182 research outputs found
Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the -process calculations
The rare-earth peak in the -process abundance pattern depends sensitively
on both the astrophysical conditions and subtle changes in nuclear structure in
the region. This work takes an important step elucidating the nuclear structure
and reducing the uncertainties in -process calculations via precise atomic
mass measurements at the JYFLTRAP double Penning trap. Nd, Pm,
Sm, and Gd have been measured for the first time and the
precisions for Nd, Pm, Eu, Gd, and
Tb have been improved considerably. Nuclear structure has been probed
via two-neutron separation energies and neutron pairing energy metrics
. The data do not support the existence of a subshell closure at .
Neutron pairing has been found to be weaker than predicted by theoretical mass
models. The impact on the calculated -process abundances has been studied.
Substantial changes resulting in a smoother abundance distribution and a better
agreement with the solar -process abundances are observed.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
Letter
Recent Upgrades of the Gas Handling System for the Cryogenic Stopping Cell of the FRS Ion Catcher
In this paper, the major upgrades and technical improvements of the buffer
gas handling system for the cryogenic stopping cell of the FRS Ion Catcher at
GSI/FAIR (in Darmstadt, Germany) are described. The upgrades include
implementation of new gas lines and gas purifiers to achieve a higher buffer
gas cleanliness for a more efficient extraction of reactive ions as well as
suppression of the molecular background ionized in the stopping cell.
Furthermore, additional techniques have been implemented for improved
monitoring and quantification of the purity of the helium buffer gas
High-precision mass measurements and production of neutron-deficient isotopes using heavy-ion beams at IGISOL
An upgraded ion-guide system for the production of neutron-deficient isotopes with heavy-ion beams has been commissioned at the IGISOL facility with an Ar-36 beam on a Ni-nat target. It was used together with the JYFLTRAP double Penning trap to measure the masses of Zr-82, Nb-84, Mo-86, Tc-88, and Ru-89 ground states and the isomeric state Tc-88(m). Of these, Ru-89 and Tc-88(m) weremeasured for the first time. The precision of measurements of Zr-82, Nb-84, and Tc-88 was significantly improved. The literature value for Mo-86 was verified. The measured states in Tc-88 were compared to shell-model calculations and additional constraints on the spins and level scheme were obtained. The masses of Mo-82 and Ru-86 have been predicted using the measured masses of their mirror partners and theoretical mirror displacement energies, resulting in more tightly bound nuclei with smaller atomic mass uncertainties than reported in the literature.Peer reviewe
Mass measurements towards doubly magic Ni-78 : Hydrodynamics versus nuclear mass contribution in core-collapse supernovae
We report the first high-precision mass measurements of the neutron-rich nuclei Ni-74,Ni-75 and the clearly identified ground state of Cu-76, along with a more precise mass-excess value of Cu-78, performed with the double Penning trap JYFLTRAP at the Ion Guide Isotope Separator On-Line (IGISOL) facility. These new results lead to a quantitative estimation of the quenching for the N = 50 neutron shell gap. The impact of this shell quenching on core-collapse supernova dynamics is specifically tested using a dedicated statistical equilibrium approach that allows a variation of the mass model independent of the other microphysical inputs. We conclude that the impact of nuclear masses is strong when implemented using a fixed trajectory as in the previous studies, but the effect is substantially reduced when implemented self-consistently in the simulation. (C) 2022 The Authors. Published by Elsevier B.V.Peer reviewe
First evidence of multiple beta-delayed neutron emission for isotopes with A > 100
The beta-delayed neutron emission probability, P-n, of very neutron-rich nuclei allows us to achieve a better understanding of the nuclear structure above the neutron separation energy, S-n. The emission of neutrons can become the dominant decay process in neutron-rich astrophysical phenomena such as the rapid neutron capture process (r-process). There are around 600 accessible isotopes for which beta-delayed one-neutron emission (beta 1n) is energetically allowed, but the branching ratio has only been determined for about one third of them. beta 1n decays have been experimentally measured up to the mass A similar to 1 5 0, plus a single measurement of Tl-210. Concerning two-neutron emitters (beta 2n), similar to 3 0 0 isotopes are accessible and only 24 have been measured so far up to the mass A = 100. In this contribution, we report recent experiments which allowed the measurement of beta 1n emitters for masses beyond A > 200 and N > 1 2 6 and identified the heaviest beta 2n emitter measured so far, Sb-136.Peer reviewe
Measurement of the heaviest beta-delayed 2-neutron emitter : Sb-136
The beta-delayed neutron emission probability, P-n, of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes and astrophysical processes such as the rapid neutron capture process (r-process). In addition beta-delayed neutrons are important in a nuclear power reactor operated in a prompt sub-critical, delayed critical condition, as they contribute to the decay heat inducing fission reactions after a shut down. The study of neutron-rich isotopes and the measurement of beta-delayed one-neutron emitters (beta 1n) is possible thanks to the Rare Isotope Beam (RIB) facilities, where radioactive beams allow the production of exotic nuclei of interest, which can be studied and analyzed using specific detection systems. This contribution reports two recent measurements of beta-delayed neutron emitters which allowed the determination of half-lives and the neutron branching ratio of isotopes in the mass region above A = 200 and N > 126, and a second experiment which confirmed Sb-136 as the heaviest double neutron emitter (beta 2n) measured so far.The beta-delayed neutron emission probability, P-n, of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes and