Isomers of astrophysical interest in neutron-deficient nuclei at masses A = 81, 85 and 86

Decay properties of neutron-deficient exotic nuclei close to A=80 have been investigated at the IGISOL facility. The studied nuclei, ⁸¹Y, ⁸¹Sr, ^81mKr, ⁸⁵Nb, ⁸⁵Zr, ⁸⁶Mo and ⁸⁶Nb, were produced by a ³²S beam from the Jyv?skyl? isochronous cyclotron on ⁵⁴Fe and ^natNi targets. The internal conversion coefficient for a 190.5 keV isomeric transition in ^81mKr has been measured and the internal transition rate has been determined. The internal transition rate has been used to estimate a neutrino capture rate on ⁸¹Br, which yields a log ft of 5.13±0.09 for the reaction ⁸¹Br( ν, e ^-)^81mKr. A new isomer with a half-life of 3.3±0.9 s has been observed in ⁸⁵Nb. The existence of an earlier reported isomer with a half-life of 56 s in ⁸⁶Nb has not been confirmed.     

The level scheme of91Tc and theβ decay of91Ru(9/2+)

The level scheme of⁹¹Tc has been studied by means of in-beamγ-ray spectroscopy in the irradiations of⁵⁸Ni and⁵⁴Fe targets by⁴⁰Ca beams from the Munich MP tandem and the heavy ion post accelerator. A large number of positive as well as of negative parity yrast-levels with excitation energies up to 8 MeV has been established. The level scheme of⁹¹Tc has been compared with shell model claculations and a good agreement for all identified levels has been found. In parallel investigations of the residual activities of the reaction⁴⁰Ca→⁵⁴Fe, theβ decay of the (9/2⁺ ground) state of⁹¹Ru has been investigated. Aβ decay scheme of⁹¹Ru(9/2⁺) has been established. The half-life of⁹¹Ru(9/2⁺) has been measured to be 9±1 s.     

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.     

Decay of 8.0-day131I to levels of131Xe and 11.77-day131mXe

The decay characteristics of¹³¹I have been determined with high accuracy. The total branch from¹³¹I to^131mXe has been measured to be 1.086±0.007%. The half life of^131mXe has been measured as 11.770±0.012 days. Theγ-ray spectrum has been determined and new transitions at 85.92, 232.17, 295.83, 302.44, and 449.57 keV established. The position, spin and parity were established for a 9/2^? level at 341.140 keV and spin and parity of 7/2^? established for a level at 666.921 keV. The log f₁t for the unique firstforbiddenβ transition from 7/2^{+ 131}I to 11/2^{? 131m}Xe has been calculated to be 9.78.     

Levels of 190Os populated in the decays of 3.3 h 190mRe and 12 d 190Ir and in the 189Os(d,p)190Os reaction

The level structure of ¹⁹⁰Os has been investigated by the techniques of radioactive decay and neutron transfer reaction spectroscopy. The existence of 3.3 h ^190mRe has been confirmed; it decays ≈ 49% by isomeric transitions and ≈ 51% by β^? decay to levels in ¹⁹⁰Os with spins $\text{\$}\text{?}\text{= 5}$. In a re-investigation of the 12 d ¹⁹⁰Ir decay, a virtually complete decay scheme has been established and discrepancies between the I^π values assigned to several ¹⁹⁰Os levels by earlier workers have been resolved. The reaction ¹⁸⁹Os(d, p)¹⁹⁰Os has been studied and information about the locations of two-quasiparticle states involving the $\text{3}\text{2}\text{[512]ν}$ orbital and about the microscopic compositions of collective excitations has been derived. Various aspects of the ¹⁹⁰Os level structure are discussed in the light of the combined radioactivity and transfer reaction results.     

Specific features of the dielectric spectrum of CaCu3Ti4O12 in the low-frequency range

The dielectric spectra of CaCu₃Ti₄O₁₂ ceramics with giant values of the dielectric constant have been presented. The spectrum exhibits Debye dispersion with an activation energy of 0.075 eV in the high-frequency range of 10⁶–10⁷ Hz, and a characteristic plateau has been seen in the frequency dependence of the dielectric constant in the range of 10⁴–10⁵ Hz. A considerable increase in the loss factor ?″ has been observed in the low-frequency part of the spectrum and a capacitive-to-inductive impedance transition has been revealed in some samples at a frequency below 10^?2 Hz. The causes of this transition have been discussed.     

