The level structure of 184Os from 184Ir decay and 185Re(p, 2nγ) in-beam spectroscopy

Levels of ¹⁸⁴Os populated in the decay of 3.1 h ¹⁸⁴Ir and in the ¹⁸⁵Re(p, 2nγ) reaction have been investigated. The measurements included γ-ray singles, β⁺ ray endpoint, conversion coefficient, β⁺-γ coincidence and detailed γ-γ coincidence determinations. The results have established an extensive ¹⁸⁴Os level scheme, which includes well developed ground state, γ-vibrational and K = 3 octupole bands and which accommodates all the intense transitions observed in both the radioactivity and in-beam γ-ray measurements. Deviations of the level energies in the K^π = 0⁺and K^π = 2⁺ bands and of the interband reduced transition probabilities from the predictions of the strong-coupling model are discussed in terms of the rotationvibration interaction, and the systematics of the octupole vibrational excitations in even-mass W and Os nuclei are reviewed. It is concluded that the ¹⁸⁴Ir ground state configuration has a spin of 5, and that it contains large admixtures of K = 0 or K = 1 character.     

Low-lying states of 184W and 184Os nuclei

The energy levels, transition energy, B （E2） values,intrinsic quadrupole moment Q₀ and potential energy surface for even-even ¹⁸⁴W and ¹⁸⁴Os nuclei were calculated using IBM-1. The predicted energy levels, transition energy, B（E2） values and intrinsic quadrupole moment Q₀ results are reasonably consistent with the experimental data. A contour plot of the potential energy surfaces shows that two interesting nuclei are deformed and have rotational characters.     

The decay of 192Ir

The decay of ¹⁹²Ir has been studied with Ge(Li) spectrometers. Gamma-ray energies and relative intensities are reported. Four previously unreported transitions at 329, 420, 593 and 703 keV have been identified by half-life and a level in ¹⁹²Os at 909 keV has been established on the basis of energy considerations. Upper limits are given for the γ-ray intensities of previously reported transitions at 110, 212, 280, 739, 765 and 1055 keV.     

The spin(6) scheme and electromagnetic transitions in 191Ir and 193Ir

The Coulomb excitation of natural Ir and Pt targets has been measured with protons and α-particles of energies between 5.0 and 6.0 MeV. Accurate γ-ray angular distributions were taken to determine the relative yields of observed γ-rays. Using ¹⁹⁴Pt as standard the reduced electric quadrupole transition probabilities to the ground states from Coulomb excited levels in the Ir and Pt isotopes were determined. Other B(E2) and B(M1) values were determined from the decay schemes obtained and from mixing ratios deduced from γ-ray angular distributions or from previously measured internal conversion coefficients. The detailed sets are compared with calcula- tions based on the Spin(6) scheme, which predicts several symmetries in ¹⁹¹Ir and ¹⁹³Ir. The possible existence of wider supersymmetry multiplets in this region of nuclei is examined on the basis of comparison of electromagnetic properties of Ir nuclei with those of Pt and Os isotopes.     

Ground-state rotational constants of 13CH3D

An analysis of the ground-state combination differences in the ν₂(A₁) band of ¹³CH₃D (ν₀ = 2190.0485 cm^?1) has been made to yield accurate values for six ground-state rotational constants, B₀, D₀^J, D₀^JK, H₀^JJJ, H₀^JJK, and H₀^JKK.     

Observation of α-decay in thallium nuclei,including the new isotopes 184Tl and 185Tl

With the use of an on-line isototpe separator α-decay was observed for the first time in thallium nuclides, including the new isotopes ¹⁸⁴Tl and ¹⁸⁵Tl. Their identification has led to the observation of the 0⁺ deformed band head in ¹⁸⁴Hg and allows for the possibility of determining whether ¹⁸⁵Hg is deformed in its ground state.     

