Low-energy excited states of 76^{76}As from the 76^{76}Ge(p,n)76^{76}As reaction

Spectra of gamma radiation and internal conversion electrons from several germanium targets bombarded with 2.9 MeV protons were measured. Eleven transitions between $^{76}$As states excited in the $^{76}$Ge(p,n)$^{76}$As reaction were identified. The energies of these states were found to be 45.5, 87, 121, 166, 265, 302, 377, 515 and 550 keV. The possible values of the spin of the 87 and 121 keV levels have been confined 1$^{+}$, 2$^{+}$ and 3$^{+}$

Lifetime measurements of short-lived excited states, and shape changes in As 69 and Ge 66 nuclei

Background: The nuclear shape is a macroscopic feature of an atomic nucleus that is sensitive to the underlying nuclear structure in terms of collectivity and the interaction between nucleons. Therefore, the evolution of nuclear shapes has attracted many theoretical and experimental nuclear structure studies. The structure of the A≈70, N≈Z nuclei, lying far from the stability line, is interesting because a particularly strong proton-neutron correlation may occur here due to the occupation of the same orbits by nucleons of both types. In this region, different particle configurations drive a nucleus towards various deformed shapes: prolate, oblate, octupole, or nonaxial. These nuclear shapes change rapidly with nucleon number and also with angular momentum. This is reflected by a presence of different structures (bands) of excited states which exhibit a broad range of lifetimes. Purpose: The aim of this paper is to determine lifetimes of some high-spin excited states in As69 and Ge66 nuclei to examine the shape evolution in these neutron-deficient nuclei. Methods: Lifetimes of high-spin states in As69 and Ge66 have been measured by using the Doppler-shift attenuation technique with the GASP and recoil filter detector setup at the Laboratori Nazionali di Legnaro. The nuclei of interest were produced in the S32(95MeV)+0.8mg/cm2 Ca40 fusion-evaporation reaction. The strongest reaction channels 3p and α2p led to the As69 and Ge66 final nuclei, respectively. Using γ-γ-recoil coincidences we were able to determine very short lifetimes (in the femtosecond range) in the residual nuclei of interest. Results: In As69, the extracted lifetimes are τ=72 (-32, +45) fs for the 33/2+ state at 7897 keV and τ<85 fs for the 37/2+ state at 9820 keV. For the Ge66 case, the lifetime of the 11- state at 7130 keV is τ=122(±41) fs. Lifetimes in As69 and Ge66 reported in this paper have been measured for the first time in the present experiment. Conclusions: The results are discussed in the terms of deformation and shape evolution in As69 and Ge66. The quadrupole moments deduced from the measured lifetimes were compared with the cranked Woods-Saxon-Strutinsky calculations by means of the total Routhian surface method. It turns out that Band 3 in As69 shows an oblate-prolate shape transition, and above spin 33/2+ it corresponds to a prolate collective structure with β2≈0.27 and γ≈20. In turn, in Ge66 the negative-parity band built on the 7- state at 4205 keV corresponds to a triaxial shape with β2=0.33 and γ=31. Analysis of the transitional quadrupole moments derived from the experimental and theoretical ones points to a significant change of deformation in the As69 and Ge66 nuclei with increasing rotational frequency

In-beam \mth{\gamma}-ray spectroscopy of \chem{^{42}Ca}

High-spin states of the $^{42}$Ca nucleus, populated in the 68 MeV $^{18}$O + $^{30}$Si reaction, have been studied in a $\gamma$-$\gamma$-recoil coincidence experiment. The level scheme of $^{42}$Ca has been extended up to 13.7  MeV. An elaborate decay pattern with various paths, together with high-quality DCO and polarization information assigns spins and parities for almost all observed levels. The sequence of non-yrast positive-parity states is discussed and compared with highly deformed bands in $^{36}$Ar and $^{40}$Ca

High-spin states in \chem{^{44}Ca}

High-spin states of the $^{44}$Ca nucleus populated in the 68 MeV $^{18}$O + $^{30}$Si reaction have been studied in a $\gamma$-$\gamma$-recoil coincidence experiment. The level scheme of $^{44}$Ca has been extended up to 12.2 MeV. In particular, the negative-parity band has been identified with the highest $I = 13^-$ level at 10.6 MeV. This state is interpreted as the band-terminating state for the ($d_{3/2}^ {-1} f_{7/2}^5$) configuration

Identification of the 13/2+{13/2^+} isomer in \chem{^{199}At}

The $13/2^+$ isomeric state in the \chem{^{199}At} nucleus has been identified at an excitation energy of 573 keV and its half-life measured to be 580(130) ns using the recoil-decay tagging technique

Collective High Spin States in the Light Odd f7/2 Nuclei

The high-spin states in 45Sc, 45Ti and 43Ca were studied with the GASP multidetector array coupled with the Recoil Mass Spectrometer in Legnaro. The nuclei were excited in the 30Si+60 MeV 18O reaction. Life-times were extracted from the analysis of the Doppler shift attenuation of gammas emitted in the reversed kinematics 12C+35Cl reaction. Energies and the transition probabilities for the observed negative-parity states agree with the shell model predictions. The lifetimes of the intruder-positive parity states in 45Sc and 45Ti suggest a deformation (\beta \approx 0.25) associated with the particle-hole excitation in the nuclei

Measurement of light charged particles in the decay channels of medium-mass excited compound nuclei

The 48Ti on 40Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels. Energy spectra and multiplicities of the emitted light charged particles have been compared to Monte Carlo simulations based on the statistical model. Indeed, in this mass region (A ~ 100) models predict that shape transitions can occur at high spin values and relatively scarce data exist in the literature about coincidence measurements between evaporation residues and light charged particles. Signals of shape transitions can be found in the variations of the lineshape of high energy gamma rays emitted from the de-excitation of GDR states gated on different region of angular momenta. For this purpose it is important to keep under control the FE and FF processes, to regulate the statistical model parameters and to control the onset of possible pre-equilibrium emissions from 300 to 600 MeV bombarding energy

Refinement of the 42Ca Level Scheme. Preliminary Results from the First AGATA Demonstrator Experiment

International audienceThe Coulomb excitation experiment to study electromagnetic properties of low-lying states in 42Ca with a focus on a presumably superdeformed band was performed at the Laboratori Nazionali di Legnaro in Italy using the \gamma -ray spectrometer AGATA Demonstrator coupled to the DANTE charged particle detector array. First results are presented, including the refinement of the 42Ca level scheme