Excited states of100Tc from100Mo(p,nγ)100Tc reaction and the parabolic rule

γ-spectra and excitation functions of the¹⁰⁰Mo(p, nγ)¹⁰⁰Tc reaction were measured in the 1.2–3.6 MeV proton energy range by using thick, enriched targets, Ge(Li) and low energy photon (hyperpure Ge) spectrometers. These detectors were used inγγ-coincidence experiments, too. Conversion electron spectrum measurements were performed by means of a superconducting magnet transporter Si(Li) spectrometer (SMS) atE _p =4 MeV and multipolarities of some transitions have been determined. Based on the experimental results a level scheme of¹⁰⁰Tc has been constructed. Level energies of¹⁰⁰Tc were calculated on the basis of the parabolic rule, derived from the cluster-vibration model.     

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.     

Der Zerfall des94Sr

The nuclide⁹⁴Sr was isolated by chemical separation methods after thermal neutron induced fission of²³⁵U. Its decay properties were investigated employing semi-conductor spectrometers and coincidence techniques. A half-life of 74.1±0.3 sec was found. Besides the 1428.3 keV γ-ray we found 4 new γ-rays which could be placed in a decay scheme comprising three excited states of⁹⁴Y. The 1⁺ states in theuu-nuclides^90,92,94Y and^88,90,92Rb are compared.     

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.     

Experimental evidence of highly energy relaxed products in the 35 MeV/u84Kr+197Au reaction

The Q_β-values of⁹⁹Rb,^99,100Sr and¹⁰⁰Y have been measured for the first time at the mass separator OSTIS of the ILL; for⁹⁹Y,^99,100Zr and¹⁰⁰Nb, the results of earlier experiments were confirmed with reduced experimental errors. The two-neutron binding energies derived from the experimental Q_β-values clearly indicate that the nuclei¹⁰⁰Sr and¹⁰⁰Y are strongly deformed.     

Theβ-decay of100Y: Discovery of a very low lying 0+ state in100Zr

Theβ-decay of¹⁰⁰Y has been investigated at the gas filled recoil separator JOSEF by means ofγ-ray and conversion electron spectroscopy. Twoβ-decay modes, of half lives 0.94±0.03 s and 0.55±0.15 s, have been observed. Using Xγ-, Xce-, γγ- andγce-coincidences the level scheme of¹⁰⁰Zr has been constructed. An excited 0 ₂ ⁺ state at 331.3 keV has been discovered in this nucleus. Theβ-decay from the 0.55 s decay mode in¹⁰⁰Y shows a strong preference for the ground state compared to the 0 ₂ ⁺ state in¹⁰⁰Zr. The structure of¹⁰⁰Zr and the nature of the 0 ₂ ⁺ level is discussed in the light of the present results.     

States in86Sr,84Sr and87Y populated in the (p,t) reaction

The (p,t) reactions on⁸⁸Sr,⁸⁴Sr and⁸⁹Y have been carried out at a bombarding energy of 49.5 MeV. Some low-lying excitations in⁸⁶Sr and⁸⁴Sr associated with configurations of 1g _9/2 and 2p _1/2 neutrons have been identified. Levels populated to 4 MeV of excitation in the strontium nuclei and to 2.5 MeV in⁸⁷Y have been studied in the present experiment. In the case of⁸⁷Y most of the levels populated are of a complex nature.     

First evidence for the 2+ level in the very neutron-rich nucleus102Sr

Evidence for the 2⁺ level in¹⁰²Sr is obtained from theβ-decay of¹⁰²Rb, mass separated at the ISOLDE facility. The energy of 126 keV and the collectivity of the 2⁺→0⁺ transition indicate that¹⁰²Sr is a strongly deformed rigid rotor. In addition, a sizeable lifetime is measured for the 94 keV transition in¹⁰²Y.     

Saturation of deformation atN=60 in the Sr isotopes

From the halflife oft _1/2=3.91 (16) ns for the 2₁ ⁺ state in¹⁰⁰Sr a deformation parameter ofβ=0.40(1) has been derived. Within the given uncertainties, this value is equal to the recently determinedβ-parameters for⁹⁸Sr and⁹⁹Sr, indicating that in the Sr isotopes saturation of deformation is reached immediately at its onset well before neutron midshell. This behaviour is reflected by the “twin” character of⁹⁸Sr and¹⁰⁰Sr with identical features of their unperturbed ground-state rotational bands. These observations are discussed in terms of strong two-nucleon interactions.     

