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.     

Derp 3/2-Analogzustand in51V

In an investigation ofT=7/2 analogue states in⁵¹V the⁵⁰Ti(p, γ) excitation curve has been measured for proton bombarding energies 1280–1480 keV and 2340–2660 keV. From the (p, γ) resonances 29 new virtual levels in the region of 9316–9510 keV excitation energy in⁵¹V were determined. The strong resonance atE _p=1 371 keV has been identified as the isobaric analogue state of the⁵¹Ti ground state by determining spin and parity of this resonance to be 3/2^?. There is no evidence for a strong analogue resonance in⁵¹V corresponding to the 1.16 MeV _{p 1/2} state in⁵¹Ti. The γ-decay of the _{p 3/2} analogue state has been studied by measuring branching ratios and angular distributions of primary γ-transitions with a Ge(Li) detector.M1E2 mixing ratios have been determined for these transitions. The total width of the resonance for γ-decay is found to be Γ_γ=1.6±0.4 eV. New bound levels in⁵¹V have been introduced at 3576, 4651 and 4661 keV excitation energy. TheJ ^π values of the 3085, 4770, and 4863 keV states are determined to be 5/2^?, 5/2^?, 3/2^?, respectively. The analogue-antianalogueM1 transition strength is found to be considerably reduced compared to the situation ins-d shell nuclei.     

The decay of62Zn

Energies and relative intensities of 31γ-transitions from the decay of⁶²Zn have been measured using an anti-Compton spectrometer. Gamma-gamma coincidence measurements were performed. Besides the levels of⁶²Cu for which the population in the decay of⁶²Zn was known, also levels at 644.82, 698.32, 1221.5 and 1525.9 keV in⁶²Cu are found to be populated. The previously proposedβ-feeding of⁶²Cu levels at 1142.5 and 1280.8 keV is ruled out.     

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.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

The decay of174Ta

Levels in¹⁷⁴Hf excited in the decay of¹⁷⁴Ta have been studied. Measurements of gamma-rays, conversion electrons and gamma-gamma-time coincidences were performed. The ground state band, the beta-vibrational band, the gamma-vibrational band with its head at 1226.81 keV, aK=3⁺ band at 1303.42 keV and aK=2^? octupole band at 1308.67 keV were observed. Several 2⁺ levels withK=0 are excited. The mainβ ⁺-branches proceed through allowed or first-forbidden transitions to the 2⁺ and 4⁺ levels of the ground state band. The character of theI ^π=3⁽⁺⁾ ground state of¹⁷⁴Ta is 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.     

Decay of 17-min, 19/2−129mSb

A 17.1min, 19/2^? isomer has been established in¹²⁹Sb at 1851 keV. It is fed by levels populated in the decay of the 6.2min, 11/2^?129Sn isomer. This isomer decays by an M4, 723keV internal transition and by β^? decay to levels in¹²⁹Te. The 723keV transition is 20 times slower than 11/2^?→3/2⁺ M4 transitions in the adjacent odd-N nuclides and is 10 times faster than the M4 transition from the 19/2^? isomer in¹³⁵Cs. A partial level scheme for the decay of the 11/2^?,¹²⁹Sn isomer is given showing levels that populate the 19/2^? isomer along with a partial level scheme for¹²⁹ Te.     

A retarded intramultipletM1 transition in214Bi

The half-life of the 53.2 keV level in²¹⁴Bi has been measured asT _1/2=0.52±0.15 ns, furtherT _1/2(295.2 keV and 351.9 keV levels)≦0.10 ns was estimated. TheB(M1,2^?→1^?) transition rates within theπh _9/2 vg _9/2 multiplet in^210,212,214Bi are found to decrease rapidly with increasing neutron number, reaching in²¹⁴Bi a value as low as those typical for intraband M1 transitions in deformed odd-odd nuclei.     

Structure of low-lying levels in91Rb and93Rb

Life-times of low-lying levels in ₃₇ ⁹¹ Rb₅₄ and ₃₇ ⁹³ Rb₅₆ have been determined fromβ ^??γ coincidence measurements at the fission-product separator JOSEF. Values oft _1/2=17.0(8) ns and 2.0(2) ns have been obtained for the levels at 1,134 keV in⁹¹Rb and 267 keV in⁹³Rb, respectively, and upper limits could be deduced for several other states. Calculations in the frame of IBFM/PTQM have been performed for⁹¹Rb, the results of which allow an interpretation of the low-lying levels of this nucleus. For the 1,134 keV level the configuration [πg _9/2?2⁺] 7/2⁺ is suggested which lies close to or even below the 9/2 ₁ ⁺ level. The calculated half-life of 14 ns for the 1,134 keV level reproduces well the experimental value. The half-life of the 267 keV level in⁹³Rb favours the assignment ofI ^π=1/2^? to this state over the alternative 3/2^?.     

Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands

The low-energy level scheme of theN=63 nucleus¹⁰¹Sr has been obtained from a β-decay study of¹⁰¹Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ? 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours⁹⁹Sr₆₁ and¹⁰¹Sr₆₃ are very similar. More generally, the identical bands at low spin in^98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.     

The energy of levels of45Sc up to 3 MeV from the44Ca (p, γ)45Sc reaction

The gamma-ray decay of the 1658 keV resonance, which is a member of the isobaric analogues of the 1904 keV 3/2^? level in⁴⁴Ca, has been studied with a Ge(Li) detector. A number of gamma-ray transitions are described and associated with the decay of 15 levels between 1.50 and 3.05 MeV. These observations have made it possible to deduce spin and parity assignments to some of the levels. By comparing excited levels of⁴³Sc and⁴⁵Sc it has been possible to assign certain levels as members of one negative-parity band and two positive-parity bands withK ^π=1/2⁺ and 3/2⁺.     

