The decay of83gSe and83mSe

The decay of the isomeric pair^83gSe (T1/2=22.6 min,I ^α = 9/2⁺) and^83mSe (T1/2=70 s,I ^α = 1/2^?) has been reinvestigated using straight Ge(Li) (^83gSe and^83mSe) and Ge(Li)-Ge(Li) coincidence spectrometry (^83gSe). Both decays populate entirely different⁸³Br levels, 11 of them being previously unreported. Fromγ-ray unbalances and from the known isomeric cross-section ratio of⁸²Se, β^?-branchings have been obtained, including a 34% branching of^83mSe to the ground state of⁸³Br. Logft-values are deduced, spin and parity values proposed and discussed.     

Proton occupancies in the even Se ground states via the (d, 3He) reaction

The spectroscopic factors for the levels of^{73,75,77,79,81}As have been measured in the Se(d, ³He)As reactions at 25.2 MeV. The proton occupation numbers deduced for the even Se isotopes show that the striking change in proton configuration, observed for the Ge isotopes between N ? 40 and N ? 42, does persist for the Se isotopes. This change is not reproduced, either by a model calculation using spectral distribution methods or by proton wave functions recently suggested for the Se isotopes to explain the results of the Se(d, ⁶Li)Ge reactions.     

In-beam study of74Br and a first cascade in75Kr

An in-beam study of⁷⁴Br has been carried out using γ-ray spectroscopy in connection with the reactions (³He,p2in) and (d,2n) on⁷⁴Se targets. Separate level schemes on top of the two β-decaying isomers of⁷⁴Br are proposed. Two cascades connecting highspin states are assigned to populate theI ^π=4⁽⁺⁾ isomer. In this level scheme, the excited states at 72.1, 188.3 and 472.0 keV are found to have half-lives of 13.3, 0.7 and 0.7 ns, respectively. The low-spin isomer of⁷⁴Br is tentatively assigned asI ^π=(0^?). This state is populated by two other cascades. For the low-spin levels two-particle configurations of proton and neutron Nilsson orbitals are proposed. The high-spin states are tentatively interpreted as arising from the configurations (πg _9/2,νg _9/2) and (πg _3/2,νg _9/2). As a by-product, a cascade of four transitions has been observed during the³He bombardment of⁷⁴Se and tentatively assigned to negative-parity states in⁷⁵Kr.     

Scattering of slow neutrons by arsenic and selenium isotopes

Coherent neutron scattering lengths and free cross sections were measured for arsenic, for ordinary selenium and its isolated isotopes. By means of the Cristiansen filter technique the following scattering lengths for the bound atoms were obtained (in fm):b(As) =6.58(1) [b ₊=6.04(5) andb _?=7.47(8)],b(Se)=7.970(9),b(⁷⁶Se)=12.2(1),b(⁷⁷Se) =08.25(8),b(⁷⁸Se)=8.24(9),b(⁸⁰Se)=7.48(3) andb(⁸²Se)=6.34(8). Transmission measurements with neutrons of 1.26 eV and 5.19 eV resulted in an energy independent free scattering cross section for arsenic ofσ _{s, t}=5.40(3)b (in the eV-region). For ordinary selenium energy dependent free cross sections ofσ _{s, t}(1.26 eV)=7.9(1)b andσ _{s, t} (5.19 eV)=7.55(3)b were found. The results were compared with the resonance parameters of the nuclei and with different sets of potential scattering radii. Thus it could be concluded that there is no evidence for a bound state of the neutron-nucleus compound⁷⁵As+n but a clear evidence for strong bound levels of⁷⁶Se+n and⁷⁷Se+n.     

Resonance spectroscopy of44Ti in the excitation energy range 9.05 to 10.28 MeV

The absolute differential cross sections for the⁴⁰Ca(α,α)⁴⁰Ca reaction have been measured in the bombarding energy range from 4.33 to 5.68 MeV at the four laboratory angles 85°, 125°, 141° and 165°. An analysis of the data using multilevelR matrix theory has provided the spin-parities and widths of 29 levels in the compound nucleus⁴⁴Ti. A comparison has been made with the levels deduced from the (α,γ) reaction and existing theoretical calculations of⁴⁴Ti levels.     

A study of 75Se by neutron capture and the SU(3)-SU(5) transition in the quadrupole-phonon representation

The γ and e^? spectra following thermal neutron capture in ⁷⁴Se were studied with curved-crystal, β, and pair spectrometers. Precise energies have been obtained for the transitions and levels at low energies. Two primary E2 transitions were found. The neutron separation energy for ⁷⁵Se was determined as 8027.6 keV. Precise γ-energies following the electron capture decay of ⁷⁵Se were also measured, resulting in precise level energies in ⁷⁵As. The calculation of the energy levels in ⁷⁵Se has been performed in the SU(6) particle-vibrational model (PTQM) and 27 theoretical states have been tentatively assigned to the experimental levels. The spectrum of the core nucleus ⁷⁴Se has been calculated in the SU(6) quadrupolephonon model (TQM). The structure of theoretical states, the relation to SU(3) and SU(5) limits, and potential energy surface are discussed. The E2, M1 and E1 transitions have been calculated in PTQM and compared to the experiment. Also, an overview is presented of theoretical explanations of the I = j, j?1, j?2 anomalous triplet emphasizing the rule with shell-model classification corrected for quadrupole phonons.     

