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Search for a 2-quasiparticle high-$$K$$ isomer in $$^{256}$$Rf

$$^{256}$$Rfの2準粒子高$$K$$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$$^{256}$$Rfの励起状態に半減期17$$mu$$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$$^{256}$$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$$K$$核異性体ではなく、4準粒子状態の$$K$$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$$^{256}$$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 $$mu$$s in $$^{256}$$Rf through a calorimetric conversion electron measurement tagged with implanted $$^{256}$$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-$$K$$ 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 $$^{256}$$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.

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パーセンタイル:16.44

分野:Physics, Nuclear

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