Decay properties of neutron deficient Kr isotopes

The decay properties of the neutron deficient isotopes^73–77Kr and^73–76Br have been studied at the ISOLDE facility at CERN. The total decay energiesQ, as determined fromβ ⁺ singles orβ ⁺ -γ coincidence measurements, are compared with mass formulae.     

Beta-delayed proton emitter kr

The nucleide ⁷³Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10⁻³ proton/decay. The protons populate the ground state and also the first excited 2⁺ state at 866 keV in ⁷²Se with a relative intensity of (35±9) %. The value of Q_EC−B_p, where B_p is the proton separation energy for the nucleus ⁷³Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay.     

Mass and excited levels of the neutron-rich nuclei 73Zn and 74Zn studied with the 76Ge(14C, 17O) and (14C, 16O) reactions

The ⁷⁶Ge(¹⁴C, ^{16, 17}O)^{74, 73}Zn reactions have been studied at 72 MeV bombarding energy. The mass excesses of ⁷³Zn and ⁷⁴Zn were determined to be ?65.41 ± 0.04 and ?65.62 ± 0.04 MeV, respectively. In addition, previously unknown excited levels were identified in both nuclei. The structure of ⁷³Zn is discussed in terms of HFB calculations.     

Levels excited in73Ge by (d,p) and (p,p′) reactions

Angular distributions from the reactions⁷²Ge(d, p)⁷³Ge and⁷³Ge(p, p′)⁷³Ge have been studied with 8.0 MeV deuterons and 12.0 MeV protons, respectively, using the Aldermaston Tandem Van de Graaff generator and multi-angle magnetic spectrograph. The ground stateQ-value of the (d, p) reaction was measured to be 4.571±0.004 MeV. The energies, values of the transferred orbital angular momenta, parities and transition strengths in both reactions were determined by use of distorted-wave Bornapproximation calculations, for levels up to 3 MeV excitation energy. The sums of the transition strengths are compared with shell model calculations as well as with values obtained in neighbouring nuclei. Discrepancies between parity and possible spin assignments of states observed in the two reactions are discussed.     

Mass excesses of60, 62Fe,68Ni,69Cu,74Zn,73, 75Ga

Accurate, confirmed mass excess values have been determined for the nuclei^{60, 62}Fe,⁶⁸Ni,⁶⁹Cu, and^{73, 75}Ga by theQ-value method. The mass of⁷⁴Zn requires further study. Good agreement was found between experimentally determined mass values and those from mass model predictions.     

Systematical study of beta delayed proton emission energies

Graphs are given of the maximum proton energies in delayed proton emitters. This quantity, equal to the difference of the electron capture decay energy of the precursor and the separation energy of a proton in the daughter, has been calculated in a least squares adjustment of mass spectroscopic data and nuclear decay and reaction energies. The graphs would lead to expect a 950 keV lower maximum proton energy in⁷³Kr(?p)⁷²Se than has been reported from experiments. They can be used to predict new cases for further studies on this subject.     

High spin states in75Se populated by the72Ge(α,n) and73Ge(α, 2n) reaction

The⁷²Ge(α, n)⁷⁵Se and⁷³Ge(α, 2n)⁷⁵Se reactions have been studied at bombarding energies of 15 MeV and 22.5 MeV respectively using Ge(Li)-detectors.γ-singles spectra,γ-γ-coincidences,γ-angular distributions and excitation functions have been taken. A level scheme has been constructed, which contains a stretched spin and a normal rotational band. Nuclear reactions⁷²Ge(α, n)⁷⁵Se,⁷³Ge(α, 2n)⁷⁵Se; measuredE _γ ,I _γ ,γ-γ-coincidences,γ-angular distribution,γ-excitation function.⁷⁵Se deduced levels,J, π, γ-multipolarity. Enriched target, Ge(Li).     

