Supernova versus cosmic ray origin for exotic nuclides in geomaterials: A test using 3He with 60Fe in marine sediments
Supernova versus cosmic ray origin for exotic nuclides in geomaterials: A test using 3He with 60Fe in marine sediments
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地质材料中外来核素的超新星与宇宙射线起源：在海洋沉积物中使用 3He 和 60Fe 进行的测试
DOI：
10.1016/j.gca.2022.09.016
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发表时间：
2022
影响因子：
5
通讯作者：
Konrad, Kevin
中科院分区：
文献类型：
--
作者：
Graham, David W.;Konrad, Kevin
我们报告了来自东南印度洋的57个沉积物样本中的3he和4he浓度，此前在这些样本的一个子集中发现了60fe过量（Wallner等人，2016）。耦合的60Fe- 3he数据允许进一步评估两个相互竞争的假设：(1)在过去的300万年中，附近的超新星（SN）向地球注入了外来的放射性核素，如60Fe；或(2)地球档案中的60Fe是由星系宇宙射线（gcr）在星际介质中照射数亿年的微陨石颗粒上的反应产生的，其中gcr产生的3he比太阳风的3he通量大。活塞芯ELT49-53沉积物显示3he和60fe之间没有相关性，沉积物3he似乎主要由行星际尘埃颗粒（IDPs）的存在所主导。因为3he不是由SN喷出的大量物质提供的，所以a3He-60Fe相关性的缺失为超新星假说提供了额外的，尽管是间接的证据。目前，在相对较少的沉积物60fe测量中存在很大的不确定性，限制了得出更确切的结论。ELT49-53在3.2 ~ 1.7 Ma期间的地外he积累速率为0.88±0.26 × 10−12cm3STP/g/kyr，与以往沉积和冰芯记录中较短和较长时间尺度的IDP3He通量估算值相似。he和60fe的累积速率分别为0.11±0.04 × 10−6cm3STP/cm2/kyr和1.9±0.5 × 104atoms/cm2/kyr。大块沉积物[4He]与沉积物caco3含量呈强反相关，表明陆源和宇宙沉积组分主要受生物成因碳酸盐沉积变化的调节。虽然在印度洋沉积地点尚未唯一确定主要的陆源来源，但它类似于来自澳大利亚大陆内部的风成物质，并且在过去的~ 3 Myrs中显示出3he /4He（从2到4 × 10−8,0.015-0.030 RA）的狭窄范围。
We report3He and4He concentrations in 57 sediment samples from the southeast Indian Ocean where60Fe excesses were previously identified in a subset of the same samples (Wallner et al., 2016). The coupled60Fe-3He data allow further evaluation of two competing hypotheses: (1) a nearby supernova (SN) showered Earth with exotic radionuclides such as60Fe during the last 3 million years, or (2)60Fe in terrestrial archives was generated by reactions of galactic cosmic rays (GCRs) on micrometeorite grains that were irradiated for hundreds of millions of years in the interstellar medium, where3He production by GCRs is larger than the solar wind3He flux.Piston core ELT49-53 sediments show no correlation between3He and60Fe, and sedimentary3He appears to be dominated by the presence of interplanetary dust particles (IDPs). Because3He is not supplied in significant amounts by SN ejecta, the absence of a3He-60Fe correlation provides additional, although circumstantial evidence for the supernova hypothesis. Large uncertainties in the relatively small number of sediment60Fe measurements currently limit a firmer conclusion.The extraterrestrial3He accumulation rate in ELT49-53 from 3.2 to 1.7 Ma was 0.88 ± 0.26 × 10−12cm3STP/g/kyr, similar to IDP3He flux estimates from previous sedimentary and ice core records that span both shorter and longer time scales.4He and60Fe accumulation rates during this time interval were 0.11 ± 0.04 × 10−6cm3STP/cm2/kyr and 1.9 ± 0.5 × 104atoms/cm2/kyr. Bulk sediment [4He] is strongly anti-correlated with sediment CaCO3content, evidence for modulation of the terrigenous and cosmic sedimentary fractions primarily by changes in biogenic carbonate deposition. Although the dominant terrigenous source has not been uniquely identified at the Indian Ocean deposition site, it resembles eolian material from the continental interior of Australia, and shows a narrow range of3He/4He (from 2 to 4 × 10−8, 0.015–0.030 RA) over the last ∼3 Myrs.