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Title: In-beam gamma ray and conversion electron study of {sup 250}Fm

Abstract

We report on a set of in-beam studies of excited states in {sup 250}Fm. We detected prompt {gamma} rays by using the JUROSPHERE IV array and conversion electrons by using the SACRED spectrometer. Both devices were used in conjunction with the RITU gas-filled recoil separator located at the University of Jyvaeskylae. {sup 250}Fm nuclei were produced through the {sup 204}Hg({sup 48}Ca,2n){sup 250}Fm fusion-evaporation reaction. An experimental excitation function gave a maximum reaction cross section of (980 {+-} 160) nb at an energy of 209 MeV in the center of the target. Tagging techniques were employed, and a number of E2 transitions were observed that connected the ground-state band levels from spin 4{sup +} up to 18{sup +}. The highly converted 4{sup +}{yields}2{sup +} transition is observed only by use of conversion electron spectroscopy. The observed ground-state band transitions indicate a rotational structure. We deduce a quadrupole deformation parameter of {beta}{sub 2}=0.28 {+-} 0.02. A low-energy background of apparent nuclear origin is observed in conversion electrons and postulated to arise from the decay of high-K bands. The half-life of {sup 250}Fm is measured to be 30.4 {+-} 1.5 0009m.

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]; ; ; ; ; ; ; ;  [2]
  1. Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE (United Kingdom)
  2. Department of Physics, P.O. Box 35 (YFL), FIN-40014, University of Jyvaeskylae (Finland) (and others)
Publication Date:
OSTI Identifier:
20771259
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 73; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevC.73.024308; (c) 2006 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; CALCIUM 48 REACTIONS; E2-TRANSITIONS; ELECTRON SPECTRA; ELECTRON SPECTROSCOPY; ELECTRONS; EVAPORATION MODEL; EXCITATION FUNCTIONS; FERMIUM 250; GAMMA RADIATION; GAMMA SPECTRA; GROUND STATES; HALF-LIFE; INTERNAL CONVERSION; MERCURY 204 TARGET; MEV RANGE; NUCLEAR DEFORMATION; QUADRUPOLES; ROTATIONAL STATES; SPIN

