Lifetime measurements in the neutron-rich 148Ce nuclide at the low-Z boundary of the N=90 shape-phase transition

A quantum shape phase transition (QSPT) in atomic nuclei is characterized by a sudden change of the shape of the nucleus due to changes in the location of the nuclear potential minimum. A first-order QSPT exists in the transition from spherical shapes to the axially symmetric deformed shapes. There are models describing even-even nuclei in terms of their shape and their oscillations and rotations symmetries, such us the U(5) symmetry (for spherical shapes - vibrator) and SU(3) symmetry (for axially symmetric deformed shapes - rotor). Along the QSPT the spherical minimum, corresponding to a spherical shape, starts vanishing and the deformed one, corresponding to a deformed shape, appears. While the nuclear potentials of a vibrator and a symmetric rotor have one minimum, the potential of a nucleus near the critical point (CP) of the first-order QSPT between them presents the two competing minima. The X(5) model provides some signatures of the isotopes at the CP. A first-order QSPT is known in the even-even N=90 isotones with Z=60−66. With Z=58, 148Ce lies in the low-Z boundary of this transition from spherical to axially symmetric deformed shapes. This nucleus is studied in this work. Key observables revealing the nuclear shape, such as the energy ratio R4/2=E(4+1)/E(2+1) and the transition strength ratio B4/2=B(E2;4+1→2+1)/B(E2;2+1→0+1), are compared with the predictions from models describing nuclei along this transition and specially near the CP. The experimental analysis to obtain the lifetimes of the first 2+ and first 4+ states of 148Ce using fast-timing techniques is shown in this work. The data were taken within the EXILL&FATIMA campaign performed at the high-flux reactor of the Institut Laue-Langevin in Grenoble, where fission fragments of 235U and 241Pu were measured by a hybrid spectrometer, consisting of high-resolution germanium and fast-responding lanthanum bromide scintillator detectors. The measurement of the lifetime of the first 4 + state of 148 Ce allows the calculation of the B4/2 observable and contributes in the study of the shape of the nucleus. Beside the comparison with the models, the whole N ≈ 90 region is being investigated within the interacting boson model. The shape evolution of the cerium, the neodymium and the samarium chains is studied and shows the importance of the increasing axially asymmetry

A Comprehensive Characterization of the Neutron Fields Produced by the Apollon Petawatt Laser

International audienceSince two decades, laser-driven neutron emissions are studied as they represent a complementary source to conventional neutron sources, with further more different characteristics (i.e. shorter bunch duration and higher number of neutrons per bunch). We report here a global, thorough characterization of the neutron fields produced at the Apollon laser facility using the secondary laser beam (F2). A Double Plasma Mirror (DPM) was used to improve the temporal contrast of the laser which delivers pulses of 24 fs duration, a mean on-target energy of ~10 J and up to 1 shot/min. The interaction of the laser with thin targets (few tens or hundreds of nm) in ultra-high conditions produced enhanced proton beams (up to 35 MeV), which were then used to generate neutrons via the pitcher-catcher technique. The characterization of these neutron emissions is presented, with results obtained from both simulations and measurements using several diagnostics (activation samples, bubble detectors and Time-of-Flight detectors), leading to a neutron yield of ~4.10^7 neutrons/shot. Similar neutron emissions were observed during shots with and without DPM, while fewer X-rays are produced when the DPM is used, making this tool interesting to adjust the neutrons/X-rays ratio for some applications like combined neutron/X-ray radiography

A Comprehensive Characterization of the Neutron Fields Produced by the Apollon Petawatt Laser

International audienceSince two decades, laser-driven neutron emissions are studied as they represent a complementary source to conventional neutron sources, with further more different characteristics (i.e. shorter bunch duration and higher number of neutrons per bunch). We report here a global, thorough characterization of the neutron fields produced at the Apollon laser facility using the secondary laser beam (F2). A Double Plasma Mirror (DPM) was used to improve the temporal contrast of the laser which delivers pulses of 24 fs duration, a mean on-target energy of ~10 J and up to 1 shot/min. The interaction of the laser with thin targets (few tens or hundreds of nm) in ultra-high conditions produced enhanced proton beams (up to 35 MeV), which were then used to generate neutrons via the pitcher-catcher technique. The characterization of these neutron emissions is presented, with results obtained from both simulations and measurements using several diagnostics (activation samples, bubble detectors and Time-of-Flight detectors), leading to a neutron yield of ~4.10^7 neutrons/shot. Similar neutron emissions were observed during shots with and without DPM, while fewer X-rays are produced when the DPM is used, making this tool interesting to adjust the neutrons/X-rays ratio for some applications like combined neutron/X-ray radiography