Level structure of78Rb

The excited states of⁷⁸Rb have been investigated by means of in-beam andβ-γ spectroscopy. The production of⁷⁸Rb and theβ radioactivity of⁷⁸Sr have been made through the⁵⁴Fe(²⁸Si,3pn) and⁵⁴Fe(²⁸Si,2p2n) reactions, respectively. Four rotational bands have been observed in the high-spin band structure. The signature splitting is large in the two bands, while the other two bands have small splitting. A detailed low-lying level scheme of⁷⁸Rb has been constructed for the first time via theβ decay of⁷⁸Sr in order to search for a linking transition between the high-spin band head and low lying states.     

The Gamow-Teller beta decay of100Cd

Neutron-deficient isotopes of cadmium were produced in thep(600 MeV)+^natSn spallation reaction. The ISOLDE facility provided mass-separated beams of these isotopes. The production yield was 10³ to 10⁴ atoms/s for¹⁰⁰Cd and roughly two orders of magnitude less for⁹⁸Cd. The properties of the¹⁰⁰Cd→¹⁰⁰Ag decay were studied in detail by X-ray,γ-ray and conversion electron spectroscopy. Forty nineγ-transitions were assigned to this decay, and all but five of them were placed in the decay scheme. The half-life was determined to be 49.1±0.5 s. TheQ _EC value of 3890±70 keV was deduced from a comparison of experimental and theoreticalβ ⁺/(EC+β ⁺ probability ratios. Seven 0⁺→1⁺ Gamow-Teller transitions with log ft values between 3.5 and 4.9 were identified. The total (summed) strength is about five times smaller than predicted by the shell model for the transformation of ag _9/2 proton into ag _7/2 neutron. The quenching of the Gamow-Teller strength and other questions of nuclear structure are discussed for the¹⁰⁰Cd decay. The properties of⁹⁸Cd are inferred by extrapolation of^104,102,100Cd data, and some preliminary experimental results on⁹⁸Cd decay are presented.     

Mass measurements far from stability around theN=Z line (100Sn,100In,100Cd)

Secondary ions of¹⁰⁰Ag,¹⁰⁰Cd,¹⁰⁰In and¹⁰⁰Sn were produced via the fusion-evaporation reaction⁵⁰Cr+⁵⁸Ni at an energy of 5.1 MeV/nucleon. TheA=100 secondary ions were accelerated in the second cyclotron of GANIL, which was used as a high-resolution mass spectrometer. The masses of the three latter isobars were measured with respect to the abundantly produced¹⁰⁰Ag. The known mass of¹⁰⁰Cd was very well reproduced and the masses of¹⁰⁰In and¹⁰⁰Sn were determined for the first time with precisions of 3×10^?6 and 10^?5, respectively.     

Der Zerfall des 2,4-sec100Nb

The nuclide¹⁰⁰Nb was produced by irradiation of enriched¹⁰⁰Mo targets with 14 MeV-neutrons, and its decay properties were investigated employing scintillation and semiconductor spectrometers and coincidence techniques. A half-life of 2.4±0.3 sec and aQ _β-value of 5.8±0.2 MeV were found. From 27 gamma-rays, 20 transitions, representing 95% of the observed gamma-ray intensity, could be placed in a decay scheme comprising 10 excited states of¹⁰⁰Mo.     

Gamma-ray spectroscopy of short-lived fission products using the recoil separator “Lohengrin”

γ-spectra and half-lives of⁹⁰Br,⁹⁵Rb,⁹⁶Rb,⁹⁶Sr,⁹⁶Y,¹³²Sb and¹³²Sn have been measured using the unslowed fission fragment separator “Lohengrin”. Preliminary decay schemes for⁹⁰Kr,⁹⁵Sr,⁹⁶Sr and⁹⁶Y are given.     

Experimentelle Untersuchungen am Elektroneneinfang des85Strontium und88Yttrium

The electron capture decay of⁸⁵Sr and⁵⁵Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results areP _K ω _K (Sr)=.5959 ± 0.0035 andP _K ω _K (Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:P _K (Sr)=0.880± 0.008 andP _K (Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsω _K (Rb)=0.677± 0.009 andω _K (Sr)=0.712± 0.010. Functions ofω _K (Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of⁸⁵Rb and the branching ratios and the positron rate of the⁸⁸Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors.     

