On the spin assignment of neutron resonances in 149Sm using (n, α) reaction
Abstract
Measurements of thermal-neutron cross sections for the 149Sm(n, α)146Nd reaction have been done using a 99% enriched 149Sm target. Results are compared with theoretical values of cross sections calculated on the basis of the compound nucleus and statistical model. Experimental and calculated values are consistent only when assuming that the spins of the bound state and the 0.0967 eV resonance in 149Sm+n are 3− and 4−, respectively. For such a spin sequence the 2200 m/sec experimental neutron cross sections are: 46.0±5 mb for 149Sm(n, α) 146Nd2+ and 8.5±1.5 mb for 149Sm(n, α)146Nd0+.
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Resonance effects in neutron scattering lengths of rare-earth nuclides
1990, Atomic Data and Nuclear Data TablesThe neutron cross-section data in the literature for all the nuclides of the rare-earth chemical group which contain significant resonance effects below about 0.5 eV are analyzed using (in most cases) a generalized single-level formalism. The complex coherent scattering lengths thus deduced as a function of neutron energy or wavelength are presented in the form of graphs and tables.
Nuclear Data Sheets for A = 150
1976, Nuclear Data SheetsNuclear Data Sheets for A=150 (last compiled in 1964) have been prepared using all pertinent experimental information from more than 300 papers (received prior to March 1975). Some information is now available for 11 elements, from Ce through Er.
This mass chain is of particular interest since it lies in a region of transition from spherical to deformed nuclei; sufficient Jπ-information is available for Sm to enable a meaningful comparison of its low-lying bands of levels with those of nearby nuclei. Less extensive level schemes now exist for Gd (about 40 levels, 7 firm Jπ-assignments) and Nd (10 levels, 3 firm Jπ-assignments). The 4 states postulated on the basis of γ-cascades in each of Ce and Dy require verification. In the odd-mass A=150 nuclei (Pr, Pm, Eu, Tb, Ho) only one excited state has been identified (in Tb) apart from isomeric states. Isomers exist for Eu, Tb and possibly Ho, but the excitation energy is unknown in each case so it is not clear which long-lived state is the ground state, although most authors assume low-spin Eu and Tb to represent the ground state. Spin measurements for Pr, Pm, Tb and Ho ground states and Eu and Tb isomeric states are needed since shell-model systematics do not give reliable predictions in this mass region and (β+ + ε)-decay does not generate definite assignments.
T½ ≈ 34 y is now adopted for high-spin Eu, and the possible existence of a third long-lived state of Eu (to explain earlier data giving T½ ≈ 6 y for the former state) is presently under investigation by J. Mihelich.
The adopted value of Q+ for 3-h Tb (based on experimental Eβ) disagrees with the value in the current mass table, presumably because the latter assumes that 3-h Tb (J=2?) a-decay populates the 4− ground state of 146Eu.
Despite the volume of Sm(n,γ) data available, the majority of transitions remain unplaced, and a number of unresolved doublets presumably persist. [Extensive, Ge(Li) detector coincidence data would probably resolve many existing ambiguities.] Separate experiments yield inconsistent intensities for a number of weak ce-lines.
Because of space limitations, theoretical conversion coefficients used to deduce multipolarities for Sm and Gd transitions are not shown but are available from the authors upon request.
Note that 3-h Tb, 34-y Eu, and 40-s Ho decay schemes and much of the Nd level scheme are based on presently unpublished data.
The following is a partial list of papers pertaining to A=150 nuclei, but containing no new experimental data for those nuclei: Ce: 71Ge15, 72Wi15, 73Fl02; Dy: 60To05, 64Ma17; Eu: 60To05; Gd: 60To05, 72Hs07; Nd: 65So04, 70Se18, 70Va22, 72Ab18, 72Br61, 72Ru08, 73Ab06, 73Gu09, 73Le19, 73Me05, 73Me08, 73Pr14, 73Pr19, 73To15, 74Ca05, 74En08; Pm: 60To05; Sm: 65Le23, 68Lu12, 69Ca02, 70Be72, 70Ra28, 70Ru05, 70Sc35, 70Se18, 70So02, 71Be95, 71Dz04, 71Ku32, 71Ta27, 72BaC7, 72BeA2, 72Ko58, 72Ma17, 72Wi15, 73Bu30, 73Gu09, 73Pe15, 73Pr14, 73Sa14, 73Si25, 74Ca05, 74Ja13, 74Kr16, 74Ku14, 74Le26; Tb: 60To05, 72Ar36.
The (n<inf>th</inf>, α) reaction on <sup>147</sup>Sm, <sup>151, 153</sup>Eu and Yb isotopes
1974, Nuclear Physics, Section AThe (n, α) reaction has been studied using the highly pure thermal neutron beam from the 87m curved neutron guide at the Grenoble high flux reactor. The 147Sm(n, α)144Nd reaction showed up five lines corresponding to the ground and the first four excited states of the final nucleus. It is shown that ≈53 % of the 581 μb (n, α) cross section comes from the neutron capture by a bound level of the 148Sm compound nucleus. The 8.7 ± 3 μb cross section of 151Eu(n, α)148Pm seems to consist principally of at least two lines corresponding to the ground and the second excited states of 148Pm. The 153Eu(n, α)149Pm cross section for thermal neutrons is ≦ 1 μb. The lower limits of (n, α) thermal neutron cross section values on ytterbium isotopes are ≈ 20 to 40 times lower than the published data.
The (n, α) reaction on samarium and neodymium isotopes induced by thermal neutrons
1970, Nuclear Physics, Section AThe (n, α) reaction was investigated on 147Sm, 149Sm, 143Nd and 145Nd with thermal neutrons, and the effective cross sections were obtained. The reaction cross sections at the neutron energy of 0.0253 eV () were deduced from the observed neutron spectrum. The reaction cross sections for the 149Sm(n, α) 146Nd reaction at 0.0253 eV are 5.0 ± 0.5 mb and 23.5 ± 3.7 mb for alpha transitions to the ground and to the first excited states of 146Nd, respectively. The disagreement of the partial cross section for an alpha transition to the first excited state of 146Nd with other reported values is discussed. The reduced alpha widths are also obtained.