Protactinium

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

In 1871, <a href="/facts/Dmitri_Mendeleev/xdouRrx8">Dmitri Mendeleev</a> <a href="/facts/Mendeleev%2527s_predicted_elements/C4vgW0uy">predicted</a> the existence of an element between <a href="/facts/Thorium/ysdWH470">thorium</a> and <a href="/facts/Uranium/n2sGWBzU">uranium</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> The actinide series was unknown at the time, so Mendeleev positioned <a href="/facts/Uranium/n2sGWBzU">uranium</a> below <a href="/facts/Tungsten/WYwbNDYX">tungsten</a> in <a href="/facts/Group_(periodic_table)/YGBcUabv"> group</a> VI, and thorium below <a href="/facts/Zirconium/y7gsoQFz">zirconium</a> in group IV, leaving the space below <a href="/facts/Tantalum/VwaxMm33">tantalum</a> in group V empty. Until the general acceptance of the <a href="/facts/Actinide_concept/1CIhwpU5">actinide concept</a> in the late 1940s, <a href="/facts/Periodic_table/umdGIfUb">periodic tables</a> were published with this structure.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> For a long time, chemists searched for <a href="/facts/Mendeleev%2527s_predicted_elements/C4vgW0uy">eka</a>-tantalum<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> as an element with similar chemical properties to tantalum, making a discovery of protactinium nearly impossible. Tantalum's heavier analogue was later found to be the transuranic element <a href="/facts/Dubnium/3CHC1lEt">dubnium</a> – although dubnium is more chemically similar to protactinium, not tantalum.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>
In 1900, <a href="/facts/William_Crookes/q8U8VVwR">William Crookes</a> isolated protactinium as an intensely radioactive material from uranium; however, he could not characterize it as a new chemical element and thus named it uranium X (UX).<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a><a class="footnote-ref" id="fnref:10" href="#fn:10">10</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> Crookes dissolved <a href="/facts/Uranium_nitrate/RdyzMLgb">uranium nitrate</a> in <a href="/facts/Diethyl_ether/Ep20vEdj">ether</a>, and the residual aqueous phase contained most of the 23490Th and 23491Pa. His method was used into the 1950s to isolate 23490Th and 23491Pa from uranium compounds.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> Protactinium was first identified in 1913, when <a href="/facts/Kasimir_Fajans/ubkxreh4">Kasimir Fajans</a> and <a href="/facts/Oswald_Helmuth_G%25C3%25B6hring/pwCsTmfH">Oswald Helmuth Göhring</a> encountered the isotope 234mPa during their studies of the decay chains of <a href="/facts/Uranium-238/QhcHm6q8">uranium-238</a>: 23892U → 23490Th → 234m91Pa → 23492U. They named the new element "<a href="/facts/Brevium/AVGw4A8U">brevium</a>" (from the Latin word brevis, meaning brief or short) because of the short half-life of 1.16 minutes for 234m91Pa (uranium X2).<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a><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><a class="footnote-ref" id="fnref:17" href="#fn:17">17</a><a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> In 1917–18, two groups of scientists, <a href="/facts/Lise_Meitner/BH51ypJ2">Lise Meitner</a> in collaboration with <a href="/facts/Otto_Hahn/7alx1Db7">Otto Hahn</a> of <a href="/facts/Germany/paluuWBX">Germany</a> and <a href="/facts/Frederick_Soddy/gR9Qk6tc">Frederick Soddy</a> and John Cranston of <a href="/facts/Great_Britain/TNgGQRPj">Great Britain</a>, independently discovered another isotope, 231Pa, having a much longer half-life of 32,760 years.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a><a class="footnote-ref" id="fnref:20" href="#fn:20">20</a><a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> Meitner changed the name "brevium" to protactinium as the new element was part of the decay chain of uranium-235 as the parent of actinium (from the <a href="/facts/Greek_language/pzDd6eIz">Greek</a>: πρῶτος prôtos, meaning "first, before").<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> The <a href="/facts/International_Union_of_Pure_and_Applied_Chemistry/2AV6myCK">IUPAC</a> confirmed this naming in 1949.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a><a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> The discovery of protactinium completed one of the last gaps in early versions of the periodic table, and brought fame to the involved scientists.<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a>
<a href="/facts/Aristid_von_Grosse/Ed81bS6j">Aristid von Grosse</a> produced 2 milligrams of Pa2O5 in 1927,<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a> and in 1934 first isolated elemental protactinium from 0.1 milligrams of Pa2O5.<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a> He used two different procedures: in the first, protactinium oxide was irradiated by 35 keV electrons in vacuum. In the other, called the <a href="/facts/Crystal_bar_process/kw3GMBhY">van Arkel–de Boer process</a>, the oxide was chemically converted to a <a href="/facts/Halide/ujYu8kGD">halide</a> (<a href="/facts/Chloride/m9NUaUDR">chloride</a>, <a href="/facts/Bromide/bHSfxGk1">bromide</a> or <a href="/facts/Iodide/JyVRGWMX">iodide</a>) and then reduced in a vacuum with an electrically heated metallic filament:<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a><a class="footnote-ref" id="fnref:29" href="#fn:29">29</a>

2 PaI5 → 2 Pa + 5 I2
In 1961, the <a href="/facts/United_Kingdom_Atomic_Energy_Authority/2pW1nh16">United Kingdom Atomic Energy Authority</a> (UKAEA) produced 127 grams of 99.9% pure protactinium-231 by processing 60 tonnes of waste material in a 12-stage process, at a cost of about US$500,000.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a><a class="footnote-ref" id="fnref:31" href="#fn:31">31</a> For many years, this was the world's only significant supply of protactinium, which was provided to various laboratories for scientific studies.<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> The <a href="/facts/Oak_Ridge_National_Laboratory/Elq84HKF">Oak Ridge National Laboratory</a> in the US provided protactinium at a cost of about US$280/gram.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a>

<h2 id="isotopes">Isotopes</h2>
Main article: <a href="/facts/Isotopes_of_protactinium/AVGw4A8U">Isotopes of protactinium</a>
Thirty <a href="/facts/Radioisotope/5WpCfbdq">radioisotopes</a> of protactinium have been discovered, ranging from 210Pa to 239Pa.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a><a class="footnote-ref" id="fnref:35" href="#fn:35">35</a> The most stable are 231Pa with a half-life of 32,650 years, 233Pa with a half-life of 26.975 days, and 230Pa with a half-life of 17.4 days. All other isotopes have half-lives shorter than 1.6 days, and the majority of these have half-lives less than 1.8 seconds. Protactinium also has six <a href="/facts/Nuclear_isomer/L8DHcqnk">nuclear isomers</a>, with the most stable being 234mPa (half-life 1.159 minutes).<a class="footnote-ref" id="fnref:36" href="#fn:36">36</a>
The primary <a href="/facts/Decay_mode/Ya6FVjt4">decay mode</a> for the most stable isotope 231Pa and lighter isotopes (210Pa<a class="footnote-ref" id="fnref:37" href="#fn:37">37</a> to 227Pa) is <a href="/facts/Alpha_decay/rCsHNIUE">alpha decay</a>, producing <a href="/facts/Isotopes_of_actinium/vnv59EsB">isotopes of actinium</a>. The primary decay mode for 228Pa to 230Pa is <a href="/facts/Electron_capture/EIccoV1u">electron capture</a> or <a href="/facts/Beta_plus_decay/psWp4bJT">beta plus decay</a>, producing <a href="/facts/Isotopes_of_thorium/lRb3opzg">isotopes of thorium</a>, while the primary decay mode for the heavier isotopes (232Pa to 239Pa) is <a href="/facts/Beta_decay/vxTBlckp">beta decay</a>, producing <a href="/facts/Isotopes_of_uranium/zWIQ6MVL">isotopes of uranium</a>.<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a>

