229mThと235mUの核壊変の化学状態依存性

Yoshitaka Kasamatsu; 笠松良崇; Hidetoshi Kikunaga; 菊永英寿

doi:10.3769/radioisotopes.67.471

^229mThと^235mUの核壊変の化学状態依存性Variation of the Nuclear Decay Constants of ^229mTh and ^235mU Affected by Their Chemical Environments

笠松良崇¹，菊永英寿²Yoshitaka Kasamatsu¹, Hidetoshi Kikunaga²

¹ 大阪大学大学院理学研究科Graduate School of Science, Osaka University ◇ 560–0043　大阪府豊中市待兼山町1–1 ◇ Machikaneyama 1–1, Toyonaka, Osaka 560–0043, Japan

² 東北大学電子光理学研究センターResearch Center for Electron Photon Science, Tohoku University ◇ 982–0826　宮城県仙台市太白区三神峯1–2–1 ◇ 1–2–1 Mikamine, Taihaku, Sendai 982–0826, Japan

発行日：2018年10月15日Published: October 15, 2018

アクチノイド元素であるトリウム（Th）とウラン（U）には，^229mThと^235mUという非常に励起エネルギーの低い核異性体（準安定な励起状態）が存在する。これらの原子核は脱励起時に外殻の軌道殻電子と相互作用し，その化学状態の変化に応じて核の壊変の様子（半減期）が大きく変化するという興味深い現象が知られている。本稿では，これらの核種を対象としたこれまでの研究成果と現在取り組まれている研究の状況について紹介する。

The nuclear excitation energy of isomers ^229mTh and ^233mU were reported to be 7.8 eV and 76.8 eV, respectively. Because of the extremely low energy for nuclear excitation state, these isomers decay interacting with outer shell electrons and thus their decay properties (half-lives) are reported (or expected) to depend on the chemical environments. In this report, we introduce the findings and ongoing projects of the researches on these isomers.

Key words: isomer; thorium-229m; uranium-235m

RADIOISOTOPES

連載講座Serial Lecture

^229mThと^235mUの核壊変の化学状態依存性Variation of the Nuclear Decay Constants of ^229mTh and ^235mU Affected by Their Chemical Environments

229mThと235mUの核壊変の化学状態依存性Variation of the Nuclear Decay Constants of 229mTh and 235mU Affected by Their Chemical Environments

^229mThと^235mUの核壊変の化学状態依存性Variation of the Nuclear Decay Constants of ^229mTh and ^235mU Affected by Their Chemical Environments