_cross_section/gAkJmXXA">cross section</a> of 710 <a href="/facts/Barn_(unit)/0yCEtKJ9">barns</a> for <a href="/facts/Neutron_temperature/UMKR4XgJ">thermal neutrons</a>, 1200 barns <a href="/facts/Neutron_capture/elsFpM12">resonance integral</a>, but very low fission cross section for thermal neutrons. In a thermal reactor, much of it will therefore be converted to berkelium-250 which quickly decays to californium-250.<a class="footnote-ref" id="fnref:129" href="#fn:129">129</a><a class="footnote-ref" id="fnref:130" href="#fn:130">130</a><a class="footnote-ref" id="fnref:131" href="#fn:131">131</a> In principle, berkelium-249 can sustain a <a href="/facts/Nuclear_chain_reaction/3l0lHBM4">nuclear chain reaction</a> in a <a href="/facts/Breeder_reactor/jt0VeXUa">fast breeder reactor</a>. Its <a href="/facts/Critical_mass/wRAnE21M">critical mass</a> is relatively high at 192 kg, which can be reduced with a water or steel reflector but would still exceed the world production of this isotope.<a class="footnote-ref" id="fnref:132" href="#fn:132">132</a>
Berkelium-247 can maintain a chain reaction both in a thermal-neutron and in a fast-neutron reactor, however, its production is rather complex and thus the availability is much lower than its critical mass, which is about 75.7 kg for a bare sphere, 41.2 kg with a water reflector and 35.2 kg with a steel reflector (30 cm thickness).<a class="footnote-ref" id="fnref:133" href="#fn:133">133</a>

<h2 id="health-issues">Health issues</h2>
Little is known about the effects of berkelium on human body, and analogies with other elements may not be drawn because of different radiation products (<a href="/facts/Electron/L0KBo5cW">electrons</a> for berkelium and <a href="/facts/Alpha_particle/dzNMs9WP">alpha particles</a>, <a href="/facts/Neutron/oRCM1geb">neutrons</a>, or both for most other actinides). The low energy of electrons emitted from berkelium-249 (less than 126 keV) hinders its detection, due to signal interference with other decay processes, but also makes this isotope relatively harmless to humans as compared to other actinides. However, berkelium-249 transforms with a half-life of only 330 days to the strong alpha-emitter californium-249, which is rather dangerous and has to be handled in a <a href="/facts/Glovebox/NnR37n6E">glovebox</a> in a dedicated laboratory.<a class="footnote-ref" id="fnref:134" href="#fn:134">134</a>
Most available berkelium toxicity data originate from research on animals. Upon ingestion by rats, only about 0.01% of berkelium ends in the blood stream. From there, about 65% goes to the bones, where it remains for about 50 years, 25% to the lungs (biological half-life about 20 years), 0.035% to the testicles or 0.01% to the ovaries where berkelium stays indefinitely. The balance of about 10% is excreted.<a class="footnote-ref" id="fnref:135" href="#fn:135">135</a> In all these organs berkelium might promote cancer, and in the <a href="/facts/Skeleton/FXc9Y2lF">skeleton</a>, its radiation can damage red blood cells. The maximum permissible amount of berkelium-249 in the human skeleton is 0.4 <a href="/facts/Kilogram/lU2zbPk8">nanograms</a>.<a class="footnote-ref" id="fnref:136" href="#fn:136">136</a><a class="footnote-ref" id="fnref:137" href="#fn:137">137</a>

<h2 id="bibliography">Bibliography</h2>
<ul><li>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-08-037941-8.</li>
<li>Holleman, Arnold F.; Wiberg, Nils (2007). Textbook of Inorganic Chemistry (102nd ed.). Berlin: de Gruyter. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-3-11-017770-1.</li>
<li>Peterson, J. R.; Hobart, D. E. (1984). <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29">"The Chemistry of Berkelium"</a>. In Emeléus, Harry Julius (ed.). <a href="https://archive.org/details/advancesininorga0000unse_p1d0/page/29">Advances in inorganic chemistry and radiochemistry</a>. Vol. 28. Academic Press. pp. <a href="https://archive.org/details/advancesininorga0000unse_p1d0/page/29">29–64</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1016%2FS0898-8838%2808%2960204-4">10.1016/S0898-8838(08)60204-4</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-12-023628-2.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.periodicvideos.com/videos/097.htm">Berkelium</a> at <a href="/facts/The_Periodic_Table_of_Videos/vC5kbN0M">The Periodic Table of Videos</a> (University of Nottingham)</li></ul>

Wikimedia Commons has media related to Berkelium.

