In-beam spectroscopy of 120Xe

Excited states of ¹²⁰Xe have been studied by in-beam γ-ray spectroscopy using the ¹¹⁰Cd(¹³C, 3n) and ¹¹¹Cd(¹²C, 3n) reactions. The yrast band was observed up to the 14⁺ level, showing backbending at the 12⁺ state. A γ-band and two new negative-parity bands were found. The low-lying levels of ¹²⁰Xe could be described by the IBA-1 hamiltonian plus a triaxial degree of freedom.     

In-beam spectroscopy of104Sn

The very neutron deficient nucleus 104Sn has been identified in in-beam spectroscopy using the reaction⁵⁰Cr(⁵⁸Ni, 2p2n) and neutron and charged particle multiplicity filter detectors. Excited states up to I ≈ 10 and E_x=4 MeV were observed and the level scheme is discussed in the frame work of the spherical shell model.     

In-beam spectroscopy of231Pa

Information on energy levels and onE 2 andM 1 matrix elements in²³¹Pa has been obtained using conversion-electron and gamma-ray spectroscopy following the²³²Th(p, 2n)²³¹Pa reaction and Coulomb excitation of the radioactive target²³¹Pa by⁴He and³²S ions. The results are analyzed in the framework of the rotational model, applied to the rotational band built on the 1/2^?[530] Nilsson state whose 3/2^? member forms the ground state of this nucleus. The deviations of the level energies from the rigid-rotor values can be described by Coriolis couplings. The analysis of the Coulomb-excitation process shows that a constant set of rotational parameters Q₀, g_R, g_K, andb can fairly well account for the measured line intensities.     

In-beam gamma-ray spectroscopy of 116Te

High-spin states of the even-even ¹¹⁶Te were studied by in-beam g-ray spectroscopy using the ¹⁰³Rh (¹⁶O, p2n) fusion-evaporation reaction at a beam energy of 80 MeV. γ-γ coincidence and γ-γ angular correlation analyses were employed for determining the level scheme of ¹¹⁶Te. Levels up to I^π = 27^? and several new states were established. We identified two rotational bands with negative parity, one of which was newly established in the present work. We suggest that such two bands be associated with two proton [(g_7/2) ? (h_11/2)] and two neutron [(d_5/2) ? (h_11/2)] configurations, respectively.     

102Ag: In-beam gamma-ray spectroscopy

Gamma-rays associated with the decay of states in the ¹⁰²Ag nucleus have been identified, sixty-four of them for the first time following the reaction ⁵⁰Cr(⁵⁶Fe, 3pn)¹⁰²Ag at a mean energy of 195 MeV. Identification was made using an array of nine escape-suppressed Ge detectors coupled to the Daresbury Recoil Separator. Excited states in ¹⁰²Ag were identified using recoil-gamma and γγ coincidences. From the intensity balance and the coincidence data, a new set of levels was identified which may be interpreted as reminiscent of “three-quasiparticle” bands in neighboring odd-mass nuclei and similar to a four-quasi-particle band observed in ¹⁰⁶Ag.     

In-beam and decay spectroscopy of transfermium nuclei

In recent years the body of experimental data on nuclei with masses A?250 has increased dramatically. Nuclei that had been out of reach for experimental studies have now become available for study through a variety of approaches, both with in-beam spectroscopic methods and through spectroscopy following the decay of isomeric states or alpha decays at the focal plane of powerful separators. This article aims to collect the currently available experimental data on nuclei between Cm (Z=96) and Db (Z=105). The review of this data builds on the evaluations in the literature and focusses on those datasets obtained most recently.     

In-beam spectroscopy of 253, 254No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei ^{253, 254}No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyv?skyl?. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of ²⁵³No are discussed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rdh@ns.ph.liv.ac.uk RID="b" ID="b"Present address: GANIL, F-14021 Caen, France. RID="c" ID="c"Permanent address: IReS Strasbourg, IN2P3-CNRS, F-67037-Strasbourg, France. RID="d" ID="d"Present address: CEA/DIF DCRE/SDE/LDN F-91680 Bruyeres-le-Chatel. RID="e" ID="e"Present address: Daresbury Laboratory, Daresbury WA4 4AD, UK. RID="f" ID="f"Permanent address: IPN Lyon, IN2P3-CNRS, F-69037 Lyon, France.     