<h3>Nuclear fission</h3>
The longest-lived and most abundant isotope, 231Pa, can fission from <a href="/facts/Neutron_temperature/UMKR4XgJ">fast neutrons</a> exceeding ~1 <a href="/facts/Electronvolt/YMT1fqX9">MeV</a>.<a class="footnote-ref" id="fnref:39" href="#fn:39">39</a> 233Pa, the other isotope of protactinium produced in nuclear reactors, also has a fission threshold of 1 MeV.<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a>

<h2 id="occurrence">Occurrence</h2>
Protactinium is one of the rarest and most expensive naturally occurring elements. It is found in the form of two isotopes – 231Pa and 234Pa, with the isotope 234Pa occurring in two different energy states. Nearly all natural protactinium is 231Pa. It is an <a href="/facts/Alpha_particle/dzNMs9WP">alpha emitter</a> and is formed by the decay of uranium-235, whereas the <a href="/facts/Beta_particle/x8b3ttLn">beta-radiating</a> 234Pa is produced as a result of uranium-238 decay. Nearly all uranium-238 (99.8%) decays first to the shorter-lived 234mPa isomer.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a>
Protactinium occurs in <a href="/facts/Uraninite/EsEwMErJ">uraninite</a> (pitchblende) at concentrations of about 0.3-3 <a href="/facts/Parts-per_notation/PozRuoLM">parts</a> 231Pa per million parts (ppm) of ore.<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a> Whereas the usual content is closer to 0.3 ppm<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a> (e.g. in <a href="/facts/J%25C3%25A1chymov/G2a4pC7j">Jáchymov</a>, <a href="/facts/Czech_Republic/vJYLD66Q">Czech Republic</a><a class="footnote-ref" id="fnref:44" href="#fn:44">44</a>), some ores from the <a href="/facts/Democratic_Republic_of_the_Congo/E2KmHDdv">Democratic Republic of the Congo</a> have about 3 ppm.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a> Protactinium is homogeneously dispersed in most natural materials and in water, but at much lower concentrations on the order of one part per trillion, corresponding to a radioactivity of 0.1 picocuries (pCi)/g. There is about 500 times more protactinium in sandy soil particles than in water, even when compared to water present in the same sample of soil. Much higher ratios of 2,000 and above are measured in <a href="/facts/Loam/nH85XD2B">loam</a> soils and clays, such as <a href="/facts/Bentonite/N9Hb8lX9">bentonite</a>.<a class="footnote-ref" id="fnref:46" href="#fn:46">46</a><a class="footnote-ref" id="fnref:47" href="#fn:47">47</a>

<h3>In nuclear reactors</h3>
Two major protactinium isotopes, 231Pa and 233Pa, are produced from thorium in <a href="/facts/Nuclear_reactor/8xqjIbge">nuclear reactors</a>; both are undesirable and are usually removed, thereby adding complexity to the reactor design and operation. In particular, 232Th, via <a href="/facts/Nuclear_reaction/202yClUr"> (n, 2n)</a> reactions, produces 231Th, which quickly decays to 231Pa (half-life 25.5 hours). The last isotope, while not a transuranic waste, has a long half-life of 32,760 years, and is a major contributor to the long-term <a href="/facts/Radiotoxic/vw0d9GaT">radiotoxicity</a> of spent nuclear fuel.<a class="footnote-ref" id="fnref:48" href="#fn:48">48</a>
Protactinium-233 is formed upon neutron capture by 232Th. It either further decays to 233U, or captures another neutron and converts into the non-fissile 234U.<a class="footnote-ref" id="fnref:49" href="#fn:49">49</a> 233Pa has a relatively long half-life of 27 days and high <a href="/facts/Cross_section_(physics)/lo014h2D">cross section</a> for neutron capture (the so-called "<a href="/facts/Neutron_poison/bkruR3yz">neutron poison</a>"). Thus, instead of rapidly decaying to the useful 233U, a significant fraction of 233Pa converts to non-fissile isotopes and consumes neutrons, degrading <a href="/facts/Neutron_economy/j5J8wj5T">reactor efficiency</a>. To limit the loss of neutrons, 233Pa is extracted from the active zone of thorium <a href="/facts/Molten_salt_reactor/aSvp1qTG">molten salt reactors</a> during their operation, so that it can only decay into 233U. Extraction of 233Pa is achieved using columns of molten <a href="/facts/Bismuth/75FLjkoX">bismuth</a> with lithium dissolved in it. In short, lithium selectively reduces protactinium salts to protactinium metal, which is then extracted from the molten-salt cycle, while the molten bismuth is merely a carrier, selected due to its low <a href="/facts/Melting_point/MY0w0h0k">melting point</a> of 271 °C, low vapor pressure, good solubility for lithium and actinides, and <a href="/facts/Miscibility/HwQaolbQ"> immiscibility</a> with molten <a href="/facts/Halide/ujYu8kGD">halides</a>.<a class="footnote-ref" id="fnref:50" href="#fn:50">50</a>

<h2 id="preparation">Preparation</h2>

Before the advent of nuclear reactors, protactinium was separated for scientific experiments from uranium ores. Since reactors have become more common, it is mostly produced as an intermediate product of <a href="/facts/Nuclear_fission/LfkIylvm">nuclear fission</a> in <a href="/facts/Thorium_fuel_cycle/mohxxkx3">thorium fuel cycle</a> reactors as an intermediate in the production of the fissile 233U:

Th
            
            
            
            90
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              →
              
                22.3
                 
                
                  min
                
              
              
                
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            Pa
            
            
            
            91
            233
          
          
            
              →
              
                26.967
                 
                
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    {\displaystyle {\ce {^{232}_{90}Th + ^{1}_{0}n -> ^{233}_{90}Th ->[\beta^-][22.3\ {\ce {min}}] ^{233}_{91}Pa ->[\beta^-][26.967\ {\ce {d}}] ^{233}_{92}U.}}}

