A modern variation of the Rutherford experiment to probe the tunneling of exotic nuclear matter from the measurement of the residues formed in the bombardment of (197)Au by extremely neutron-rich ...(8)He nuclei is presented. Using a novel off-beam technique the most precise and accurate measurements of fusion and neutron transfer involving reaccelerated unstable beams are reported. The results show unusual behavior of the tunneling of (8)He compared to that for lighter helium isotopes, highlighting the role of the intrinsic structure of composite many-body quantum systems and pairing correlations.
The Graph Model for Conflict Resolution (GMCR) is a flexible model and has been widely used for describing and analyzing conflicts. Stability analysis is used in the GMCR to determine possible ...solutions for the conflict. Several solution concepts have been proposed which accommodate different decision makers’ (DMs) behavior. Some of them are: Nash, General Metarationality (GMR) and Sequential Stability (SEQ). For a state to be Nash stable for a DM, such DM cannot move to a more preferred state in a single step. For GMR and SEQ, while considering moving to a more preferred state, the DM foresees whether the opponent can react leading the conflict to a state not preferred to the current one. What differs GMR and SEQ is that, in SEQ the opponent’s move simultaneously sanctions the focal DM and benefits the opponent. We show, by means of an example, that there are situations in which the opponent’s reaction is implausible in the sense that it involves the opponent leaving an SEQ stable state for him. In order to avoid that problem, we propose new solution concepts for the GMCR, called Higher-order Sequential Stabilities, and explore their relation with other solution concepts commonly used in the GMCR.
Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge ...of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus (92)Pd. Gamma rays emitted following the (58)Ni((36)Ar,2n)(92)Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Conceptual design of the AGATA 1π array at GANIL Clément, E.; Michelagnoli, C.; de France, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2017, Letnik:
855
Journal Article
Recenzirano
Odprti dostop
The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This set-up exploits the stable and radioactive heavy-ions beams delivered by the cyclotron ...accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam γ-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy γ rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA 1π array are presented.
Abstract
Eight EXOGAM-type, Ge-clover detectors of the EXILL array,
arranged on an octagon plan and acting as Compton polarimeters, were
used to measure directional-polarization correlations of
γ
...rays populated in various processes. Measurements of
γ
radiation following neutron-induced fission of
235
U and
241
Pu targets;
β
-
-decay following fission; (n,
γ
)
reactions on various stable targets and measurements using
radioactive sources of
60
Co,
133
Ba and
152
Eu were
performed at the PF1B cold-neutron facility of the Institut
Laue-Langevin in Grenoble. Digital electronics and a trigger-less
acquisition system allowed the collection of signals from Ge
detectors down to about 20 keV, providing measurements of linear
polarization down to 120 keV. The precise sensitivity
calibration was determined for the set of eight EXILL clover
polarimeters in a range from 100 keV to 10000 keV. A new formula
for calculating the directional-polarization correlations for the
upper transition in a
γγ
cascade is derived from first
principles. Directional-polarization correlations were measured for
a few dozens of transitions in a number of nuclei, including values
for twenty transitions in the
152
Sm nucleus measured for the
first time, and compared against the calculated values, to
illustrate the quality of the technique. The combined analysis of
angular and directional-polarization correlations is presented,
which helps the determination of spin-parity assignments to excited
levels.
Multi-nucleon transfer reaction between 136Xe beam and 198Pt target was performed using the VAMOS++ spectrometer at GANIL to study the structure of n-rich nuclei around N=126. Unambiguous charge ...state identification was obtained by combining two supervised machine learning methods, deep neural network (DNN) and positional correction using a gradient-boosting decision tree (GBDT). The new method reduced the complexity of the kinetic energy calibration and outperformed the conventional method improving the charge state resolution by 8%.
Measurements of prompt γ rays in coincidence with isotopically-identified fission fragments, produced in collisions of 238U on a 9Be target, at an energy around the Coulomb barrier are reported. This ...technique provides simultaneous access to the spectroscopy of many nuclei, extending to very neutron-rich isotopes and fairly high angular momenta. The structural evolution of the neutron-rich zirconium isotopes is discussed in the light of the present measurements in Zr105,106 and in the context of the interacting boson model with a global parameterization that includes triaxiality but no shape coexistence.
A study of the dimensions and performance of a single detector of the future neutron detector array NEDA was performed by means of Monte Carlo simulations, using GEANT4. Two different liquid ...scintillators were evaluated: the hydrogen based BC501A and the deuterated BC537. The efficiency and the probability that one neutron will trigger a signal in more than one detector were investigated as a function of the detector size. The simulations were validated comparing the results to experimental measurements performed with two existing neutron detectors, with different geometries, based on the liquid scintillator BC501.
The multi-nucleon transfer reaction between 136Xe beam and 198Pt target at the beam energy 7 MeV/u was studied using the large acceptance spectrometer VAMOS++ coupled with the newly installed second ...arm time-of-flight and delayed γ-ray spectrometer CATLIFE (Complementary Arm for Target LIke FragmEnts). The CATLIFE detector is composed of a large area multi-wire proportional chamber and the EXOGAM HPGe clover detectors with an ion flight length of 1230 mm. Direct measurement of the target-like fragments (TLF) and the delayed γ-rays from the isomeric state helps to improve TLF identification. The use of the velocity of TLFs and the delayed γ-ray demonstrate the proof of principle and effectiveness of the new setup.
The proton-rich isotope 68Br was discovered in secondary fragmentation reactions of fast radioactive beams. Proton-rich secondary beams of 70,71,72Kr and 70Br, produced at the RIKEN Nishina Center ...and identified by the BigRIPS fragment separator, impinged on a secondary 9Be target. Unambiguous particle identification behind the secondary target was achieved with the ZeroDegree spectrometer. Based on the expected direct production cross sections from neighboring isotopes, the lifetime of the ground or long-lived isomeric state of 68Br was estimated. The results suggest that secondary fragmentation reactions, where relatively few nucleons are removed from the projectile, offer an alternative way to search for new isotopes, as these reactions populate preferentially low-lying states.
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