Odd Neutron Research Articles

Interpretation of the fragmentation of Nilsson strength amongst high-lying states in the HfOs region

It is shown that the significantly varying trends and some of the fine structure in the fragmentation of Nilsson strength among the high-lying states in the odd neutron nuclei near the end of the rare earth deformed region can be qualitatively explained as a natural outcome of rapidly varying quadrupole and hexadecapole deformations. While details of individual states can emerge only from calculations incorporating more degrees of freedom, an understanding of the gross behavior of ensembles of states in this neglected region of excitation thus appears possible in an unexpectedly simple way.

Shape coexistence inGd151

A microscopic justification of the experimental observation of shape coexistence in /sup 151/Gd is given. The potential energy as a function of nuclear deformation in ..beta..-..gamma.. space is calculated. The Hartree-Bogolyubov method is used with the usual pairing-plus-quadrupole schematic interaction. The location of the potential minimum is strongly dependent on which single particle state the odd neutron occupies. Three distinct nuclear shapes are predicted in agreement with the data. The stability of these shapes is tested by a dynamic calculation.

High spin states in lead isotopes with 193<=A<=199

Theγ de-excitation of odd neutron deficient lead isotopes with mass numbers 193–199, produced by (heavy ion,x n) reactions, was studied with the particular aim of searching for high spin states of the (i13/2)−3 configuration. The properties of levels in199, 197, 195Pb are compared with the predictions of a three quasi-particle calculation, forJ=29/2−15/2, and with the corresponding results in the neighbouring even lead isotopes.

Magnetic moment of the first excited state ofMo99

We have measured the g factor of the 5/2/sup +/ first-excited state of /sup 99/Mo. We obtained for this state, which has an excitation energy of 98 keV and a mean life of 24.5 ..mu..s, a value g = - 0.310 +- 0.002. This result is consistent with the g factor observed for the d/sub 5/2/ level in neighboring odd neutron nuclei, and in approximate agreement with theoretical calculations.

Resonance (n, γ) measurements and weak-coupling model calculations of levels inSn119,Sn117, andSn115

Neutron capture $\ensuremath{\gamma}$-ray measurements have been performed upon enriched samples of $^{118}\mathrm{Sn}$, $^{116}\mathrm{Sn}$, and $^{114}\mathrm{Sn}$ following resonance capture. The $\ensuremath{\gamma}$ rays, measured with a Ge(Li) detector, have been incorporated in level schemes for $^{119}\mathrm{Sn}$, $^{117}\mathrm{Sn}$, and $^{115}\mathrm{Sn}$. Spin and parity assignments have been made for many of the levels. Neutron separation energies for $^{119}\mathrm{Sn}$, $^{117}\mathrm{Sn}$, and $^{115}\mathrm{Sn}$ were determined to be 6484.6\ifmmode\pm\else\textpm\fi{}1.5, 6942.9\ifmmode\pm\else\textpm\fi{}2.0, and 7545.3\ifmmode\pm\else\textpm\fi{}2.0 keV, respectively. The level schemes have been compared with those of heavier Sn isotopes to investigate systematic behavior. Various spectroscopic properties (level energies, electromagnetic moments, and transition rates) of $^{119}\mathrm{Sn}$, $^{117}\mathrm{Sn}$, and $^{115}\mathrm{Sn}$ were calculated on the basis of a model which pictures these nuclei as being formed by coupling the motion of the odd neutron quasiparticle to the states of the neighboring even-mass core. The experimentally determined level properties of these Sn isotopes have been qualitatively reproduced by these calculations.NUCLEAR REACTIONS $^{118}\mathrm{Sn}(n, \ensuremath{\gamma})$, $E=0.3\ensuremath{-}5.1$ keV, $^{116}\mathrm{Sn}(n, \ensuremath{\gamma})$, $E=0.09\ensuremath{-}1.6$ keV, $^{114}\mathrm{Sn}(n, \ensuremath{\gamma})$, $E=0.09\ensuremath{-}2.4$ keV; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$. $^{119}\mathrm{Sn}$ deduced resonances, $J$. $^{117,115}\mathrm{Sn}$, deduced resonances. $^{119,117,115}\mathrm{Sn}$ deduced levels, $J$, $\ensuremath{\pi}$, neutron separation energies. $^{115,117,119,121,123,125}\mathrm{Sn}$ systematics. Enriched targets.NUCLEAR STRUCTURE Weak-coupling model. $^{119,117,115}\mathrm{Sn}$ calculated $E(\mathrm{level})$, $\ensuremath{\mu}$, $Q$, $B(E2)$ and $B(M1)$. Comparison with experiment.