The isotope 231Pa can be prepared by irradiating 230Th with <a href="/facts/Neutron_temperature/UMKR4XgJ"> slow neutrons</a>, converting it to the beta-decaying 231Th; or, by irradiating 232Th with fast neutrons, generating 231Th and 2 neutrons.
Protactinium metal can be prepared by reduction of its <a href="/facts/Fluoride/LpqNMzwa">fluoride</a> with <a href="/facts/Calcium/hf252CC0">calcium</a>,<a class="footnote-ref" id="fnref:51" href="#fn:51">51</a> <a href="/facts/Lithium/7vXX6BWA">lithium</a>, or <a href="/facts/Barium/IkL09XHQ">barium</a> at a temperature of 1300–1400 °C.<a class="footnote-ref" id="fnref:52" href="#fn:52">52</a><a class="footnote-ref" id="fnref:53" href="#fn:53">53</a>

<h2 id="properties">Properties</h2>
Protactinium is an <a href="/facts/Actinide/kHC4lxJV">actinide</a> positioned in the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a> to the left of <a href="/facts/Uranium/n2sGWBzU">uranium</a> and to the right of <a href="/facts/Thorium/ysdWH470">thorium</a>, and many of its physical properties are intermediate between its neighboring actinides. Protactinium is denser and more rigid than thorium, but is lighter than uranium; its melting point is lower than that of thorium, but higher than that of uranium. The thermal expansion, electrical, and thermal conductivities of these three elements are comparable and are typical of <a href="/facts/Post-transition_metal/wjp3aeGn">post-transition metals</a>. The estimated <a href="/facts/Shear_modulus/9e9IvJnz">shear modulus</a> of protactinium is similar to that of <a href="/facts/Titanium/53ArnDoy">titanium</a>.<a class="footnote-ref" id="fnref:54" href="#fn:54">54</a> Protactinium is a metal with silvery-gray luster that is preserved for some time in air.<a class="footnote-ref" id="fnref:55" href="#fn:55">55</a><a class="footnote-ref" id="fnref:56" href="#fn:56">56</a> Protactinium easily reacts with oxygen, water vapor, and acids, but not with alkalis.<a class="footnote-ref" id="fnref:57" href="#fn:57">57</a>
At room temperature, protactinium crystallizes in the body-centered <a href="/facts/Tetragonal_crystal_system/12Aop255">tetragonal</a> structure, which can be regarded as distorted body-centered cubic lattice; this structure does not change upon compression up to 53 GPa. The structure changes to face-centered cubic (fcc) upon cooling from high temperature, at about 1200 °C.<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a><a class="footnote-ref" id="fnref:59" href="#fn:59">59</a> The thermal expansion coefficient of the tetragonal phase between room temperature and 700 °C is 9.9×10−6/°C.<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a>
Protactinium is <a href="/facts/Paramagnetism/vj1SMbbp">paramagnetic</a> and no magnetic transitions are known for it at any temperature.<a class="footnote-ref" id="fnref:61" href="#fn:61">61</a> It becomes <a href="/facts/Superconductivity/pqQAlSzJ">superconductive</a> at temperatures below 1.4 K.<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a><a class="footnote-ref" id="fnref:63" href="#fn:63">63</a> Protactinium tetrachloride is paramagnetic at room temperature, but becomes <a href="/facts/Ferromagnetism/fH3HFnSl">ferromagnetic</a> when cooled to 182 K.<a class="footnote-ref" id="fnref:64" href="#fn:64">64</a>
Protactinium exists in two major <a href="/facts/Oxidation_state/W53W6s6V">oxidation states</a>: +4 and +5, both in solids and solutions; and the +3 and +2 states, which have been observed in some solids. As the electron configuration of the neutral atom is [Rn]5f26d17s2, the +5 oxidation state corresponds to the low-energy (and thus favored) 5f0 configuration. Both +4 and +5 states easily form <a href="/facts/Hydroxide/zW0wxpWD">hydroxides</a> in water, with the predominant ions being Pa(OH)3+, Pa(OH)2+2, Pa(OH)+3, and Pa(OH)4, all of which are colorless.<a class="footnote-ref" id="fnref:65" href="#fn:65">65</a> Other known protactinium ions include PaCl2+2, PaSO2+4, PaF3+, PaF2+2, PaF−6, PaF2−7, and PaF3−8.<a class="footnote-ref" id="fnref:66" href="#fn:66">66</a><a class="footnote-ref" id="fnref:67" href="#fn:67">67</a>

