High-spin states in the single-closed-shell nucleus 142Nd

The excited states of ¹⁴²₆₀Nd₈₂ have been studied using the ¹⁴⁰Ce(α, 2nγ)¹⁴²Nd and ¹⁴²Ce(α, 4γ)¹⁴²Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in ¹⁴²Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.     

In-beam study of 144Gd

A level scheme of ¹⁴⁴Gd has been established using the ¹⁴⁴Sm(α, 4nγ) reaction and in-beam spectroscopy methods. Excitation functions, γ-ray angular distributions, γ-γ coincidence spectra, γ-spectra time related to the cyclotron beam bursts and conversion coefficients for the delayed transitions have been measured.The level scheme comprises 11 levels with spins up to I = 12. Two isomers, a 13 ± 2 ns, 7^? state at 2471.4 keV and a 145 ± 30 ns, 10⁺ state at 3433.0 keV have been observed. The former has similar excitation energy as the 7^? isomers in ¹⁴²Sm, ¹⁴⁰Nd and ¹³⁸Ce and it may arise from the $\text{{ν}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{× ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{}}$ configuration although its lifetime seems to indicate some degree of collectivity. The 10⁺ state has a similar excitation energy as the 10⁺ isomer found in ¹³⁸Ce and it may arise from the dominant $\text{ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?2}}$ configuration. Below the 10⁺ isomer in ¹⁴⁴Gd only two excited states have positive parity; the hitherto known first 2⁺ and 4⁺ states. The 11⁺ and 12⁺ states must include four-particle configurations or they have to be of collective nature. The latter possibility is supported by the considerable E2/M1 mixture (≈ 20 %) observed for the 11⁺ to 10⁺ transition. An analysis of the systematics of ground band levels in the N = 80 isotones shows the same gradual behavior between the two VMI solutions previously found for the Te isotopes.     

The level scheme of 137Pr; evidence for prolate nuclear shape

The level scheme of ¹³⁷Pr was investigated by means of the γ-rays following the β-decay of ¹³⁷Nd as well as by prompt γ-rays accompanying (α, xn) reactions. We measured γ-ray single spectra, γγ coincidences (both in-beam and off-beam), angular distributions of prompt γ-rays and conversion electrons. About 100 γ-rays were assigned to the 38 min decay of ¹³⁷Nd most of which fit into a scheme of 26 deduced levels. From in-beam experiments we tentatively assigned an $\text{11}\text{2}$^? level which is the basis of a strong cascade of stretched E2 transitions with a probable level sequence of $\text{23}\text{2}$^? ?$\text{19}\text{2}$^? ?$\text{15}\text{2}$^? ?$\text{11}\text{2}$^?. The interpretation of this cascade in the framework of a strong coupling model indicates a prolate deformation of ¹³⁷Pr. Another indication for such a deformation was obtained from the very low energy (75 keV) of the first $\text{3}\text{2}$⁺ level which could not be interpreted in an intermediate coupling model, but is suggested by a Nilsson scheme.     

States in 53Mn from the 52Cr(p, γ)53Mn reaction

Eight resonances have been observed in the ⁵²Cr(p, γ)⁵³Mn reaction between E_p = 0.90 and 1.03 MeV. Gamma-ray spectra have been accumulated at four of the resonances. Spin assignments have been made to the resonant states on the basis of the measured angular distributions of primary γ-rays. Excitation energies and γ-ray branching ratios have been determined for 36 levels between 2.0 and 5.6 MeV. Mean lives for nine of the states have been extracted by the Doppler shift attenuation method.     

