Paul R. Renne Leah E. Morgan Jack N. Carter 2023 <div id="abstracts" class="Abstracts u-font-gulliver text-s"><div id="ab005" class="abstract author"><div id="as005"><p id="sp0005">Various interference reactions producing unwanted Ar isotopes from K, Ca, Cl and Ar require correction to satisfy the<span>&nbsp;</span>⁴⁰Ar/³⁹Ar age equation. Using GEANT4, we design and build a model Cadmium Lined In Core Irradiation Tube (CLICIT) irradiation facility, as used in the Oregon State TRIGA Reactor (OSTR). We illustrate the complexity of the irradiation of geologic samples within this framework and determine an overlooked production channel of<span>&nbsp;</span>³⁶Ar. The production of<span>&nbsp;</span>³⁶Ar is fed from the<span>&nbsp;</span>³⁹K(n,<i>α</i>)³⁶Cl nuclear channel,<span>&nbsp;</span>³⁶Cl subsequently decays to<span>&nbsp;</span>³⁶Ar (³⁹K(n,<i>α,<span class="math"><span id="MathJax-Element-3-Frame" class="MathJax_SVG" data-mathml="<math xmlns=">β</span></span></i>)<span>&nbsp;</span>³⁶Ar). Simulations in this work using a<span>&nbsp;</span>²³⁵<span>U fission neutron&nbsp;energy spectrum&nbsp;and modelled CLICIT facility, determine a production ratio for this reaction (</span>³⁶Cl/³⁹Ar)_K&nbsp;=&nbsp;0.40&nbsp;±&nbsp;0.01 (1<i><span class="math"><span id="MathJax-Element-4-Frame" class="MathJax_SVG" data-mathml="<math xmlns=">σ</span></span></i><span>); greater than an order of magnitude larger than any other K interference. The magnitude of the resulting age bias for an unknown sample will be a function of the integrated&nbsp;neutron flux, the length of irradiation (fluence), the time elapsed since irradiation, and the age relationship between the unknown and neutron&nbsp;fluence&nbsp;monitor. We show using the raw data of (Niespolo et al., 2017) that the age of Alder Creek&nbsp;sanidine&nbsp;can be modified to be ca. 0.1% older (1</span><i><span class="math"><span id="MathJax-Element-5-Frame" class="MathJax_SVG" data-mathml="<math xmlns=">σ</span></span></i>), at the 2σ level of current analytical precision for the Alder Creek age for this study. The<span>&nbsp;</span>³⁹K(n,<i><span class="math"><span id="MathJax-Element-6-Frame" class="MathJax_SVG" data-mathml="<math xmlns=">α</span></span></i>,<i><span class="math"><span id="MathJax-Element-7-Frame" class="MathJax_SVG" data-mathml="<math xmlns=">β</span></span></i>)³⁶<span>Ar inference should be incorporated into routine data analysis and may be especially important in the&nbsp;intercalibration&nbsp;of the&nbsp;</span>⁴⁰Ar/³⁹Ar system with other chronometers (e.g.,<span>&nbsp;</span>²⁰⁶Pb/²³⁸U).</p></div></div></div> application/pdf 10.1016/j.gca.2023.07.017 en Elsevier Potassium-39-derived 36Ar production during fission-neutron irradiation and its effect on 40Ar/39Ar ages article