Alpha decay from excited states of samarium isotopes
Abstract
The (n,α) reactions on 147Sm and 149Sm have been investigated at neutron energies up to 200 eV. The life times with respect to alpha-decay have been obtained for thirteen excited states of 148Sm and 150Sm with Jπ = 4- and 3-. Calculations, made according to the statistical theory, of the probabilities of 4- → 2+ transitions in 150Sm are in good agreement with the experiments. The life times of nine 148Sm states are in the region of 0.2 to 4 ns. The life times of the 3- and 4- levels differ by an order of magnitude.
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Cited by (7)
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.
Beta-delayed alpha-particle emission in the decay of 3.6s <sup>181</sup>Hg
1975, Physics Letters BThe emission of α-particles with energies between 10 and 12 MeV has been observed in the decay of 181Hg in an intensity of (9 ± 3) × 10−8. These events are taken to represent β-delayed α-particle emission from levels at 4–6 MeV excitation energy in 181Au and provide an estimate of the α-strength function for this excitation energy. The results are discussed in terms of an α-particle cluster model. As a by-product the experiment gives new values for the α-particle branching ratios of 181Hg and .
Investigation of α-decay of <sup>148</sup>Sm resonance states
1972, Nuclear Physics, Section ABy means of two large multisectional grid ionization chambers the yield of the 147Sm (n, α)144Nd reaction in the neutron energy interval En ≈ 0–230 eV was measured. The α-particle spectra of the decay of 14 resonances were obtained. The values of the total α-widths or their upper limits were calculated for 24 resonances. The partial α-widths of transitions to the ground and two first excited levels of the final nucleus and the spin of 10 resonances are given. A comparison of the partial and total α-widths with statistical-model predictions was made. The prediction of the α-width distribution is reasonably consistent with the experimental one. This may be regarded as a confirmation of the Porter-Thomas assumptions concerning the distribution of partial α-widths and the independence of fluctuations of the reduced α-widths in the individual exit channels. There was made an attempt to interpret some of the results obtained and their relationship to decay characteristics on the basis of the semi-microscopic description of high excited states proposed by V.G. Soloviev.
Investigation of the (n, α) reaction on sm and nd isotopes in the neutron energy region below 1 keV
1970, Nuclear Physics, Section AAlpha widths for sixteen resonances in the 149Sm(n, α) reaction have been measured on the IBR Pulsed Reactor of the Joint Institute for Nuclear Research. The results obtained are discussed together with the improved data on α-widths for the 143Nd, 145Nd and 147Sm resonances in the neutron energy region 0.04–900 eV. From the dependence of α-widths on resonance spins, spin assignment of the 143Nd resonances is made. The experimental values of the average α-widths for the given isotopes are compared with those calculated from the statistical nuclear model. The effect of neutron pairing correlations on the probability of α-decay of excited states is discussed. Alpha-width fluctuations relative to the average value are considered.
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.