0000000000216915
AUTHOR
A. Goasduff
Shape coexistence in neutron-deficient Hg188 investigated via lifetime measurements
Background: Shape coexistence in the Z≈82 region has been established in mercury, lead, and polonium isotopes. For even-even mercury isotopes with 100≤N≤106 multiple fingerprints of this phenomenon are observed, which seems to be no longer present for N≥110. According to a number of theoretical calculations, shape coexistence is predicted in the Hg188 isotope. Purpose: The aim of this work was to measure lifetimes of excited states in Hg188 to infer their collective properties, such as the deformation. Extending the investigation to higher-spin states, which are expected to be less affected by band-mixing effects, can provide additional information on the coexisting structures. Methods: The…
The GALILEO γ-ray array at the Legnaro National Laboratories
Abstract GALILEO, a new 4 π high-resolution γ -detection array, based on HPGe detectors, has been developed and installed at the Legnaro National Laboratories. The GALILEO array greatly benefits from a fully-digital read-out chain, customized DAQ, and a variety of complementary detectors to improve the resolving power by the detection of particles, ions or high-energy γ -ray transitions. In this work, a full description of the array, including electronics and DAQ, is presented together with its complementary instrumentation.
Neutron detection and γ-ray suppression using artificial neural networks with the liquid scintillators BC-501A and BC-537
Abstract In this work we present a comparison between the two liquid scintillators BC-501A and BC-537 in terms of their performance regarding the pulse-shape discrimination between neutrons and γ rays. Special emphasis is put on the application of artificial neural networks . The results show a systematically higher γ -ray rejection ratio for BC-501A compared to BC-537 applying the commonly used charge comparison method. Using the artificial neural network approach the discrimination quality was improved to more than 95% rejection efficiency of γ rays over the energy range 150 to 1000 keV for both BC-501A and BC-537. However, due to the larger light output of BC-501A compared to BC-537, neu…
Multinucleon transfer reactions and proton transfer channels
Transfer reactions have always been of great importance for nuclear structure and reaction mechanism studies. So far, in multinucleon transfer studies, proton pickup channels have been completely identified in atomic and mass numbers at energies close to the Coulomb barrier only in few cases. We measured the multinucleon transfer reactions in the 40Ar+208Pb system near the Coulomb barrier, by employing the PRISMA magnetic spectrometer. By using the most neutron-rich stable 40Ar beam we could populate, besidesneutron pickup and proton stripping channels, also neutron stripping and proton pickup channels. Comparison ofcross sections between different systems with the 208Pb target and with pro…
Evidence of octupole-phonons at high spin in 207Pb
A lifetime measurement of the 19/2 state in Pb has been performed using the Recoil Distance Doppler-Shift (RDDS) method. The nuclei of interest were produced in multi-nucleon transfer reactions induced by a Pb beam impinging on a Mo enriched target. The beam-like nuclei were detected and identified in terms of their atomic mass number in the VAMOS++ spectrometer while the prompt γ rays were detected by the AGATA tracking array. The measured large reduced transition probability B(E3,19/2→13/2)=40(8) W.u. is the first indication of the octupole phonon at high spin in Pb. An analysis in terms of a particle-octupole-vibration coupling model indicates that the measured B(E3) value in Pb is compa…
Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors
WOS: 000433206800010 The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and.. standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigate…
Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in 106,108Sn
The lifetimes of the low-lying excited states 2(+) and 4(+) have been directly measured in the neutron-deficient Sn-106,Sn-108 isotopes. the nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. the emitted gamma rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2; 2(1)(+) -> 0(g.s)(+)) values and it describes well the experimental pattern for Sn104-114 ; the B…
Performance of the Advanced GAmma Tracking Array at GANIL
The performance of the Advanced GAmma Tracking Array (AGATA) at GANIL is discussed, on the basis of the analysis of source and in-beam data taken with up to 30 segmented crystals. Data processing is described in detail. The performance of individual detectors are shown. The efficiency of the individual detectors as well as the efficiency after $\gamma$-ray tracking are discussed. Recent developments of $\gamma$-ray tracking are also presented. The experimentally achieved peak-to-total is compared with simulations showing the impact of back-scattered $\gamma$ rays on the peak-to-total in a $\gamma$-ray tracking array. An estimate of the achieved position resolution using the Doppler broadeni…
Transfer reactions in 206Pb+118Sn: From quasielastic to deep-inelastic processes
We measured multinucleon transfer reactions for the 206Pb+118Sn system at Elab=1200 MeV by employing the large solid angle magnetic spectrometer PRISMA. Differential and total cross sections and Q-value distributions have been obtained for a variety of neutron and proton pick-up and stripping channels. The Q-value distributions show how the quasielastic and deep inelastic processes depend on the mass and charge of the transfer products. The corresponding cross sections have been compared with calculations performed with the grazing code. An overall good agreement is found for most of the few nucleon transfer channels. The underestimation of the data for channels involving a large number of …
First trap-assisted decay spectroscopy of the $$^{81}$$Ge ground state
AbstractThe $$\beta $$ β -delayed $$\gamma $$ γ spectroscopy of $$^{81}$$ 81 As has been performed using a purified beam of $$^{81}$$ 81 Ge $$(9/2^+)$$ ( 9 / 2 + ) ground state at the Ion Guide Isotope Separator On-Line facility (IGISOL). The $$^{81}$$ 81 Ge$$^+$$ + ions were produced using proton-induced fission of $$^{232}$$ 232 Th and selected with the double Penning trap JYFLTRAP for the post-trap decay spectroscopy measurements. The low-spin $$(1/2^+)$$ ( 1 / 2 + ) isomeric-state ions $$^{81m}\hbox {Ge}^+$$ 81 m Ge + were not observed in the fission products. The intrinsic half-life of the $$^{81}$$ 81 Ge ground state has been determined as $$T_{1/2}=6.4(2)~\hbox {s}$$ T 1 / 2 = 6.4 ( …
Population of lead isotopes in binary reactions using a Rb 94 radioactive beam
8 pags., 9 figs.
Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni78 Region: A Hint from Lifetime Measurements
Lifetime measurements of excited states of the light N = 52 isotones 88 Kr , 86 Se , and 84 Ge have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B ( E 2 ; 2 + → 0 + ) and B ( E 2 ; 4 + → 2 + ) were obtained for the first time for the hard-to-reach 84 Ge . While the B ( E 2 ; 2 + → 0 + ) values of 88 Kr , 86 Se saturate the maximum quadrupole collectivity offered by the natural valence ( 3 s , 2 d , 1 g 7 / 2 , 1 h 11 / 2 ) space of an inert 78 Ni core, the value obtained for 84 Ge largely exceeds it, suggesting that sh…