Novel technique to study nuclear isomers via atomic processes

B.Q. Lee S.Q. Lim G. Kessedjian 1 C. Sage 1 A. Chebboubi 1 U. Köester 2 M.W. Reed T. Kibédi A.E. Stuchbery
1 LPSC - Laboratoire de Physique Subatomique et de Cosmologie
2 ILL - Institut Laue-Langevin
Abstract : Nuclear isomers can decay through multiple processes; in many cases the dominant mechanism is internal conversion (IC). This is an excitation of an atomic-electron resulting in ionization and the creation of atomic vacancies. These vacancies are propagated towards the outer-shells by the emission of X-rays and Auger electrons. Auger-electron emission increases the ionic charge of decaying ions thus affecting the charge-state distribution. We propose a novel technique to identify and study nuclear isomers by investigating the charge-state distribution of residual ions following isomeric decays. This technique is based on the fact that the residual charge-state distribution is sensitive to the internal conversion coefficient (number of IC events occurring), which could be used to extract useful information about nuclear isomers. As a proof of concept, the technique has been applied to study nuclear isomers in 144Cs. The residual charge-state distribution of 144Cs following isomeric decays has been measured using the Lohengrin fission fragment mass spectrometer at the Institut Laue-Langevin, France [1]. Based on a level scheme proposed in Ref. [1], we simulated the nuclear cascade decays and the subsequent emissions of X-rays and Auger electrons in 144Cs using an Auger cascade model [2]. The simulations started in pre-ionized ions since an equilibrium charge-state distribution (q - 20) was established after the ions passed through a nickel foil 0.3 mm away from the 235U target. The simulation provides very good agreement with the experimental measurement and has enabled the extraction of a limit on the isomeric lifetime, an isomeric ratio, and deduction of the unknown level X [1] to be a state at 92.2 keV.
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Conference papers
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http://hal.in2p3.fr/in2p3-01368271
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Submitted on : Monday, September 19, 2016 - 12:16:58 PM
Last modification on : Tuesday, May 22, 2018 - 9:48:11 PM

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B.Q. Lee, S.Q. Lim, G. Kessedjian, C. Sage, A. Chebboubi, et al.. Novel technique to study nuclear isomers via atomic processes. Heavy Ion Accelerator Symposium for Fundamental and Applied Research (HIAS), Sep 2015, Canberra, Australia. ⟨in2p3-01368271⟩

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