Decay of 59.3 min 128Sn to levels of 128Sb

The γ-ray spectra associated with the decay of 59.3 min ¹²⁸Sn have been measured with Ge(Li) detectors. In order to recognize γ-rays of ¹²⁸Sn and ^128mSb, the decay and/or growth of γ-rays emitted from a tin sample separated chemically from fission products were measured. The decay of ¹²⁸Sn is followed by the intense Sb X-rays and 32.1, 45.8, 75.1, 80.9, 115.9, 152.6, 404.4, 482.3, 557.3 and 680.2 keV γ-rays. On the basis of the measured singles and γ-γ coincidence spectra and the analysis of intensities of true sum peaks, a new decay scheme has been constructed. The 10.0 min isomer in ¹²⁸Sb decays by β-emission (96.4%) to excited levels in ¹²⁸Te and by an isomeric transition (3.6 %) to the 9.1 h ground state.     

A Kπ = 4− rotational band in 48V

From γ-ray linear polarization measurements, γ-ray angular distributions and γ?γ coincidences, the following levels were identified in ⁴⁸V (E_Xin keV): 4^? at 1099, (5^?) at 1685, (6^?) at 2397, (7^?) at 3171 and (8^?) at 3976. This sequence of states is interpreted as a K^π = 4^? rotational band.     

Radiative capture of fast neutrons by 89Y and 140Ce

The γ-ray spectra from the reactions ⁸⁹Y(n, γ)⁹⁰Y and ¹⁴⁰Ce(n, γ)¹⁴¹Ce have been measured in the neutron energy range of 6.2–15.6 MeV. The pulse-height spectra were recorded with NaI(Tl) spectrometers and time-of-flight techniques were used to improve signal-to-background ratio. Capture cross sections were determined for γ-ray transitions to the two $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels at 0 and 203 keV of ⁹⁰Y and to the $\text{2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ ground state of ¹⁴¹Ce as well as integrated cross sections to bound states in these nuclei. The observed γ-ray spectra and partial radiative capture cross sections were compared with predictions of the direct-semidirect capture theory. The resonance behaviour with neutron energy of both the ground-state and integrated partial capture cross sections shows the validity of the semidirect model for ⁸⁹Y and ¹⁴⁰Ce in the region of neutron energy encompassing the giant-dipole resonance. The observed symmetry of the cross sections about the peak of the resonance argues strongly for the complex form of the particle-vibration coupling interaction. A detailed comparison of the predictions of the DSD model using the complex coupling interaction shows that the capture cross sections are relatively insensitive to the real part of the interaction.     

Collective and two-quasiparticle states in 158Gd observed through study of radiative neutron capture in 157Gd

The level structure of ¹⁵⁸Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in ¹⁵⁷Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for ¹⁵⁸Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for ¹⁵⁸Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the K^π = 0^?, 1^? and 2^? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited K^π = 0⁺ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and K^π assignments) of 1380 (4⁺), 1636 (4^?), 1847 (1⁺), 1856 (1^?), 1920 (4⁺) and 1930 (1⁺). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0⁺ bands are derived. For three of these 0⁺ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0⁺ bands.     

Spin-parity assignments for the excited states of 91Nb from the 91Zr(p,nγ)91Nb reaction

The energy levels of ⁹¹Nb were studied by means of the (p, nγ) reaction. The de-excitation γ-rays were observed with a Ge(Li) detector in the proton energy range from 3.25 to 5.51 MeV in steps of about 30 keV. Resonances attributed to isobaric analog states in the compound system ⁹¹Nb were observed in the excitation functions of the de-excitation γ-rays. From an analysis of these analog resonances, a Hauser-Feshbach analysis and the γ-decay scheme, the spin-parities of the levels up to 2792.6 keV (22 levels) were assigned.     

Gamma transitions in 59Ni following the β+ decay of 59Cu

The γ-ray decay spectrum of 82 s ⁵⁹Cu produced by the ⁵⁸Ni(p, γ) ⁵⁹Cu reaction has been studied with a 40 cm³ Ge(Li) detector. The number of γ-rays now known for this decay has more than doubled. Additional direct β⁺ branches to the 1679.7($\text{5}\text{2}{}^{\mathrm{?}}$), 2414.8($\text{3}\text{2}{}^{\mathrm{?}}$) and 2681 keV states of ⁵⁹Ni have been identified with log ft values of 5.5, 5.5 and 6.0, respectively. A major change is the reassignment of the 1340.4 keV γ-ray to a 1679.7 → 339.3 keV transition. A limit of log $\text{ft ≧ 6.9}$ is given for the direct feeding of the 1337($\text{7}\text{2}{}^{\mathrm{?}}$) keV state, together with limits for direct population of other energetically available states. The new weak γ-ray branches found for the 878.0, 1301.5 and 1679.7 keV levels are in excellent agreement with the recent theoretical calculations of Glaudemans et al.     

