95 research outputs found
Isospin dependence of mass-distribution shape of fission fragments of Hg isotopes
Using an improved scission-point model, the mass distributions are calculated for induced fission of even Hg isotopes with mass numbers A=174 to 196. With increasing A of a fissioning AHg nucleus the mass distribution evolves from symmetric for 174Hg, to asymmetric for isotopes close to 180Hg, and back to more symmetric for 192,194,196Hg. In the fissioning Hg isotopes their excitation energy weakly influences the shape of the mass distribution. In 180,184Hg, the mass distributions of fission fragments remain asymmetric even at high excitation energies
Muon Bremsstrahlung and Muonic Pair Production in Air Showers
The objective of this work is to report on the modifications in air shower
development due to muon bremsstrahlung and muonic pair production. In order to
do that we have implemented new muon bremsstrahlung and muonic pair production
procedures in the AIRES air shower simulation system, and have used it to
simulate ultra high energy showers in different conditions.
The influence of the mentioned processes in the global development of the air
shower is important for primary particles of large zenith angles, while they do
not introduce significant changes in the position of the shower maximum.Comment: To be presented at the International Symposium on Very High Energy
Cosmic Ray Interactions X
Colloquium: Beta delayed fission of atomic nuclei
This Colloquium reviews the studies of exotic type of low-energy nuclear fission, the beta-delayed fission (bDF). Emphasis is made on the new data from very neutron-deficient nuclei in the lead region, previously scarcely studied as far as fission is concerned. These data establish the new region of asymmetric fission in addition to the previously known one in the transuranium nuclei. New production and identification techniques, which emerged in the last two decades, such as the wider use of electromagnetic separators and the application of selective laser ionization to produce intense isotopically or even isomerically pure radioactive beams are highlighted. A critical analysis of presently available DF data is presented and the importance of detailed quantitative DF studies, which become possible now, is stressed, along with the recent theory efforts in the domain of low-energy fission
Shapes of the Pb ground states from beta decay studies using the total absorption technique
The beta decay of Pb has been studied using the total absorption
technique at the ISOLDE(CERN) facility. The beta-decay strength deduced from
the measurements, combined with QRPA theoretical calculations, allow us to
infer that the ground states of the Pb isotopes are spherical.
These results represent the first application of the shape determination method
using the total absorption technique for heavy nuclei and in a region where
there is considerable interest in nuclear shapes and shape effects
Fission fragments mass distributions of nuclei populated by the multinucleon transfer channels of the 18O + 232Th reaction
It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the 18OÂ +Â 232Th reaction are used to study fission of fourteen nuclei 231,232,233,234Th, 232,233,234,235,236Pa, and 234,235,236,237,238U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of 231,234Th and 234,235,236Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuationâdissipation model
Shape Coexistence in the Relativistic Hartree-Bogoliubov approach
The phenomenon of shape coexistence is studied in the Relativistic
Hartree-Bogoliubov framework. Standard relativistic mean-field effective
interactions do not reproduce the ground state properties of neutron-deficient
Pt-Hg-Pb isotopes. It is shown that, in order to consistently describe binding
energies, radii and ground state deformations of these nuclei, effective
interactions have to be constructed which take into account the sizes of
spherical shell gaps.Comment: 19 pages, 8 figures, accepted in Phys. Rev.
Octupole states in 207TI studied through ÎČ decay
The ÎČ decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through Îł -ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the Ïs â1 1/2, Ïdâ1 3/2, and Ïhâ1 11/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with state-of-the-art large-scale shell model calculations and previous observations made in this region, and systematic underestimation of the energy of the octupole vibrational states is noted. We suggest that in order to resolve the difference in predicted energies for collective and noncollective t = 1 states (t is the number of nucleons breaking the 208Pb core), the effect of t = 2 mixing may be reduced for octupole-coupled states. The inclusion of mixing with t = 0, 2, 3 excitations is necessary to replicate all t = 1 state energies accurately.The research leading to these results has received funding
from the European Unionâs Horizon 2020 Research and Innovation Programme under Grant Agreement No. 654002. Support from the European Union Seventh Framework through
ENSAR Contract No. 262010, the Science and Technology Facilities Council (UK), the MINECO Projects No.
FPA2015-64969-P and No. FPA2017-87568-P (Spain), FWO Vlaanderen (Belgium), GOA/2015/010 (BOF KU Leuven),
the Excellence of Science Programme (EOS-FWO), the Interuniversity Attraction Poles Programme initiated by the
Belgian Science Policy Office (BriX network P7/12), the
German BMBF under Contract No. 05P18PKCIA + âVerbundprojekt 05P2018,â the Polish National Science Centre
under Contracts No. UMO-2015/18/M/ST2/00523 and No.
UMO-2019/33/N/ST2/03023, the National Science Foundation (US) Grant No. PHY-1811855 and the Romanian
IFA project CERN-RO/ISOLDE is acknowledged. P.H.R. and
S.M.J. acknowledge support from the UK Department for
Business, Energy and Industrial Strategy via the National
Measurement Office
Population of a low-spin positive-parity band from high-spin intruder states in 177Au : The two-state mixing effect
The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state
Beta decay of the axially asymmetric ground state of 192Re
The ÎČ decay of 75192Re117, which lies near the boundary between the regions of predicted prolate and oblate deformations, has been investigated using the KEK Isotope Separation System (KISS) in RIKEN Nishina Center. This is the first case in which a low-energy beam of rhenium isotope has been successfully extracted from an argon gas-stopping cell using a laser-ionization technique, following production via multi-nucleon transfer between heavy ions. The ground state of 192Re has been assigned JÏ=(0â) based on the observed ÎČ feedings and deduced logft values towards the 0+ and 2+ states in 192Os, which is known as a typical Îł-soft nucleus. The shape transition from axial symmetry to axial asymmetry in the Re isotopes is discussed from the viewpoint of single-particle structure using the nuclear Skyrme-Hartree-Fock model
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