The β-decay of98Y and the level scheme of98Zr

Study of theβ-decay of⁹⁸Y and of the level scheme of⁹⁸Zr was undertaken by the use of the two recoil fission product separators JOSEF and LOHENGRIN. Twoβ-decay modes have been detected for⁹⁸Y, the half-lives of which are 0.65±0.05 s and 2.0±0.2 s. The spins and parities of the two states which undergoβ-decay are proposed to be 1⁺ and 4^?, respectively, with the configurations (π1g _9/2)(ν1g _7/2) and (π2p _1/2 (ν1g _7/2). The measuredQ _β -value is 7300±400 keV for the 0.65 s decay. The level scheme of⁹⁸Zr was deduced fromγ,γ-coincidence data. Absoluteγ-intensities were obtained from two independent measurements. The half-life of the first excited state of⁹⁸Zr at 853.0 keV with spin and parity 0⁺ was determined through delayedγ, e^?-measurements to be 63 ±7ns. No indication of the coexistence of two different nuclear shapes of⁹⁸Zr was found.     

Investigation of 89Y and 87Rb by (p,p′) reactions

The (p, p′) reaction on ⁸⁹Y at incident energies of 20.51 MeV and 14.33 MeV and on ⁸⁷Rb at 20.89 MeV has been studied. In ⁸⁹Y 28 levels with E_ex between 2 and 4.2 MeV and 79 levels with E_ex between 4.2 and 6 MeV have been identified. In ⁸⁷Rb 45 levels with E_ex up to 4.2 MeV have been found. Transferred orbital angular momenta and deformation parameters have been deduced from a macroscopic DWBA analysis of the differential cross sections. The experimental results are not consistent with the interpretation of states in ⁸⁹Y and ⁸⁷Rb as resulting from the weak-coupling of a proton or proton-hole to excited states of the ⁸⁸Sr core. Simple shell model arguments are able to yield at least a qualitative agreement with the level scheme as found for ⁸⁹Y.     

Der Zerfall des95Sr

The nuclide⁹⁵Sr was isolated by chemical separation methods after thermal neutron induced fission of²³⁵U. It's decay properties were investigated employing semiconductor spectrometers and coincidence techniques. A half-life of 24.4±0.2 sec was found. Out of 29 gamma rays, 25 transitions representing 97% of the observed gamma-ray intensity were placed in a decay scheme comprising 19 excited states of⁹⁵Y.     

Experimental indication of the onset of nuclear deformation in neutron-rich Sr isotopes at mass 98

A partial decay scheme for 0.1 sec ⁹⁸Rb has been deduced from γ-singles, γ-multispectra ana γγ coincidence measurements taken at the OSTIS mass-separator system at the Institut Laue-Langevin. The low-lying levels of ⁹⁸Sr follow the energy level systematics of the even-AN = 60 isotones. The onset of nuclear deformation in even-A neutron-rich Sr isotopes appears to occur at mass 98, as the first 2⁺ level energy drops from the nearly constant value of about 800 keV for masses 90–96 to 144 keV at mass 98. Energy level systematics indicate that a transition in the nuclear structures of the more neutron-rich nuclei near mass 100 occurs rather sharply at neutron number N = 60.     

PräziseQ β -Wert-Messungen mit einem Intrinsic-Germanium Detektor an leichten,neutronenreichen Spaltprodukten

An intrinsic Germanium detector of 10 mm depth and 300 mm² sensitive area has been used to determineβ-endpoint energies for Rb, Sr and Y fission products. It was calibrated with monoenergetic electrons supplied by a magnetic conversion electron spectrometer for the energy range from 1.6 to 8 MeV. The energy calibration of the detector is linear with deviations less than 2 · 10^?4, and the detector was recalibrated daily using precisely known gamma rays of⁹⁰Rb. At the on-line fission product separator OSTIS at the ILL, Grenoble the endpoints ofβ-singles-spectra have been determined andQ-values deduced if possible also from beta-gamma coincidence measurements. The obtainedQ-values are:⁸⁸Rb:(5 318±4) keV,⁸⁹Rb: (4 510 ± 8) keV,⁹⁰Rb: (6 578 ± 15) keV,⁹¹Rb: (5 857 ± 8) keV,⁹¹Sr: (2 704.5 ±3) keV,⁹²Rb: (8 111 + 15) keV,⁹³Rb:(7 485 ± 15) keV,⁹⁴Rb: (10 304 ± 30) keV,⁹⁴Sr: (3 512 ± 5) keV,⁹⁴Y: (4 920 ±5)keV,⁹⁵Rb: (8 947 ±100) keV,⁹⁵Y: (4 445±5) keV,⁹⁶Rb: (11 303±250) keV,⁹⁶Sr: (5 413±20) keV,⁹⁶Y: (7 120 ±50) keV,⁹⁷Rb: (10 020 ±50) keV.