N=127同中子素^(219)U和^(216)Ac的α衰变研究

α-decay Studies of the N=127 Isotones ^(219)U and ^(216) Ac

本工作通过重离子熔合蒸发反应^(40)Ar+^(183)W,产生了质子滴线附近的轻锕系核素^(219)U和^(216)Ac。实验在兰州充气反冲谱仪(SHANS)上开展,目标核产生后从薄靶中反冲出来,在飞行中与大量的本底粒子进行分离并偏转到位于焦平面的探测系统中。探测系统对注入的反冲核和随后的α衰变进行探测,并利用寻找α衰变链的方法对产物进行寻找和鉴别。在本次工作中,^(219)U已知的α衰变数据得到改善,其基态衰变到子核215Th基态的α粒子能量被确定为E_(α)=9 763(15)keV,半衰期为T_(1/2)=60(7)μs。首次发现了^(219)U两个新的α衰变分支,其能量为E_(α)=9246(17)keV,8975(17)keV,并指认它们分别是从^(219)U的基态衰变到子核215Th的低激发态(5/2^(-))和(3/2^(-))。此外,通过对^(216)Ac的α衰变数据的分析,证实了^(216)Ac存在同核异能态。

The light actinide nuclei ^(219)U and ^(216)Ac were produced in fusion-evaporation reaction using a ^(183)W target and ^(40) Ar beam.After recoiling from thin target,the fusion-evaporation residues were separated by the gas-filled recoil separator SHANS(Spectrometer for Heavy Atoms and Nuclear Structure) and transported into the focal plane detector systems,where their impantations and decays were measured.The method of searching for α-decay chains was used to identify the nuclei.In this work,the known a decay of ^(219) U was measured with improved precision and the α-particle energy of 9763(15)keV and a half-life of 60(7) μs was determined.In addition,two new α-decay lines at 9246(17)keV and 8975(17)keV were observed and assigned as the decays from the ground state of^(219) U to the(5/2^(-)) and(3/2^(-)) states of 215Th,respectively.The existence of an α-decaying isomeric state in ^(216) Ac was also confirmed.