<h2 id="chemical-compounds">Chemical compounds</h2>
Main article: <a href="/facts/Protactinium_compounds/Pg6ao1wx">Protactinium compounds</a>
<table><tbody><tr><th>Formula</th><th>color</th><th>symmetry</th><th><a href="/facts/Space_group/2XQx0J7M">space group</a></th><th>No</th><th><a href="/facts/Pearson_symbol/K3qljnNu">Pearson symbol</a></th><th>a (pm)</th><th>b (pm)</th><th>c (pm)</th><th>Z</th><th>density (g/cm3)</th></tr><tr><td>Pa</td><td>silvery-gray</td><td><a href="/facts/Tetragonal_crystal_system/12Aop255">tetragonal</a><a class="footnote-ref" id="fnref:68" href="#fn:68">68</a></td><td>I4/mmm</td><td>139</td><td>tI2</td><td>392.5</td><td>392.5</td><td>323.8</td><td>2</td><td>15.37</td></tr><tr><td>PaO</td><td></td><td>rocksalt<a class="footnote-ref" id="fnref:69" href="#fn:69">69</a></td><td>Fm3m</td><td>225</td><td>cF8</td><td>496.1</td><td></td><td></td><td>4</td><td>13.44</td></tr><tr><td><a href="/facts/Protactinium(IV)_oxide/rXRWTsDA">PaO2</a></td><td>black</td><td>fcc<a class="footnote-ref" id="fnref:70" href="#fn:70">70</a></td><td>Fm3m</td><td>225</td><td>cF12</td><td>550.5</td><td></td><td></td><td>4</td><td>10.47</td></tr><tr><td><a href="/facts/Protactinium(V)_oxide/jgnWQV1Y">Pa2O5</a></td><td>white</td><td></td><td>Fm3m<a class="footnote-ref" id="fnref:71" href="#fn:71">71</a></td><td>225</td><td>cF16</td><td>547.6</td><td>547.6</td><td>547.6</td><td>4</td><td>10.96</td></tr><tr><td>Pa2O5</td><td>white</td><td>orthorhombic<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a></td><td></td><td></td><td></td><td>692</td><td>402</td><td>418</td><td></td><td></td></tr><tr><td>PaH3</td><td>black</td><td>cubic<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a></td><td>Pm3n</td><td>223</td><td>cP32</td><td>664.8</td><td>664.8</td><td>664.8</td><td>8</td><td>10.58</td></tr><tr><td>PaF4</td><td>brown-red</td><td>monoclinic<a class="footnote-ref" id="fnref:74" href="#fn:74">74</a></td><td>C2/c</td><td>15</td><td>mS60</td><td></td><td></td><td></td><td>2</td><td></td></tr><tr><td>PaCl4</td><td>green-yellow</td><td><a href="/facts/Tetragonal_crystal_system/12Aop255">tetragonal</a><a class="footnote-ref" id="fnref:75" href="#fn:75">75</a></td><td>I41/amd</td><td>141</td><td>tI20</td><td>837.7</td><td>837.7</td><td>748.1</td><td>4</td><td>4.72</td></tr><tr><td>PaBr4</td><td>brown</td><td>tetragonal<a class="footnote-ref" id="fnref:76" href="#fn:76">76</a><a class="footnote-ref" id="fnref:77" href="#fn:77">77</a></td><td>I41/amd</td><td>141</td><td>tI20</td><td>882.4</td><td>882.4</td><td>795.7</td><td></td><td></td></tr><tr><td><a href="/facts/Protactinium(V)_chloride/2nKvk20t">PaCl5</a></td><td>yellow</td><td><a href="/facts/Monoclinic_crystal_system/5PCwXvzX">monoclinic</a><a class="footnote-ref" id="fnref:78" href="#fn:78">78</a></td><td>C2/c</td><td>15</td><td>mS24</td><td>797</td><td>1135</td><td>836</td><td>4</td><td>3.74</td></tr><tr><td>PaBr5</td><td>red</td><td>monoclinic<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a><a class="footnote-ref" id="fnref:80" href="#fn:80">80</a></td><td>P21/c</td><td>14</td><td>mP24</td><td>838.5</td><td>1120.5</td><td>1214.6</td><td>4</td><td>4.98</td></tr><tr><td>PaOBr3</td><td></td><td>monoclinic<a class="footnote-ref" id="fnref:81" href="#fn:81">81</a></td><td>C2</td><td></td><td></td><td>1691.1</td><td>387.1</td><td>933.4</td><td></td><td></td></tr><tr><td>Pa(PO3)4</td><td></td><td>orthorhombic<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a></td><td></td><td></td><td></td><td>696.9</td><td>895.9</td><td>1500.9</td><td></td><td></td></tr><tr><td>Pa2P2O7</td><td></td><td>cubic<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a></td><td>Pa3</td><td></td><td></td><td>865</td><td>865</td><td>865</td><td></td><td></td></tr><tr><td>Pa(C8H8)2</td><td>golden-yellow</td><td>monoclinic<a class="footnote-ref" id="fnref:84" href="#fn:84">84</a></td><td></td><td></td><td></td><td>709</td><td>875</td><td>1062</td><td></td><td></td></tr></tbody></table>
Here, a, b, and c are lattice constants in picometers, No is the space group number, and Z is the number of <a href="/facts/Formula_unit/P6LUge8g">formula units</a> per <a href="/facts/Unit_cell/znygJqdx">unit cell</a>; fcc stands for the <a href="/facts/Cubic_crystal_system/92Co7BKM">face-centered cubic</a> symmetry. Density was not measured directly but calculated from the lattice parameters.

<h3>Oxides and oxygen-containing salts</h3>
Protactinium oxides are known for the metal oxidation states +2, +4, and +5. The most stable is the white pentoxide <a href="/facts/Protactinium(V)_oxide/jgnWQV1Y">Pa2O5</a>, which can be produced by igniting protactinium(V) hydroxide in <a href="/facts/Air/6IyFHIpG">air</a> at a temperature of 500 °C.<a class="footnote-ref" id="fnref:85" href="#fn:85">85</a> Its crystal structure is cubic, and the chemical composition is often non-stoichiometric, described as PaO2.25. Another phase of this oxide with orthorhombic symmetry has also been reported.<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a><a class="footnote-ref" id="fnref:87" href="#fn:87">87</a> The black dioxide <a href="/facts/Protactinium(IV)_oxide/rXRWTsDA">PaO2</a> is obtained from the pentoxide by reducing it at 1550 °C with hydrogen. It is not readily soluble in either dilute or concentrated <a href="/facts/Nitric_acid/UDbwGp6s">nitric</a>, <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric</a>, or <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>, but easily dissolves in <a href="/facts/Hydrofluoric_acid/wdXqu4bE">hydrofluoric acid</a>.<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a> The dioxide can be converted back to pentoxide by heating in oxygen-containing atmosphere to 1100 °C.<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a> The monoxide PaO has only been observed as a thin coating on protactinium metal, but not in an isolated bulk form.<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a>
Protactinium forms mixed binary oxides with various metals. With alkali metals A, the crystals have a chemical formula APaO3 and <a href="/facts/Perovskite_structure/Gu39aNyo">perovskite structure</a>; A3PaO4 and distorted rock-salt structure; or A7PaO6, where oxygen atoms form a hexagonal close-packed lattice. In all of these materials, the protactinium ions are octahedrally coordinated.<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a><a class="footnote-ref" id="fnref:92" href="#fn:92">92</a> The pentoxide Pa2O5 combines with rare-earth metal oxides R2O3 to form various nonstoichiometric mixed-oxides, also of perovskite structure.<a class="footnote-ref" id="fnref:93" href="#fn:93">93</a>
Protactinium oxides are <a href="/facts/Basic_oxide/E9w18zQF">basic</a>; they easily convert to hydroxides and can form various salts, such as <a href="/facts/Sulfate/yuWVxsUf">sulfates</a>, <a href="/facts/Phosphate/FDGVCxUG">phosphates</a>, <a href="/facts/Nitrate/5AnVlYnL">nitrates</a>, etc. The nitrate is usually white but can be brown due to <a href="/facts/Radiolysis/BzPNnEvu">radiolytic</a> decomposition. Heating the nitrate in air at 400 °C converts it to the white protactinium pentoxide.<a class="footnote-ref" id="fnref:94" href="#fn:94">94</a> The polytrioxophosphate Pa(PO3)4 can be produced by reacting the difluoride sulfate PaF2SO4 with <a href="/facts/Phosphoric_acid/l6NbwyCv">phosphoric acid</a> (H3PO4) under an inert atmosphere. Heating the product to about 900 °C eliminates the reaction by-products, which include <a href="/facts/Hydrofluoric_acid/wdXqu4bE">hydrofluoric acid</a>, <a href="/facts/Sulfur_trioxide/Ijvm08Lq">sulfur trioxide</a>, and phosphoric anhydride. Heating it to higher temperatures in an inert atmosphere decomposes Pa(PO3)4 into the diphosphate PaP2O7, which is analogous to diphosphates of other actinides. In the diphosphate, the PO3 groups form pyramids of C2v symmetry. Heating PaP2O7 in air to 1400 °C decomposes it into the pentoxides of phosphorus and protactinium.<a class="footnote-ref" id="fnref:95" href="#fn:95">95</a>