<h2 id="references">References</h2>

<ol>
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<li id="fn:82">Peterson & Hobart 1984, p. 51. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:82" class="footnote-back-ref">↩</a></li>
<li id="fn:83">Holleman & Wiberg 2007, p. 1969. - Holleman, Arnold F.; Wiberg, Nils (2007). Textbook of Inorganic Chemistry (102nd ed.). Berlin: de Gruyter. ISBN 978-3-11-017770-1. <a href="#fnref:83" class="footnote-back-ref">↩</a></li>
<li id="fn:84">Peterson & Hobart 1984, p. 47. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:84" class="footnote-back-ref">↩</a></li>
<li id="fn:85">Young, J. P.; Haire, R. G.; Peterson, J. R.; Ensor, D. D.; Fellows, R. L. (1980). "Chemical consequences of radioactive decay. 1. Study of californium-249 ingrowth into crystalline berkelium-249 tribromide: a new crystalline phase of californium tribromide". Inorganic Chemistry. 19 (8): 2209. doi:10.1021/ic50210a003. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:85" class="footnote-back-ref">↩</a></li>
<li id="fn:86">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:86" class="footnote-back-ref">↩</a></li>
<li id="fn:87">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:87" class="footnote-back-ref">↩</a></li>
<li id="fn:88">Peterson & Hobart 1984, p. 51. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:88" class="footnote-back-ref">↩</a></li>
<li id="fn:89">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:89" class="footnote-back-ref">↩</a></li>
<li id="fn:90">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:90" class="footnote-back-ref">↩</a></li>
<li id="fn:91">Peterson & Hobart 1984, p. 48. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:91" class="footnote-back-ref">↩</a></li>
<li id="fn:92">Young, J. P.; Haire, R. G.; Peterson, J. R.; Ensor, D. D.; Fellows, R. L. (1980). "Chemical consequences of radioactive decay. 1. Study of californium-249 ingrowth into crystalline berkelium-249 tribromide: a new crystalline phase of californium tribromide". Inorganic Chemistry. 19 (8): 2209. doi:10.1021/ic50210a003. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:92" class="footnote-back-ref">↩</a></li>
<li id="fn:93">Burns, J.; Peterson, J. R.; Stevenson, J. N. (1975). "Crystallographic studies of some transuranic trihalides: 239PuCl3, 244CmBr3, 249BkBr3 and 249CfBr3". Journal of Inorganic and Nuclear Chemistry. 37 (3): 743. doi:10.1016/0022-1902(75)80532-X. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:93" class="footnote-back-ref">↩</a></li>
<li id="fn:94">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:94" class="footnote-back-ref">↩</a></li>
<li id="fn:95">Greenwood & Earnshaw 1997, p. 1270. - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="#fnref:95" class="footnote-back-ref">↩</a></li>
<li id="fn:96">Peterson & Hobart 1984, p. 48. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:96" class="footnote-back-ref">↩</a></li>
<li id="fn:97">Ensor, D.; Peterson, J. R.; Haire, R. G.; Young, J. P. (1981). "Absorption spectrophotometric study of berkelium(III) and (IV) fluorides in the solid state". Journal of Inorganic and Nuclear Chemistry. 43 (5): 1001. doi:10.1016/0022-1902(81)80164-9. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:97" class="footnote-back-ref">↩</a></li>
<li id="fn:98">Keenan, Thomas K.; Asprey, Larned B. (1969). "Lattice constants of actinide tetrafluorides including berkelium". Inorganic Chemistry. 8 (2): 235. doi:10.1021/ic50072a011. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:98" class="footnote-back-ref">↩</a></li>
<li id="fn:99">Peterson & Hobart 1984, p. 48. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:99" class="footnote-back-ref">↩</a></li>
<li id="fn:100">Ensor, D.; Peterson, J. R.; Haire, R. G.; Young, J. P. (1981). "Absorption spectrophotometric study of berkelium(III) and (IV) fluorides in the solid state". Journal of Inorganic and Nuclear Chemistry. 43 (5): 1001. doi:10.1016/0022-1902(81)80164-9. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:100" class="footnote-back-ref">↩</a></li>
