Studies of the low-lying levels in192Pt and192Os

The energy level schemes of¹⁹²Os and¹⁹²Pt have been established on the basis ofγ- γ coincidence studies using a dual parameter data collection system. Ge(Li) detectors were employed to study the gamma spectra produced in the E.C. andβ ^? decays of¹⁹²Ir to¹⁹²Os and¹⁹²Pt, respectively. Thirteen new transitions and three new levels at 1,146.95, 1,237.35 and 1,913.76 keV are suggested. Relative intensities from singles measurements, branching ratios,α(K) and log ft values were calculated and multipolarities, spins and parities deduced. Comparisons are made with predictions of the Interacting Boson Model calculated on the basis of an O(6) to SU(3) transition.     

Levels in189Os populated in the decay of189Re

The excited level scheme of¹⁸⁹Os as populated by the decay of 23.4-h¹⁸⁹Re has been studied by use of Ge(Li) and Si(Li) detectors in the γ-ray singles and coincidence mode. The data confirm the presence of excited levels in¹⁸⁹Os at 30.8 (J ^π=9/2^?), 36.2 (1/2^?), 69.5 (5/2^?), 95.2 (3/2^?), 216.7 (7/2^?), 219.4 (7/2^?), 233.6 (3/2^?), 275.8 (5/2^?), 496.8 (1/2^?, 3/2⁺) and 599.8 (1/2^?, 3/2⁺) keV. The spin and parity assignments are based on multipolarities determined by internal conversion coefficient measurements and decay systematics. A decay scheme is established for¹⁸⁹Re which accommodates 98% of the electromagnetic transition intensity. No evidence for the 150-d¹⁸⁹Re isomer was found in this study.     

Study of the radioactive decay of192Ir

Theβ ^? and electron capture decays of¹⁹²Ir to the levels of¹⁹²Pt and¹⁹²Os respectively have been investigated to verify the existence of some of weak gamma transitions reported earlier. Gamma-gamma directional correlation measurements have been done for 13-cascades. Multipole admixture of 201, 283, 485 keV gamma transitions in¹⁹²Os and 296, 308, 416, 604 keV gamma transitions in¹⁹²Pt have been deduced. A spin value of 4⁺ has been reaffirmed on the basis of almost zero intensity of 1201 keV gamma ray (4⁺→0⁺) and 416→(468)→316 keV cascade directional correlation measurements.     

166Er levels populated in the166Tm decay

The decay of¹⁶⁶Tm has been investigated with samples obtained by chemical extraction and mass-separation from spallation products of tantalum irradiated with 660 MeV protons. Measurements of gamma rays, - bi-dimensional coincidences, CE- coincidences and internal conversion electrons have been performed. About 300 -transitions have been observed; most of them are placed in a level scheme of¹⁶⁶Er. The properties of some rotational and vibrational bands and of some other levels are discussed.The authors express their thanks to A. V.Zolotavin for his extended discussions on different aspects of the¹⁶⁶Tm decay, N. A.Lebedev, I. I.Gromova for the preparation of the targets and to co-workers of refs. [4, 5, 14, 15 and 16], who participated in this work at different stages.     

Properties of the low-lying levels in the transitional Ir and Au nuclei

We try to determine to what extent an “axial prolate rotor +1 or 2 quasiparticle model” succeeds in describing the transitional odd and odd-odd Ir and Au nuclei. The relative location of the excited states, as well as the properties of the ground and isomeric states, particularly the magnetic and spectroscopic quadrupole moments, is compared to the predictions of the model.     

Energy levels of Kr populated by Br decay

The γ-rays following the β-decay of ⁸²Br have been investigated using a 220 mm³ Ge(Li) detector, an anti-Compton NaI(Tl) spectrometer and a two-dimensional coincidence arrangement. The ⁸²Br was produced by thermal neutron activation of ammonium bromide. The presence of eight, well-known and 11 weak γ-rays has been established. It has been shown through half-life measurements that the newly identified γ-rays belong to ⁸²Br decay and that the high-energy peaks are not to summing effects. All the reported transitions have been incorporated in a level scheme of ⁸²Kr by introducing levels at 0, 776, 1474, 1820, 1953, 2093, 2426, 2554, 2647 and 2828 keV. Limits on probable spin and parity values for the newly-introduced levels have been established. The level introduced at 2828 keV on the basis of a 1008–1043 keV γγ-coincidence must be fed by a weak β-branch of ⁸²Br with an end-point energy of 263 keV and log ft of approximately 6.1.     

Nuclear levels in228Th populated in the decay of228Pa

The electron-capture decay of²²⁸Pa to levels in²²⁸Th has been studied using mass-separated sources and high-resolutionγ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2⁺ member of a second excited K_π=0⁺ band, with the 0⁺ band head at 938.6 keV. The 2⁺ and 3⁺ members of a second excited K_π=2⁺ band at 1153.5 and 1200.5 keV, which decay by strongE0 transitions to the 969 keVγ-vibrational band, are confirmed. In addition we tentatively propose a K_π=1⁺ band at 944 keV. The K_π=0^?, 1^? and 2^? members of the octupole quadruplet are confirmed, and theγ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for theE1 transition moments. A total of 29 levels is observed between ～1.4 and ～2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear.     

Energy levels of174Yb populated in the decay of174Tm

The decay of the¹⁷⁴Tm activity has been studied with Ge(Li) detectors and with a Ge(Li)—NaI(Tl) coincidence arrangement. Gamma ray energies and relative intensities were determined. Five new gamma transitions are reported, four of which have been placed in the decay scheme in addition to the previously observed but unplaced 1305 keV transition. Five energy levels at 1557.7, 1762.1, 1781.1, 1877.5 and 2050.1 keV not earlier reported to be populated in the decay of¹⁷⁴Tm are suggested. Some spin and parity assignments are proposed and the intrinsic structure of several states is discussed in terms of two quasi-particle excitations. For the half-life of¹⁷⁴Tm a value 5.4±0.1 min was measured.     

