Lifetime measurement in the mass region A~100 with the PreSPEC-AGATA setup

Mid-shell nuclei in the mass region A~100 show collective behavior. For instance, neutron rich even-even molybdenum isotopes are associated with a shape-phase transition. A spherical vibrator nucleus is observed for N=48 neutrons, while measurements indicate a deformed rotor nucleus for N=64 neutrons. In order to characterize the shape of molybdenum nuclei better, thus the shape-phase transition in molybdenum isotopes, a PreSPEC-AGATA experiment was performed at GSI. In particular, the experiment aimed at measuring the lifetime of the 4+ excited state of 108Mo to deduce the decay transition rate of the 4+ state. The production of 108Mo was performed in two steps. First, the GSI Fragment-Separator (FRS) selected 109Tc ions produced via fission of a 238U beam. Then, 109Tc ions underwent a fragmentation reaction on a beryllium secondary target. Half-speed of light fragments produced in this second reaction were identified by the Lund-York-Cologne CAlorimeter (LYCCA). gamma-rays were detected by the AGATA array positioned around the secondary target at forward angles. A complex electronics and data-acquisition system was set up to record the coincidences between a flying ion and the gamma-rays it emitted. The interaction position of gamma-rays inside an AGATA crystal is determined with good resolution. Therefore, combined with the large Doppler shift of the gamma-ray, it provides a unique possibility to measure lifetime with the Geometrical-Doppler-Shift-Attenuation method. From the data analysis which included several new techniques, the half-life of T1/2 = 11 (+16;-6) ps was extracted for the first 4+ state of 108Mo. The statistics recorded in this experiment is relatively low which leads to a large uncertainty on this measurement. With this large uncertainty, it is not possible to conclude on the exact behavior of the 108Mo nucleus, even though the comparison of our measurement with geometrical models would favor a transitional nucleus with approximate X(5) solution of the Bohr-Hamiltonian. However, this measurement proves the possibility of lifetime determination coupling relativistic ion beams with the AGATA array. Therefore, it represents a crucial step towards more precise measurements that will be performed at HISPEC with the increased beam intensity provided by the Super-FRS at FAIR

Preliminary results of lifetime measurements in neutron-rich 53Ti

To study the nuclear structure of neutron-rich titanium isotopes, a lifetime measurement was performed at the Grand Accélérateur National d'Ions Lourds (GANIL) facility in Caen, France. The nucleiwere produced in a multinucleon-transfer reaction by using a 6.76 MeV/u 238U beam. The Advanced Gamma Tracking Array (AGATA) was employed for the γ-ray detection and target-like recoils were identified event-by-event by the large-acceptance variable mode spectrometer (VAMOS++). Preliminary level lifetimes of the (5/2−) to 13/2− states of the yrast band in the neutron-rich nucleus 53Ti were measured for the first time employing the recoil distance Doppler-shift (RDDS) method and the compact plunger for deep inelastic reactions. The differential decay curve method (DDCM) was used to obtain the lifetimes from the RDDS data

Lifetime measurement in the mass region A~100 with the PreSPEC-AGATA setup

Mid-shell nuclei in the mass region A~100 show collective behavior. For instance, neutron rich even-even molybdenum isotopes are associated with a shape-phase transition. A spherical vibrator nucleus is observed for N=48 neutrons, while measurements indicate a deformed rotor nucleus for N=64 neutrons. In order to characterize the shape of molybdenum nuclei better, thus the shape-phase transition in molybdenum isotopes, a PreSPEC-AGATA experiment was performed at GSI. In particular, the experiment aimed at measuring the lifetime of the 4+ excited state of 108Mo to deduce the decay transition rate of the 4+ state. The production of 108Mo was performed in two steps. First, the GSI Fragment-Separator (FRS) selected 109Tc ions produced via fission of a 238U beam. Then, 109Tc ions underwent a fragmentation reaction on a beryllium secondary target. Half-speed of light fragments produced in this second reaction were identified by the Lund-York-Cologne CAlorimeter (LYCCA). gamma-rays were detected by the AGATA array positioned around the secondary target at forward angles. A complex electronics and data-acquisition system was set up to record the coincidences between a flying ion and the gamma-rays it emitted. The interaction position of gamma-rays inside an AGATA crystal is determined with good resolution. Therefore, combined with the large Doppler shift of the gamma-ray, it provides a unique possibility to measure lifetime with the Geometrical-Doppler-Shift-Attenuation method. From the data analysis which included several new techniques, the half-life of T1/2 = 11 (+16;-6) ps was extracted for the first 4+ state of 108Mo. The statistics recorded in this experiment is relatively low which leads to a large uncertainty on this measurement. With this large uncertainty, it is not possible to conclude on the exact behavior of the 108Mo nucleus, even though the comparison of our measurement with geometrical models would favor a transitional nucleus with approximate X(5) solution of the Bohr-Hamiltonian. However, this measurement proves the possibility of lifetime determination coupling relativistic ion beams with the AGATA array. Therefore, it represents a crucial step towards more precise measurements that will be performed at HISPEC with the increased beam intensity provided by the Super-FRS at FAIR

Preliminary results of lifetime measurements in neutron-rich 53Ti

To study the nuclear structure of neutron-rich titanium isotopes, a lifetime measurement was performed at the Grand Accélérateur National d'Ions Lourds (GANIL) facility in Caen, France. The nucleiwere produced in a multinucleon-transfer reaction by using a 6.76 MeV/u 238U beam. The Advanced Gamma Tracking Array (AGATA) was employed for the γ-ray detection and target-like recoils were identified event-by-event by the large-acceptance variable mode spectrometer (VAMOS++). Preliminary level lifetimes of the (5/2−) to 13/2− states of the yrast band in the neutron-rich nucleus 53Ti were measured for the first time employing the recoil distance Doppler-shift (RDDS) method and the compact plunger for deep inelastic reactions. The differential decay curve method (DDCM) was used to obtain the lifetimes from the RDDS data

Magnetic Moment of the Isomeric State of 75^{75}Cu Measured with a Highly Spin-aligned Beam

International audienceThe magnetic moment of the isomeric state of the neutron-rich ^75Cu nucleus was measured using a highly spin-aligned beam produced via a two-step reaction scheme. In the experiment carried out at the BigRIPS at RIBF, we achieved to produce spin alignment reaching 30% by employing the one-proton removal from ^76Zn to produce ^75Cu. In the magnetic moment measurement, a method of time-differential perturbed angular distribution (TDPAD) was employed. Precession of the isomeric state with spin parity of 3/2^− was clearly observed with significance larger than 5σ in the TDPAD spectrum. The magnetic moment of the isomeric state of ^75Cu was determined to be μ = 1.40(6)μ_N