<h3>Halides</h3>
Protactinium(V) fluoride is a white compound that forms tetragonal crystals, <a href="/facts/Isomorphism_(crystallography)/f1XqB5Iq">isomorphic</a> to β-<a href="/facts/Uranium_pentafluoride/K7qkhXIA">UF5</a>.<a class="footnote-ref" id="fnref:96" href="#fn:96">96</a> Protactinium(V) chloride forms yellow crystals where protactinium ions are arranged in pentagonal bipyramids and <a href="/facts/Coordination_number/mf48hsoX">coordinated</a> by 7 other ions. The coordination changes to octahedral in the brown protactinium(V) bromide, but is unknown for protactinium(V) iodide. The protactinium coordination in all its tetrahalides is 8, but the arrangement is square antiprismatic in protactinium(IV) fluoride and dodecahedral in the chloride and bromide. Brown-colored protactinium(III) iodide has been reported, where protactinium ions are 8-coordinated in a bicapped trigonal prismatic arrangement.<a class="footnote-ref" id="fnref:97" href="#fn:97">97</a>

Protactinium(V) chloride has a polymeric structure of monoclinic symmetry.<a class="footnote-ref" id="fnref:98" href="#fn:98">98</a> There, within one polymeric chain, all chlorine atoms lie in one graphite-like plane and form planar pentagons around the protactinium ions. The 7-coordination of protactinium originates from the five chlorine atoms and two bonds to protactinium atoms belonging to the nearby chains. It easily hydrolyzes in water.<a class="footnote-ref" id="fnref:99" href="#fn:99">99</a> It melts at 300 °C and sublimates at even lower temperatures.
Protactinium(V) fluoride can be prepared by reacting protactinium oxide with either <a href="/facts/Bromine_pentafluoride/mCtsa5ja">bromine pentafluoride</a> or <a href="/facts/Bromine_trifluoride/yHaNctl0">bromine trifluoride</a> at about 600 °C, and protactinium(IV) fluoride is obtained from the oxide and a mixture of hydrogen and <a href="/facts/Hydrogen_fluoride/XfQxlqR6">hydrogen fluoride</a> at 600 °C; a large excess of hydrogen is required to remove atmospheric oxygen leaks into the reaction.<a class="footnote-ref" id="fnref:100" href="#fn:100">100</a>
Protactinium(V) chloride is prepared by reacting protactinium oxide with <a href="/facts/Carbon_tetrachloride/S2ekjT0E">carbon tetrachloride</a> at temperatures of 200–300 °C.<a class="footnote-ref" id="fnref:101" href="#fn:101">101</a> The by-products (such as PaOCl3) are removed by fractional sublimation.<a class="footnote-ref" id="fnref:102" href="#fn:102">102</a> Reduction of protactinium(V) chloride with hydrogen at about 800 °C yields protactinium(IV) chloride – a yellow-green solid that sublimes in vacuum at 400 °C. It can also be obtained directly from protactinium dioxide by treating it with carbon tetrachloride at 400 °C.<a class="footnote-ref" id="fnref:103" href="#fn:103">103</a>
Protactinium bromides are produced by the action of <a href="/facts/Aluminium_bromide/RjaCD8er">aluminium bromide</a>, <a href="/facts/Hydrogen_bromide/rUw1duLA">hydrogen bromide</a>, <a href="/facts/Carbon_tetrabromide/sokAWGTC">carbon tetrabromide</a>, or a mixture of hydrogen bromide and <a href="/facts/Thionyl_bromide/BqBDkvEp">thionyl bromide</a> on protactinium oxide. They can alternatively be produced by reacting protactinium pentachloride with hydrogen bromide or thionyl bromide.<a class="footnote-ref" id="fnref:104" href="#fn:104">104</a> Protactinium(V) bromide has two similar monoclinic forms: one is obtained by sublimation at 400–410 °C, and another by sublimation at a slightly lower temperature of 390–400 °C.<a class="footnote-ref" id="fnref:105" href="#fn:105">105</a><a class="footnote-ref" id="fnref:106" href="#fn:106">106</a>
Protactinium iodides can be produced by reacting protactinium metal with elemental iodine at 600 °C, and by reacting Pa2O5 with AlI3 at elevated temperatures.<a class="footnote-ref" id="fnref:107" href="#fn:107">107</a> Protactinium(III) iodide can be obtained by heating protactinium(V) iodide in vacuum.<a class="footnote-ref" id="fnref:108" href="#fn:108">108</a> As with oxides, protactinium forms mixed halides with alkali metals. The most remarkable among these is Na3PaF8, where the protactinium ion is symmetrically surrounded by 8 F− ions, forming a nearly perfect cube.<a class="footnote-ref" id="fnref:109" href="#fn:109">109</a>
More complex protactinium fluorides are also known, such as Pa2F9<a class="footnote-ref" id="fnref:110" href="#fn:110">110</a> and ternary fluorides of the types MPaF6 (M = Li, Na, K, Rb, Cs or NH4), M2PaF7 (M = K, Rb, Cs or NH4), and M3PaF8 (M = Li, Na, Rb, Cs), all of which are white crystalline solids. The MPaF6 formula can be represented as a combination of MF and PaF5. These compounds can be obtained by evaporating a hydrofluoric acid solution containing both complexes. For the small alkali cations like Na, the crystal structure is tetragonal, whereas it becomes orthorhombic for larger cations K+, Rb+, Cs+ or NH4+. A similar variation was observed for the M2PaF7 fluorides: namely, the crystal symmetry was dependent on the cation and differed for Cs2PaF7 and M2PaF7 (M = K, Rb or NH4).<a class="footnote-ref" id="fnref:111" href="#fn:111">111</a>

<h3>Other inorganic compounds</h3>
Oxyhalides and oxysulfides of protactinium are known. PaOBr3 has a monoclinic structure composed of double-chain units where protactinium has coordination 7 and is arranged into pentagonal bipyramids. The chains are interconnected through oxygen and bromine atoms, and each oxygen atom is related to three protactinium atoms.<a class="footnote-ref" id="fnref:112" href="#fn:112">112</a> PaOS is a light-yellow, non-volatile solid with a cubic crystal lattice isostructural to that of other actinide oxysulfides. It is obtained by reacting protactinium(V) chloride with a mixture of <a href="/facts/Hydrogen_sulfide/UbCqjMMk">hydrogen sulfide</a> and <a href="/facts/Carbon_disulfide/b04Tadmy">carbon disulfide</a> at 900 °C.<a class="footnote-ref" id="fnref:113" href="#fn:113">113</a>
In hydrides and nitrides, protactinium has a low oxidation state of about +3. The hydride is obtained by direct action of hydrogen on the metal at 250 °C, and the nitride is a product of ammonia and protactinium tetrachloride or pentachloride. This bright yellow solid is thermally stable to 800 °C in vacuum. Protactinium carbide (PaC) is formed by the reduction of protactinium tetrafluoride with barium in a carbon crucible at a temperature of about 1400 °C.<a class="footnote-ref" id="fnref:114" href="#fn:114">114</a> Protactinium forms <a href="/facts/Borohydride/5zFNIPw7">borohydrides</a>, which include Pa(BH4)4. It has an unusual polymeric structure with helical chains, where the protactinium atom has coordination number of 14 and is surrounded by six BH4− ions.<a class="footnote-ref" id="fnref:115" href="#fn:115">115</a>