On the structure of71As and 73As

The structure of the nuclei ⁷¹As and ⁷³As has been investigated by studying the decay of ⁷¹Se, ^73gSe and ^73mSe, the ⁷²Ge(p, 2nγ)⁷¹As reaction, the ⁷³Ge(p, nγ)⁷³As reaction and the ⁷²Ge(³He, d) ⁷³As reaction. Level schemes of ⁷¹As and ⁷³As are constructed on basis of the energies and intensities of the gamma transitions and their coincidence relations. Spins and parities are deduced from log ft values, l-values and the decay properties of the excited states. The measured half-life of the lowest excited state in ⁷¹As is $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 59 ± 10}\text{ns}$. The experimental level-schemes are compared with the predictions of the cluster-vibrational coupling model.     

IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M^–1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition ^natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of ⁷⁶Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (⁷²Ge,⁷³Ge, ⁷⁴Ge), we found no significant difference in the band gap width at room temperature.     

Nuclear structure of low-lying 0+ states in Ge and Se isotopes

The following meanlives of levels in⁷²Se have been measured using the recoildistance Doppler-shift method:Τ(2⁺, 862 keV)=3.1±0.6 ps,Τ(2⁺′, 1317 keV)=12.5±2.6 ps,Τ(4⁺, 1638 keV)=1.2±0.3 ps andΤ(6⁺, 2469 keV)≦0.7 ps. These meanlives yield sixB(E2) values which are discussed together with the known data of the depopulation of the excited 0⁺′ state at 937 keV. Systematics of 0⁺′ states in the mass region 70?A?100 show that the low excitation energy of the 0⁺′ states is correlated with subshell closures. This suggests that the previous interpretation of the 0⁺′ state in⁷²Se as a rotational band head is questionable.     

The infrared spectrum of GeO

The high-temperature infrared spectrum of the Δv = 1 sequence of GeO has been investigated from 882 to 955 cm⁻¹ with a tunable diode laser spectrometer. Transitions from ⁷⁰Ge¹⁶O, ⁷²Ge¹⁶O, ⁷³Ge¹⁶O, ⁷⁴Ge¹⁶O, and ⁷⁶Ge¹⁶O were measured for vibrational transitions from v = 1−0 to v = 6−5 and fit to a single set of eight Dunham potential coefficients.     

Lifetimes in73Se

Lifetimes of 8 levels in⁷³Se have been measured by the recoil distance Doppler shift technique via the reaction⁶⁰Ni(¹⁶O, 2pn)⁷³Se. Energies of negative and positive parity states as well asE 2 transition strengths are compared with theoretical values obtained from a symmetric rotor plus particle model and a triaxial rotor model.     

Evidence for shape coexistence in the N=Z nucleus 7236Kr36

Gamma rays associated with the decay of states in the N=Z nucleus ⁷²Kr have been identified following the ¹⁶O(⁵⁸Ni, 2n) ⁷²Kr reaction at a mean beam energy of 170 MeV. Identification was made using the Daresbury Recoil Separator. The first excited state was found to be at 709.1 ± 0.3 keV and to be populated with a cross section of 60 ± 25 υb. The pattern of gamma rays associated with ⁷²Kr indicates the co-existence of nuclear shapes.     

Beiträge zu den Niveauschemata der Ge-Isotope71Ge,73Ge,74Ge und75Ge aus der Untersuchung von (n, γ)-Reaktionen in natürlichem Germanium

Low energy γ-spectra from neutron capture in natural germanium have been studied with several high resolution Ge(Li)-detectors. Measurements have been made with two different target configurations. In the first measurement a normal Ge-target was irradiated with neutrons; no neutrons were allowed to enter the Ge(Li)-detector. In the second measurement the Ge(Li)-detector was used simultaneously as target and as γ- ande ^?-detector. By combination of the results convertion coefficients of several transitions in⁷³Ge have been determined. Several unknown low energy transitions in Ge isotopes have been found with the aid of the second method. The level schemes of⁷¹Ge,⁷³Ge,⁷⁴Ge and⁷⁵Ge have been revised by means of coincidence measurements with a Ge(Li)-Ge(Li)-coincidence system of high efficiency and resolution.     