Scattering and reactions of 14C + 14C and 14C + 14C

We have studied elastic scattering, inelastic scattering and several transfer channels of the systems ¹⁴C + ¹⁴C and ¹⁴C + ¹²C over a wide range of energies up to E_c.m. = 35 eMeV and 32 MeV, respectively. The reaction channels were identified by means of kinematic coincidences between solid-state detectors, γγ coincidences were measured to determine cross sections for mutual inelastic scattering of ¹⁴C + ¹⁴C.Pronounced regular gross structures, similar to those found for ¹⁶O + ¹⁶O, are observed in the elastic excitation function of ¹⁴C + ¹⁴C at θ_c.m. = 90°, The angular distributions measured at the energies of the maxima and an optical-model analysis suggest that one or a few surface partial waves dominate the scattering behaviour. Correlated structure of narrower width is found in the inelastic channels and, to a lesser degree, in the transfer channels which appear with rather small cross sections.In ¹⁴C + ¹²C elastic scattering the gross structures are strongly fragmented, in contrast to ¹⁴C + ¹⁴C but similar to ¹²C + ¹²C. While the ¹²C(2⁺) excitation is very weak, the observed strengths of the ¹⁴C(3^?) excitation and of neutron transfer point to a substantial role of these channels as coupling partners to the elastic configuration and to their influence on the elastic scattering behaviour. A correlated intermediate structure is observed near 23.5 MeV, where a dominance of l = 18 is suggested by the elastic scattering angular distribution. This unexpectedly high l-value exceeds l_graz at this energy by at least two units of ?.     

Levels of 188os populated in the 189Os(d,t)188Os reaction and in the decay of 41h 188Ir

The 0 level structure of ¹⁸⁸Os has been investigated by the ¹⁸⁹Os(d, t)¹⁸⁸Os reaction using a broad range magnetic spectrograph, and the properties of the ¹⁸⁸Os levels populated in the decay of ¹⁸⁸Ir have been re-examined. The (d, t) results yield new information about the location of two-neutron excitations in ¹⁸⁸Os involving the $\text{3}\text{2}$[512] orbital. Since the ¹⁸⁸Os ground state contains admixtures of both $\text{K =}\text{3}\text{2}\text{and}\text{K =}\text{1}\text{2}$ character, cross-section formulae for single-neutron transfer from a target state which is not pure in K are considered, and it is found that rather small $\text{K =}\text{1}\text{2}$ admixtures in the ¹⁸⁹Os ground state give rise to striking interference effects, which are manifested in the experimental (d, t) cross sections into the members of the ¹⁸⁸Os ground state band. The consequences of the mixed character of the target state on the (d, t) population of members of the K^π = 2⁺ γ-vibration and of higher-lying two-quasiparticle bands are also discussed.     

The level structure of 184W FROM THE β− decay of 184Ta

Levels of ¹⁸⁴W populated in the decay of 8.7 h ¹⁸⁴Ta have been studied by a variety of experimental techniques. As a result of β and γ-ray energy and intensity determinations and extensive β-γ and γ-γ coincidence measurements, a detailed ¹⁸⁴Ta decay scheme accommodating more than 99.5% of the decay intensity has been established. Intense β-ray groups of end-point energies 1165±26 and 1123±26 keV populate levels in ¹⁸⁴W at 1699 and 1746 keV, which de-excite predominantly to the 8.3 μs isomeric level at 1285 keV, recently identified as the $\text{1}\text{2}{}^{\mathrm{?}}\text{[510]ν?}\text{11}\text{2}{}^{\mathrm{+}}\text{[615]ν K}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}$ band origin. The 1699 keV level also de-excites to members of a $\text{1}\text{2}{}^{\mathrm{?}}\text{[510]ν?}\text{7}\text{2}\text{[503]ν K}{}^{\mathrm{\pi }}\text{= 3}{}^{\mathrm{+}}$ band based at 1425 keV. New information about the properties of the γ-vibrational and K = 2 octupole bands in ¹⁸⁴W is presented and the possible configurations of the levels directly populated in the β^? decay are discussed. The configuration $\text{7}\text{2}{}^{\mathrm{+}}\text{[404]π ?}\text{3}\text{2}{}^{\mathrm{?}}\text{[512]ν K}{}^{\mathrm{\pi }}\text{= 5}{}^{\mathrm{?}}$ is indicated for the ¹⁸⁴Ta ground state.     

