Detailed Ge(Li)-Ge(Li) coincidence studies of levels in152Sm and152Gd

The decay of 12.4 y¹⁵²Eu to¹⁵²Sm and¹⁵²Gd was studied in a high resolution singles measurement and two 4096×2048 Ge(Li)-Ge(Li) coincidence studies. Forty-five gates were analyzed in order to confirm or establish the placement of the γ rays as well as to accurately determine the intensities of the 12 doublets, which included several not previously reported. A new γ-β interband transition, 4 _γ ⁺ →2 _β ⁺ (561.4 keV), a possible 3 _γ ⁺ →2 _β ⁺ (423.7 keV) transition, and a new 330.9 keV transition between the 4 _γ ⁺ level and theI ^π K=3^?0 octupole level were established from coincidence data. Levels at 1757.0 keV in¹⁵²Sm and 1282.5, 1318.7, and 1692.2 keV in¹⁵²Gd are now established on the basis of coincidence data. These data also establish for the first time the population in the¹⁵²Eu decay levels at 1680.0 and 1047.9 keV in¹⁵²Sm and¹⁵²Gd, respectively, as well as a new level at 1700.8 keV in¹⁵²Sm.     

OnE0 transitions in the decay of152Eu m (9.3 h)

The conversion electron spectrum of the decay of¹⁵²Eu ^m (9.3 h) has been specially investigated forE0 transitions with the aid of a magnetic spectrometer and coincidence techniques. Besides the knownE0 transitions of 685 keV in¹⁵²Sm and 615 keV in¹⁵²Gd two further pureE0 transitions of 432 keV and 1048 keV have been observed. It is shown that theseE0 transitions are identical with those observed previously in the decay of¹⁵²Tb. NoE0 transitions could be found from a 0⁺ state of 1083 keV in¹⁵²Sm. The measured intensities together with the gamma spectrum measured by Barretteet al. give a consistent decay scheme of¹⁵²Eu ^m . Furthermore the half-life of the 0⁺ level at 615 keV in¹⁵²Gd was measured using the method of “delayed coincidences”. The result was (0.2≦t _1/2≦2.1)×10^?10 s. From this theE0 transition probability for the level was derived as (0.3≦W _K (E0)≦3.7)× 10⁹ s^?1 and theρ-value as 0.10≦¦ρ¦≦0.36. The results are discussed within the framework of the collective model.     

Thex- (orΔ) transition in152Dy

A 53.3 keV E2 transition de-exciting the 60 ns isomer in¹⁵²Dy has been identified in γγ-coincidence measurements, which locates that isomer at E_x=5088 keV. The half life of the 11^? level at 3161 keV was measured to be T_1/2=4.3±0.9 ns.     

TheK-shell particle parameter of the 122 keV transition in152Sm

TheK-shell particle parameter of the 122 keV transition in¹⁵²Sm has been investigated using different sources and different experimental arrangements. From our measurements we obtain the mean valueb ₂=1.77±0.03. This result deviates from the theoretical value by (6.5±1.5)%. We do not observe hygroscopic effects as reported in Ref.     

Half-life of the 89.83 keV level in152Eu

The half-life of the 89.83 keV level in¹⁵²Eu was measured in the¹⁵¹Eu(n, γ)¹⁵²Eu reaction to be 381±19 nsec. This results in the determination of the absolute transition probabilities of the 89.83 keVE1+M2 transition to the ground state, yielding hindrance factors relative to the Weisskopf estimateF _W(E1)=(2.3 ± 0.4) × 10⁶ andF _W=0.20±0.08.     

Inner conversion process of electric dipole transitions in180Hf and182W

The conversion electron process of the retarded electric dipole transitions of 58keV in¹⁸⁰Hf and 67, 116, 152, 156 and 222 keV in¹⁸²W have been studied by means of high resolution double focusing beta-ray spectrometers. No penetration effects were found in the conversion process of the retarded 58 keV and 67, 116 and 222 keV E1 transitions. While the retarded 152 and 156 keV transitions in¹⁸²W show an anomalous internal conversion ratios compared with theoretical values. Implications of the results for current nuclear theories are discussed.     

