Search for a 2-quasiparticle high- isomer in Rf

Rfの2準粒子高核異性体の探索

Robinson, A. P.*; Khoo, T. L.*; Seweryniak, D.*; Ahmad, I.*; 浅井 雅人  ; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; Davids, C. N.*; Greene, J.*; Greenlees, P. T.*; Hauschild, K.*; Heinz, A.*; Herzberg, R.-D.*; Janssens, R. V. F.*; Jenkins, D. G.*; Jones, G. D.*; Ketelhut, S.*; Kondev, F. G.*; Lauritsen, T.*; Lister, C. J.*; Lopez-Martens, A.*; Marley, P.*; McCutchan, E.*; Papadakis, P.*; Peterson, D.*; Qian, J.*; Rostron, D.*; Shirwadkar, U.*; Stefanescu, I.*; Tandel, S. K.*; Wang, X.*; Zhu, S.*

Robinson, A. P.*; Khoo, T. L.*; Seweryniak, D.*; Ahmad, I.*; Asai, Masato; Back, B. B.*; Carpenter, M. P.*; Chowdhury, P.*; Davids, C. N.*; Greene, J.*; Greenlees, P. T.*; Hauschild, K.*; Heinz, A.*; Herzberg, R.-D.*; Janssens, R. V. F.*; Jenkins, D. G.*; Jones, G. D.*; Ketelhut, S.*; Kondev, F. G.*; Lauritsen, T.*; Lister, C. J.*; Lopez-Martens, A.*; Marley, P.*; McCutchan, E.*; Papadakis, P.*; Peterson, D.*; Qian, J.*; Rostron, D.*; Shirwadkar, U.*; Stefanescu, I.*; Tandel, S. K.*; Wang, X.*; Zhu, S.*

104番元素Rfの励起状態に半減期17秒の核異性体があることを実験的に明らかにした。実験はアルゴンヌ国立研究所の反跳核分離装置を用いて行い、検出器に打ち込まれたRfと同時計数する内部転換電子を測定することで同定した。核異性体の生成率から、この核異性体は中性子数152の原子核で通常観測される2準粒子状態の核異性体ではなく、4準粒子状態の核異性体であると考えられる。2準粒子状態の核異性体が観測されなかった理由は、その核異性体が核分裂によって崩壊し、その半減期がRfの基底状態の半減期に近いと考えれば説明できる。あるいは、原子核の4重極変形度が104番元素から突然小さくなり、2準粒子状態の核異性体がまったく存在しない、という可能性も考えられる。

We have identified an isomer with a half-life of 17 s in Rf through a calorimetric conversion electron measurement tagged with implanted Rf nuclei using the fragment mass analyzer at Argonne National Laboratory. The low population yield for this isomer suggests that this isomer should not be a 2-quasiparticle high- isomer which is typically observed in the N = 152 isotones, but should be a 4-quasiparticle one. Possible reasons of the non-observation of a 2-quasiparticle isomer are this isomer decays by fission with a half-life similar to that of the ground state of Rf. Another possibility, that there is no 2-quasiparticle isomer at all, would imply an abrupt termination of axially symmetric deformed shape at Z=104.