Influence of protons on backbending

Backbending in (at least the first half of) the rare earth nuclei seems to be determined by the alignment of an i 13 2 neutron pair. This is supported by the disappearance of backbending due to the blocking of an i 13 2 level by an odd neutron for example in 165Yb. Contrary to expectations backbending disappears also by adding an odd h 9 2 ,proton to 70 166Yb in 71 167Lu for this state (but is present if the odd proton is in the g 7 2 level). A theory is presented which explains the odd neutron and the odd proton nuclei. It turns out that the odd proton in 167Lu serves only as a type of catalyst for the alignment of an i 13 2 neutron pair. The odd proton changes the deformation and moves the Fermi surface nearer ( g 7 2 ) or farther away ( h 9 2 ) from the nearest i 13 2 neutron level. In one case one finds backbending and in the other case no backbending in 167Lu.

High spin level structure in127Ba produced by the118Sn(12C, 3n) reaction

High-spin states in127Ba have been produced by the reaction128Sn(12C,3n)127Ba and studied by in-beamγ-ray spectroscopic techniques. The odd-parity states form a level system based upon a 9/2− state and generated by an odd neutron in theh11/2 shell coupled to a triaxial core. Theg7/2 shell is responsible for theΔ I=1, even-parity band.

The properties of 116in excited states

Gamma and conversion electron spectra from the 115In(n, γ) 116In reaction in the energy range 20–700 keV and 20–850 keV respectively have been measured with bent crystal and magnetic spectrometers. Gamma-gamma coincidences in the energy range 50–500 keV have been investigated with Ge(Li)-Ge(Li) arrangement. Proton spectra from the 12 MeV deuteron-induced (d, p) reaction taken at the University of Pittsburgh Tandem Van de Graaf accelerator were reanalysed. The 116In level scheme consisting of 56 levels in the energy range 0–1.4 MeV has been constructed. Parity is determined for all the levels introduced. Unique spin values are assigned to 37 levels. The information obtained was used to place limits to the J-values for the rest of the levels. The main components of the wave function are established for 23 levels, considered to be components of p-n multiplets in which the proton hole and odd neutron are in in one of the Z = 28 → 50 and N = 50 → 82 shell states, respectively. Energy splittings of p-n configurations by residual interactions taken as a combination of short range Wigner and singlet forces have been calculated. It is noted that many excited states cannot be described in the framework of two-quasiparticle configurations.

Spectroscopy of 75Se studied with the 72Ge(α, nγ) reaction

States in 75Se have been excited by the reaction 72Ge(α, n) 75Se and a level scheme built up from the observed γ-ray spectra. Gamma-ray angular distribution measurements have been analysed to yield spin assignments, mixing ratios and branching ratios. Comparison of the positive parity spectrum with the levels predicted by a Coriolis coupling calculation shows good agreement. In particular the model can successfully predict the occurrence of “anomalous” states with J π = 5 2 + and 7 2 + which lie close to the 9 2 + state in this nucleus, and which ar general feature of many neighbouring nuclei. Calculated E2 and M1 transition rates among these levels agree with available experimental data to within a factor of two. A strong case can therefore be made for regarding the low-lying levels in 75Se as arising from an odd neutron coupled to a deformed prolate core.

A Rigorous Application of the Collective Model to Some Rare Earth Nuclei

The collective model of an odd neutron in an axially symmetric deformed Woods–Saxon potential, coupled to a rotating core, and containing the full RPC and pairing corrections has been used to predict the full low lying rotational band spectrum of the nuclei with N = 91 to 97. Only three adjustable parameters were used in each nucleus to fit the complete spectrum. It was possible in several nuclei to obtain the correct level sequence and in most to confirm level assignments, and the adjusted parameters were in good agreement with accepted values. However, the accuracy of this method is insufficient, in most nuclei, to provide reliable predictions for as yet unidentified bands. The lack of good overall agreements in the low lying spectra of these nuclei confirms that the core shape parameters do change from one band to another.

The beta decay of Pm146 with microscopic nuclear wave functions

Explicit numerical values are given for the matrixelements of the first forbiddenβ−-decay of Pm146 to the 2+-state of Sm146. The odd-odd nucleus Pm146 is assumed to have a structure similar to neighboured even-even nuclei to which an odd neutron and an odd proton are coupled. The wavefunctions of the even-even nuclei are calculated starting from Bohrs Hamiltonian.