Decay of 185Au: Sign of shape coexistence in 185Pt

The decay of ¹⁸⁵Au has been studied on-line with mass-separated sources from the ISOCELE facility. Precise conversion-electron measurements have been performed with a 180° magnetic spectrograph. The level scheme of ¹⁸⁵Pt has been established, and the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 33}$ min isomeric state has been located at 103.2 keV with respect to the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 71}$ min ground state. Two highly converted transitions have been observed. The level scheme is discussed in the framework of an “axial-rotor + quasiparticle” approach: numerous states are interpreted assuming a prolate shape of the nucleus. Ten levels with low spin and negative parity ($\text{I ?}\text{7}\text{2}{}^{\mathrm{?}}$) decay mainly to the $\text{1}\text{2}{}^{\mathrm{?}}\text{[521]}$ band via strong M1 transitions and are not expected from the calculations performed with the prolate cores. The possibility of shape coexistence is discussed.     

Neutron resonances in 185Re and 187Re

In a search for intermediate structure, neutron time-of-flight spectra corresponding to 1 and 4 MeV capture γ-ray thresholds were measured for the target isotopes ^{185, 187}Re. The data were analyzed from the point of view of level spacings as well as intermediate structure. A method was developed for estimating the neutron widths of the resonances even in those cases where the neutron widths are comparable to the γ-widths. On the basis of this analysis it was decided which resonances were most likely to be due to p-wave capture. While some unusual behavior was observed, there is no conclusive evidence for intermediate structure. The statistics of level spacings agree with the long range ordering described in the theory of Dyson and Mehta, and are inconsistent with an uncorrelated Wigner distribution. Energies, estimated neutron widths and p-wave probabilities (if over 10 %) for 488 resonances in ¹⁸⁵Re and 335 resonances in ¹⁸⁷Re are tabulated for the energy range 24 eV to 2 keV.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

g-factors of 2.7 h 93Tc, 4.9 h 94Tc and 20 h 95Tc

The hyperfine splitting frequencies gμ_NB_H.F./h of 2.7 h ⁹³Tc $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}\text{)}$, 4.9 h ⁹⁴Tc (J^π = 7⁺) and 20 h ⁹⁵Tc $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}\text{)}$ as dilute impurities in Fe have been measured with NMR on oriented nuclei as 336.36(5) MHz, 175.11(1) MHz and 315.97(2) MHz, respectively. From the resonance shifts with an external magnetic field B₀ the hyperfine field of Tc$\text{Fe}$ has been determined as -317(5) kG. Taking this into account the nuclear g-factors are deduced as $\text{g(}{}^{93}\text{Tc}\text{) = 1.392(22), g(}{}^{94}\text{Tc}\text{) = 0.725(11)}\text{and}\text{g(}{}^{95}\text{Tc}\text{) = 1.308(21)}$.     

Electron scattemng studies of 184W and 186W

Anomalous results obtained in recent electron-nucleus scattering experiments suggest that a dispersion correction may contribute significantly to elastic cross sections in the region of the first diffraction minimum. Such a dispersion correction describes the effect of possible virtual nuclear excitations neglected in the conventional phase-shift analyses of electron scattering data. To investigate these effects, the Yale University electron accelerator has been used to study the scattering from ¹⁸⁴W and ¹⁸⁶W at incident energies between 40 and 65 MeV and scattering angles between 70° and 150°. No evidence of a dispersion effect is seen in the nucleus ¹⁸⁶W. In the case of ¹⁸⁴W, a comparison of the measured cross sections with those expected on the basis of the results of muonic X-ray experiments indicates that any dispersive effect is limited to less than 10% in the region of the first diffraction minimum. A summary of the results of this laboratory's search for dispersion effects in Nd, Sm, and W is appended.     

