Nuclear structure studies with the PRISMA/CLARA setup

A program on nuclear structure studies in nuclei populated by multi‐nucleon transfer and deep‐inelastic collisions is being carried on at LNL with the PRISMA/CLARA setup. The large acceptance of the spectrometer PRISMA allows to detect nuclear species produced over a wide mass and Z range. Prompt gamma rays following the de‐excitation of these nuclei can be observed with the CLARA array. The high granularity of CLARA, combined with velocity vector measured with PRISMA, allows precise Doppler correction for the gamma rays emitted by in‐flight recoils. Typical gamma‐ray energy resolution obtained after Doppler correction is below 1% for recoil velocities v/c∼10%. Having high efficiency and good resolving power, PRISMA/CLARA is an ideal tool for reaction mechanisms studies and for gamma spectroscopy of the nuclei produced in multi‐nucleon transfer reactions or deep‐inelastic collisions. Following a recent campaign dedicated to the study of medium‐mass neutron‐rich nuclei, significant experimental information..

Exploring the performance of the spectrometer prisma in heavy zirconium and xenon mass regions

We present results from two recent runs which illustrate the performance of the PRISMA spectrometer in the proximity of the upper limit of its operational interval, namely 96Zr + 124Sn at Elab = 500 MeV and 136Xe + 208Pb at Elab = 930 MeV. In the latter run, the γ array CLARA also allowed us to identify previously unknown γ transitions in the nuclides 136Cs and 134I

Multinucleon transfer reactions in closed-shell nuclei

Multinucleon transfer reactions in 40Ca+96Zr and 90Zr+208Pb have been measured at energies close to the Coulomb barrier in a high resolution gamma-particle coincidence experiment. The large solid angle magnetic spectrometer PRISMA coupled to the CLARA gamma-array has been employed. Trajectory reconstruction has been applied for the complete identification of transfer products. Mass and charge yields, total kinetic energy losses, gamma transitions of the binary reaction partners, and comparison of data with semiclassical calculations are reported. Specific transitions in 95Zr populated in one particle transfer channels are discussed in terms of particle-phonon couplings. The gamma decays from states in 42Ca in the excitation energy region expected from pairing vibrations are also observed

Shape transitions far from stability: The nucleus 58Cr

Abstract Excited states up to I π = 8 + in the neutron-rich nucleus 58Cr have been identified by using a new experimental setup composed of the large acceptance magnetic spectrometer PRISMA and the highly efficient γ-detector array CLARA. Interestingly, the excitation energy sequence of the ground-state band follows the one expected by the E ( 5 ) dynamical symmetry for a nucleus at the critical point of the shape phase transition from a spherical vibrator ( U ( 5 ) ) to a γ-soft rotor ( O ( 6 ) ). For the first time, in the same physical system, large scale shell-model calculations in the full fp shell are compared to the E ( 5 ) analytical model results and to the Interacting Boson Model. The theoretical results are in excellent agreement with the present data

Excited States in 52Fe and the Origin of the Yrast Trap at I=12+

Excited states in 52Fe have been determined up to spin 10\hbar in the reaction 28Si + 28Si at 115 MeV by using \gamma-ray spectroscopy methods at the GASP array. The excitation energy of the yrast 10+ state has been determined to be 7.381 MeV, almost 0.5 MeV above the well known \beta+-decaying yrast 12+ state, definitely confirming the nature of its isomeric character. The mean lifetimes of the states have been measured by using the Doppler Shift Attenuation method. The experimental data are compared with spherical shell model calculations in the full pf-shell.Comment: 9 pages, RevTeX, 7 figures include

Evolution of deformation in neutron-rich Ba isotopes up to A=150

The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N = 90. To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z = 56 isotopic chain accessible at present, Ba-148,Ba-150, has been studied via beta decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive-and negative-parity low-spin excited states of 150Ba and presents an extension of the beta-decay scheme of Cs-148. Employing the fast timing technique, half-lives for the 2(1)(+) level in both nuclei have been determined, resulting in T-1/2 = 1.51(1) ns for Ba-148 and T-1/2 = 3.4(2) ns for Ba-150. The systematics of low-spin states, together with the experimental determination of the B(E2 : 2(+) -> 0(+)) transition probabilities, indicate an increasing collectivity in Ba148-150, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.Peer reviewe

Normal and intruder configurations in Si- 34 populated in the beta(-) decay of Mg-34 and Al-34

The structure of Si-34 was studied through gamma spectroscopy separately in the beta(-) decays of Mg-34 and Al-34 at the ISOLDE facility of CERN. Different configurations in Si-34 were populated independently from the two recently identified beta-decaying states in Al-34 having spin-parity assignments J(pi) = 4(-) dominated by the normal configuration pi(d(5/2))(-1) circle times nu(f(7/2)) and J(pi) = 1(+) by the intruder configuration pi(d(5/2))(-1) circle times nu(d(3/2))(-1) (f(7/2))(2). The paper reports on spectroscopic properties of Si-34 such as an extended level scheme, spin and parity assignments based on log(ft) values and gamma-ray branching ratios, absolute beta feeding intensities, and neutron emission probabilities. A total of 11 newly identified levels and 26 transitions were added to the previously known level scheme of Si-34. Large scale shell-model calculations using the SDPF-U-MIX interaction, able to treat higher order intruder configurations, are compared with the new results and conclusions are drawn concerning the predictive power of SDPF-U-MIX, the N = 20 shell gap, the level of mixing between normal and intruder configurations for the 0(1)(+), 0(2)(+), and 2(1)(+) states, and the absence of triaxial deformation in Si-3(4).Peer reviewe