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Title: Energy Splitting of the Ground-State Doublet in the Nucleus {sup 229}Th

Abstract

The energy splitting of the {sup 229}Th ground-state doublet is measured to be 7.6{+-}0.5 eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of {sup 233}U (105 {mu}Ci) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19{yields}0 keV)

Authors:
; ; ; ;  [1];  [2]; ; ;  [3]
  1. Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
  2. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
  3. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)
Publication Date:
OSTI Identifier:
20951206
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 14; Other Information: DOI: 10.1103/PhysRevLett.98.142501; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ALPHA DECAY; CALORIMETERS; ELECTRON BEAMS; ENERGY RESOLUTION; EV RANGE 01-10; EV RANGE 10-100; GAMMA RADIATION; GROUND STATES; KEV RANGE 10-100; SPECTROMETERS; THORIUM 229; URANIUM 233; X RADIATION

Citation Formats

Beck, B. R., Becker, J. A., Beiersdorfer, P., Brown, G. V., Moody, K. J., Wilhelmy, J. B., Porter, F. S., Kilbourne, C. A., and Kelley, R. L. Energy Splitting of the Ground-State Doublet in the Nucleus {sup 229}Th. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.142501.
Beck, B. R., Becker, J. A., Beiersdorfer, P., Brown, G. V., Moody, K. J., Wilhelmy, J. B., Porter, F. S., Kilbourne, C. A., & Kelley, R. L. Energy Splitting of the Ground-State Doublet in the Nucleus {sup 229}Th. United States. doi:10.1103/PHYSREVLETT.98.142501.
Beck, B. R., Becker, J. A., Beiersdorfer, P., Brown, G. V., Moody, K. J., Wilhelmy, J. B., Porter, F. S., Kilbourne, C. A., and Kelley, R. L. Fri . "Energy Splitting of the Ground-State Doublet in the Nucleus {sup 229}Th". United States. doi:10.1103/PHYSREVLETT.98.142501.
@article{osti_20951206,
title = {Energy Splitting of the Ground-State Doublet in the Nucleus {sup 229}Th},
author = {Beck, B. R. and Becker, J. A. and Beiersdorfer, P. and Brown, G. V. and Moody, K. J. and Wilhelmy, J. B. and Porter, F. S. and Kilbourne, C. A. and Kelley, R. L.},
abstractNote = {The energy splitting of the {sup 229}Th ground-state doublet is measured to be 7.6{+-}0.5 eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of {sup 233}U (105 {mu}Ci) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19{yields}0 keV)},
doi = {10.1103/PHYSREVLETT.98.142501},
journal = {Physical Review Letters},
number = 14,
volume = 98,
place = {United States},
year = {Fri Apr 06 00:00:00 EDT 2007},
month = {Fri Apr 06 00:00:00 EDT 2007}
}
  • It has been known from some time that the intrinsic state labeled by the asymptotic quantum numbers (3/2){sup +}(631) lies quite close ({lt}0.1 keV) to the (5/2){sup +}(633) ground state of {sup 229}Th. Using the energies of selected {gamma} rays emitted following the {alpha} decay of {sup 233}U, we have obtained a value of 1{plus minus}4 eV for the energy separation of these two intrinsic states.
  • The lowest-known excited state in nuclei is the 7.6 eV isomer of {sup 229}Th. This energy is within the range of laser-based investigations that could allow accurate measurements of possible temporal variation of this energy splitting. This in turn could probe temporal variation of the fine-structure constant or other parameters in the nuclear Hamiltonian. We investigate the sensitivity of this transition energy to these quantities. We find that the two states are predicted to have identical deformations and thus the same Coulomb energies within the accuracy of the model (viz., within roughly 30 keV). We therefore find no enhanced sensitivitymore » to variation of the fine-structure constant. In the case of the strong interaction the energy splitting is found to have a complicated dependence on several parameters of the interaction, which makes an accurate prediction of sensitivity to temporal changes of fundamental constants problematical. Neither the strong- nor Coulomb-interaction contributions to the energy splitting of this doublet can be constrained within an accuracy better than a few tens of keV, so that only upper limits can be set on the possible sensitivity to temporal variations of the fundamental constants.« less
  • The 7.6 eV electromagnetic transition between the nearly degenerate ground state and first excited state in the {sup 229}Th nucleus may be very sensitive to potential changes in the fine-structure constant, {alpha}=e{sup 2}/({Dirac_h}/2{pi})c. However, the sensitivity is not known, and nuclear calculations are currently unable to determine it. We propose measurements of the differences of atomic transition frequencies between thorium atoms (or ions) with the nucleus in the ground state and in the first excited (isomeric) state. This will enable extraction of the change in nuclear charge radius and electric-quadrupole moment between the isomers, and hence the {alpha} dependence ofmore » the isomeric transition frequency with reasonable accuracy.« less
  • The 1/2(530) decoupled band in {sup 229}Pa has been identified up to the 19/2{sup {minus}} level in ({ital p},{ital t}) and ({ital p},2{ital n}{gamma}) experiments. It is found that the 3/2{sup {minus}} band head has an excitation energy of 19(10) keV, and can thus not be identified with a 123 keV level observed in the {sup 229}U electron capture decay. This removes the evidence presented earlier for a spin-parity assignment of 5/2{sup +-}5/2{sup {minus}} to a proposed nearly degenerate ground-state doublet in {sup 229}Pa.
  • The half-life of the ground state of {sup 229}Th ({sup 229}Th{sup g}) has become an important factor in nuclear technology, for example, in the geological disposal of nuclear spent fuel. However, the values reported in two previous studies are not in agreement. This study reevaluates the half-life of {sup 229}Th{sup g} by using a simple and reliable method. The {sup 232}U/{sup 233}U activity ratio of a {sup 232,233}U sample was measured by high-resolution {alpha}-particle spectrometry. Next, the {sup 228}Th/{sup 229}Th{sup g} activity ratio of the Th sample, which was grown from the {sup 232,233}U sample, was also measured. The half-lifemore » of {sup 229}Th{sup g} was calculated from these activity ratios, the growth time, and the half-lives of {sup 232}U, {sup 233}U, and {sup 228}Th. From the results of these five measurements, the half-life of {sup 229}Th{sup g} is determined to be 7932 {+-} 55 yr at a confidence level of 2{sigma}.« less