In-beamγ-ray spectroscopy of102In

Neutron deficient nuclei close to ¹⁰⁰Snhave been investigated in-beam by γ-ray spectroscopic methods using the NORDBALL detector array. A beam of 270 MeV ⁵⁸Niwas used to bombard a target of ⁵⁴Fe.Reaction channel separation was achieved with a 4π charged particle multidetector setup together with a 1π neutron detector wall placed in the forward direction. Excited states of ¹⁰²Inwere identified for the first time. The level scheme constructed from γ-γ-particle-coincidence and γ-γ-angular correlation analysis is presented. The structure of ¹⁰² In is discussed and compared to neighboring nuclei in the framework of the nuclear shell-model.     

In-beam γ-ray spectroscopy on56Ni

Yrast levels in the doubly-magic nucleus⁵⁶Ni have been studied by in-beam gg-spectroscopy with the reaction⁵⁴Fe(α, 2n)⁵⁶Ni. A cascade of five γ -transitions is established. A shell model calculation of 2p2h, T=0 states, using empirical matrix elements, suggests the assignments 8⁺ and 10⁺ for the two highest levels.     

In-beam gamma-ray spectroscopy of 190, 197Po

γ -ray transitions in the neutron-deficient nuclei ^{190, 197}Po have been identified using the JUROGAM Ge detector array coupled to the RITU gas-filled separator and the GREAT spectrometer. The yrast band of ¹⁹⁰Po has been firmly established through γ -γ coincidences and extended up to a spin and parity of 14⁺. It displays similar behaviour to its isotones ¹⁸⁶Hg and ¹⁸⁸Pb above the 4⁺ level, thus confirming its prolate nature. In ¹⁹⁷Po the band built upon the 13/2⁺ isomer has been extended up to a spin and parity of 33/2⁺, while the non-yrast band has been observed for the first time. The behaviour of ¹⁹⁷Po is found to be similar to that of the nearby even-mass isotopes, which is consistent with the model in which the i _13/2 neutron is weakly coupled to the states in the even-even core.     

In-beam spectroscopy of 126Ce and 127Pr

High spin states in ₁₂₆Ce and ₁₂₇Pr were populated via heavy ion reactions with 182-MeV ₃₅Cl projectiles on a thick ₉₆Ru target. Prompt γ–γ coincidences were measured. New states in ₁₂₆Ce and ₁₂₇Pr were found. The results are discussed in the framework of the core–quasiparticle coupling model. Received: 16 June 1998     

In-beam conversion electron spectroscopy using the SACRED array

Conversion electron studies of medium-heavy to heavy nuclear mass systems are important where the internal conversion process begins to dominate over gamma-ray emission. The use of a segmented detector array sensitive to conversion electrons has been used to study multiple conversion electron cascades from nuclear transitions. The application of the Silicon Array for ConveRsion Electron Detection (SACRED) for in-beam measurements has successfully been implemented.     

In-beam Mössbauer spectroscopy at heavy-ion accelerators

The method of “in-beam Mössbauer spectroscopy (IBMS)” as presently performed at heavy-ion accelerators is presented and reviewed. Experimental aspects are outlined and special features of this technique in comparison with more conventional radioactive ion implantation are stressed. The review is centered on the fate of⁵⁷Fe atoms implanted in metals and semi-conductors in which very limited or vanishing solubility for Fe exists. Under these conditions Fe takes up to a rather large extent interstitial positions. These can be characterized by the Mössbauer parameters, in particular by the isomer shift. Already at rather low temperatures one observes in several materials a dynamic behaviour of the Fe interstitial which can be described in some cases as localized motion and in others as onset of long-range interstitial diffusion. Additional information on the dynamic behaviour and the electronic structure in some of the systems presented comes from Perturbed Angular Distribution of γ-rays (PAD). which also is an “in-beam” technique working with a 10⁺ isomeric state of⁵⁴Fe.     

In-beam gamma-ray spectroscopy with exotic beams at the NSCL

Projectile fragmentation provides radioactive beams at intermediate velocities (v/c = 0.3-0.5) by physical means of fragment separation. With the development of position-sensitive photon detectors it has become possible to measure the energies and directions of photons emitted in-flight from such fast-moving exotic beams. This allows the reconstruction of the photons' energies emitted from an exotic projectile with high accuracy. It can be advantageous to employ photon detection in experiments with exotic beams since photons can traverse matter easily and their attenuation can be calculated. Experiments with standard luminosities can be carried out at intermediate beam energies with thick secondary targets (order of g/cm²) and very low incident beam rates (order of particle/s or less). Experimental success in this field is strongly correlated with the development of photon detectors such as position-sensitive scintillation detectors or segmented germanium detectors. In-beam gamma-ray spectroscopy of fast exotic beams has been successfully used at all projectile fragmentation facilities in intermediate-energy heavy-ion inelastic scattering experiments, knockout reactions and fragmentation reactions. Here, we focus on experimental results for neutron-rich exotic nuclei in the π(sd )-shell. Measurements and detector developments carried out at the NSCL at Michigan State University during the last four years are discussed. Received: 1 May 2001 / Accepted: 4 December 2001     