High-spin levels in137,139Ce and139,141Nd evidence for hole-core coupling

Excited states of the¹³⁷Ce,¹³⁹Ce,¹³⁹Nd and¹⁴¹Nd nuclei have been studied using the¹³⁸Ba(α, 5nγ)¹³⁷Ce,¹³⁸Ba(³He, 4nγ)¹³⁷Ce,¹³⁸Ba(α, 3nγ)¹³⁹Ce,¹⁴⁰Ce(α, 5nγ)¹³⁹Nd,¹⁴⁰Ce(³He,4nγ)¹³⁹Nd,¹⁴⁰Ce(α, 3nγ)¹⁴¹Nd and¹⁴²Ce(α, 5nγ)¹⁴¹Nd reactions. Singlesγ-ray spectra,γ —γ coincidence spectra, angular distributions and time distributions ofγ-rays with respect to beam pulses have been measured. Gamma transitions between excited states with spin values up to 21/2, 23/2 or 25/2 have been observed. Isomeric states with T_1/2=70 ns have been observed in¹³⁹Ce at 2631.5 keV (19/2) and in¹⁴¹Nd probably at 2952.0 keV (19/2). The level structure observed in the nuclei studied can be explained if the neutron-holes are coupled to the doubly even core excitations. The coupling of theh _11/2 neutron-hole with the 2⁺, 4⁺ and 3^? collective excitations are calculated in terms of the weak and intermediate coupling models. The intermediate coupling results seem to be in better agreement with the experimental data. The energies of theree-particle states, being the result of the coupling of theh _11/2 neutron-hole with the two-proton excitations in the core, are well reproduced in the calculations when empirical values of the two-body interaction matrix elements were used.     

The γ-decay of excited states of 141Ce observed in the 140Ce(d,pγ) reaction

The reaction ¹⁴⁰Ce(d, pγ)¹⁴¹Ce was studied at 8 MeV bombarding energy. Protons and γ-rays were detected in coincidence. The decay scheme is deduced, and the branching ratios are compared to the results of other experiments and to model calculations.     

The level scheme of 135Pr: Prolate deformation of the 112− isomer

The level scheme of ¹³⁵Pr has been investigated by means of off-beam γ-ray and conversion electron measurements as well as by methods of in-beam γ-spectroscopy. We measured γ-ray and conversion electron singles spectra, off-beam and in-beam γγ coincidences and γ-angular distributions. From the experimental data a detailed scheme of 22 excited levels for ¹³⁵Pr has been constructed. In addition to members of the decoupled band based on the $\text{11}\text{2}{}^{\mathrm{?}}$ state six further negative parity states were identified. These states are strongly populated in the β-decay of a $\text{9}\text{2}$ isomer in the parent nucleus ¹³⁵Nd. A comparison of all the negative parity states with predictions of the alignment coupling model showed a nearly quantitative agreement, if softness of the core is taken into account. In this case, a prolate deformation with a deformation parameter β ≈ 0.13 was obtained for the $\text{11}\text{2}{}^{\mathrm{?}}$ isomer in ¹³⁵Pr.     

Recherche de l'isotope 19N par la réaction 10Be(11B, 2p)19N

The ¹⁰Be(¹¹B, 2p)¹⁹N reaction has been used to search for the ¹⁹N isotope. No evidence was found for delayed γ-rays from ¹⁹N(β^?)¹⁹O. Delayed neutrons were observed with a half-life of 0.42 ± 0.04 s, which are tentatively assigned to the neutron emitting states in ¹⁹O fed by the β-decay of ¹⁹N. Analysis of the data implies allowed β-transitions to neutron emitting ¹⁹O states, and makes probable an assignment of even parity for the 3.945 MeV ¹⁹O state.     