<h3>Organometallic compounds</h3>

Protactinium(IV) forms a tetrahedral complex tetrakis(cyclopentadienyl)protactinium(IV) (or Pa(C5H5)4) with four <a href="/facts/Cyclopentadienyl_complex/rezSmzLI">cyclopentadienyl</a> rings, which can be synthesized by reacting protactinium(IV) chloride with Be(C5H5)2. One ring can be substituted with a halide atom.<a class="footnote-ref" id="fnref:116" href="#fn:116">116</a> Another organometallic complex is the golden-yellow bis(π-cyclooctatetraene) protactinium, or <a href="/facts/Protactinocene/tG8phIFL">protactinocene</a> (Pa(C8H8)2), which is analogous in structure to <a href="/facts/Uranocene/7cJHsK0X">uranocene</a>. There, the metal atom is sandwiched between two <a href="/facts/Cyclooctatetraene/fdCNPh7K">cyclooctatetraene</a> ligands. Similar to uranocene, it can be prepared by reacting protactinium tetrachloride with dipotassium <a href="/facts/Cyclooctatetraene/fdCNPh7K">cyclooctatetraenide</a> (K2C8H8) in <a href="/facts/Tetrahydrofuran/P5t6SkMK">tetrahydrofuran</a>.<a class="footnote-ref" id="fnref:117" href="#fn:117">117</a>

<h2 id="applications">Applications</h2>
Although protactinium is situated in the periodic table between uranium and thorium, both of which have numerous applications, there are currently no uses for protactinium outside scientific research owing to its scarcity, high radioactivity, and high toxicity.<a class="footnote-ref" id="fnref:118" href="#fn:118">118</a>
231Pa arises naturally from the decay of natural 235U, and artificially in nuclear reactors by the reaction 232Th + n → 231Th + 2n and the subsequent <a href="/facts/Beta_decay/vxTBlckp">beta decay</a> of 231Th. It was once thought to be able to support a nuclear chain reaction, which could in principle be used to build <a href="/facts/Nuclear_weapon/QVdBcMdm">nuclear weapons</a>; the <a href="/facts/Physicist/cQcgvSIm">physicist</a> Walter Seifritz [de] once estimated the associated <a href="/facts/Critical_mass/BrzhevQR">critical mass</a> as 750±180 kg.<a class="footnote-ref" id="fnref:119" href="#fn:119">119</a> However, the possibility of criticality of 231Pa has since been ruled out.<a class="footnote-ref" id="fnref:120" href="#fn:120">120</a><a class="footnote-ref" id="fnref:121" href="#fn:121">121</a>
With the advent of highly sensitive <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometers</a>, an application of 231Pa as a tracer in geology and <a href="/facts/Paleoceanography/hKd7raqy">paleoceanography</a> has become possible. In this application, the ratio of 231Pa to 230Th is used for <a href="/facts/Radiometric_dating/bDFjdPqV">radiometric dating</a> of sediments which are up to 175,000 years old, and in modeling of the formation of minerals.<a class="footnote-ref" id="fnref:122" href="#fn:122">122</a> In particular, its evaluation in oceanic sediments helped to reconstruct the movements of <a href="/facts/North_Atlantic/EI4uChIb">North Atlantic</a> water bodies during the last melting of <a href="/facts/Ice_age/agSMvAgX">Ice Age</a> <a href="/facts/Glacier/8GrKVUSS">glaciers</a>.<a class="footnote-ref" id="fnref:123" href="#fn:123">123</a> Some of the protactinium-related dating variations rely on analysis of the relative concentrations of several long-living members of the uranium decay chain – uranium, protactinium, and thorium, for example. These elements have 6, 5, and 4 valence electrons, thus favoring +6, +5, and +4 oxidation states respectively, and display different physical and chemical properties. Thorium and protactinium, but not uranium compounds, are poorly soluble in aqueous solutions and precipitate into sediments; the precipitation rate is faster for thorium than for protactinium. The concentration analysis for both protactinium-231 (half-life 32,760 years) and 230Th (half-life 75,380 years) improves measurement accuracy compared to when only one isotope is measured; this double-isotope method is also weakly sensitive to inhomogeneities in the spatial distribution of the isotopes and to variations in their precipitation rate.<a class="footnote-ref" id="fnref:124" href="#fn:124">124</a><a class="footnote-ref" id="fnref:125" href="#fn:125">125</a>

<h2 id="precautions">Precautions</h2>
Protactinium is both toxic and highly radioactive; thus, it is handled exclusively in a sealed <a href="/facts/Glove_box/NnR37n6E">glove box</a>. Its major isotope 231Pa has a <a href="/facts/Specific_activity/KIv7s4N4">specific activity</a> of 0.048 <a href="/facts/Curie_(unit)/LeS60aVv">curies</a> (1.8 <a href="/facts/Becquerel/4C3yrsqp">GBq</a>) per gram and primarily emits alpha-particles with an energy of 5 MeV, which can be stopped by a thin layer of any material. However, it slowly decays, with a half-life of 32,760 years, into 227Ac, which has a specific activity of 74 curies (2,700 GBq) per gram, emits both alpha and beta radiation, and has a much shorter half-life of 22 years. 227Ac, in turn, decays into lighter isotopes with even shorter half-lives and much greater specific activities (SA).<a class="footnote-ref" id="fnref:126" href="#fn:126">126</a>