<li id="fn:101">Peterson, J. R.; Cunningham, B. B. (1968). "Crystal structures and lattice parameters of the compounds of berkelium—IV berkelium trifluoride☆". Journal of Inorganic and Nuclear Chemistry. 30 (7): 1775. doi:10.1016/0022-1902(68)80353-7. <a href="https://escholarship.org/uc/item/1mn5c30t" target="_blank">https://escholarship.org/uc/item/1mn5c30t</a> <a href="#fnref:101" class="footnote-back-ref">↩</a></li>
<li id="fn:102">Laubereau, Peter G.; Burns, John H. (1970). "Microchemical preparation of tricyclopentadienyl compounds of berkelium, californium, and some lanthanide elements". Inorganic Chemistry. 9 (5): 1091. doi:10.1021/ic50087a018. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:102" class="footnote-back-ref">↩</a></li>
<li id="fn:103">Holleman & Wiberg 2007, p. 1969. - Holleman, Arnold F.; Wiberg, Nils (2007). Textbook of Inorganic Chemistry (102nd ed.). Berlin: de Gruyter. ISBN 978-3-11-017770-1. <a href="#fnref:103" class="footnote-back-ref">↩</a></li>
<li id="fn:104">Peterson, J. R.; Cunningham, B. B. (1968). "Crystal structures and lattice parameters of the compounds of berkelium—IIBerkelium trichloride". Journal of Inorganic and Nuclear Chemistry. 30 (3): 823. doi:10.1016/0022-1902(68)80443-9. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:104" class="footnote-back-ref">↩</a></li>
<li id="fn:105">Peterson, J. R.; Young, J. P.; Ensor, D. D.; Haire, R. G. (1986). "Absorption spectrophotometric and x-ray diffraction studies of the trichlorides of berkelium-249 and californium-249". Inorganic Chemistry. 25 (21): 3779. doi:10.1021/ic00241a015. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:105" class="footnote-back-ref">↩</a></li>
<li id="fn:106">Peterson & Hobart 1984, p. 52. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:106" class="footnote-back-ref">↩</a></li>
<li id="fn:107">Peterson & Hobart 1984, p. 38. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:107" class="footnote-back-ref">↩</a></li>
<li id="fn:108">Young, J. P.; Haire, R. G.; Peterson, J. R.; Ensor, D. D.; Fellows, R. L. (1980). "Chemical consequences of radioactive decay. 1. Study of californium-249 ingrowth into crystalline berkelium-249 tribromide: a new crystalline phase of californium tribromide". Inorganic Chemistry. 19 (8): 2209. doi:10.1021/ic50210a003. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:108" class="footnote-back-ref">↩</a></li>
<li id="fn:109">Peterson & Hobart 1984, p. 47. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:109" class="footnote-back-ref">↩</a></li>
<li id="fn:110">Stevenson, J.; Peterson, J. (1979). "Preparation and structural studies of elemental curium-248 and the nitrides of curium-248 and berkelium-249". Journal of the Less Common Metals. 66 (2): 201. doi:10.1016/0022-5088(79)90229-7. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:110" class="footnote-back-ref">↩</a></li>
<li id="fn:111">Damien, D.; Haire, R. G.; Peterson, J. R. (1980). "Preparation and lattice parameters of 249Bk monopnictides". Journal of Inorganic and Nuclear Chemistry. 42 (7): 995. doi:10.1016/0022-1902(80)80390-3. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:111" class="footnote-back-ref">↩</a></li>
<li id="fn:112">Peterson & Hobart 1984, p. 53. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:112" class="footnote-back-ref">↩</a></li>
<li id="fn:113">Peterson & Hobart 1984, pp. 39–40. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:113" class="footnote-back-ref">↩</a></li>
<li id="fn:114">Stevenson, J.; Peterson, J. (1979). "Preparation and structural studies of elemental curium-248 and the nitrides of curium-248 and berkelium-249". Journal of the Less Common Metals. 66 (2): 201. doi:10.1016/0022-5088(79)90229-7. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:114" class="footnote-back-ref">↩</a></li>
<li id="fn:115">Peterson & Hobart 1984, p. 53. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:115" class="footnote-back-ref">↩</a></li>
<li id="fn:116">Peterson & Hobart 1984, p. 47. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:116" class="footnote-back-ref">↩</a></li>