The decay scheme of 228Fr and K = 0 BANDS in 228Ra

The γ-rays following the β^?-decay of ²²⁸Fr have been studied by means of γ-ray singles including multi-spectrum analysis and γ-γ coincidence measurements using Ge(Li) spectrometers. Most of the observed γ-transitions could be placed in the level scheme of ²²⁸Ra. The accuracy the energy of the first-excited state in ²²⁸Ra has been improved and 35 new excited levels have been established, 11 of them grouped into the ground-state band, the low-lying K^π = 0^? band with the head at 474.14 keV and two excited K^π = 0⁺ bands with heads at 721.17 and 1041.9 keV. Candidates for two close-lying K^π = 2⁺ bands have also been found. It is concluded that the ground state octupole deformation, if any, is less pronounced in ²²⁸Ra than in lighter radium isotopes.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

Angular distribution studies in 14460Nd

Forty-seven energy levels in ¹⁴⁴Nd up to 3.532 MeV have been populated using the (n, n'γ) reaction with reactor fast neutrons. Angular distributions of γ-rays with respect to the neutron beam have been measured. Ten new states at 2270.0, 2563.8, 2581.6, 2591.6, 2600.5, 2692.4, 2978.5, 3100.6, 3242.6 and 3531.7 keV have been established and four additional new levels at 3069.5, 3253.2, 3292.1 and 3395.4 keV tentatively proposed. The present study has also led to unique spin assignments for 22 levels, eight of which were established for the first time. The mixing ratios for a number of γ-transitions were deduced and compared, where possible, with values obtained by the complete alignment method and with those previously reported by other authors.     

Circular polarization and γ-γ angular correlation measurements in the 39K(n, γ)40K reaction

Circular polarization measurements of the γ-radiation from polarized neutron capture combined with γ-γ angular correlation measurements in the ³⁹K(n,γ)⁴⁰K reaction lead to J^π = 2^? assignments to the E_x = 0.80, 2.05 and 2.42 MeV states of ⁴⁰K, and to spin restrictions for the states at E_x = 2.10, 3.44 and 4.25 MeV. Multipole mixing ratios for the γ-rays which de-excite these levels have been determined.     

10+ isomers observed in even-even 78-neutron nuclei

Isomeric states with spinI ^π=10⁺ were found in the nuclei¹³⁸Nd and¹⁴⁰Sm. These states are interpreted as having a [vh _11/2]^?2 configuration. The systematical behaviour of these isomers in the isotones¹³⁶Ce,¹³⁸Nd and¹⁴⁰Sm is discussed.     

Investigation of i132 excitations in 197Hg and 191Pt

The level schemes of the odd-neutron nuclei ¹⁹⁷Hg and ¹⁹¹Pt have been studied using in-beam spectroscopic methods. Energies, intensities, angular distributions and coincidences of the γ-rays following (α, 2n) reactions were measured. Also conversion electrons and delayed γ-ray spectra were recorded. Most of the levels in both nuclei are de-populated via the $\text{13}\text{2}{}^{\mathrm{+}}$ isomers. Besides the yrast states, several additional states with spin values between $\text{13}\text{2}$ and $\text{21}\text{2}$ were identified. The negative parity of a side band in ¹⁹⁷Hg starting with an $\text{f =}\text{21}\text{2}$ state was proved by the conversion electron measurement. The families of positive-parity states were compared with model calculations where the core was described as rigid triaxial rotor or anharmonic vibrator. For ¹⁹⁷Hg both models give similarly good results for the energy spectrum and the branching ratios of electromagnetic transitions. Several negative-parity states found in ¹⁹⁷Hg are compared with the predictions of a pairing-plus-quadrupole model.