<table><tbody><tr><th>Isotope</th><td>231Pa</td><td>227Ac</td><td>227Th</td><td>223Ra</td><td>219Rn</td><td>215Po</td><td>211Pb</td><td>211Bi</td><td>207Tl</td></tr><tr><th>SA (<a href="/facts/Curie_(unit)/LeS60aVv">Ci</a>/g)</th><td>0.048</td><td>73</td><td>3.1×104</td><td>5.2×104</td><td>1.3×1010</td><td>3×1013</td><td>2.5×107</td><td>4.2×108</td><td>1.9×108</td></tr><tr><th>Decay</th><td>α</td><td>α, β</td><td>α</td><td>α</td><td>α</td><td>α</td><td>β</td><td>α, β</td><td>β</td></tr><tr><th><a href="/facts/Half-life/kGVH8BAB">Half-life</a></th><td>33 ka</td><td>22 a</td><td>19 days</td><td>11 days</td><td>4 s</td><td>1.8 ms</td><td>36 min</td><td>2.1 min</td><td>4.8 min</td></tr></tbody></table>
As protactinium is present in small amounts in most natural products and materials, it is ingested with food or water and inhaled with air. Only about 0.05% of ingested protactinium is absorbed into the blood and the remainder is excreted. From the blood, about 40% of the protactinium
deposits in the bones, about 15% goes to the liver, 2% to the kidneys, and the rest leaves the body. The biological half-life of protactinium is about 50 years in the bones, whereas its biological half-life in other organs has a fast and slow component. For example, 70% of the protactinium in the liver has a biological half-life of 10 days, and the remaining 30% for 60 days. The corresponding values for kidneys are 20% (10 days) and 80% (60 days). In each affected organ, protactinium promotes cancer via its radioactivity.<a class="footnote-ref" id="fnref:127" href="#fn:127">127</a><a class="footnote-ref" id="fnref:128" href="#fn:128">128</a> The maximum safe dose of Pa in the human body is 0.03 μCi (1.1 kBq), which corresponds to 0.5 micrograms of 231Pa.<a class="footnote-ref" id="fnref:129" href="#fn:129">129</a> The maximum allowed concentrations of 231Pa in the air in Germany is 3×10−4 Bq/m3.<a class="footnote-ref" id="fnref:130" href="#fn:130">130</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Ada_Hitchins/wYJCd0Kp">Ada Hitchins</a>, who helped Soddy in discovering the element protactinium</li></ul>
<h2 id="notes">Notes</h2>

<h2 id="bibliography">Bibliography</h2>
<ul><li><a href="/facts/Norman_Greenwood/XRDmRE8L">Greenwood, Norman N.</a>; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). <a href="/facts/Butterworth%25E2%2580%2593Heinemann/c9nUxIVF">Butterworth–Heinemann</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0080379418.</li></ul>
<h2 id="external-links">External links</h2>

Wikimedia Commons has media related to Protactinium.

Look up protactinium in Wiktionary, the free dictionary.

<ul><li><a href="http://www.periodicvideos.com/videos/091.htm">Protactinium</a> at <a href="/facts/The_Periodic_Table_of_Videos/vC5kbN0M">The Periodic Table of Videos</a> (University of Nottingham)</li></ul>