Ab initio determination of crystal lattice constants and thermal expansion for germanium isotopes

The temperature dependence of the equilibrium lattice constants for five isotopically pure Ge crystals (⁷⁰Ge, ⁷²Ge, ⁷³Ge, ⁷⁴Ge and ⁷⁶Ge) and naturally occurring Ge were calculated from ab initio electronic theory within the quasiharmonic approximation. It is shown that at very low temperature, calculations including zero point motions contribution to the free energy correctly reproduced the experimental unit cell parameters for the five isotopes. For ⁷⁰Ge, ⁷⁴Ge, ⁷⁶Ge and naturally occurring Ge, the predicted thermal expansion coefficients agree very well with experiments. The calculated thermal expansitivity for ⁷³Ge does not agree well with experiment. It is speculated that this anomaly may due to the non-zero nuclear spin of the ⁷³Ge isotope.     

The effect of nuclear structure in the emission of reaction products in heavy-ion reactions

Study of intermediate mass fragments (IMFs) and light charged particles (LCPs) emission has been carried out for a few reactions involving α-cluster and non- α-cluster systems to see how the emission processes are affected by nuclear clustering. Li, Be, B and α-particles have been studied from α-clustered system ¹⁶O + ¹²C for 117, 125, 145 and 160 MeV bombarding energies respectively. The enhanced yields of near-entrance channel fragment B and large quadrupole deformation of the produced composite ²⁸Si^? extracted from LCP spectra indicate the survival of orbiting-like process in ¹⁶O + ¹²C system at these energies. The same IMFs emitted from the α-cluster system ¹²C (77 MeV) + ²⁸Si and nearby non- α cluster ¹¹B (64 MeV) + ²⁸Si and ¹²C (73 MeV) + ²⁷Al (all having the same excitation energy of ～67 MeV) have also been studied. The fully energy damped (fusion–fission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time-scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.     

Neutron interactions with germanium isotopes and amorphous and crystalline GeO2

Coherent neutron scattering lengths and total cross sections have been measured on elemental and oxide samples of ordinary Ge and of isotopically enriched substances. From the experimental results the following values were obtained:

the coherent scattering lengths (in fm) of the bound atoms Ge(8.185±0.020);⁷⁰Ge(10.0±0.1);⁷²Ge(8.51±0.10);⁷³Ge(5.02±0.04);⁷⁴Ge(7.58±0.10) and⁷⁶Ge(8.2 ±1.5);

the absorption cross sections at 0.0253 eV (in barn) for Ge(2.20±0.04);⁷⁰Ge(2.9±0.2);⁷²Ge(0.8±0.2);⁷³Ge(14.4±0.4) and⁷⁴Ge(0.4±0.2);

the free cross sections for epithermal neutrons and the zero energy scattering cross sections.

On the basis of this data, the isotopic- and spin-incoherent cross sections and thes-wave resonance contributions to the coherent scattering lengths have been determined and discussed. Transmission measurements at 0.57 meV on amorphous and crystalline GeO₂ yielded for the amorphous sample an inelastic cross section eight times larger than for the crystalline samples. This effect corresponds to a clearly higher density of low energy states in the amorphous than in the crystalline substances.     

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^?.     

Results of the pilot experiment to search for inelastic interactions of WIMPs with 73Ge

A pilot search for the excitation of ⁷³Ge to the first excited state at 13.26 keV by spin-dependent interactions of Weakly Interacting Massive Particles (WIMPs) was performed. The first experimental results have been analyzed with a new method. The background for these reactions is ≤0.0012 events/(keV kg(⁷³Ge) d). Although there is no theory for E2 excitations by WIMPs, this very large suppression of the background may promise an enlarged version of this experiment to be competitive. It is appropriate to propose an experiment with several kg of enriched ⁷³Ge detectors based on these results.     

Band crossing phenomena inN=Z nuclei a probe toT=0 pairing correlations?

The structure of theN=Z nuclei⁶⁰Zn,⁶²Ga,⁶⁴Ge, and⁷²Kr has been investigated at GASP. Total Routhian surface (TRS) calculations have been performed for theN=36, 38 and 40 Kr isotones. In the case of⁷²Kr the four quasi-particleg _9/2 alignment is observed to be significantly delayed in rotational frequency with respect to the heavier Kr isotopes. Such a delay contradicts the predictions of mean field calculations and may be viewed as the first sign of additional correlations in theT=0 pairing channel.