The complex transfer reaction (14C, 15O) on Ni,Zn and Ge targets: Existence and mass of 69Ni

The (¹⁴C, ¹⁵O) complex transfer reaction has been studied at 72 MeV incident energy on ^58,60,62.64Ni ^68,70Zn and ^74,76Ge targets. Spectra and differential cross sections have been measured in a 5° angular range centred around a laboratory angle of 6°. The nucleus ⁶⁹Ni has been observed for the first time and its mass determined.     

Beta decay of22O

The beta-gamma spectroscopic study of²²O is presented. This nucleus, produced as a projectile-like fragment from the interaction of a 60 MeV/n⁴⁰Ar beam with a Be target, has been separated by the LISE spectrometer. Several gamma rays from²²O decay have been observed, from which a half-life of (2.25±0.15)s has been determined. Accurate excitation energies have been deduced for several states in²²F. A partial beta decay scheme of²²O has been established. Experimental results have been compared with shell model calculations.     

Vibrational Analysis of the A3Π0−X1Σ+ and B3Π1−X1Σ+ Subsystems of the GaBr Molecule

Abstract

The emission band spectrum of gallium monobromide has been excited in a dc hollow cathode discharge. bands of the ³Π_0,1?X¹Σ⁺ system, lying in the range from 340 to 370 nm have been recorded at high resolution and measured. The previous vibrational analysis has been revised and corrected. New vibrational assignment has been proposed and improved vibrational constants of the upper and lower electronic states have been determined.     

New β-delayed proton precursor 135Gd

Unknown β-delayed proton precursor ¹³⁵Gd has been synthesized by the reaction ¹⁰⁶Cd ( ³²S, 3n ) and identified using a helium-jet recoil fast tape-transport system with a γ(X)-p coincidence measurements. Its β-delayed proton spectrum has been observed. The half-life of ¹³⁵Gd decay has been determined to be 1.1 ± 0.2 s.     

Multiparticle break-up of 10B induced by fast neutrons

The reaction $\text{n}\text{+}{}^{10}\text{B}\text{→ α + α +}\text{d}\text{+}\text{n}$ induced by 14.4 MeV neutrons has been investigated in a kinematically complete experiment. Several final-state interactions have been observed in the sequential decay of the n + ¹⁰B system. The angular distribution of the ¹⁰B(n, ⁶Li₁)⁵He₀ reaction, leading to two unstable particles and consequently measurable only in a kinematically complete experiment, has been measured. It has been analysed in the framework of DWBA as a pick-up process with the transfer of the five-nucleon cluster ⁵Li. The presence of quasifree scattering and quasifree reaction with the deuteron as spectator has also been observed.     

Search for a narrow resonance in 6Be with the 4He(3He,n) reaction

The ⁴He(³He, n)⁶Be reaction has been investigated at 36.20 MeV bombarding energy in search for a narrow resonance near the ³He-³He threshold which has been proposed as a possible explanation for the missing solar neutrinos in Davis' experiment. Neutrons have been detected at θ_b = 0° with an effective resolution < 25 keV in the c.m. system, in coincidence with protons emitted at θ_p = 50°. No indication for the existence of such a resonance has been found and an upper limit (dσ/dω)_res ≦ 7.5 μb/sr has been established.     

The mass of the nucleus148Dy

Usingγγ coincidences theEC(K)/β ⁺ ratio for theβ decay¹⁴⁸Dy→¹⁴⁸Tb has been determined.¹⁴⁸Dy has been produced through the irradiation of⁹³Nb with 249 MeV⁵⁸Ni ions. The mass of¹⁴⁸Dy has been deduced. With the help of knownQα values the masses of¹⁵²Er,¹⁵⁶Yb,¹⁶⁰Hf and¹⁶⁴W have been obtained. The experimental masses are compared with different current mass formulae.     

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.     