Citation Formats

Bastin, J.E., Herzberg, R.-D., Butler, P.A., Jones, G.D., Page, R.D., Jenkins, D.G., Amzal, N., Brew, P.M.T., Hammond, N.J., Humphreys, R.D., Ikin, P.J.C., Page, T., Greenlees, P.T., Jones, P.M., Julin, R., Juutinen, S., Kankaanpaeae, H., Keenan, A., Kettunen, H., and Kuusiniemi, P. In-beam gamma ray and conversion electron study of {sup 250}Fm. United States: N. p., 2006. Web. doi:10.1103/PhysRevC.73.024308.
Bastin, J.E., Herzberg, R.-D., Butler, P.A., Jones, G.D., Page, R.D., Jenkins, D.G., Amzal, N., Brew, P.M.T., Hammond, N.J., Humphreys, R.D., Ikin, P.J.C., Page, T., Greenlees, P.T., Jones, P.M., Julin, R., Juutinen, S., Kankaanpaeae, H., Keenan, A., Kettunen, H., & Kuusiniemi, P. In-beam gamma ray and conversion electron study of {sup 250}Fm. United States. doi:10.1103/PhysRevC.73.024308.
Bastin, J.E., Herzberg, R.-D., Butler, P.A., Jones, G.D., Page, R.D., Jenkins, D.G., Amzal, N., Brew, P.M.T., Hammond, N.J., Humphreys, R.D., Ikin, P.J.C., Page, T., Greenlees, P.T., Jones, P.M., Julin, R., Juutinen, S., Kankaanpaeae, H., Keenan, A., Kettunen, H., and Kuusiniemi, P. Wed . "In-beam gamma ray and conversion electron study of {sup 250}Fm". United States. doi:10.1103/PhysRevC.73.024308.
@article{osti_20771259,
title = {In-beam gamma ray and conversion electron study of {sup 250}Fm},
author = {Bastin, J.E. and Herzberg, R.-D. and Butler, P.A. and Jones, G.D. and Page, R.D. and Jenkins, D.G. and Amzal, N. and Brew, P.M.T. and Hammond, N.J. and Humphreys, R.D. and Ikin, P.J.C. and Page, T. and Greenlees, P.T. and Jones, P.M. and Julin, R. and Juutinen, S. and Kankaanpaeae, H. and Keenan, A. and Kettunen, H. and Kuusiniemi, P.},
abstractNote = {We report on a set of in-beam studies of excited states in {sup 250}Fm. We detected prompt {gamma} rays by using the JUROSPHERE IV array and conversion electrons by using the SACRED spectrometer. Both devices were used in conjunction with the RITU gas-filled recoil separator located at the University of Jyvaeskylae. {sup 250}Fm nuclei were produced through the {sup 204}Hg({sup 48}Ca,2n){sup 250}Fm fusion-evaporation reaction. An experimental excitation function gave a maximum reaction cross section of (980 {+-} 160) nb at an energy of 209 MeV in the center of the target. Tagging techniques were employed, and a number of E2 transitions were observed that connected the ground-state band levels from spin 4{sup +} up to 18{sup +}. The highly converted 4{sup +}{yields}2{sup +} transition is observed only by use of conversion electron spectroscopy. The observed ground-state band transitions indicate a rotational structure. We deduce a quadrupole deformation parameter of {beta}{sub 2}=0.28 {+-} 0.02. A low-energy background of apparent nuclear origin is observed in conversion electrons and postulated to arise from the decay of high-K bands. The half-life of {sup 250}Fm is measured to be 30.4 {+-} 1.5 0009m.},
doi = {10.1103/PhysRevC.73.024308},
journal = {Physical Review. C, Nuclear Physics},
number = 2,
volume = 73,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • We have measured deexcitation {gamma} rays in the neutron-rich nuclei of {sup 240}U, {sup 246}Pu, and {sup 250}Cm produced by the ({sup 18}O, {sup 16}O) two-neutron transfer reactions, in coincidence with the {sup 16}O particles using Si {delta}E-E detectors. The {gamma} rays in these nuclei were identified by selecting the kinetic energies of {sup 16}O particles, which correspond to the excitation energies in the residual nuclei below the neutron separation energies. The ground-state bands of {sup 240}U, {sup 246}Pu, and {sup 250}Cm were established up to 12{sup +} states and the K{sup {pi}} = 0{sup -} octupole band of {supmore » 240}U was established up to 9{sup -} states. The systematics of the moments of inertia of the ground-state bands for actinide nuclei shows that the deformed subshell closure at N = 152 is sustained for {sub 96}Cm isotopes and that it disappears for {sub 94}Pu isotopes.« less
  • The cross section for production of Fm/sup 250/ in the reaction Pu/sup 241/(Csup 13/,4n) and U/sup 238/(O/sup 16/,4n) was determined as a func tion of the energy of the bombarding particles. Comparison of the cross section for production of Fm/sub 250/ with the fission cross section in these reactions shows that in the overwhelming majority of cases the excited compound Fm/sup 254/ nucleus undergoes fission, and only in a very few cases deexcitation takes place as a result of neutron emission. The maximal cross section for production of Fm/ sup 250/ by irradiation with oxygen or carbon ions is, respectively,more » 1 x 10/sup - 30/ cm/sup 2/ and 5 x 10/sup -30/ cm/sup 2/. The difference betwee n the cross sections is probably due to the effect of the Coulomb barrier. (auth)« 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
  • We have used the /sup 209/Bi(t,2n)/sup 210/Po reaction with standard in-beam ..gamma..-ray and conversion-electron spectroscopic techniques to study the two-proton states in /sup 210/Po. With the possible exception of the (f/sub 7/2//sup 2/)/sub =/, all states of the proton h/sub 9/2//sup 2/, h/sub 9/2/f/sub 7/2/, f/sub 7/2//sup 2/, and h/sub 9/2/i/sub 13/2/ configurations have been identified. The level energies agree within 100 keV, typically, with results from shell-model calculations. Relative intensities of M1 and E2 ..gamma.. transitions from the h/sub 9/2/f/sub 7/2/ and f/sub 7/2//sup 2/ configurations are compared with calculated intensities. Published experimental single-proton transition matrix elements were usedmore » for the calculations, which were performed both for pure and for mixed states. The results indicate admixture amplitudes of only a few percent or less into the main components of the wave functions.« less
  • Low-lying states of /sup 200/Pt have been studied by the /sup 198/Pt(t,p..gamma..) and (t,pe/sup -/) reactions with 16-MeV tritons. From detailed p-..gamma.., p-e/sup -/, and p-..gamma..-..gamma.. coincidence measurements, a level scheme that includes 16 excited states has been established. A 14.3-ns isomer is observed and is believed to correspond to the 7/sup -/ isomers prevalent in the lighter even-mass platinum nuclei. Limited comparisons are made with the U(5) and O(6) symmetries of the interacting boson model.