A study on the decay of81As

The decay of⁸¹As was investigated with Ge(Li) spectrometers. Accurate energy and intensity determinations for 29 gamma rays have been performed, from which a level scheme was deduced for⁸¹Se. Beta component intensities were obtained from the measured gamma intensities. Spin and parity assignments for most of the levels were made in agreement with the reaction and neutron capture studies. The half life of⁸¹As is measured to be (35.8±1.6) sec. Shell model calculations as well as unified model calculations have been performed in order to study the level scheme of⁸¹Se.     

Isomere Wirkungsquerschnittsverhältnisse beim thermischen Neutroneneinfang im Bereich der 2p 1/2 und 1g 9/2 Schalenmodellzustände

Thermal capture cross sections and isomeric cross section ratios in thermal neutron capture were determined for even-even nuclei in the region of the 2p _1/2-1g _9/2 neutron shell. Capture cross sections for formation of Zn 69 ^m , Zn 71 ^m , Zn 71, Ge 71, Ge 75 ^m , Ge 77 ^m , Se 77 ^m , Se 79 ^m , Se 83 ^m , Se 83, Sr 85 ^m and Sr 87 ^m were measured by the activation method. From these data and additional measurements of cross section ratios the isomeric ratios for thermal capture in Zn 68, Zn 70, Ge 70, Ge 74, Ge 76, Se 76, Se 78, Se 80, Se 82 and Sr 84 were determined. In addition epithermal capture isomer ratios were determined for Zn 68, Ge 74, Ge 76, Se 80 and Sr 84. The isomer ratios are compared with calculations based on the statistical model ofHuizenga andVandenbosch. With the exception of Se 80 the measured ratios can be explained theoretically with reasonable values of the spin-cutoff-factorσ and gamma-ray multiplicityN, however there seems to be unexplained difference in eitherσ orN between the two groups of nuclei leading to either 1/2–7/2 or 1/2–9/2 isomers.     

Über die selbständige Polarisierung des Spins der Elektronen durch Ausstrahlung bei der Bewegung auf einer Spiralbahn im Magnetfeld

The nuclear half-life of the 287 keV second excited state of⁷⁵Se, populated by the reaction⁷⁵As(p, n)⁷⁵Se^* has been measured by the delayed coincidence technique. NaJ(Tl)- and Ge(Li)-detectors were used for measuringγ-energies and time-spectra. By slope analysis of the time-spectra we obtained a half-life of T_1/2(⁷⁵Se, 287 keV)=(30.0±0.4) ns. Possible spin assignments for the 287 keV state in⁷⁵Se from logft-values derived fromβ ⁺-decay data of⁷⁵Br to this level byBaskova et al are 3/2^? and 1/2^?. Application of an external magnetic field of 24 kG to the target nuclei yielded no measurable perturbation of the time-spectra, thus a spin value of 1/2^? for this level seems to be more probable.     

In-beam gamma-ray and electron spectroscopy following the75As(p,n)75Se reaction

The level scheme of⁷⁵Se has been studied through the⁷⁵As (p, n) reaction at proton energies from 1.5 to 5.0 MeV.γ-ray and internal conversion electron measurements were made using NaI (T1) and Ge(Li) detectors and a six-gap electron spectrometer. A proportional counter and a thin window NaI(T1) detector were used to detectγ-rays with energies less than 30 keV. The level scheme has been established by observing the thresholds of variousγ-rays and byγ-γ and e^?-γ coincidence measurements. New levels at 133.0, 293.2, 790.0, 953.0, 1020.8, 1184.3, 1198.5 and 1258.2 keV not observed in earlier (p, n) studies have been established. Conversion coefficients of most of the low-lying transitions have been determined. Angular distributions of some of theγ-rays were also measured and compared with the statistical model calculations. DefiniteJ ^π assignments have been made to most of the low-lying levels. Life-times of the 112.1, 133.0, 286.7 and 293.2 keV levels have been measured to be 0.69±0.12, 5.3±0.6, 1.35±0.15 and 31±2 nsec respectively. The reduced transition probabilities for various low-lying transitions have been determined and compared with recent calculations. The 1/2^? and 9/2⁺ levels hitherto unknown in this nucleus has been identified. The structure of the low-lying levels is discussed in terms of the existing models.     