Decay of 183Ir: Shape of 183Os and 185Pt in their low-spin states

The decay of ¹⁸³Ir has been studied with mass-separated sources from the ISOCELE facility. A level scheme of ¹⁸³Os has been established. It is discussed in the framework of an “axial-rotor + quasi-particle” model: all the states located below 700 keV are interpreted assuming a prolate shape of the nucleus. This study has shed a new light on the interpretation of the ¹⁸⁵Pt low-spin states. Highly converted transitions in ¹⁸⁵Pt are discussed.     

New levels observed in188Os from the decay of188Re

The level structure of¹⁸⁸Os has been investigated following the decay of 17h¹⁸⁸Re. The energies and relative intensities of 41 gamma rays were determined using large volume high resolution Ge(Li) detectors. The decay was observed to populate the 0⁺ states at 1478 and 1704 keV which were recently observed in (p, t) reaction studies. Additional states at 1414 and 1843 keV were also observed in the decay.     

Proton states in193Ir and195Ir populated via the (α) reaction

The nuclear structures of¹⁹³Ir and¹⁹⁵Ir have been studied using the¹⁹⁴Pt(t, α) and¹⁹⁶Pt(t, α) reactions. Levels up to ～2MeV in excitation energy were studied with a resolution of ～13keV (FWHM) and spectroscopic strengths were extracted. The low-lying states in¹⁹³Ir have been interpreted in terms of both the Nilsson and the rotation-vibration models including Coriolis, particle-vibration and rotation-vibrational couplings. The previously assigned 3/2⁺ [402], 11/2^? [505], 1/2⁺[400] and 1/2⁺[411] bands were populated and candidates for the 5/2⁺ [402] and 7/2⁺ [404] bandheads were observed. TheK ₀ +2 gamma vibration based on the ground state was populated because it is mixed with the 7/2⁺ [404] state. Surprisingly, there was no significant difference between the stripping and pick-up strengths for the low-lying states in¹⁹³Ir, suggesting that the equilibrium nuclear shape of¹⁹³Ir has large overlaps with the shapes of both¹⁹²Os and¹⁹⁴Pt. The nuclear level structure of¹⁹⁵Ir appears to be similar to those of the lighter iridium isotopes.     

Nuclear levels in 228Th populated in the decay of 228Pa (II)

The electron-capture decay of ²²⁸Pa to levels in ²²⁸Th was studied using mass-separated sources and a γ-ray detection system consisting of five Compton-suppressed Ge detectors. A total of 87 levels were observed up to an excitation energy of 2 MeV which are connected by approximately 500 γ-ray transitions. The complete octupole quadruplet, three excited K ^π=0⁺ bands and two K ^π=2⁺ bands were identified below 1.4 MeV. The observed level structure is compared to calculations within the quasiparticle-phonon nuclear model. The surprisingly good agreement indicates that ²²⁸Th has less transitional character than hitherto assumed. Received: 30 March 1998     

The decay of the isotopes179Ir and180Ir

The probability for non-radiative (n.r.) excitations in muonic²⁰⁹Bi was determined from a ( ^–,)-measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of P_n.r(3p1s)=(17.9±2.0)% and P_n.r.(3d1s)=(3.0±2.2)% were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2±2.2)%. The n.r. transition probabilities of two subcomplexes of the (2p1s)-transition leading to different mean excitation energies are (3.2±1.8)% and (5.0±2.0)%, respectively.We are indebted to the following institutes or organizations for financial support: Bundesministerium ffir Forschung und Technologic der Bundesrepubfik Deutschland contract number 06 BN 271 (HP, PD, HH, FR, CR), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK, CTAMdL, WL, AT) and the Schweizer Nationalfonds (LS).     

The decay of the isotopes176Ir and177Ir

^176,177Ir were produced by irradiation of¹⁴¹Pr with⁴⁰Ar. β-delayed γ-rays of^176,177Ir were observed for the first time. From γγ-coincidence data decay schemes could be constructed. A new half-life of¹⁷⁷Ir was obtained yielding t_1/2=30 (2) s. α-branching ratios of 3.1(6) % for¹⁷⁶Ir and 0.06(1)% for¹⁷⁷Ir were measured.     

Radioactive decay of Os191 and Os191m

Beta and gamma spectra of Os¹⁹¹ were studied using a magnetic double-focusing beta-spectrometer and a scintillation spectrometer. The isomeric state Os^191m decays through the 74·4 ± 0·1 keV (E3/M4=50) transition with a half-lifeT _1/2=13·0 ± 0·5 hours. A continuous beta spectrum withE _max=147 ± 3 keV and the gamma transitions 41·83 ± 0·05 keV (E3), 82·5 ± 0·3 keV and 129·4 ± 0·1 keV (70%M1 + 30%E2) were observed in the decay of the ground state of Os¹⁹¹. The conversion coefficient of the last transition was determined as 1·94 ±± — 0·10. Gamma transitions with energies of 47 keV and 185·8 keV were not observed.     

Gamma-gamma directional correlation measurements in192Os

E2/M1 mixing ratios of transitions in¹⁹²Os have been determined by the gammagamma directional correlation technique. The results are: δ(484.5 keV)= ?10±1, δ(283.3 keV)= ?3.8± 0.7 and δ(201.3 keV)= ?4.6±1.