Structure of the Triplet of low-lying states in101Mo

The properties of the triplet of low-lying states in¹⁰¹Mo have been studied through spectroscopy of theγ radiation following thermal neutron capture in¹⁰⁰Mo and β^? decay of¹⁰¹Nb and through a measurement of the proton angular distributions in the¹⁰⁰Mo(d,p) reaction with 14 MeV deuteron energy. The half-lives of the 13.5 keV state and the 57.0 keV 5/2⁺ state have been measured as 226(7) and 133(7)ns, respectively. These values and the quadrupole/dipole mixing ratios of the 13.5 keV and 43.5 keV transitions yield spin and parity 3/2⁺ for the 13.5 keV level. The E2 components in the 13.5 (3/2⁺ →1/2⁺) and 43.5 keV (5/2⁺→3/2⁺) transitions are ≦ 8·10^?4 and 54(9)%, respectively. The possibility of an additional state near to the 57.0 keV level is discussed. IBFM/PTQM calculations, taking into consideration the transitional character of the¹⁰⁰Mo boson core, account for the electromagnetic-transition and transfer-reaction pattern of the triplet of states.     

Decay of the 21/2− isomer in211Bi and structure of thevg 9 2/2 πh 9/2 levels

Gamma rays and conversion electrons have been measured in²¹¹Bi populated by the²⁰⁹Bi(t,p) reaction, and the near yrast levels were observed up to 21/2^?. The 21/2^? state is isomeric withT _1/2=70(5) ns. No alpha decaying isomer was found in²¹¹Bi. ObservedM1 transitions reveal mixing of the²¹⁰Pb parent states in the levels of²¹¹Bi. The levels and transitions are well reproduced by the shell model with experimental matrix elements and pure configurations.     

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.     

High resolution studies of transitions in the decay chain146Gd to146Eu to146Sm

Transitions in¹⁴⁶Eu and¹⁴⁶Sm were studied using a double-focussing beta-ray spectrometer and a Ge(Li) detector. Internal conversion and gamma-ray intensities were determined. The internal conversion spectrum of the three 155, 115 and 116 keV cascading transitions in¹⁴⁶Eu was studied for all subshells.K-,L- andM-subshell ratios were determined andE2/M1 mixing ratios were deduced for these three transitions. Intensities from theN- andO+P-shells were determined and compared to theoretical calculations. All internal conversion intensities were found to be in agreement with theoretical data for pureM1 character with smallE2 admixtures for all the three transitions. Selected parts of the internal conversion spectrum of the transitions in¹⁴⁶Sm were restudied at 0.06% momentum resolution. This study was mainly concentrated on four transition doublets feeding and deexciting the close lying levels at 1,380 and 1,381 keV. A new transition with 702.20 keV energy was detected in the 702–703 keV transition group. Internal conversion coefficients were deduced using reported gamma-ray intensities. Multipole characters of the transitions were deduced and used as a basis for a discussion of the spins and parities of the lower lying excited states of¹⁴⁶Sm.     

Decay of a new nuclide:89m Mo

The half-life of the 1/2^? isomer in⁸⁹Mo has been determined in an experiment where an enriched⁹²Mo target was irradiated by 350 or 700 ms bursts of 60 MeV protons. Analysis of the gamma-ray spectra collected as a function of time between irradiations revealed gamma rays at 118.8 and 268.5 keV decaying with a 190±15 ms half-life. The hindrance ofE3 transitions inN=47 andZ=47 nuclides is discussed.     

Rotational bands in77Kr

Collective bands in⁷⁷Kr have been studied with the help ofγ singles spectra,γγ coincidences,γ ray angular distributions and recoil-distance life time experiments measured during the irradiation of⁶³Cu and⁶⁴Ni targets with¹⁶O ions. Positive and negative parity bands with the following level energies, spins, and parities have been found: g.s. 5/2⁺; 150.1 keV 7/2⁺; 279.1 9/2⁺; 784.8 11/2⁺; 1003.7 13/2⁺; 1660.5 15/2⁺; 1919.1 (17/2⁺); 66.5 keV (3/2)^?; 245.3 (5/2)^?; 499.6 (7/2)^?; 799.5 (9/2)^?; 1177.3 (11/2)^?; 1569.9 (13/2)^?; 2063.2 (15/2)^?. A mean life time of 170±17 nsec for the 66.5 keV state was measured withγγt coincidences and a mean life time of 48±13 psec for the 245.3 keV state was obtained with a recoildistance Doppler shift measurement.     

γγ-Winkelkorrelationsmessungen an155Gd

Two Ge(Li) detectors were used to investigateγ transitions in¹⁵⁵Gd produced by the decay of¹⁵⁵Eu. Relative intensities were determined for the weak lines at 18.8, 26.5, 58.0, and 86.0 keV. Angular correlations for fourγ cascades were measured. As results, the mixing ratios of the 45.3 and 86.5 keVγ lines were determined, and it was shown that the sign of the mixing ratio is positive for theγ line at 18.8 keV and negative for the line at 60.0 keV. Spins 5/2 and 3/2 for the 86.5 and 105.3 keV levels, respectively, are consistent with the data, and spin 5/2 for the 105.3 keV level is inconsistent with it.     

On the decay of73Ga to levels in73Ge

Theγ-radiation following the β^? decay of⁷³Ga has been studied. Singlesγ andγγ coincidence spectra were recorded with Ge(Li)-detectors. 17γ-rays were assigned to transitions in⁷³Ge, where 11 excited levels are proposed. From logft values based onγ-transition intensities, spin and parity assignments for the levels were deduced. The half-life of⁷³Ga was measured to (4.86±0.03) h. From allowedβ-transitions the ground state of⁷³Ga was assigned 3/2^?.