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.     

Isomeric states in180Os

Two new isomers have been observed in¹⁸⁰Os. A high-K isomer withI, K ≧20 and a half-life ofT _1/2=12+4 ns have been established. It deexcites via two transitions into the 18⁺ level of the yrare band indicating an unusually smallK-hindrance factor. Evidence for an isomer withI, K>16 and a half-life ofT _1/2=41±10 ns was found. A half-life of 17±3 ns was measured for the previously known 7^? state at 1862 keV. The decay scheme of the previously known 7^? isomer at 1928 keV has been extended and a revised version is presented.     

High-spin isomers in 183Os

High-spin states in ¹⁸³Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I ^π= ((43/2)⁻) and (43/2)⁺ have been identified at excitation energies of E _x = 5.068 and 5.168 MeV. The half-lives are determined as T _1/2= 27 ± 3 and 24 ± 2 ns. Received: 22 December 1997     

Isomeric transitions in203Bi and205Bi

High spin states in^{203, 205}Bi, populated in the^{203, 205}Tl (α,4n) reactions, have been studied using gamma-ray and conversion-electron spectroscopy. Several previously unobserved isomeric transitions were identified by electron-electron coincidence measurements in both isotopes and in²⁰⁵Bi a new isomer was found. The observed states can be explained as arising from couplings of the oddh _9/2 proton to neutron states in the neighbouring Pb cores. Reduced transition probabilities are derived and discussed.     

Isomeric γ-ray transitions in 98Tc

Delayed γ-rays from ⁹⁸Tc have been observed following pulsed proton beam bombardment of an enriched ⁹⁸Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.     

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.     

Isomeric E1 and M1 transitions in 177Ta and in neighbouring odd-A Lu and Ta isotopes

Delayed γ-ray spectra as well as time distributions have been measured applying the r.f.-γ method and the method of delayed γ-γ coincidences. Using the reaction ¹⁷⁵Lu(α, 2n)¹⁷⁷Ta, the half-lives of the levels at 70.6 and 73.6 keV in ¹⁷⁷Ta have been determined as $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 80±10}\text{ns}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 370±50}\text{ns}$, respectively. In further experiments, upper limits for the lifetimes of the $\text{9}\text{2}{}^{\mathrm{?}}\text{[514]}$ and $\text{5}\text{2}{}^{\mathrm{+}}\text{[402]}$ states in ¹⁷¹Lu and ¹⁷³Lu were estimated. Comparisons of the experimental half-lives to Weisskopf and Nilsson model predictions are performed taking into account pairing correlations. For the calculations, a modified Nilsson Hamiltonian has been used. The hindrance factors obtained are summarized together with those deduced for corresponding transitions in neighbouring odd-proton nuclei. From the experimental results in ¹⁷⁷Ta, conclusions have been drawn on the possible value of the constant k₂ occurring in the magnetic dipole operator.     

Description of the Pt and Os isotopes in the interacting boson model

Properties of the even-even Pt and Os isotopes are investigated in the framework of the interacting boson approximation, including the neutron-proton degree of freedom. It is shown that the transition between the gamma unstable region of the heavier Pt isotopes towards the more axially symmetric deformed festures of the lighter Os and Pt isotopes can be described very well by the IBA hamiltonian; qualitatively the properties of the transitional region are reproduced by the smooth change of one parameter, χ_ν, which determines the character of the quadrupole-quadrupole interaction. Calculated excitation energies and electromagnetic properties are compared with experiment.     

High-spin negative parity states in doubly even Hg,Pt and Os nuclei

A systematic study of the level structure of ²⁰⁰Hg, ¹⁹⁸Hg, ¹⁹⁶Hg, ¹⁹⁴Pt, ¹⁹²Pt, ¹⁹⁰Pt, ¹⁸⁸Os, ¹⁸⁶Os and ¹⁸⁴Os has been performed by means of (α, 2nγ) and (p, 2nγ) in-beam γ-ray spectroscopy. Much new information has been obtained about the individual level spectra, and arguments based on level energy and population intensity systematics have been used to trace the behaviour of interesting spectral features through this series of transitional nuclei. Of particular interest is a 5^?, 7^?, 9^? … sequence of levels which appears to be a recurring feature in the spectra of the doubly even Pt and Hg nuclei in the mass range A = 190–200. These negative parity levels are connected by enhanced E2 transitions and they are very strongly populated in the de-excitation of the residual nuclei formed in (α, 2n) reactions. It is proposed that the 5^?, 7^?, 9^? … sequences constitute rotation-aligned bands analogous to the decoupled bands identified by Stephens and co-workers in odd-A transitional nuclei. In the doubly even nuclei, the bands may arise from the coupling of an $\text{i}\text{13}\text{2}$ neutron with a low-j neutron partner (from the $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ orbitals). Negative parity levels in the Os nuclei are populated much less strongly in the (α, 2nγ) reactions. While 5^? levels corresponding to those in the Pt and Hg nuclei appear to be fairly well established in ¹⁸⁶Os, ¹⁸⁸Os (and ¹⁹⁰Os), it is not yet clear whether the 5^?, 7^?, 9^? … band sequence extends into the Os nuclei.     

