The decay of93g Ru,93m Ru,91g Mo,91m Mo,91g Tc and91m Tc

Decay studies on a number of short-lived odd nuclei in theN=50 region are described. The 59.6-s ⁹³Ru ground state decay was studied in detail for the first time; in these experiments the 10.8-s activity^93m Ru was discovered. The⁹¹Tc activities were also observed for the first time. The ground state and an isomeric state of this nucleus decay with nearby equal half-lives (3.14 and 3.3-min). The activities^91g Mo (16.6-min) and^95m Mo (65.1-s) have been reinvestigated. A number ofγ-rays, previously erroneously assigned to the⁹¹Mo activities, could be eliminated. A strong similarity is noted for the decay schemes of theN=49 isotones^91m Mo and^93m Ru. The energy of the 1/2^? isomeric state in⁹³Ru and theB(M4)-value of the isomeric transition fit well into the systematics of the previously knownN=49 isotones.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

Beta delayed proton emission from the 14s 21/2+ spin gap isomer in95Pd

The residual activities of the projectile-target system⁴⁰Ca→⁵⁸Ni have been investigated with gamma and proton multi spectrum analyses,γγ andpγ coincidences. Aβ decaying high-spin isomer in⁹⁵Pd withJ ^π=(21/2⁺), a half-life of 14±1 s and an excitation energy of about 2 MeV has been identified. It has been found that⁹⁵Pd ^m is aβ delayed proton precursor. The totalβ branching to proton emitting states has been determined to be (0.74±0.19)·10^?2. It has been observed that the final state in⁹⁴Ru, populated after proton emission, is dominantly the 8⁺ state. A decay scheme of⁹⁵Pd ^m has been derived.     

Properties of electromagnetic transitions from high-spin states in94Mo

The multipole mixing ratios of transitions from 6⁺ and 8⁺ states in⁹⁴Mo, following the decay of⁹⁴Tc, have been measured by means ofγγ angular correlations. The spin of the 2423.4 keV state, being important for the interpretation ofγ cascades feeding this level, has been firmly established as 6⁺ by a method in which the angular correlation data are utilized in a non-conventional way. Furthermore, properties of electromagnetic transitions in⁹⁴Mo have been calculated in the shell model framework and are compared with the corresponding experimental quantities.     

Alignments and band termination in99,100Ru

h11/2 neutron and g9/2 proton alignments in ^99,100Ru deduced from comparisons of experimental Routhians and aligned angular momenta to cranking model calculations. There is indication of band termination in¹⁰⁰Ru.     

The decay of 26-s 94Rh and 71-s 94Rh isomers

The structure of⁹⁴Ru is investigated through the beta decay of two isomers of⁹⁴Rh, and whose half-lives are measured to be 25.8±0.2 s and 70.6±0.6 s respectively. The decay properties are studied by means of beta and gamma spectroscopy techniques. The level structure of⁹⁴Ru populated in the decays of both isomers is proposed with deducedJ ^π values. Theβ-decay energy for71-s ⁹⁴Rh is measured to be 10.0±0.4 MeV. The structure is discussed in terms of shell model.     

On the assignment of high-spin cascades to98Rh and98Pd isotopes

Isotopic assignment of high-spin cascades in⁹⁸Rh and⁹⁸Pd have unambigously been obtained by a suitable combination of the⁹⁶Ru(α, xn yp) and the⁹⁹Ru(d, xn yp) reactions. As a result the band headed by the 841.3 keV line was assigned to⁹⁸Rh and the one headed by the 862.6 keVγ-ray has been found to belong to⁹⁸Pd. In the case of⁹⁸Rh the band is based on the (2⁺) ground state.     