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

<ol>
<li id="fn:1">Meitner, Lise (1918). "Die Muttersubstanz des Actiniums, Ein Neues Radioaktives Element von Langer Lebensdauer". Zeitschrift für Elektrochemie und angewandte physikalische Chemie. 24 (11–12): 169–173. doi:10.1002/bbpc.19180241107. ISSN 0372-8323. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"Protactinium" (PDF). Human Health Fact Sheet. ANL (Argonne National Laboratory). November 2001. Retrieved 4 September 2023. The name comes from the Greek work protos (meaning first) and the element actinium, because protactinium is the precursor of actinium. <a href="http://hpschapters.org/northcarolina/NSDS/Protactinium.pdf" target="_blank">http://hpschapters.org/northcarolina/NSDS/Protactinium.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">John Arnold Cranston Archived 11 March 2020 at the Wayback Machine. University of Glasgow <a href="http://www.universitystory.gla.ac.uk/biography/?id=WH3023&type=P" target="_blank">http://www.universitystory.gla.ac.uk/biography/?id=WH3023&type=P</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
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<li id="fn:7">The prefix "eka" is derived from the Sanskrit एक, meaning "one" or "first." In chemistry, it was formerly used to denote an element one period below the element name following it. <a href="/wiki/Sanskrit" target="_blank">/wiki/Sanskrit</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
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<li id="fn:17">Eric Scerri, A tale of seven elements, (Oxford University Press 2013) ISBN 978-0-19-539131-2, p.67–74 <a href="/wiki/Eric_Scerri" target="_blank">/wiki/Eric_Scerri</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
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<li id="fn:19">Meitner, Lise (1918). "Die Muttersubstanz des Actiniums, Ein Neues Radioaktives Element von Langer Lebensdauer". Zeitschrift für Elektrochemie und angewandte physikalische Chemie. 24 (11–12): 169–173. doi:10.1002/bbpc.19180241107. ISSN 0372-8323. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
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<li id="fn:22">"Protactinium - Element information : Chemistry in its element: protactinium". www.rsc.org. Royal Society of Chemistry. Retrieved 20 October 2023. At this point Fajans withdrew the name brevium since the custom was to name an element according to longest-lived isotope. Meitner than chose the name protactinium. <a href="https://www.rsc.org/periodic-table/element/91/protactinium" target="_blank">https://www.rsc.org/periodic-table/element/91/protactinium</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
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<li id="fn:28">Hammond, C. R. (29 June 2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9. <a href="978-0-8493-0485-9" target="_blank">978-0-8493-0485-9</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">Grosse, A. V. (1934). "Metallic Element 91". Journal of the American Chemical Society. 56 (10): 2200–2201. Bibcode:1934JAChS..56R2200G. doi:10.1021/ja01325a508. <a href="/wiki/Journal_of_the_American_Chemical_Society" target="_blank">/wiki/Journal_of_the_American_Chemical_Society</a> <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">Hammond, C. R. (29 June 2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9. <a href="978-0-8493-0485-9" target="_blank">978-0-8493-0485-9</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
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<li id="fn:34">Zhang, M. M.; Wang, J. G.; Ma, L.; Gan, Z. G.; Zhang, Z. Y.; Huang, M. H.; Yang, H. B.; Yang, C. L.; Andreyev, A. N.; Yuan, C. X.; Tian, Y. L.; Wang, Y. S.; Wang, J. Y.; Qiang, Y. H.; Wu, X. L.; Xu, S. Y.; Zhao, Z.; Huang, X. Y.; Li, Z. C.; Zhou, H.; Zhang, X.; Xie, G.; Zhu, L.; Guan, F.; Zheng, J. H.; Sun, L. C.; Li, Y. J.; Yang, H. R.; Duan, L. M.; Lu, Z. W.; Huang, W. X.; Sun, L. T.; He, Y.; Xu, H. S.; Niu, Y. F.; He, X. T.; Ren, Z. Z.; Zhou, S. G. (29 May 2025). "Discovery of the α-emitting isotope 210Pa". Nature Communications. 16 (1): 5003. doi:10.1038/s41467-025-60047-2. ISSN 2041-1723. Retrieved 1 June 2025. <a href="https://www.nature.com/articles/s41467-025-60047-2" target="_blank">https://www.nature.com/articles/s41467-025-60047-2</a> <a href="#fnref:34" class="footnote-back-ref">↩</a></li>
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<li id="fn:112">Brown, D.; Petcher, T. J.; Smith, A. J. (1968). "Crystal Structures of some Protactinium Bromides". Nature. 217 (5130): 737. Bibcode:1968Natur.217..737B. doi:10.1038/217737a0. S2CID 4264482. <a href="/wiki/Nature_(journal)" target="_blank">/wiki/Nature_(journal)</a> <a href="#fnref:112" class="footnote-back-ref">↩</a></li>
<li id="fn:113">Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society. 76 (23): 5935. Bibcode:1954JAChS..76.5935S. doi:10.1021/ja01652a011. <a href="https://digital.library.unt.edu/ark:/67531/metadc172625/" target="_blank">https://digital.library.unt.edu/ark:/67531/metadc172625/</a> <a href="#fnref:113" class="footnote-back-ref">↩</a></li>
<li id="fn:114">Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society. 76 (23): 5935. Bibcode:1954JAChS..76.5935S. doi:10.1021/ja01652a011. <a href="https://digital.library.unt.edu/ark:/67531/metadc172625/" target="_blank">https://digital.library.unt.edu/ark:/67531/metadc172625/</a> <a href="#fnref:114" class="footnote-back-ref">↩</a></li>
<li id="fn:115">Greenwood, p. 1277 - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 978-0080379418. <a href="#fnref:115" class="footnote-back-ref">↩</a></li>
<li id="fn:116">Greenwood, pp. 1278–1279 - Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 978-0080379418. <a href="#fnref:116" class="footnote-back-ref">↩</a></li>
<li id="fn:117">Starks, David F.; Parsons, Thomas C.; Streitwieser, Andrew; Edelstein, Norman (1974). "Bis(π-cyclooctatetraene) protactinium". Inorganic Chemistry. 13 (6): 1307. doi:10.1021/ic50136a011. <a href="/wiki/Andrew_Streitwieser" target="_blank">/wiki/Andrew_Streitwieser</a> <a href="#fnref:117" class="footnote-back-ref">↩</a></li>
<li id="fn:118">Protactinium Archived 7 March 2008 at the Wayback Machine, Argonne National Laboratory, Human Health Fact Sheet, August 2005 <a href="http://www.ead.anl.gov/pub/doc/protactinium.pdf" target="_blank">http://www.ead.anl.gov/pub/doc/protactinium.pdf</a> <a href="#fnref:118" class="footnote-back-ref">↩</a></li>
<li id="fn:119">Seifritz, Walter (1984) Nukleare Sprengkörper – Bedrohung oder Energieversorgung für die Menschheit, Thiemig-Verlag, ISBN 3-521-06143-4. <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">Grosse, A. v.; Booth, E. T.; Dunning, J. R. (15 August 1939). "The Fission of Protactinium (Element 91)". Physical Review. 56 (4): 382. Bibcode:1939PhRv...56..382G. doi:10.1103/PhysRev.56.382. Retrieved 17 February 2023. <a href="https://journals.aps.org/pr/pdf/10.1103/PhysRev.56.382" target="_blank">https://journals.aps.org/pr/pdf/10.1103/PhysRev.56.382</a> <a href="#fnref:120" class="footnote-back-ref">↩</a></li>
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<li id="fn:122">Articles "Protactinium" and "Protactinium-231 – thorium-230 dating" in Encyclopædia Britannica, 15th edition, 1995, p. 737 <a href="#fnref:122" class="footnote-back-ref">↩</a></li>
<li id="fn:123">McManus, J. F.; Francois, R.; Gherardi, J.-M.; Keigwin, L. D.; et al. (2004). "Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes" (PDF). Nature. 428 (6985): 834–837. Bibcode:2004Natur.428..834M. doi:10.1038/nature02494. PMID 15103371. S2CID 205210064. Archived from the original (PDF) on 10 April 2013. Retrieved 29 November 2010. <a href="https://web.archive.org/web/20130410051109/http://www.seas.harvard.edu/climate/pdf/mcmanus-2004.pdf" target="_blank">https://web.archive.org/web/20130410051109/http://www.seas.harvard.edu/climate/pdf/mcmanus-2004.pdf</a> <a href="#fnref:123" class="footnote-back-ref">↩</a></li>
<li id="fn:124">Articles "Protactinium" and "Protactinium-231 – thorium-230 dating" in Encyclopædia Britannica, 15th edition, 1995, p. 737 <a href="#fnref:124" class="footnote-back-ref">↩</a></li>
<li id="fn:125">Cheng, H.; Edwards, R.Lawrence; Murrell, M. T.; Benjamin, T. M. (1998). "Uranium-thorium-protactinium dating systematics". Geochimica et Cosmochimica Acta. 62 (21–22): 3437. Bibcode:1998GeCoA..62.3437C. doi:10.1016/S0016-7037(98)00255-5. <a href="/wiki/Geochimica_et_Cosmochimica_Acta" target="_blank">/wiki/Geochimica_et_Cosmochimica_Acta</a> <a href="#fnref:125" class="footnote-back-ref">↩</a></li>
<li id="fn:126">Protactinium Archived 7 March 2008 at the Wayback Machine, Argonne National Laboratory, Human Health Fact Sheet, August 2005 <a href="http://www.ead.anl.gov/pub/doc/protactinium.pdf" target="_blank">http://www.ead.anl.gov/pub/doc/protactinium.pdf</a> <a href="#fnref:126" class="footnote-back-ref">↩</a></li>
<li id="fn:127">Protactinium Archived 7 March 2008 at the Wayback Machine, Argonne National Laboratory, Human Health Fact Sheet, August 2005 <a href="http://www.ead.anl.gov/pub/doc/protactinium.pdf" target="_blank">http://www.ead.anl.gov/pub/doc/protactinium.pdf</a> <a href="#fnref:127" class="footnote-back-ref">↩</a></li>
<li id="fn:128">Grossmann, R.; Maier, H.; Szerypo, J.; Friebel, H. (2008). "Preparation of 231Pa targets". Nuclear Instruments and Methods in Physics Research A. 590 (1–3): 122. Bibcode:2008NIMPA.590..122G. doi:10.1016/j.nima.2008.02.084. <a href="/wiki/Nuclear_Instruments_and_Methods_in_Physics_Research_A" target="_blank">/wiki/Nuclear_Instruments_and_Methods_in_Physics_Research_A</a> <a href="#fnref:128" class="footnote-back-ref">↩</a></li>
<li id="fn:129">Palshin, E.S.; et al. (1968). Analytical chemistry of protactinium. Moscow: Nauka. <a href="#fnref:129" class="footnote-back-ref">↩</a></li>
<li id="fn:130">Grossmann, R.; Maier, H.; Szerypo, J.; Friebel, H. (2008). "Preparation of 231Pa targets". Nuclear Instruments and Methods in Physics Research A. 590 (1–3): 122. Bibcode:2008NIMPA.590..122G. doi:10.1016/j.nima.2008.02.084. <a href="/wiki/Nuclear_Instruments_and_Methods_in_Physics_Research_A" target="_blank">/wiki/Nuclear_Instruments_and_Methods_in_Physics_Research_A</a> <a href="#fnref:130" class="footnote-back-ref">↩</a></li>
</ol>

Protactinium open-in-new

Protactinium