Levels of 190Os populated in the decays of 3.3 h 190mRe and 12 d 190Ir and in the 189Os(d,p)190Os reaction

The level structure of ¹⁹⁰Os has been investigated by the techniques of radioactive decay and neutron transfer reaction spectroscopy. The existence of 3.3 h ^190mRe has been confirmed; it decays ≈ 49% by isomeric transitions and ≈ 51% by β^? decay to levels in ¹⁹⁰Os with spins $\text{\$}\text{?}\text{= 5}$. In a re-investigation of the 12 d ¹⁹⁰Ir decay, a virtually complete decay scheme has been established and discrepancies between the I^π values assigned to several ¹⁹⁰Os levels by earlier workers have been resolved. The reaction ¹⁸⁹Os(d, p)¹⁹⁰Os has been studied and information about the locations of two-quasiparticle states involving the $\text{3}\text{2}\text{[512]ν}$ orbital and about the microscopic compositions of collective excitations has been derived. Various aspects of the ¹⁹⁰Os level structure are discussed in the light of the combined radioactivity and transfer reaction results.     

Ground-state rotational band in 181Ta

The ground-state rotational band in ¹⁸¹Ta has been observed up to a spin of $\text{21}\text{2}{}^{\mathrm{+}}$ using Coulomb excitation with ⁸⁴Kr ions. The nuclear lifetimes of the band members have been determined from the Doppler-broadened lineshapes of the de-excitation γ-rays, and the angular distributions of the γ-rays have been measured. It is found that the E2 transition rates from higher spin states $\text{(≧}\text{17}\text{2}{}^{\mathrm{+}}\text{)}$ are retarded relative to the rotational model predictions. A suggestion is made that this retardation may be due to the Coriolis antipairing effect.     

Competition between strong and decoupling schemes in 187Ir

Low spin states (J < j) for transitional nuclei with a typical decoupling spectrum built on a single particle level j show systematic discrepancies between theory and experiment. To account for the discrepancies the decoupling scheme is extended to include also strong coupling. Excellent agreement including that for the low spin states is found in ¹⁸⁷Ir to which this theory is applied.     

Angular-correlation study of the level scheme of 193Ir

The decay of ¹⁹³Os to ¹⁹³Ir has been studied by γγ angular correlations. Inconsistencies between previous angular correlations, internal conversion coefficients, and nuclear orientation angular distributions have been satisfactorily resolved by the present results. These data are used to derive a set of $\text{E2}\text{M 1}$ multipole mixing ratios of the transitions between low-lying states. The resulting electromagnetic transition moments are compared with calculations based on the Nilsson model with Coriolis mixing and on the interacting boson-fermion model.     

Charge exchange reaction 14C(6Li, 6He)14N

Angular distributions of the charge exchange reaction ¹⁴C(⁶Li, ⁶He)¹⁴N leading to the 1⁺ ground state and 3.95 MeV 1⁺, and 5.20 MeV 2^? excited states at the 34 MeV incident beam energy were analyzed and measured. The 62 MeV data of Goodman et al. were also reanalyzed. The direct one-step charge exchange caused by the spin-isospin dependent term in the two-body interaction can account well for the observed data. The strength of spin-isospin dependent effective interaction (gaussian form with a range parameter of 1.8 fm) was extracted to be 18.5 MeV.     

The 26Mg(14N, 10B)30Si and 26Mg(14N, 11B)29Si reactions

Reactions induced by ¹⁴N on ²⁶Mg at bombarding energies of 60–95 MeV have been studied. Angular distributions for states populated in ²⁹Si by the (¹⁴N, ¹¹B) reaction and in ³⁰Si by the (¹⁴N, ¹⁰B) reaction have been compared with Hauser-Feshbach and DWBA calculations to determine the reaction mechanism and to deduce spectroscopic information. The cross sections for the states populated in ²⁹Si and ³⁰Si are in poor agreement with statistical model calculations, indicating a non-compound nucleus mechanism.