Decay studies of101m Rh and101g Rh

The level structure of¹⁰¹Ru has been investigated from the decays of^101m Rh and^101g Rh. For the gamma-ray measurements Ge(Li) detectors with effective volumes of 24 and 43 cm³ were used for singles and coincidence work, and several new transitions were observed. Conversion electron spectra from the^101m Rh decay were investigated with a 50 cm double-focussing beta spectrometer.K-conversion coefficients were determined by combining internal conversion and gamma-ray intensities. For the stronger transitions probable multipolarity assignments have been obtained from these coefficients and also fromK/L andL-subshell ratios. All transitions observed were fitted into a decay scheme, in which tentative spin-parity assignments of all states are given.     

Der Zerfall des122Xe (T 1/2=20,l h) und des122J (T 1/2=3,6min)

Theγ spectra emitted in the decay of¹²²Xe and¹²²I have been investigated using Ge(Li) detectors and a Ge(Li)-NaI coincidence apparatus. 14γ transitions with energies between 61.8 and 416.9 keV have been identified in the decay of¹²²Xe, 44 transitions between 564.0 and 3,291.0 keV in the decay of¹²²I. Level schemes having 7 excited levels for¹²²I and 21 excited levels for¹²²Te are proposed.     

Decay properties of139mSm and139Eu

The structure of¹³⁹Sm is investigated through the decay properties of^139mSm and¹³⁹Eu. The decay of^139mSm is measured to have a half-life of (10.7±0.6) s. Gamma-ray and internal conversion electron measurements lead to the construction of a decay pattern comprising seven transitions among five states. The decay of¹³⁹Eu with a measured half-life of (17.9± 0.6) s is studied with beta decay spectroscopy techniques. A decay scheme consisting fourteen states in¹³⁹Sm is proposed. Using deducedft values and transition multipolarities,J ^ρ assignments are made. Nuclear systematics of the odd-A, N=77 and 76 are discussed.     

Competition betweenβ +- andβ −-decays from the transitional nucleus74As

A theoretical study of theβ ⁺- andβ ^?-decays of the⁷⁴As nucleus is performed. Both non-relativistic and relativistic formfactor coefficients are calculated in the framework of the asymmetric rotor model with admixtures of two quasiparticles for transitional nuclei. The induced interactions are shown to have small contributions to the values of the formfactor coefficients in this case. The theoretical results for the principal observables are in good agreement with the experimental data in the case of the beta decays to the 2⁺ final states. The failure in describing the beta observables corresponding to the transitions to the ground states points to the existence of a more complex structure of the 0⁺-states in the daughter nuclei⁷⁴Se and⁷⁴Ge.     

The decay of 20 min179Re

The decay of 20 min¹⁷⁹Re has been studied by means of Ge(Li) and Si(Li) detectors and a magneticβ-ray spectrometer. From the measured positon endpoint aQ-value of 2690±50 keV has been deduced. The decay scheme given is supported by coincidence relations. Fast beta transitions (logft≈5.1) to levels at 720keV and 1680 keV in¹⁷⁹W can be explained by a three quasi-particle character for these states. Nilsson assignments to these and other levels are discussed.     

Shell model calculations for heavy deformed nuclei

The pseudo SU(3) model is shown to be a powerful scheme for describing the excitation spectra as well asB(E2) andB(M1) transition strengths in heavy deformed nuclei. It is also useful for describing double beta decay amplitudes for transitions from the ground state of an even-even nucleus to the ground and excited states of the daughter nucleus, both for the two and zero neutrino emitting modes. The existence of selection rules which strongly restricts the decays is discussed. Anti-correlations between the quadrupole deformation and the Gamow-Teller (GT⁺) strength are found in an extension of the pseudo SU(3) model which explicitly includes pairing, which is also able to describe the fragmentation of the scissors mode. The projected shell model is introduced and proposed as an alternate means for studying single and double beta decay processes. Presented by J.G. Hirsch at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997. This work was supported in part by CONACyT (México), CONICET (Argentina), NSF and DOE (U.S.A.).     

E0 transitions in 70Ge and shape-coexistence interpretation of even-mass Ge isotopes

The branching ratios of E0 and E2 transitions depopulating the 0⁺₂ and 0⁺₃ states in ⁷⁰Ge have been studied using conversion-electron and γ-ray spectroscopy, as well as a new internal-pair measurement technique. A value of 3.7 (2) ns has been obtained in a remeasurement of the half-life of the 0⁺₂ state. Two new E0 transitions, 0⁺₃ → 0⁺₂ and 0⁺₃ → 0⁺₁, have been observed. A comparison of the measured X(E0/E2), ρ²(E0) and B(E2) values for the excited 0⁺ states in ⁷⁰Ge with the corresponding ¹⁵⁰Sm data supports a recent shape-coexistence interpretation of the even-mass Ge isotopes.     

