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首页> 外文期刊>Quaternary geochronology >The effects of a hydrogen-rich ground cover on cosmogenic thermal neutrons: Implications for exposure dating
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The effects of a hydrogen-rich ground cover on cosmogenic thermal neutrons: Implications for exposure dating

机译：富氢地面覆盖物对宇宙热中子的影响：对暴露年代的影响

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We present results of thermal neutron flux measurements in experimental granite piles that were tailored to study the effect of hydrogen-rich covers on that flux. We find that hydrogen-rich covers(polyethylene, water), used as proxies for snow, dead and/or live plant matter, increase the thermal neutron flux in an underlying rock surface significantly, as compared to the state without cover. The rock serves as the main source for thermal neutrons, the hydrogen-rich cover as a neutron reflector. In situations where the thickness of such a cover would be negligible in terms of high-energy neutron(>10 MeV) attenuation, e.g. 2-3 cm water equivalent cover, a significant enhancement of the thermal neutron flux (factor >2.5 ± 0.5) can be achieved. This increase is made up of three components (Masarik et al., 2007): (1) reflected thermal neutrons (albedo neutrons), (2) moderated fast neutrons from the ground, and (3) moderated fast neutrons from the atmospheric cascade (Masarik et al., 2007). The higher thermal neutron flux increases the production rates of those cosmogenic nuclides that have a significant thermal neutron production pathway (~3He, ~(36)Cl, ~(41)Ca). Ignoring this effect in situations where target nuclei (~6Li, ~(35)Cl, ~(40)Ca) are abundant will severely underestimate production rates. The effect of hydrogenrich ground cover on the thermal neutron flux has the potential to be used for studies that are aimed at reconstructing the persistence of past plant/snow cover. Isotopic ratios of spallogenic versus predominantly thermal neutron produced nuclides, would reveal the presence or absence of hydrogen-rich cover in the past as compared to the present-day situation.
机译：我们介绍了实验花岗岩桩中热中子通量测量的结果，这些结果专门用于研究富氢覆盖层对该通量的影响。我们发现，与没有覆盖层的状态相比，用作积雪，枯死植物和/或有生命的植物物质的代理的富含氢的覆盖层（聚乙烯，水）显着增加了下层岩石表面中子的热中子通量。岩石是热中子的主要来源，富氢层是中子的反射器。就高能中子（> 10 MeV）衰减而言，例如这种覆盖层的厚度可以忽略不计。 2-3厘米水当量的覆盖层可以显着提高热中子通量（系数> 2.5±0.5）。这种增加由三部分组成（Masarik等，2007）：（ 1）反射的热中子（反照率中子）;（2）来自地面的缓和快中子;以及（3）来自大气层级的缓和快中子（（ Masarik等，2007）。较高的热中子通量会增加具有显着的热中子产生路径（〜3He，〜（36）Cl，〜（41）Ca）的宇宙核素的生产率。在目标原子核（〜6Li，〜（35）Cl，〜（40）Ca）丰富的情况下忽略此效应将严重低估生产率。富氢地面覆盖物对热中子通量的影响有可能用于旨在重建过去植物/雪覆盖物持久性的研究中。散裂性与主要由热中子产生的核素的同位素比，将揭示过去与现在相比是否存在富氢覆盖层。

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