Role of thermal and photobeta decays in processes of nucleosynthesis of problematic p nuclei of 113In, 115Sn, 92,94Mo, and 96,98Ru in massive stars

The temperature dependence of the rates of ¹¹³Cd →¹¹³In, ¹¹⁵In →¹¹⁵Sn, ⁹²Zr→⁹²Nb →⁹²Mo, ⁹⁴Zr→⁹⁴Nb →⁹⁴Mo, ⁹⁶Mo →⁹⁶Tc→⁹⁶Ru, and ⁹⁸Mo→⁹⁸Tc→⁹⁸Ru thermal beta transitions was studied at temperatures of massive-star matter in the range of 1 × 10⁸–6 × 10⁹ K. These decays are the possible channel of synthesis of the p nuclei of ¹¹³In, ¹¹⁵Sn, ⁹²,⁹⁴Mo, and ⁹⁶,⁹⁸Ru. The abundances of these nuclei present a challenge for models that study the explosivemechanism of synthesis. The contribution of photobeta decay to the synthesis of the aforementioned p nuclei was estimated. It was shown that the channel of thermal beta decay for ¹¹³In, ¹¹⁵Sn, ⁹⁴Mo, and ⁹⁸Ru p nuclei and the channel of photobeta decay for the ⁹⁶Mo p nucleus could be efficient at the high-temperature quasiequilibrium stage of massive-star evolution.     

Evidence for excited 0+ states in94Sr

Beta-delayed neutron measurements on⁹⁵Rb have indicated evidence for two heretofore unknown excited O⁺ states in⁹⁴Sr which are not fed by ß -decay from the J^π = 3^? ground state of⁹⁴Rb.     

Properties of the 13/2+ isomeric decay in201Hg

The isomeric decay of theT _1/2=94 us isomeric state in²⁰¹Hg was studied in beam via the reaction¹⁹⁸Pt(α, n). Gamma-ray and conversion-electron spectra were recorded. From the conversion coefficients, the multipolarities of the two depopulating transitions were determined to beM 2 + 10%E 3 andE 2, respectively. These assignments give the depopulating transitions to be 13/2⁺ → 9/2^? and 9/2^? → 5/2^?, and these thus substantiate the previous suggestion that the isomeric state hasJ ^π=13/2⁺. For the 13/2⁺ → 9/2^? M 2 transition a detailed study ofE 3 andM 4 admixed amplitudes was done. The microscopic properties of the 13/2⁺ and 9/2^? states are discussed, and a comparison to the corresponding ones in^199,203,205Hg is made.     

Lebensdauer- und Spinrotationsmessungen an den ersten angeregten Zuständen in197Pt und197Hg

The magnetic moment of the 134 keV state of¹⁹⁷Hg was measured by the differential angular correlation method. The half life of the state was redetermined and the half life of the 53 keV state in¹⁹⁷Pt was determined. The results are:μ(134 keV state in¹⁹⁷Hg)=+0.950(65) nmT _1/2(134 keV state in¹⁹⁷Hg)=7.3(2) nsT _1/2(53 keV state in¹⁹⁷Pt)=16.5(1.5) ns.     

High spin states in116,118Te

High spin states in^116,118Te, populated in¹⁰²Ru(¹⁹F,p ⁴ n) and¹¹⁰Pd (¹³C, 5n) reactions, have been studied throughγ-ray spectroscopy. The level schemes have been established up toI?25?. A favouredI ^π = 16⁺ state in these nuclei is suggested to be based on the fully alignedπ[(g _7/2)²]₆ ⁺?ν[(h _11/2)²]₁₀ ⁺ non-collective oblate configuration. This assignment is supported by TRS cranking calculations, which also predict similar non-collective oblate assignment for states at 14^?, 19^? and 22^? in these nuclei.     

The collective structure of106,108Ru

Levels in^106,108Ru have been studied by measuringγγ coincidences andγγ directional correlations of theγ-rays following theβ ^?-decay of 36 s¹⁰⁶Tc and 5 s¹⁰⁸Tc. Tc activities were separated chemically from the fission products of thermal neutron induced fission of²³⁹Pu by the continuously running system “SISAK 2” and theγ-radiation was measured on-line. An extended level scheme for¹⁰⁸Ru, spin assignments,E2/M1 multipole mixing ratios andB(E2) ratios for¹⁰⁶Ru and¹⁰⁸Ru have been obtained. The collective structure of the two nuclei is discussed in the framework of different nuclear models.     