Particle plus octupoleM2/E3 isomers and high-spin particle-hole states in147Tb and148Tb

The level structures of theN=82 andN=83 nuclei¹⁴⁷Tb and¹⁴⁸Tb have been studied by means of (α, 8n) and (α,7n) reactions induced by 68 to 110 MeVα particle bombardments of¹⁵¹Eu targets. In-beam conversion electron measurements have established that isomers withT _1/2=4.8(6)ns in¹⁴⁷Tb andT _1/2=22(1)ns in¹⁴⁸Tb decay byM2+E3 transitions to the ground states. The measuredB(E3) values show that the isomeric states arise from the coupling of the valence nucleon(s) to the¹⁴⁶Gd core octupole. Particlephonon coupling in these nuclei and in the one-neutron nucleus¹⁴⁷Gd is discussed and compared with well known cases involving the²⁰⁸Pb core. The higher lying yrast states in the two Tb nuclei are described as shell-model particle-hole excitations using empirical single particle energies and nucleon-nucleon interactions.     

AbsoluteE0 andE2 transition rates and collective states in116Sn

AbsoluteE0 andE2 transition rates in¹¹⁶Sn have been measured using several newly developed techniques. ManyE2 transitions are observed to have a collective character withB(E2) values of up to 60 W.u. The presence of deformed excited states in¹¹⁶Sn is discussed in view of the results obtained.     

Thermal neutron captureγ-ray spectroscopy of59Ni and61Ni

Theγ-radiation emitted after thermal neutron capture in isotopically enriched⁵⁸Ni and⁶⁰Ni was measured at the ILL high flux reactor by means of Ge/NaI detectors operated in Compton suppression and pair spectrometer mode. The neutron binding energies were determined asB _n (⁵⁹Ni)=8999.15(23) keV and B_n(⁶¹Ni)=7820.07(20) keV; some 95% of the totalγ-ray fluxes through^59,61Ni were assigned. Theγ-ray strength functions of the primary transitions and the level densities are discussed.     

The141Eu nuclide and its decay properties

The nuclide¹⁴¹Eu is identified to have two beta decaying isomers,^141g Eu and^141m Eu, whose decay half-lives are measured to be 40.0±0.7 s and 3.3±0.3s, respectively. Their decay properties are studied by means of beta and gamma spectroscopy techniques. The states withJ ^π assignments in¹⁴¹Sm thus deduced are compared with those of the other odd-A, N=79 isotones. The total decay energy of^141g Eu is measured to be 6.03±0.10 MeV, which is compared with the predictions of several mass formulae and with the decay energy systematics of theN=78 isotones. The^141g Eu and^141m Eu are deduced to haveJ ^π =5/2⁺ and 11/2^?, respectively. A 96.4 keV isomeric transition between them is found to be anE3 transition with aB(E3)=1.6±0.4e ²fm⁶. The structure of¹⁴¹Eu is compared with that of the otherN = 78 isotones.     

Properties of the 2' and 2” states in 106, 112, 114Cd

Angular correlations have been measured between γ-rays from the 2 → 2 → 0 cascades in ^106,112,114Cd and the beam of 11.0 MeV α particles effecting Coulomb excitation. Multipole admixtures for the 2 → 2 transitions, as deduced from these correlations, when combined with earlier results establish their B(E2) and B(M1) values. For the transitions from the 1312 and 1208 keV states in ^112,114Cd the B(E2) values in single-particle units are 18±4 and 24±7. These values are typical for transitions from “two-quadrupole-phonon” states in this mass region whereas that of the 1718 keV transition in ¹⁰⁶Cd has the smaller value of 7.0±2.3. The B(E2) values of the 2 → 2 transitions in ^112,114Cd from the 1468 and 1363 keV states are < 0.3 single-particle units. The B(M1) values of all five transitions are ≈ 10^?2$\text{(}\text{e}\text{h}\text{?}\text{2Mc}\text{)}{}^2$.     

Level structure of 42K from the 41(n, γ) and 41K(d,p) reactions

The γ-ray spectrum emitted after thermal neutron capture in ⁴¹K has been measured with pair and Ge(Li) spectrometers at the ILL high-flux reactor. About 630 transitions have been assigned to the decay of 133 excited states in ⁴²K. The level energies have been determined with a precison of 20 ppm; the neutron binding energy was determined to be E_B = 7533.82(15) keV. On the basis of the many transitions to known states, several spin-parity assignments have been made. In addition, high-resolution proton spectra of the reaction ⁴¹K(d,p) have been taken at 20MeV deuteron energy with the München Q3D spectrometer. These data have been essential in establishing the newly-found levels and in differentiating between primary and secondary transitions in the (n, γ) work. A statistical analysis of the level density and relative strengths of primary transitions is given.     