In-beam γ-ray spectroscopy of the neutron deficient 100Ag

Conversion coefficients and conversion ratios of someγ-transitions in²⁰¹Tl and²⁰³Tl were measured by means of simultaneous spectroscopy ofγ-quanta and conversion electrons employing intensity calibrated semiconductor detectors. The experiments aimed at a precision as high as possible within the limits of the experimental methode used. Theγ-transitions were of the typeM 1(+E2). From the measured values the penetration parameters of the internal conversion for theM 1 components (λ) together with the multipol mixing ratios (δ²) were deduced. The necessary theoretical coefficients were taken from the tables of Hager and Seltzer. The results are for the ?-forbidden 331 keV transition in²⁰¹Tl,λ=+4.0±1.0,δ ²=1.78±0.16; for the ?-allowed 361 keV transition in²⁰¹Tl,λ=+0.5±0.5,δ ²=0.02±0.02; for the ?-forbidden 279 keV transition in²⁰³Tl,λ=+ 5.71±0.45,δ ²=1.55±0.08.     

In-beamγ-ray spectroscopy of the odd-odd nucleus144Tb

The level scheme of theN=79 nucleus¹⁴⁴Tb was investigated via in beamγ-ray spectroscopy using the¹¹²Sn (³⁵Cl,n2p),¹¹⁶Sn(³²S, 3np) and⁸⁹Y(⁵⁸Ni, 2np) reactions. States up toI～20 andE _x～5 MeV were established above the 6^? β ⁺ decaying isomer. Two new isomers with half-life of 0.67(6) µs and 2.8(3) µs were identified. The level scheme of¹⁴⁴Tb is interpreted in the framework of the spherical shell model with a few valence nucleons outside the¹⁴⁶Gd core.     

In-beam γ spectroscopy using DIC with a radioactive Ne beam

A study of deep-inelastic and multi-nucleon transfer reactions to populate neutron-rich O, Ne and F nuclei is here presented. The reaction under analysis employed a beam of radioactive ²⁴Ne at 7.9 AMeV, provided by the SPIRAL facility at Ganil, impingin on a ²⁰⁸Pb target. The reaction products have been detected in the VAMOS spectrometer in coincidence with gamma rays measured by the EXOGAM array. Preliminary results here presented show a selectivity in the population of states of different nature.     

In-beam Mössbauer spectroscopy:57Fe in Si and Ge

Fe has been studied in the semiconductors Si and Ge with the Coulomb excitation recoil implantation technique in a wide temperature range. In the case of Fe inSilicon it was found that one third of the implanted atoms land on interstitial sites. The long range diffusion of these atoms could be observed microscopically at temperatures around 600 K. The isomer shift of interstitial Fe in Si was determined. The remaining atoms exhibit a strong quadrupole splitting on disturbed sites. This component seems to relax into a state with higher symmetry above 700 K. InGermanium a similar situation is found. Whereas iron on disturbed sites dominates the spectra, the direct implantation into interstitial sites is also observed below 200 K. At higher temperatures the substitutional position is preferred. The isomer shifts for interstitial and substitutional Fe in Si and in Ge are in good agreement with calculated electron densities.     

In-beam Mössbauer spectroscopy on single iron atoms in alkali metals

In-beam Mössbauer spectroscopy is applied to study implanted Fe atoms in the alkali metals Li, Na and K. From the Mössbauer parameters we infer that the Fe implants take up substitutional as well as interstitial sites. The strongly increased electron density at the interstitial position is qualitatively explained by the pressure resulting from the small interstitial volume. It is concluded that recently reported local moment formation in these systems cannot be due to substitutional Fe only.     

In-beam Mössbauer spectroscopy on isomer shift and diffusion of interstitial Fe

In-beam Mössbauer spectroscopy (IBMS) is used to study single isolated⁵⁷Fe impurities after implantation in metals and semiconductors with very restricted or even vanishing solubility for Fe. From the Mössbauer parameters it can be inferred that the Fe implants take up substitutional as well as interstitial sites. The strongly increased electron density at the interstitial position in metals is qualitatively explained by the pressure resulting from the small interstitial volume. In Si, Sc and Pb exponential line broadening due to interstitial diffusion has been observed. Additional information on the dynamic behavior and local magnetic structure in some of the systems presented comes from perturbed angular distribution experiments (PAD) performed on an isomeric state of⁵⁴Fe.