Nested neutron spectrometer

<h2 id="principles-of-operation">Principles of operation</h2>
<p>The NNS operates under the same principle as a <a href="/facts/Bonner_sphere/UVK0Juqr">Bonner sphere</a> neutron spectrometer.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> The sensitive part of the spectrometer is the Helium-3 <a href="/facts/Proportional_counter/pooxNkmI">proportional counter</a>, which detects neutrons through the reaction 3He(n,p)3H. This particular reaction has a significant cross-section only at thermal neutron energies. In order for a higher energy neutrons to be detected their energies must be decreased, or "moderated". To slow down neutrons at higher energies the NNS uses different amounts of high-density polyethylene (HDPE). The He-3 proportional counter is surrounded by varying amounts of HDPE to sample various energy regions of the neutron field. The standard NNS has seven HDPE cylinders which are nested together, similar to Russian nesting dolls, to measure neutrons of higher and higher energies.
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<h2 id="sample-neutron-spectra">Sample neutron spectra</h2>
<p>Shown below are spectra of two standard calibration sources measured by the NNS.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The measured spectra (blue) is compared to the ISO standard spectra (red). Both Measurements were made at the <a href="/facts/NIST/gr9Fnh85">NIST</a> low scatter facility in Washington, DC.
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<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>J. Atanackovic; W. Matysiak; S. S. Hakmana Witharana; I. Aslam; J. Dubeau & A. J. Wake (September 2012). "Neutron Spectrometry and nd Dosimetry Study at Two Research Nuclear Reactors Using Bonner Sphere Spectrometer (BSS), Rotational Spectrometer (ROSPEC) and Cylindrical Nested Neutron Spectrometer (NNS)". Radiation Protection Dosimetry. 154 (3): 364–374. doi:10.1093/rpd/ncs248. PMID 23019598. <a href="/wiki/Radiation_Protection_Dosimetry" target="_blank">/wiki/Radiation_Protection_Dosimetry</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Dubeau, J.; Hakmana Witharana, S. S.; Atanackovic, J.; Yonkeu, A.; Archambault, J. P. (June 2012). "A neutron spectrometer using nested moderators". Radiation Protection Dosimetry. 150 (2): 217–222. doi:10.1093/rpd/ncr381. ISSN 1742-3406. PMID 21964903.
 <a href="https://pubmed.ncbi.nlm.nih.gov/21964903/" target="_blank">https://pubmed.ncbi.nlm.nih.gov/21964903/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Detec (June 10, 2013). "NNS Calibration Results" (PDF). Retrieved July 24, 2013.
 <a href="http://detecsciences.com/api/files/53501df88cd6be252e000098-NNS_Calibration.pdf" target="_blank">http://detecsciences.com/api/files/53501df88cd6be252e000098-NNS_Calibration.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Nested neutron spectrometer open-in-new

Nested neutron spectrometer