Online ISSN: 1884-4111 Print ISSN: 0033-8303
Radioisotopes 67(6): 291-298 (2018)

連載講座Serial Lecture

超重核の殻構造を実験的に探るExperimental Studies on Shell Structure of Superheavy Nuclei

日本原子力研究開発機構先端基礎研究センターJapan Atomic Energy Agency ◇ 319–1195 茨城県那珂郡東海村白方2–4 ◇ 2–4 Shirakata, Tokai, Ibaraki Pref. 319–1195, Japan

発行日:2018年6月15日Published: June 15, 2018

超重元素の存在は超重核の殻構造に本質的に依存する。理論的には,陽子数114~126,中性子数172~184の領域に球形で安定な二重閉殻構造を持つ超重核の存在が予測されているが,その閉殻の位置や強さは理論によって大きく異なり,確立されているとは言い難い。一方,実験的には,人類は既に陽子数118, 中性子数177までの超重核の合成に成功しており,二重閉殻領域に足を踏み入れつつある。更に最近では,核分光学的手法により超重核の基底状態や励起準位の構造を直接的に明らかにする試みも行われている。本稿では,それら超重核の殻構造に関する実験的研究の現状を紹介する。

Existence of superheavy elements essentially depends on shell structure of superheavy nuclei. It is theoretically predicted that stable doubly-closed-shell spherical superheavy nuclei should exist around the region of the proton number 114 to 126 and the neutron number 172 to 184, although their exact locations and degree of stability have not been established because of large variety of theoretical predictions. On the other hand, we have already succeeded in producing superheavy nuclei with the proton number up to 118 and the neutron number up to 177, indicating that we have already reached the doubly-closed-shell superheavy region. In addition, some pioneering experiments have been performed to directly establish the level structure of superheavy nuclei through spectroscopic methods. This paper introduces the current status of experimental studies on nuclear shell structure of superheavy nuclei.

Key words: superheavy nuclei; shell structure; double closed shell; alpha decay; nuclear spectroscopy

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