<li id="fn:117">Peterson & Hobart 1984, p. 54. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:117" class="footnote-back-ref">↩</a></li>
<li id="fn:118">Laubereau, Peter G.; Burns, John H. (1970). "Microchemical preparation of tricyclopentadienyl compounds of berkelium, californium, and some lanthanide elements". Inorganic Chemistry. 9 (5): 1091. doi:10.1021/ic50087a018. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:118" class="footnote-back-ref">↩</a></li>
<li id="fn:119">Christoph Elschenbroich Organometallic Chemistry, 6th Edition, Wiesbaden 2008, ISBN 978-3-8351-0167-8, pp. 583–584 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:119" class="footnote-back-ref">↩</a></li>
<li id="fn:120">Peterson & Hobart 1984, pp. 41, 54. - Peterson, J. R.; Hobart, D. E. (1984). "The Chemistry of Berkelium". In Emeléus, Harry Julius (ed.). Advances in inorganic chemistry and radiochemistry. Vol. 28. Academic Press. pp. 29–64. doi:10.1016/S0898-8838(08)60204-4. ISBN 978-0-12-023628-2. <a href="https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29" target="_blank">https://books.google.com/books?id=U-YOlLVuV1YC&pg=PA29</a> <a href="#fnref:120" class="footnote-back-ref">↩</a></li>
<li id="fn:121">Russo, Dominic R.; Gaiser, Alyssa N.; Price, Amy N.; Sergentu, Dumitru-Claudiu; Wacker, Jennifer N.; Katzer, Nicholas; Peterson, Appie A.; Branson, Jacob A.; Yu, Xiaojuan; Kelly, Sheridon N.; Ouellette, Erik T.; Arnold, John; Long, Jeffrey R.; Lukens, Wayne W.; Teat, Simon J. (28 February 2025). "Berkelium–carbon bonding in a tetravalent berkelocene". Science. 387 (6737): 974–978. doi:10.1126/science.adr3346. <a href="https://www.science.org/doi/10.1126/science.adr3346" target="_blank">https://www.science.org/doi/10.1126/science.adr3346</a> <a href="#fnref:121" class="footnote-back-ref">↩</a></li>
<li id="fn:122">Hobart, David E.; Peterson, Joseph R. (2006). "Berkelium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1444–98. doi:10.1007/1-4020-3598-5_10. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 17 July 2010. Retrieved 30 September 2010. <a href="978-1-4020-3555-5" target="_blank">978-1-4020-3555-5</a> <a href="#fnref:122" class="footnote-back-ref">↩</a></li>
<li id="fn:123">Stwertka, Albert. A Guide to the Elements, Oxford University Press, 1996, p. 211. ISBN 0-19-508083-1 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:123" class="footnote-back-ref">↩</a></li>
<li id="fn:124">Hobart, David E.; Peterson, Joseph R. (2006). "Berkelium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1444–98. doi:10.1007/1-4020-3598-5_10. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 17 July 2010. Retrieved 30 September 2010. <a href="978-1-4020-3555-5" target="_blank">978-1-4020-3555-5</a> <a href="#fnref:124" class="footnote-back-ref">↩</a></li>
<li id="fn:125">Hobart, David E.; Peterson, Joseph R. (2006). "Berkelium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1444–98. doi:10.1007/1-4020-3598-5_10. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 17 July 2010. Retrieved 30 September 2010. <a href="978-1-4020-3555-5" target="_blank">978-1-4020-3555-5</a> <a href="#fnref:125" class="footnote-back-ref">↩</a></li>
<li id="fn:126">Haire, Richard G. (2006). "Californium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1499–1576. doi:10.1007/1-4020-3598-5_11. ISBN 978-1-4020-3555-5. Archived from the original (PDF) on 17 July 2010. <a href="978-1-4020-3555-5" target="_blank">978-1-4020-3555-5</a> <a href="#fnref:126" class="footnote-back-ref">↩</a></li>
<li id="fn:127">Collaboration Expands the Periodic Table, One Element at a Time Archived 18 July 2011 at the Wayback Machine, Science and Technology Review, Lawrence Livermore National Laboratory, October/November 2010 <a href="https://str.llnl.gov/OctNov10/shaughnessy.html" target="_blank">https://str.llnl.gov/OctNov10/shaughnessy.html</a> <a href="#fnref:127" class="footnote-back-ref">↩</a></li>
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</ol>

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