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Title: Energy levels of {sup 251}Cf populated in the {alpha} decay of {sub 100}{sup 255}Fm and EC decay of {sub 99}{sup 251}Es

Abstract

Gamma-ray singles spectra of extremely pure (chemically and isotopically) samples of {sup 255}Fm, with strengths of {approx}1 mCi, have been measured with a high-resolution 2-cm{sup 2}x10-mm germanium LEPS detector and with a 25% Ge spectrometer. Gamma rays with intensities as low as 1.0x10{sup -6}% per {sup 255}Fm {alpha} decay have been identified. The electron spectrum of a mass-separated {sup 251}Es source was measured with a cooled Si(Li) electron spectrometer. The spectrum provided the conversion coefficients of low-energy transitions in {sup 251}Cf and thereby their multipolarities. The present measurements confirm the previous assignments of single-particle states in {sup 251}Cf. These include 1/2{sup +}[620], 0.0 keV; 7/2{sup +}[613], 106.30 keV; 3/2{sup +}[622], 177.59 keV; 11/2{sup -}[725], 370.47 keV; 9/2{sup -}[734], 433.91 keV; 5/2{sup +}[622], 543.98 keV; 1/2{sup -}[750], 632.0 keV; 9/2{sup +}[615], 683 keV; and 9/2{sup +}[604], 974.0 keV. A vibrational band was identified in previous studies at 981.4 keV and given an assignment of {l_brace}7/2{sup +}[613]x2{sup -}{r_brace}3/2{sup -}. Three new vibrational bands are identified in the present work at 942.5, 1086.5, and 1250.0 keV with tentative assignments {l_brace}7/2{sup +}[613]x1{sup -}{r_brace}5/2{sup -},{l_brace}7/2{sup +}[613]x1{sup -}{r_brace}9/2{sup -}, and {l_brace}7/2{sup +}[613]x0{sup +}{r_brace}7/2{sup +}, respectively. A level was identified at 1185.5 keV with spin of 5/2more » or 7/2 but it was not given any configuration assignment. Another level was identified at 1077.5 keV and given a spin of 9/2. Again, no configuration could be assigned to this level.« less

Authors:
; ; ; ; ; ;  [1];  [2]
  1. Argonne National Laboratory, Argonne, Illinois 60439 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20699113
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 72; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevC.72.054308; (c) 2005 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; ALPHA PARTICLES; CALIFORNIUM 251; CONVERSION; EINSTEINIUM 251; ELECTRON SPECTRA; ENERGY-LEVEL TRANSITIONS; FERMIUM 255; GAMMA SPECTRA; KEV RANGE; L-S COUPLING; MULTIPOLARITY; SPIN; VIBRATIONAL STATES

