Systematics and uncertainties of Hamiltonian parameters of soft-rotator model for actinides and their implications for nuclear data calculations

アクチノイド原子核に対する軟回転体模型ハミルトニアンパラメータの系統性及びその誤差と、核データ計算における影響

千葉 敏; 小浦 寛之   ; 丸山 敏毅  ; 国枝 賢  ; Soukhovitskij, E. Sh.*

Chiba, Satoshi; Koura, Hiroyuki; Maruyama, Toshiki; Kunieda, Satoshi; Soukhovitskij, E. Sh.*

われわれが開発してきた軟回転体模型に基づく原子核集団準位構造の記述と、それを用いるチャンネル結合法は核データ計算の強力な手法として認識されてきた。この研究では、アクチノイド原子核の構造に対して包括的な解析を行い、ハミルトニアンパラメータ及びその系統性を導出した。この結果は未知核に対して用いることができるため、断面積の予測精度が大幅に向上するものと期待できる。またその誤差を共分散の形で求めて、断面積計算に対して核構造解析の不確定性がどの程度の影響を与えるかを定量的に見積もった。

A coupled-channel (CC) method based on the soft-rotator model (SRM) wave functions, SRM-CC, has been recognized as a powerful tool to calculate, estimate and evaluate the nucleon-induced cross sections. It is because that this method can take account of the information from the nuclear structure and reaction studies simultaneously. For example, the coupling strengths required in the coupled-channel calculation is determined from analyses of low-lying collective level structure of target nuclei. However, nobody has looked into so far how the uncertainties of the SRM parameters affects the calculated cross section data. In this work, collective level structure of 19 even-even actinide nuclei are analyzed in terms of the soft-rotator model (SRM). Hamiltonian parameters of SRM to describe the low-lying level scheme and their uncertainties are obtained. Systematic trends are found for major Hamiltonian parameters as a function of ground-state quadrupole deformation which are important to estimate low-lying level structure of other e-e nuclei for which level structure is unknown or only partly known. Then, those parameters and their uncertainties are used to calculate neutron cross sections and their covariance of actinides in terms of SRM-CC. Furthermore, effects of side-band coupling is investigated. Especially, effects of coupling are noticeable for low-energy observables, e.g., strength functions. Such saturated calculations are not possible in RRM (rigid rotor model)-CC approach, making SRM-CC an effective method for investigations of reaction mechanisms and nuclear data evaluation.