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Preliminary research for iridium in cretaceous-tertiary boundary clay using multi $$gamma$$ ray detection

多重$$gamma$$線検出を用いたK-T境界粘土中のイリジウム分析

大澤 崇人  ; 初川 雄一; 小泉 光生 ; 大島 真澄; 藤 暢輔   ; 木村 敦   ; 古高 和禎 

Osawa, Takahito; Hatsukawa, Yuichi; Koizumi, Mitsuo; Oshima, Masumi; Toh, Yosuke; Kimura, Atsushi; Furutaka, Kazuyoshi

6500万年前のK-T境界は隕石衝突による大量絶滅が起きた時である。衝突した隕石の種類を明らかにするために、デンマークのスティーブンスクリントにて採取した堆積物の予備分析を行った。結果、最大30ppbものイリジウムを検出した。

The Cretaceous-Tertiary (K-T) boundary about 65 million years ago records a mass extinction event caused by a bolide impact. In order to clarify the type of the bolide, K-T boundary clay collected from Stevns Klint, Denmark was preliminarily investigated in this work [1]. The specimens were removed from a thin layer of marl, which is known as fish clay. Iridium concentrations of fish clays across the K-T boundary were determined using a multiple $$gamma$$-ray analysis system after neutron activation. The iridium in the geological samples was determined using the multi-parameter coincidence method with no chemical separation after neutron irradiation. Fifty to one hundred mg of ground homogenized fish clay sediment samples were sealed in pure quartz vials and then irradiated for 48 hours in the JRR-3 reactor. In the analysis, anomalously high Ir concentrations were detected in some marl samples, with the highest concentration being about 30 ppb.

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