Coriolis-coupling model applied to odd-neutron nuclear spectra of the1g92shell

A Coriolis-coupling model extended to include a residual pairing type interaction is applied to investigate the energy levels of low lying states of the odd nuclei of the $1{g}_{\frac{9}{2}}$ shell $73<A<87$. This deformed rotational treatment includes spectra of both parities originating from overlapping states of the $N=4$ and $N=3$ positive and negative parity shells. Single particle energy levels and wave functions throughout a shell are computed using spin-orbit and well-flattening parameters $C=\ensuremath{-}0.26\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$ and ${D}_{N=4,3}=\ensuremath{-}0.040\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$ $\ensuremath{-}0.053\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$, respectively, the latter values being consistent with ${d}_{\frac{5}{2}}$ parentage states of $^{79}\mathrm{Se}$ (positive parity) and ${f}_{\frac{5}{2}}$ states of $^{83}\mathrm{Kr}$ (negative parity). Inclusion of an extracore pairing interaction primarily introduces a multiplicative effective overlap which serves as a quenching factor to the strength of off-diagonal Coriolis coupling terms. All parameters in the analysis are taken from available experimental considerations. The rotational constant $A$ and deformation $\ensuremath{\beta}$, in particular, are derived from the location of the first excited ${2}^{+}$ state of the neighboring even-even nucleus and its observed $E2$ transition rate to the ground state. For each set of parameters both a single particle and a Coriolis coupling diagonalization are performed over an entire shell of 10 or 15 Nilsson states to obtain final negative or positive parity spectra and wave functions. The results of this essentially fixed parameter model are presented and compared with experimental determinations with which they are in substantial agreement. In general, the model favors a prolate description for the nuclei in this region. Energy excitation spectra are all in general agreement, and in particular: (a) ground state spins and lowest lying opposite parity spins are always correctly predicted; (b) many otherwise anomalous low lying and often ground state ${7/2}^{+}$, ${5/2}^{+}$ spins are well predicted. The systematic reproduction of experimental spectra provided by the model points to the validity of a statically deformed interpretation of the odd neutron nuclei of the $1{g}_{\frac{9}{2}}$ shell, in contrast to the purely spherical and vibrational approaches to which the region has been restricted in the past.NUCLEAR STRUCTURE $^{73}\mathrm{Ge}$, $^{75,77,79,81}\mathrm{Se}$, $^{83,85}\mathrm{Kr}$, $^{87}\mathrm{Sr}$; calculated levels, $I$ $\ensuremath{\pi}$. Deformed Coriolis coupling treatment with pairing. Both parties.

The magnetic dipole moments of doubly odd antimony isotopes with [formula omitted] neutron configuration

The half-life, g-factor and spin of the 118mSb ground state have been measured using the technique of NMR/ON to be 5.00 ± 0.01 h, 0.290 ± 0.005 n.m. and 8 respectively. The ground state spin of 120mSb was also determined as 8. A more accurate measurement of the hyperfine field at Sb in Fe yields new values for the moments of 120mSb, 124Sb and 125Sb. A model including configuration mixing and collective effects is used to interpret the moments of those doubly odd isotopes from 116mSb to 128Sb, whose odd neutron is ( h 11 2 ) .

Nuclear reaction studies of 168Tm

The intrinsic structure of 168Tm has been studied using the ( 3He, d) and (α, t) proton stripping reactions as well as the (d, t) and ( 3He, α) neutron pick-up reactions. The beams of 24 MeV 3He particles, 25 MeV α-particles and 12 MeV deuterons were obtained from the McMaster tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge-type magnetic spectrograph and detected with photographic emulsions. The spectra have been interpreted in terms of the coupling of an odd proton and an odd neutron, each moving independently in a spheroidal potential, which gives rise to intrinsic two-quasiparticle states with K = ¦Ω 1±Ω 2¦ . The identification of the intrinsic states was made by comparing the experimental cross-section patterns with those predicted with the aid of Coriolis coupling and distorted-wave Born approximation (DWBA) calculations. Rotational bands superimposed on the K π = 3 + and K π = 4 +, { 7 2 + [633] n± 1 2 + [411] p} configurations, the first of which is the ground state, ha been observed in the spectra of all four reactions. New assignments have been made for configurations resulting from coupling the 1 2 − [541], 7 2 + [404], 5 4 + [402] and 1 2 − [530] p to the 7 2 + [633] neutron state. The neutron pick-up measurements confirmed the earlier assignments based on (d, t) reaction studies and suggested tentative assignments for the { 1 2 + [400] n± 1 2 + [411] p} and { 3 2 + [402] n± 1 2 + [411] p}

Magnetic Moment of the 80-keV1−State ofPr144

The magnetic moment of the 80-keV ${1}^{\ensuremath{-}}$ state of $^{144}\mathrm{Pr}$ has been determined using the integral-reversed-field method of the perturbed angular correlations. The value of $\ensuremath{\mu}=(\ensuremath{-}4.3\ifmmode\pm\else\textpm\fi{}1.4){\ensuremath{\mu}}_{N}$ indicates a structure of the 80-keV level based on the mixing between two shell-model states, both having the odd neutron in ${f}_{\frac{7}{2}}$ configuration --- the odd proton occupying ${g}_{\frac{7}{2}}$ and ${d}_{\frac{5}{2}}$ configurations, respectively.