Citation Formats

Ahmad, I., Greene, J.P., Moore, E.F., Kondev, F.G., Chasman, R.R., Porter, C.E., Felker, L.K., and Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831. Energy levels of {sup 251}Cf populated in the {alpha} decay of {sub 100}{sup 255}Fm and EC decay of {sub 99}{sup 251}Es. United States: N. p., 2005. Web. doi:10.1103/PhysRevC.72.054308.
Ahmad, I., Greene, J.P., Moore, E.F., Kondev, F.G., Chasman, R.R., Porter, C.E., Felker, L.K., & Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831. Energy levels of {sup 251}Cf populated in the {alpha} decay of {sub 100}{sup 255}Fm and EC decay of {sub 99}{sup 251}Es. United States. doi:10.1103/PhysRevC.72.054308.
Ahmad, I., Greene, J.P., Moore, E.F., Kondev, F.G., Chasman, R.R., Porter, C.E., Felker, L.K., and Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831. Tue . "Energy levels of {sup 251}Cf populated in the {alpha} decay of {sub 100}{sup 255}Fm and EC decay of {sub 99}{sup 251}Es". United States. doi:10.1103/PhysRevC.72.054308.
@article{osti_20699113,
title = {Energy levels of {sup 251}Cf populated in the {alpha} decay of {sub 100}{sup 255}Fm and EC decay of {sub 99}{sup 251}Es},
author = {Ahmad, I. and Greene, J.P. and Moore, E.F. and Kondev, F.G. and Chasman, R.R. and Porter, C.E. and Felker, L.K. and Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831},
abstractNote = {Gamma-ray singles spectra of extremely pure (chemically and isotopically) samples of {sup 255}Fm, with strengths of {approx}1 mCi, have been measured with a high-resolution 2-cm{sup 2}x10-mm germanium LEPS detector and with a 25% Ge spectrometer. Gamma rays with intensities as low as 1.0x10{sup -6}% per {sup 255}Fm {alpha} decay have been identified. The electron spectrum of a mass-separated {sup 251}Es source was measured with a cooled Si(Li) electron spectrometer. The spectrum provided the conversion coefficients of low-energy transitions in {sup 251}Cf and thereby their multipolarities. The present measurements confirm the previous assignments of single-particle states in {sup 251}Cf. These include 1/2{sup +}[620], 0.0 keV; 7/2{sup +}[613], 106.30 keV; 3/2{sup +}[622], 177.59 keV; 11/2{sup -}[725], 370.47 keV; 9/2{sup -}[734], 433.91 keV; 5/2{sup +}[622], 543.98 keV; 1/2{sup -}[750], 632.0 keV; 9/2{sup +}[615], 683 keV; and 9/2{sup +}[604], 974.0 keV. A vibrational band was identified in previous studies at 981.4 keV and given an assignment of {l_brace}7/2{sup +}[613]x2{sup -}{r_brace}3/2{sup -}. Three new vibrational bands are identified in the present work at 942.5, 1086.5, and 1250.0 keV with tentative assignments {l_brace}7/2{sup +}[613]x1{sup -}{r_brace}5/2{sup -},{l_brace}7/2{sup +}[613]x1{sup -}{r_brace}9/2{sup -}, and {l_brace}7/2{sup +}[613]x0{sup +}{r_brace}7/2{sup +}, respectively. A level was identified at 1185.5 keV with spin of 5/2 or 7/2 but it was not given any configuration assignment. Another level was identified at 1077.5 keV and given a spin of 9/2. Again, no configuration could be assigned to this level.},
doi = {10.1103/PhysRevC.72.054308},
journal = {Physical Review. C, Nuclear Physics},
number = 5,
volume = 72,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 2005},
month = {Tue Nov 01 00:00:00 EST 2005}
}
  • Gamma-ray spectra of a 20-h {sup 255}Fm source containing {approx}1 mCi activity were measured with a 25% Ge detector and a low-energy photon spectrometer (LEPS). Gamma lines with intensities as low as 1.0x10{sup -6}% per {sup 255}Fm {alpha} decay were observed. Gamma-gamma coincidence spectra of a {sup 255}Fm sample were measured with the GAMMASPHERE array. A comparison of the {gamma}-ray spectrum gated by the Cf K{sub {alpha}} x-ray peak with the {gamma}-singles spectrum provided spins of the excited states in {sup 251}Cf. The {gamma}-ray data, in conjunction with previously measured {sup 250}Cf(d,p) reaction data, allowed us to characterize several single-particlemore » and vibrational states above the N=152 subshell gap.« less
  • Gamma-ray spectra of a 20-h {sup 255}Fm source containing -1 mCi activity were measured with a 25% Ge detector and a low-energy photon spectrometer (LEPS). Gamma lines with intensities as low at 1.0 x 10{sup -6}% per {sup 255}Fm {alpha} decay were observed. Gamma-gamma coincidence spectra of a {sup 255}Fm sample were measured with the GAMMASPHERE array. A comparison of the {gamma}-ray spectrum gated by the Cf K{sub {alpha}} x-ray peak with the {gamma}-singles spectrum provided spins of the excited states in {sup 251}Cf. The {gamma}-ray data, in conjunction with previously measured {sup 250}Cf(d,p) reaction data, allowed us to characterizemore » several single-particle and vibrational states above the N=152 subshell gap.« less
  • Level structure of the Z = 99 nucleus, /sup 251/Es, has been investigated by measuring the ..gamma.. rays and conversion electrons associated with the electron capture decay of 5.3-h /sup 251/Fm, and from triton spectra produced in the /sup 250/Cf(..cap alpha..,t)/sup 251/Es reaction. The ..gamma..-ray spectra were measured with a 2-cm/sup 2/ x 5-mm planar and a 25-cm/sup 3/ coaxial Ge(Li) detector and the electron spectra were measured with a cooled Si(Li) detector. Forty-five ..gamma.. rays were identified in /sup 251/Es and the multipolarities of most of the transitions were deduced. Logft values for the observed electron capture transitions weremore » derived from the measured electron capture transition intensities. A two-parameter ..gamma..-..gamma.. coincidence experiment was performed to determine the relationships between various ..gamma.. transitions. Triton spectra from the /sup 250/Cf(..cap alpha..,t)/sup 251/Es reaction were analyzed with an Enge split-pole magnetic spectrograph. On the basis of the present investigation the following intrinsic states were identified in /sup 251/Es: 3/2 - (521), 0; 7/2 + (633), 8.3; 1/2 - (521), 411; 7/2 - (514), 461.4; 9/2 + (624), 777.9; )7/2 + (633) x 2 + )/sub 11/2+/ vibrational state, 889.1; )n(734)9/2 - ; n(620)1/2 + ; p(521)3/2 - )/sub 11/2+/ three-quasiparticle state, 1239.0 keV. A K..pi.. = 11/2 + state at 1264.9 keV was interpreted as a three-quasiparticle state but could not be given a definite assignment. This is the first time a definite identification of the proton orbitals 1/2 -(521) and 7/2 - (514) has been made in any nucleus.« less
  • Excited states in {sup 251}Fm populated via the {alpha} decay of {sup 255}No are studied in detail through {alpha}-{gamma} coincidence and {alpha} fine-structure measurements. Five excited states reported previously in {sup 251}Fm are firmly established through the {alpha}-{gamma} coincidence measurement, and rotational bands built on one-quasiparticle states are newly established through the {alpha} fine-structure measurement. Spin-parities and neutron configurations of the excited states in {sup 251}Fm as well as the ground state of {sup 255}No are definitely identified on the basis of deduced internal conversion coefficients, lifetimes of {gamma} transitions, rotational-band energies built on one-quasiparticle states, and hindrance factors ofmore » {alpha} transitions. It is found that the excitation energy of the 1/2{sup +}[620] state in N=151 isotones increases with the atomic number, especially at Z{>=}100, while that of the 1/2{sup +}[631] state decreases at Z=100. Ground-state deformations and energies of neutron one-quasiparticle states in the N=151 isotones are calculated using a macroscopic-microscopic model, and the energy systematics of the one-quasiparticle states in the isotones are discussed in terms of the evolution of nuclear deformation involving the hexadecapole ({beta}{sub 4}) and hexacontatetrapole ({beta}{sub 6}) deformations.« less