An IBM description of76Se and neighbouring Se-isotopes

The level structure of⁷⁶Se is discussed within the framework of Interacting Boson Models. The calculated energy levels, transition probabilities, mixing ratios,Q _{2 1} ⁺ andg _{2 1} ⁺ are compared with experimental data. Mixed-symmetry states are investigated in the isotopes⁷²Se,⁷⁴Se,⁷⁶Se,⁷⁸Se and⁸⁰Se. Two mixed symmetry states with spin 1⁺ and 3⁺ are proposed for⁷⁶Se, and also six other 1⁺ and 2⁺ levels in the neighbouring selenium isotopes.     

Levels of146Ce studied through the decay of high-spin isomer of146La

The decay of 10.0 s high-spin isomer of¹⁴⁶La to levels of¹⁴⁶Ce has been studied using the on-line isotope separator KUR-ISOL. Gamma-ray singles,γ -γ coincidence and conversion-electron spectra have been measured. A level scheme containing 90 levels and 206γ-ray transitions has been constructed for¹⁴⁶Ce, populated in the decay of the high-spin isomer of¹⁴⁶La. Among these, 39 levels are reported for the first time. Spins and parities for some levels are proposed on the basis ofγ-decay mode, logft values and conversion-electron measurements. The band structure of the low-lying levels in¹⁴⁶Ce is discussed.     

The decay of 33 70 Se37

The decay of⁷⁰Se was studied using a 75 cm³ Ge(Li) detector, placed in an anti-compton shield, and a low-energy detector. Of the 36γ-rays observed 31 are placed in a levelscheme of⁷⁰As, based on coincidence- and sumrelations. Conversion electrons of two low energy transitions were observed in order to determine their multipolarity. The halflife is measured (41.1 min). Spins and parities of the excited levels were deduced and compared with shell model predictions and logft values of theEC/β ⁺ branches were calculated.     

The decay of 22·1 min83gSe and 69·2 SEC83mSe to the levels of83Br

The decay of⁸³Se isomers has been studied using Ge (Li) detectors and multi-parameter analyser system. In the case of^83gSe decay, it was possible to observe coincidences in Ge (Li) -Ge (Li) configuration. A total of 90 γ-rays are assigned to the decay of^83gSe and 25 to that of^83mSe. The half-lives of^83gSe and^83mSe are found to be 22·1±0·1 min and 69·2±0·6 sec, respectively. Excited states of⁸³Br are observed at 356·74, 799·2, 866·9, 988·1, 1030·8, 1053·9, 1092·1, 1352·7, 1420·9, 1439·0, 1660·4, 1701·5, 1804·7, 1810·4, 1915·6, 2051·9, 2058·7, 2398·2, 2647·2, 2694·3, 2738·3, 2777·5, 2946·7 and 3137·8 keV. The log ft values for the branching to the excited levels of⁸³Br are established and spin-parity assignments for these levels are deduced.     

Levels in160Yb from the radioactive decay of160Lu

Theγ-rays following the radioactive decay of¹⁶⁰Lu into¹⁶⁰Yb have been studied. The Lu source was produced in the¹⁴⁴Sm(¹⁹F, 3n) reaction at 85 MeV. Excitation functions, half-lives,γ-γ andγ-X-ray coincidences and conversion electrons were measured. Twoβ ⁺ decaying states in¹⁶⁰Lu were found with half-lives of 36.2(3) s and 40(1) s.¹⁶⁰Yb levels deduced from the decay of¹⁶⁰Lu are presented.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

Ion molecule collisions investigated via nuclear resonance fluorescence

The method of nuclear resonance fluorescence has been applied to analyse the profileN(E) of the 285 keV gamma line of⁷⁵As after electron capture decay of⁷⁵Se in gaseous⁷⁵SeH₂ sources. The profileN(E) depends on the velocity distribution of the radioactive As ions at the moment of γ-decay and, hence, is strongly dependent on the slowing down mechanism. Investigating sources with pressures of 1.5, 15, and 177 Torr different states of the slowing down process could be studied. A simple model is developed that describes the basic properties of the experimental line profiles.     

Der Zerfall des77Kr

⁷⁷Kr (T _1/2=1.2 h) was produced by bombarding⁷⁶Se with 48 MeV-α-particles. After irradiation the radioactive⁷⁷Kr gas was collected in glass ampoules filled with charcoal and cooled by liquid air. The decay of⁷⁷Kr has been investigated using Ge(Li)-counters and a Ge(Li)-Ge(Li)-coincidence circuit. 27 γ-transitions, 13 of them unknown up to the present, have been found and their relative intensities have been determined. A level scheme for⁷⁷Kr→⁷⁷Br having 14 levels is proposed. This accounts for all the observed γ-transitions.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.