The decay of78Rb and the level scheme of78Kr

The level scheme of⁷⁸Kr has been studied with the techniques of γ ray spectroscopy: decay spectra of⁷⁸Rb produced by the reactions⁶⁴Zn(¹⁶O,pn) and⁶⁵Cu(¹⁶O,3n) have been measured; in-beam γγ coincidences have been taken during the irradiation of⁶⁴Zn with¹⁶O ions; and an angular distribution measurement of γ rays from the reaction⁶⁴Ni(¹⁶O, 2n)⁷⁸Kr has been performed. Fifteen excited states in⁷⁸Kr have been observed and spins have been proposed for most of these levels. A⁷⁸Rb decay with a half-life of 17.5 ± 2 min has been found in addition to the previously known 6.0 ±0.2 min decay.     

Levels and transition probabilities in 121Cd

The decay of isotope-separated ¹²¹Ag has been studied. A level scheme for ¹²¹Cd has been constructed. Information on lifetimes of excited states has been obtained by the method of delayed coincidences. Some low-lying energy levels of ¹²¹Cd show a considerable deviation from the systematics of similar levels in the lighter isotopes of Cd. This may be attributed to a different spatial symmetry of ¹²¹Cd.     

The spectra of YF+ and YF molecules in the 3400–3700 Å region

The violet-degraded band system (3400–3700 Å) has been found in the spectrum of a discharge through helium with a trace of YF₃ vapor. The emitter of this system is the hitherto unknown YF⁺ ion. Vibrational analysis of the band system has been carried out. Rotational analysis has shown that the bands are due to the ²Π-²Δ transition. Molecular orbital configurations which give rise to both participating states are discussed. The ¹Σ-X¹Σ (0-0) band of YF (λ3572 Å) obtained in absorption has been reanalyzed.     

The 130Nd↦130Pr↦130Ce decay chain revisited

An investigation of low-lying energy levels of ¹³⁰Pr and ¹³⁰Ce has been made via β-decay. The radioactive parent nuclei were produced via ^94,96Mo + ⁴⁰Ca reactions at 6.8 MeV/nucleon and transported by a He-jet system. Gamma-γ-t, γ-X-t, γ-e^--t coincidence measurements were performed. Internal conversion coefficients have been measured with a magnetic spectrometer. The new β-decay half-life of ¹³⁰Nd has been determined to be 21(3) s. A partial level scheme of ¹³⁰Pr at low-spin has been constructed. The β-decay of ¹³⁰Pr to ¹³⁰Ce suggests the existence of three β-instable isomeric states in ¹³⁰Pr, while only one half-life T _1/2 = 40(4) s has been measured. Based on the present work and low-lying excited states in neighbouring odd-mass nuclei, the spins and parities of isomeric states in ¹³⁰Pr are proposed to be 2⁺, (4,5)⁺ and (7,8^±). The ground state in ¹³⁰Pr is still undetermined. Received: 20 August 2001 / Accepted: 6 November 2001     

Paramagnetic resonance of Mn<Superscript>4+</Superscript> and Mn<Superscript>2+</Superscript> centers in lanthanum gallate single crystals

An increase in the manganese concentration in lanthanum gallate in the range 0.5–5.0% has been found to result in a complete replacement of individual Mn⁴⁺ ions by Mn²⁺ ions. The relative concentrations and binding energies of individual Mn⁴⁺, Mn³⁺, and Mn²⁺ ions have been determined. The spin Hamiltonians of the Mn²⁺ and Mn⁴⁺ centers in the rhombohedral and orthorhombic phases, respectively, have been constructed and the orientation of the principal axes of the fine-structure tensor of Mn⁴⁺ at room temperature has been found. The possibility of using electron paramagnetic resonance for determining the rotation angles of oxygen octahedra of lanthanum gallate with respect to the perovskite structure has been discussed.     

g-Factor of the first 2+ state in theN=82 nucleus138Ba

The 2 ₁ ⁺ level of¹³⁸Ba has been Coulomb excited with a 105 MeV³²S beam. The precession of the gamma ray angular distribution induced by the transient magnetic field when traversing a 2.14 mg/cm² iron foil, has been measured to be 15.6(1.7) mr. A value of g(¹³⁸Ba 2 ₁ ⁺ )=0.72(11) was obtained assuming for the transient field strength the Chalk River calibration. The field parametrization has been checked using the first 2⁺ state in¹⁵⁰Sm as probe. Theg value obtained is sensibly lower than predicted by large scale shell model calculations in a proton subspace. Theg-factor of the first 2⁺ state in¹⁴⁸Sm has been remeasured yieldingg(¹⁴⁸Sm 2 ₁ ⁺ )=0.246(22).