Double beta decay andSU(4) symmetry

The amplitude for ββ decay with 2ν emission is shown to be related to (p,n) and (n,p) reactions on the initial and final states, respectively. The suppression of both ββ and (n,p) reaction is connected, and its origin is discussed by referring to theSU(4) symmetry. From present data on the first ones, we estimate the forward (n, p) strength of relevance for the ββ problem. The interest of the experimental determination of this strength is emphasized. Assuming a perturbative breaking of theSU(4) symmetry, results are given for⁷⁶Ge,⁸²Se,¹²⁸Te and¹³⁰Te.     

Levels and transitions in126Te

The decay of¹²⁶Sb to¹²⁶Te is studied by use of Ge(Li) detectors in singles and coincidence arrangements. The gamma-gamma directional correlations of six cascades are measured. A level scheme is constructed where all transitions observed are located. The characteristics of several of the levels are assigned, on basis of the logft values deduced and the directional correlation results. Mixing ratios are deduced for three transitions. From the comparison of the relative intensities ofE1 andE2 transitions depopulating the same levels, threeE1 transitions are concluded to be strongly retarded.     

Ground state properties and β-decay half-lives near 132Sn in a self-consistent theory

The level scheme of⁹⁵Tc has been investigated with Ge(Li)-detectors by observing the γ-rays after the decay of 1.65 h⁹⁵Ru. The energies and intensities of theγtransitions were extracted fromγ-singles andγγ-coincidence spectra. In the decay of⁹⁵Ru 88γ-transitions were observed; a scheme of⁹⁵Tc with 25 levels is proposed into which 86 transitions could be accomodated. Spin and parity assignments were made from log (ft) values andγ-ray branching ratios. The level structure of⁹⁵Tc is compared with that of the other odd Tc isotopes.     

Spin-flipβ − decay of even-even deformed nuclei110Ru and112Ru

Neutron-rich nuclides¹¹⁰Ru and¹¹²Ru produced in symmetric fission of²³⁸U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of¹¹⁰Ru and¹¹²Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for¹¹⁰Ru and 1.75±0.07 s for¹¹²Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the¹¹²Rh 1⁺ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for¹¹⁰Ru and 4.52 ±0.08 MeV for¹¹²Ru. The beta decay schemes of¹¹⁰Ru and¹¹²Ru isotopes indicate that the main fraction of their beta strength resides in two 0⁺→1⁺ spin-flip transitions with their logf t values between 4.4 and 4.7. The decay energies and the energies of the 1⁺ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.     

Search for ξ(2.2) andX(2.2) in radiative decays of ϒ-meson

The results of an experiment on the search for ξ(2.2) andX(2.2) in the radiative decays of the Υ-meson are presented. The experiment was carried out with the MD-1 detector at the VEPP-4 collider. An upper limitB(Υ→γξ)B(ξ→K ⁺ K ^?)<2·10^?4 is obtained at 90% C.L. Results are presented on the search for the decay Υ→γX, X→ ?? not previously investigated. For this decay the upper limitB(Υ→γX)B(X→??)<3·10^?3 is obtained at 90% C.L.     

The level structure of69Ge

Theγ-ray decay of the states in⁶⁹Ge has been studied using the reaction⁶⁶Zn(α, nγ)⁶⁹Ge atE _α =13 and 19 MeV. The level scheme and spin assignments were established by means of coincidence measurements, angular distributions and excitation functions. 27 new levels could be found or confirmed. It is suggested that⁶⁹Ge is a further example for the weak coupling phenomenon in the medium mass nuclei. Nuclear Reactions: ⁶⁶Zn(α, nγ)⁶⁹Ge,E _α =13–22 MeV, measuredE _γ ,I _γ ,I _γ (θ),E _γ =f(E _α ),γ-γ coincidences,⁶⁹Ge deduced levels,J, enriched target.     

Boson description of nuclear collective motion

Nuclear system interacting via quadrupole and octupole particle-hole forces is studied by the boson expansion technique. Energy spectra of the negative parity yrast band and the ground state band are calculated and compared with experiment for¹⁰⁰Ru,¹¹²Cd,¹⁵⁰Sm and¹⁵⁰Gd. ExperimentalB(E1)/B(E2) ratios show strong hindrance for E1 transitions, and are used to deduce the static polarizability of E1 transitions.