A Comprehensive Characterization of the Neutron Fields Produced by the Apollon Petawatt Laser

International audienceSince two decades, laser-driven neutron emissions are studied as they represent a complementary source to conventional neutron sources, with further more different characteristics (i.e. shorter bunch duration and higher number of neutrons per bunch). We report here a global, thorough characterization of the neutron fields produced at the Apollon laser facility using the secondary laser beam (F2). A Double Plasma Mirror (DPM) was used to improve the temporal contrast of the laser which delivers pulses of 24 fs duration, a mean on-target energy of ~10 J and up to 1 shot/min. The interaction of the laser with thin targets (few tens or hundreds of nm) in ultra-high conditions produced enhanced proton beams (up to 35 MeV), which were then used to generate neutrons via the pitcher-catcher technique. The characterization of these neutron emissions is presented, with results obtained from both simulations and measurements using several diagnostics (activation samples, bubble detectors and Time-of-Flight detectors), leading to a neutron yield of ~4.10^7 neutrons/shot. Similar neutron emissions were observed during shots with and without DPM, while fewer X-rays are produced when the DPM is used, making this tool interesting to adjust the neutrons/X-rays ratio for some applications like combined neutron/X-ray radiography

A Comprehensive Characterization of the Neutron Fields Produced by the Apollon Petawatt Laser

International audienceSince two decades, laser-driven neutron emissions are studied as they represent a complementary source to conventional neutron sources, with further more different characteristics (i.e. shorter bunch duration and higher number of neutrons per bunch). We report here a global, thorough characterization of the neutron fields produced at the Apollon laser facility using the secondary laser beam (F2). A Double Plasma Mirror (DPM) was used to improve the temporal contrast of the laser which delivers pulses of 24 fs duration, a mean on-target energy of ~10 J and up to 1 shot/min. The interaction of the laser with thin targets (few tens or hundreds of nm) in ultra-high conditions produced enhanced proton beams (up to 35 MeV), which were then used to generate neutrons via the pitcher-catcher technique. The characterization of these neutron emissions is presented, with results obtained from both simulations and measurements using several diagnostics (activation samples, bubble detectors and Time-of-Flight detectors), leading to a neutron yield of ~4.10^7 neutrons/shot. Similar neutron emissions were observed during shots with and without DPM, while fewer X-rays are produced when the DPM is used, making this tool interesting to adjust the neutrons/X-rays ratio for some applications like combined neutron/X-ray radiography

A Comprehensive Characterization of the Neutron Fields Produced by the Apollon Petawatt Laser

International audienceSince two decades, laser-driven neutron emissions are studied as they represent a complementary source to conventional neutron sources, with further more different characteristics (i.e. shorter bunch duration and higher number of neutrons per bunch). We report here a global, thorough characterization of the neutron fields produced at the Apollon laser facility using the secondary laser beam (F2). A Double Plasma Mirror (DPM) was used to improve the temporal contrast of the laser which delivers pulses of 24 fs duration, a mean on-target energy of ~10 J and up to 1 shot/min. The interaction of the laser with thin targets (few tens or hundreds of nm) in ultra-high conditions produced enhanced proton beams (up to 35 MeV), which were then used to generate neutrons via the pitcher-catcher technique. The characterization of these neutron emissions is presented, with results obtained from both simulations and measurements using several diagnostics (activation samples, bubble detectors and Time-of-Flight detectors), leading to a neutron yield of ~4.10^7 neutrons/shot. Similar neutron emissions were observed during shots with and without DPM, while fewer X-rays are produced when the DPM is used, making this tool interesting to adjust the neutrons/X-rays ratio for some applications like combined neutron/X-ray radiography

Multi-quasiparticle sub-nanosecond isomers in 178W^{178}W

We report on the first measurement of the half-lives of Kπ=11− and 12+ four-quasiparticle states in the even-even nucleus 178 W. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr 3 (Ce) scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became experimentally accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array. The measured half-lives are 476(44)ps and 275(65)ps for the Iπ=11− and 12+ states, respectively. The decay transitions include weakly hindered E 1 and E 2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E 1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band

Spectroscopy of neutron-rich scandium isotopes

Within the SEASTAR III campaign at the Radioactive Isotope Beam Factory, at the RIKEN Nishina Center, neutron-rich isotopes in the vicinity of 53K were produced from the fragmentation of the primary 70Zn beam on a 9Be target. After nucleon knockout reactions on the secondary liquid hydrogen MINOS target the known γ rays of the neutron-rich 55Sc isotope were observed (shown in this proceedings) and γ rays from 57,59Sc isotopes have been identified for the first time. The evolution of the occupied nucleon orbitals of these nuclei in the ground and excited state is investigated under the prism of the tensor force