Study of very neutron deficient nuclei 178Pt and 181Au

The ¹⁷⁸Pt and ¹⁸¹Au nuclei have been studied with the (230 MeV) ⁴⁶Ti +¹⁴²Nd fusion-evaporation reaction; γ-rays, evaporated particles and recoiling nuclei have been detected by the γ-array GASP + the Si ball ISIS + the recoil mass spectrometer RMS. The newly observed structures in ¹⁷⁸Pt and ¹⁸¹Au are most probably built on the proton and quasi-proton h_9/2 and i_13/2 configurations. Received: 2 January 1998 / Revised version: 27 May 1998     

Nuclear deorientation of W,Os and Pt recoiling in vacuum at 0.02c

The attenuations of γ-ray angular correlations have been measured for some 2⁺ and 4⁺ nuclear states in W. Os and Pt ions recoiling in vacuum with a velocity of 0.02c. The states were Coulomb excited by beams of 100 MeV³²S ions and the recoil-distance method was used to measure the time-dependence of the attenuations during the first 70 ps of the flight time. A simple parametrization was found to fit all the data and was used in a re-analysis of a published recoil-in-vacuum experiment on^{204, 206}Pb to give upper limits on theg factors of the 2 ₁ ⁺ states of |g(204)|<0.01 and |g(206)|<0.015.     

Isomeric transitions between shape coexisting states in iodine isotopes withA=115, 119 and 121

Applying delayed- r.f. coincidences and generalized centroid-shift analysis, nanosecond isomers in some odd-A iodine isotopes are studied in-beam. The reactions¹⁰⁶Cd(¹²C,p2n) and^116,118Sn(⁶Li,3n) have been used. The following half-lives were determined:T _1/2(565 keV)=0.50±0.10 ns andT _1/2(837 keV) =0.90±0.20 ns in¹¹⁵I,T _1/2(687 keV)=5.50±0.50 ns andT _1/2(2418 keV)=4.0±0.50 ns in¹¹⁹I as well asT _1/2(812 keV)=0.35±0.20 ns andT _1/2(445 keV)<0.10 ns=">¹²¹I. A systematics of the absolute probabilities for the transitions deexciting theg _9/2 9/2⁺ and _11/2 11/2 ₁ ^– band heads in^115–125I is presented and discussed.Partly supported by the Bulgarian National Research Foundation under contracts PH14, and PH31 and Kernforschungszentrum Karlsruhe, Stabsabteilung Internationale Beziehungen     

Studies on the low-lying levels in192Pt and192Os populated in192Ir decay

Low-lying levels in¹⁹²Os and¹⁹²Pt are reinvestigated through¹⁹²Ir (73.831d) decay with improved system performance and counting statistics. Experiments show that gamma rays reported in literature with energies 1413, 1237, 1147, 911, 773, 629, 362 and 325 keV are not from the decay of¹⁹²Ir and gamma rays reported with energies 1200, 1056, 920, 904, 784 and 624 keV are resulted from sum-up or pile-up effects of low energy intensive gamma rays. New gamma-gamma coincidence relations are obtained with 105 cm³–110 cm³ germanium detector system. A level at 1384 keV is established in the decay scheme and four newly proposed levels at 1118.31 keV in¹⁹²Os and 1146.95, 1237.35 and 1413.76 keV in¹⁹²Pt are excluded from the decay scheme. Predictions of Interacting Boson Model on level energies andE2 absolute reduced transition probabilities are compared with experimental results.     

Systematic measurements of transient fields for W,Os and Pt ions traversing Fe

Transient magnetic fields were measured for W, Os and Pt ions traversing iron hosts with average velocities in the range from approximately 1.6v ₀ to 4.8v ₀ (v ₀=c/137, Bohr velocity). Transient fields for W and Os in Fe are consistent with behaviour found for lighter rare-earth ions and are about 20% stronger than those for Pt in Fe over the majority of the velocity range examined. A measurement was made to confirm that possible heavy-ion beam induced attenuations of the transient field are negligible for low-velocity Pt ions excited by Ni beams. Results are discussed in terms of both empirical and model-based parameterizations of the transient field strength.     

Charge radii and shape transitions in short-lived Hg,Au and Pt isotopes

The hyperfine structure and the isotope shift of very neutron-deficient Au and Pt isotopes have been determined at the on-line isotope separator ISOLDE/CERN by resonance ionization mass spectroscopy combined with pulsed-laser induced desorption of the implanted radioactive sample. The changes of the mean-square charge radii were determined for the isotopes¹⁸⁴Au (T_1/2=53 s) and¹⁸³Au (T_1/2=42 s) as well as for 15 isotopes of platinum in the range between¹⁹⁸Pt (stable) and¹⁸³Pt (T_1/2=6.5 min). The strong deformation of¹⁸⁵Au (|β₂|≃0.25) persits down to¹⁸³Au. In¹⁸³Pt nearly the same value of |β₂| is reached but the deformation is build up rather smoothly in contrast to the neighbouring isotopes of gold and mercury. The magnetic moment of¹⁸³Pt was found to be μ₁=+0.51(3)μ _N .     

Temperature dependence of a lattice defect induced electric fieldgradient at181Ta in Pt

By implantation of¹⁸¹Hf ions radiation damage is produced in platinum. Subsequent annealing of the samples leads to the trapping of a unique defect at the probe atoms. The temperature dependence of the resulting electric field gradient eq(T) is measured by use of the TDPAC-method. Assuming a relation eq(T)=eq(0)·(1–B·T ^3/2) one findsB=(1.9±0.7)×10^–6 K^–3/2. This low value is of the same magnitude as the corresponding values for¹¹¹Cd in various locally distorted cubic metals.