アクチノイド偶々核の第一励起準位エネルギー

Energies of the first-excited 2 states in even-even actinide nuclei

浅井 雅人  ; 塚田 和明  ; 笠松 良崇*; 豊嶋 厚史; 佐藤 哲也   ; 永目 諭一郎 ; 佐藤 望; 石井 哲朗  

Asai, Masato; Tsukada, Kazuaki; Kasamatsu, Yoshitaka*; Toyoshima, Atsushi; Sato, Tetsuya; Nagame, Yuichiro; Sato, Nozomi; Ishii, Tetsuro

アクチノイド偶々核の第一励起準位エネルギーを、高分解能線測定並びに-同時計数測定によって精密に決定した。Pu, Cm, Cf, Fm同位体の合計8核種について系統的に測定し、アクチノイド領域の偶々核の第一励起準位エネルギーの陽子数・中性子数依存性を系統的に明らかにした。第一励起準位エネルギーは、Cm及びCf同位体において最小値を取り、その後陽子数の増加とともに増大することが明らかとなった。この傾向は、陽子数114の球形閉殻の存在を考慮することで定性的に説明できる。また、Fmにおいて極小値を取り、陽子数100と中性子数152の二重変形閉殻の存在を実験的に明らかにした。

Energies of the first-excited states in even-even actinide nuclei were determined precisely through high-resolution -particle measurements and - coincidence measurements. Those energies were measured for a total of 8 isotopes in Pu, Cm, Cf and Fm, and dependences of those energies on the proton and neutron numbers were systematically clarified. It was found that the energy of the first-excited state takes the minimum around Cm and Cf isotopes, and increases with increasing atomic number. This trend was qualitatively explained by taking account of the existence of the spherical closed shell at the proton number . It was also found that the first-excited state takes the local minimum at Fm, which clearly indicates the existence of the doubly deformed shell gaps at and .