Structure information on 26Mg from the 26Mg(p, d)25Mg reaction at 20 MeV

Abstract The angular distributions of 26Mg(p, d)25Mg deuteron groups to the levels in 25Mg up to 3.903 MeV, which were resolved with 30 keV resolution, were compared with DWBA pick-up theory. Several levels, particularly those which are weakly populated do not fit well. A spectroscopic factor analysis was made where 25Mg was assumed to consist of a deformed core with the odd neutron in a mixture of all possible N = 2 Nilsson states. The band-head spectroscopic factors then gave the filling of Nilsson states in 26Mg, as V9 = 0.57, V11 = 0.30 and V5 = 0.78. Good agreement with the spectroscopic factors for the other N = 2 particle states in 25Mg was found. However the 7 2 + and 9 2 + levels appear much more strongly than would be predicted by direct neutron pick-up theory.

The Total Particle Parameter of the 212 keV Transition in 121Te

The conversion coefficient of the 212 keV 3/2+-1/2+ transition in the odd neutron nucleus 121Te has been determined by e-e coincidence measurements, giving αK=0.0768(17), and the total particle parameter, B2K = -0.22 (11), by e-e and e-γ directional correlations. These values give the multipole mixing ratio δ(E2/M1) = -0.226(8) and little or no anomalous M1 conversion, λ = -0.7 (17). The λ-value is compared with a theoretical estimate.

Properties of phonon-coupled levels: The levels of 135Ba populated in the decay of 135La

The radioactive decay of 135La has been studied with the aid of ordinary Ge(Li) spectrometers and Compton suppression Ge(Li) spectrometers. The levels in the deduced decay scheme are discussed in terms of the odd neutron coupled to the core vibration. Some evidence is given for the preferential decay of the levels to other phonon-coupled configurations rather than by the expected E2 phonon de-excitation mechanism.

Neutron-Proton Interaction in Odd-Odd Deformed Nuclei

Calculations of the energy splittings between the parallel and antiparallel coupling states of odd neutron and odd proton in deformed nuclei have been made for both zero-range and finite-range nuclear forces. The energy splittings for both types of forces agree with the corresponding experimental energies. Calculations have also been made for the odd-even shift in $K=0$ bands. Finite-range interactions improve the agreement between experiment and theory for the odd-even shift, but the results are still unsatisfactory. It is shown that a tensor force is important in reproducing the experimental odd-even shift, especially in the case where ${\ensuremath{\Sigma}}_{n}+{\ensuremath{\Sigma}}_{p}=1$.

Application of the unified model with Coriolis coupling to 22Na, 26Al and 30P

The collective rotational model of Bohr, Mottelson and Nilsson is applied to the doubly odd sd shell nuclei 22Na, 26Al and 30P. The odd neutron and odd proton are placed in Nilsson orbitals generated by the axially symmetric deformed core. The Hamiltonian is composed of the collective rotational energy, including the Coriolis terms; the single-particle Nilsson energies; and a residual interaction between the last odd neutron and proton. The effective matrix elements calculated by Kuo and Brown from the Hamada-Johnston nucleon-nucleon potential are used for the residual interaction between the last two nucleons. Nuclear energy levels and wave functions are calculated by diagonalizing this Hamiltonian on a basis consisting of the rotational bands built on single-particle states obtained by placing the odd neutron and odd proton in all available sd shell Nilsson single-particle and single-hole orbitals. The deformation parameter β is determined for each nucleus by fitting the experimental energy spectrum. The other model parameters are assigned the same value for all the nuclei treated, except for the coefficient {ce:inline-formula}D{/ce:inline-formula} of the {ce:inline-formula}l·l{/ce:inline-formula} term in the Nilsson Hamiltonian, which must be varied to produce a satisfactory spectrum for 30P. Magnetic moments, electric quadrupole moments, and Ml and E2 transition rates and mixing ratios are calculated. The calculated results are compared with experimental data. Agreement between the theoretical and experimental energy spectra is satisfactory for all three nuclei for states below 2 MeV, but there are discrepancies for states above 2 MeV in 22Na. For the electromagnetic properties, agreement is satisfactory for transitions from states below 2 MeV in 22Na and 30P, but there are discrepancies for states above 2 MeV in 30P and for low-lying states in 26Al.