Conversion electron measurements of 152Nd

Abstact: Multipolarities of γ-rays in ¹⁵²Nd have been studied by conversion electron measurements in the β⁻ decay of ¹⁵²Pr. The praseodymium activities were obtained by the thermal neutron fission of ²³⁵U and followed with the on-line isotope separator KUR–ISOL. Conversion electrons and γ-rays were measured with a Si(Li) detector and a HPGe detector, respectively. The two γ-rays, 226 keV and 285 keV, were decided to have the multipolarities of the E1 transition. The spins and parities of the 1600 keV and 1542 keV levels were determined to be 3⁺ and 2⁺, respectively. Received: 14 April 1998     

Decay of the 4.2-min152Pm into levels of152Sm

After bombardments of enriched¹⁵²Sm with 14-MeV neutrons, three isomers of¹²⁵Pm reaction, have been observed with half-lives of 4.2±0.2 min, 7.5±0.2 min and 15.0±1.0 min. Sources of pure 4.2-min¹⁵²Pm were obtained by separating the promethium from its parent 11-min¹⁵²Nd produced by thermal-neutron induced fission of²³⁵U. The beta and gamma radiations of the 4.2-min¹⁵²Pm have been investigated using semiconductor and scintillation spectrometers. Most of theγ-ray transitions could be placed in a level scheme for 152Sm. Especially interesting is a level at 1083 keV for which the assignmentI ^π=0⁺ is proposed. In a 4πβγ experiment, the ground state feeding of¹⁵²Sm in theβ ^?-decay of the 4.2-min¹⁵²Pm has been measured to be 61% of allβ-ray transitions. AQ _β-value of 3.4±0.2 MeV has been obtained.     

Comparison of the elastic and inelastic scatterings between152Sm+12C and148 Nd+16O

Angular distributions of elastic and inelastic scattering have been measured for¹⁵²Sm+¹²C at 63.2 MeV and¹⁴⁸Nd+¹⁶O at 90.9 MeV. An evident interference pattern in the inelastic scattering has been observed for the first time in a strong Coulomb coupling system.We are indebted to Dr. S. Pieper for supplying the Ptolemy Program. One of us (Chenglie Jiang) would like to acknowledge the Argonne National Laboratory for the opportunity given, to perform theoretical calculations with the code Ptolemy during his visit there. Thanks are also due to Mr. H. Folger (GSI, Germany) for supplying the targets. This work was supported in part by China National Nature Science Fundation.     

High-spin states in the N = 84 nucleus 152Er

High-spin states in ¹⁵²Er have been populated through the ¹⁴⁴Sm(¹²C, 4n)¹⁵²Er reaction. Excitation functions, angular distributions, prompt and delayed coincidences against the beam burst were measured. Three isomeric states at 2183 keV (τ = 1.8 ns), 4519 keV (τ = 1.2 ns) and 4915 keV (τ = 6.6 ns) have been observed. The decay scheme is developed up to 7 MeV and is discussed and compared with that of ¹⁵⁰Dy.     

New results in the decay of150Ho and152Tm

A new isotope¹⁵²Tm (T _1/2=5.2±0.6 s) and a new isomeric state in¹⁵⁰Ho (T _1/2=88±15 s) were observed with the on-line isotope separator ISOCELE II at Orsay. The decay of¹⁵²Tm is similar to the one of the high spin state (9⁺) in¹⁵⁰Ho. The new¹⁵⁰Ho isomer, probably with a low spin (2 or 3), decays mainly to the 2⁺ level in¹⁵⁰Dy.     

Nuclear orientation of152,154Tb in gadolinium

The anisotropy in the directional distribution of gamma-rays from the decay of^152,154Tb oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction at temperature of (15±1) mK. Unambiguous values of spin have been deduced for several levels in¹⁵²Gd. Multipole mixing ratios of many gamma-ray transitions occurring in¹⁵²Gd have been found and results are compared with the similar transitions in^150,154,156Gd and they are discussed in terms of the rotational-vibrational model and dynamic deformation theory based on the Strutinsky method. Our results confirm the spin value of 0 for 21·4 h isomer in¹⁵⁴Tb and they establish the spin value of 3 for the 2277·0 and 2336·1 keV levels and the spin value of 4 for the 2416·3 keV level in¹⁵⁴Gd.     

The search for Hyperdeformation in152Dy

Three experiments have been carried out to search for the existence of Hyperdeformed states (HD) in the nucleus¹⁵²Dy. These three experiments were designed to test different properties of the expected HD structures. As a result of these experiments no clear evidence for HD states in¹⁵²Dy has been observed.     

Level structure of proton-richN=83 Nuclei150Ho and152Tm

The yrast levels of theN=83 odd-odd nuclei¹⁵⁰Ho and¹⁵²Tm have been studied byγ-ray spectroscopy following reactions induced by 240–250 MeV⁶⁰Ni ions. Isomers have been identified in¹⁵⁰Ho at 1.096, 2.625 and ～8.0 MeV and in¹⁵²Tm at 2.555 and ～ 6.3 MeV, and the level schemes of both nuclei have been established up to 2.6 MeV. The level spectra are interpreted using the shell model in terms of the coupling of anf _7/2,h _9/2 or i_13/2 valence neutron to the yrast excitations of the neighboring N=82 nuclei.     

