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Title: Resonance conversion as a dominant decay mode for the 3.5-eV isomer in {sup 229m}Th

Abstract

on the basis of calculations performed within the relativistic multiconfiguration Dirac-Fock method, it is shown that the probability of the decay of the 3.5-eV nuclear level in the {sup 229m}Th isomer via resonance conversion exceeds the probability of its direct radiative decay by at least a factor of about 600. The possibility of experimentally observing delayed soft photons or alpha particles in the decay of this isomer is discussed.

Authors:
 [1];  [2]
  1. St. Petersburg State University, Institute of Physics (Russian Federation)
  2. Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation), E-mail: trzhask@thd.pnpi.spb.ru
Publication Date:
OSTI Identifier:
21076089
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Atomic Nuclei; Journal Volume: 69; Journal Issue: 4; Other Information: DOI: 10.1134/S106377880604003X; Copyright (c) 2006 Nauka/Interperiodica; Article Copyright (c) 2006 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ALPHA PARTICLES; BASES; CONVERSION; EV RANGE 01-10; HARTREE-FOCK METHOD; ISOMERS; PHOTONS; PROBABILITY; RADIATIVE DECAY; RELATIVISTIC RANGE; RESONANCE; THORIUM 229

Citation Formats

Karpeshin, F. F., and Trzhaskovskaya, M. B. Resonance conversion as a dominant decay mode for the 3.5-eV isomer in {sup 229m}Th. United States: N. p., 2006. Web. doi:10.1134/S106377880604003X.
Karpeshin, F. F., & Trzhaskovskaya, M. B. Resonance conversion as a dominant decay mode for the 3.5-eV isomer in {sup 229m}Th. United States. doi:10.1134/S106377880604003X.
Karpeshin, F. F., and Trzhaskovskaya, M. B. Sat . "Resonance conversion as a dominant decay mode for the 3.5-eV isomer in {sup 229m}Th". United States. doi:10.1134/S106377880604003X.
@article{osti_21076089,
title = {Resonance conversion as a dominant decay mode for the 3.5-eV isomer in {sup 229m}Th},
author = {Karpeshin, F. F. and Trzhaskovskaya, M. B.},
abstractNote = {on the basis of calculations performed within the relativistic multiconfiguration Dirac-Fock method, it is shown that the probability of the decay of the 3.5-eV nuclear level in the {sup 229m}Th isomer via resonance conversion exceeds the probability of its direct radiative decay by at least a factor of about 600. The possibility of experimentally observing delayed soft photons or alpha particles in the decay of this isomer is discussed.},
doi = {10.1134/S106377880604003X},
journal = {Physics of Atomic Nuclei},
number = 4,
volume = 69,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • Pressing problems concerning the optical pumping of the 7.6-eV {sup 229m}Th nuclear isomer, which is a candidate for a new nuclear optical reference point for frequencies, are examined. Physics behind the mechanism of the two-photon optical pumping of the isomer is considered. It is shown that, irrespective of the pumping scheme, a dominant contribution comes, in accord with what was proven earlier for the 3.5-eV isomer, from the resonance 8s–7s transition. Details of an optimum experimental scheme are discussed. It is shown that, after isomer excitation, the atom involved remains with a high probability in an excited state at anmore » energy of about 0.5 eV rather than in the ground state, the required energy of the two photons being equal to the energy of the nuclear level plus the energy of the lowest 7s state of the atom. The estimated pumping time is about 1.5 s in the case where the field strength of each laser is 1 V/cm.« less
  • Lifetimes for the M1 transitions from the isomeric 3.5 eV 3/2+ state to the ground state are predicted to be enhanced in the hydrogen-like {sup 229}Th89+ relative to the bare 229Th nucleus by several orders of magnitude. A possibility of experimental study of this phenomenon is discussed.
  • A hollow-cathode electric discharge, a well-established source in optical spectroscopy, was used to populate the ''3.5-eV isomer'' in {sup 229}Th with use of nuclear excitation by electron transition (NEET). The radiochemically purest {sup 229}Th sample was loaded into the hollow cathode in which the electric discharge excited the {sup 229}Th to atomic states some of which could be expected to lie close to the excitation energy of the sought isomer. Although there remain some uncertainties, our experiments indicate that the isomer was populated by NEET and its {alpha} decay observed after switching off the electric discharge with a corresponding isomermore » half-life 1 min < or approx. T{sub 1/2}{sup m} < or approx. 3 min. From the present NEET condition, the isomer appears to lie between 3 eV and 7 eV. The probability of the isomer population by NEET is discussed.« less
  • No abstract prepared.