The decay of 18.2m 104Tc

¹⁰⁴Tc was produced through the¹⁰⁴Ru(n, p)¹⁰⁴Tc reaction using target material enriched to 99.7% in¹⁰⁴Ru. The energies and intensities of theγ-rays emitted by¹⁰⁴Tc were measured with a multichannel Ge(Li) spectrometer. A revised level scheme is proposed which contains 33 levels and incorporates 85γ- ray transitions. The half life of¹⁰⁴Tc was observed to be 18.2±0.5 min.     

Experimental study of the isomeric states101mRu,103mRu and101mTc

In natural Ruthenium isomeric states were produced by photonuclear reactions with LINAC Bremsstrahlung of 26 MeV. They were identified as: 526.6±0.7 keVT _1/2=22.5±0.5 μsec in¹⁰¹Ru 192.0±0.2 keVT _1/2=760±50 μsec in¹⁰¹Tc 210.9±0.2 keVT _1/2=1560±50 μsec in¹⁰³Ru The experimental techniques are described.     

Structure of the neutron-rich nucleus 37 94 rb57

A level scheme has been established for ₃₇ ⁹⁴ Rb₅₇ based on studies at the fission-product separator JOSEF ofγγ coincidences following theβ- decay of⁹⁴Kr. For the 190.7 keV level a half-life of 2.5(8) ns has been determined through the centroid-shift method. The majorβ-decay branch of⁹⁴Kr proceeds with log ft=3.7 into the 988.4 keV state in⁹⁴Rb. This transition must be of the 0⁺→1⁺ GT type involving the transitionνg_7/2→πg_9/2. IBFFM calculations have been performed for⁹⁴Rb, starting from the parametrization used in the previous IBM investigations for the isotope⁹³Rb and the isotone⁹⁶Y. A theoretical interpretation of the low-lying levels including propositions for the spins is given in a comparison to the available data.     

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.     

Properties of the 69 150 Tm81 6− β-decaying isomer

Decay experiments for¹⁴⁸Ho 6^? and¹⁵⁰Tm 6^? were carried out at the GSI On-line mass separator using 5 MeV/A⁵⁸Ni-beams on⁹⁴Mo and⁹⁶Ru targets. Gammaγ-andγX-coincidences established the¹⁵⁰Tm 6^? decay scheme, and e^? gave firm I ^π assignments for¹⁴⁸Dy and¹⁵⁰Er levels fed in the decays. It was found that the previously unknown 6 ₁ ^? state in¹⁵⁰Er receives significantβ-strength, which strongly suggestsπh _11/2 νs ₁ ^2/?1 character for the¹⁵⁰Tm 6^? isomer. The results are discussed in terms of the expected GT strength function. Shell model calculations for theπh ₁₁ ^2/4 yrast states are presented.     

High spin states in97Rh

High spin states in⁹⁷Rh were excited via the⁹⁶Ru (α,2np) reaction at 45 MeV. As a main finding we have observed a positive parity band, built on the 9/2⁺ ground state, which depopulated levels at 3,550.7 (25/2⁺), 3,259.1 (23/2⁺), 2,895.1 (23/2⁺), 1,961.3 (19/2⁺), 1,553.1 (17/2⁺) and 857.1 (13/2⁺). Also we have excited levels at 3,055.8 (21/2), 2,225.4 (17/2) and 1,463.5 (15/2), which most likely are negative parity states.     

Absence of proton weak coupling states in93Nb

The reactions⁹³Nb(p, p)⁹³Nb,⁹³Nb(p, n)⁹³Mo, and⁹³Nb(p, p′) through isobaric analog resonances in⁹⁴Mo have been used to study the structure of low-lying⁹³Nb states, specifically the degree to which these states can be described as single protons coupled to the core states of⁹²Zr. Excitation curves were obtained from 5.8 to 7.6 MeV incident proton energy, for eight states in⁹³Nb. Results of this work are compared to results from Coulomb excitation studies,⁹³Nb(n, n′γ),⁹³Nb(d,p),⁹²Zr(³He,d),⁹⁴Mo(d,³He) and other related work.