Measurements ofE4 matrix elements in152Sm and154Sm

TheE4 transition matrix element from the ground state to the 4⁺ state has been measured in¹⁵²Sm and¹⁵⁴Sm, by comparing relative thick targetγ-ray intensities following Coulomb excitation with 12 MeV⁴He, 24–30 MeV¹⁶O, and 35–40 MeV³²S projectiles. Values for 〈0⁺∥?(E4)∥4⁺〉 of (+0.31 _?0.20 ^+0.12 ) barn in¹⁵²Sm and (+0.50 _?0.12 ^+0.09 ) barn in¹⁵⁴Sm are found.     

Relativmessung der longitudinalen Polarisation der β-Teilchen des Eu152

The longitudinal polarizationP of theΒ-rays from the 1.49 MeV transition of Eu¹⁵² (T=13 y) has been measured relatively to P³² using the MØeller-scattering method (electron-electron-scattering). Taking the polarization of P³² asP(P³²)=?(v/c) we getP(Eu¹⁵²)=?(0.959±0.028) (v/c) at a mean energy of 1100 keV. This result is in good agreement with the set of matrix elements taken from measurements of other observables.     

Nuclear levels in152Eu

The transitional nucleus¹⁵²Eu has been studied using the (n, e), (n, γ), (n _res,γ), (n, γγ), (d, p), (d, t) and (p, d) reactions. The experiments have been performed at nine different laboratories. A model independent level scheme was established including 95 levels below 510 keV and nearly 900 transitions by combination of low energy transitions and reaction data. More than 20 additional levels result from gamma rays and/or charged particle reactions. The level scheme is interpreted in terms of the Nilsson model indicating that¹⁵²Eu is a deformed nucleus. Seven rotational bands and Nilsson configurations are established. An additional 27 rotational bands are tentatively or speculatively assugned. Gallagher-Moszkowski splittings are discussed. The neutron binding energy was determined as 6305.2±0.5 keV. The energy of the 9.3 h 0^? isomer is 45.599 keV. The lifetimes of four levels were measured. Nuclear Reactions¹⁵¹Eu(n,γ),E _n =thermal and resonance; measuredE _γ ,I _γ ,E _c.e.,I _c.e.,γγ Coinc.,γγΔt coinc.;¹⁵¹Eu(d, p),E=12MeV and 14MeV;¹⁵³Eu(d, t),E=12MeV;¹⁵³Eu(p, d),E =18MeV; deduced level scheme of¹⁵²Eu,J, π, T _1/2,cc, Nilsson configurations. Magnetic electron spectrometer, curved crystal spectrometer, Ge(Li) and Si(Li) detectors, magnetic spectrographs. Enriched targets.     

Activation cross sections and isomeric ratios in reactions induced by 14.5 MeV neutrons on152Sm,154Sm and178Hf

Cross sections for the reactions¹⁵²Sm(n, p)^152g,m1,m2 Pm,¹⁵⁴Sm(n, p)^154g,m Pm,¹⁷⁸Hf(n, p)^178m,g Lu,¹⁵⁴Sm(n, d)¹⁵³Pm and¹⁵²Sm(n, α)¹⁴⁹Nd were measured at 14.5 MeV neutron energy by the activation method. On the basis of these cross sections, the associated isomeric ratios in¹⁵⁴Pm,¹⁵²Pm,¹⁷⁸Lu and the comparison with the predictions of different compound and precompound models, conclusions are drawn about the role of the preequilibrium processes in 14.5 MeV neutron induced reactions. Calculations for equal angular momentum removal by equilibrium and preequilibrium emitted particles better reproduced the experimental isomeric ratios, than for higher angular momentum removal in the preequilibrium phase. The isomeric ratios may be used as a source of additional information about the spin of the isomeric states in¹⁵²Pm and¹⁵⁴Pm for which the spectroscopic information is uncertain.     

Nuclear polarization generated in multi tilted-foil arrays

I first met Kenzo Sugimoto in 1957 at MIT and at theg factor of the 2⁺ state in¹⁵²Sm — a crossroad of nuclear and atomic physics. After that our ways diverged until they came together again half a lifetime later at another crossroad and another playfield — the tilted-foil nuclear polarization. I submit here for his pleasure, together with my colleague Yehuda Niv, a glimpse into the mysteries of multi-foil assemblies.Supported in part by the National Science Foundation.     

Superdeformed states in rotating152Dy

The recently observed gamma-spectrum of¹⁵²Dy at angular momenta 25>~I>~60 is interpreted in terms of a strongly deformed shape isomer. A pronounced minimum is found for these angular momenta in the sum of liquid-drop energy (including rotational part) and shell-correction (calculated in the Nilsson model) of¹⁵²Dy. The general criteria for stability of this minimum against rotation are discussed.