astrophysical processes such as the rapid neutron capture process (r-process). In addition beta-delayed neutrons are important in a nuclear power reactor operated in a prompt sub-critical, delayed critical condition, as they contribute to the decay heat inducing fission reactions after a shut down. The study of neutron-rich isotopes and the measurement of beta-delayed one-neutron emitters (beta 1n) is possible thanks to the Rare Isotope Beam (RIB) facilities, where radioactive beams allow the production of exotic nuclei of interest, which can be studied and analyzed using specific detection systems. This contribution reports two recent measurements of beta-delayed neutron emitters which allowed the determination of half-lives and the neutron branching ratio of isotopes in the mass region above A = 200 and N > 126, and a second experiment which confirmed Sb-136 as the heaviest double neutron emitter (beta 2n) measured so far.The beta-delayed neutron emission probability, P-n, of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes and astrophysical processes such as the rapid neutron capture process (r-process). In addition beta-delayed neutrons are important in a nuclear power reactor operated in a prompt sub-critical, delayed critical condition, as they contribute to the decay heat inducing fission reactions after a shut down. The study of neutron-rich isotopes and the measurement of beta-delayed one-neutron emitters (beta 1n) is possible thanks to the Rare Isotope Beam (RIB) facilities, where radioactive beams allow the production of exotic nuclei of interest, which can be studied and analyzed using specific detection systems. This contribution reports two recent measurements of beta-delayed neutron emitters which allowed the determination of half-lives and the neutron branching ratio of isotopes in the mass region above A = 200 and N > 126, and a second experiment which confirmed Sb-136 as the heaviest double neutron emitter (beta 2n) measured so far.Peer reviewe
The Functional DRD3 Ser9Gly Polymorphism (rs6280) Is Pleiotropic, Affecting Reward as Well as Movement
Abnormalities of motivation and behavior in the context of reward are a fundamental component of addiction and mood disorders. Here we test the effect of a functional missense mutation in the dopamine 3 receptor (DRD3) gene (ser9gly, rs6280) on reward-associated dopamine (DA) release in the striatum. Twenty-six healthy controls (HCs) and 10 unmedicated subjects with major depressive disorder (MDD) completed two positron emission tomography (PET) scans with [11C]raclopride using the bolus plus constant infusion method. On one occasion subjects completed a sensorimotor task (control condition) and on another occasion subjects completed a gambling task (reward condition). A linear regression analysis controlling for age, sex, diagnosis, and self-reported anhedonia indicated that during receipt of unpredictable monetary reward the glycine allele was associated with a greater reduction in D2/3 receptor binding (i.e., increased reward-related DA release) in the middle (anterior) caudate (p<0.01) and the ventral striatum (p<0.05). The possible functional effect of the ser9gly polymorphism on DA release is consistent with previous work demonstrating that the glycine allele yields D3 autoreceptors that have a higher affinity for DA and display more robust intracellular signaling. Preclinical evidence indicates that chronic stress and aversive stimulation induce activation of the DA system, raising the possibility that the glycine allele, by virtue of its facilitatory effect on striatal DA release, increases susceptibility to hyperdopaminergic responses that have previously been associated with stress, addiction, and psychosis
First investigation on the isomeric ratio in multinucleon transfer reactions: Entrance channel effects on the spin distribution
The multinucleon transfer (MNT) reaction approach was successfully employed
for the first time to measure the isomeric ratios (IRs) of Po
(25/2) isomer and its (9/2) ground state at the IGISOL facility using a
945 MeV Xe beam impinged on Bi and Pb targets. The
dominant production of isomers compared to the corresponding ground states was
consistently revealed in the -decay spectra. Deduced IR of Po
populated through the Xe+Pb reaction was found to enhance
1.8-times than observed for Xe+Bi. State-of-the-art
Langevin-type model calculations have been utilized to estimate the spin
distribution of an MNT residue. The computations qualitatively corroborate with
the considerable increase in IRs of Po produced from Xe+Pb compared to Xe+Bi. Theoretical investigations indicate
a weak influence of target spin on IRs. The enhancement of the Po
isomer in the Xe+Pb over Xe+Bi can be
attributed to the different proton ()-transfer production routes.
Estimations demonstrate an increment in the angular momentum transfer,
favorable for isomer production, with increasing projectile energy. Comparative
analysis indicates the two entrance channel parameters, projectile mass and
-transfer channels, strongly influencing the population of the high-spin
isomer of Po (25/2). This is the first experimental and theoretical
investigation on the IRs of nuclei produced via different channels of MNT
reactions, with the latter quantitatively underestimating the former by a
factor of two.Comment: 5 figure
Binding energies of ground and isomeric states in neutron-rich ruthenium isotopes: measurements at JYFLTRAP and comparison to theory
We report on precision mass measurements of Ru performed with
the JYFLTRAP double Penning trap mass spectrometer at the Accelerator
Laboratory of University of Jyv\"askyl\"a. The phase-imaging
ion-cyclotron-resonance technique was used to resolve the ground and isomeric
states in Ru and enabled for the first time a measurement of the
isomer excitation energies, Ru keV and
Ru keV. The ground state of Ru was measured
using the time-of-flight ion-cyclotron-resonance technique. The new mass-excess
value for Ru is around 36 keV lower and 7 times more precise than the
previous literature value. With the more precise ground-state mass values, the
evolution of the two-neutron separation energies is further constrained and a
similar trend as predicted by the BSkG1 model is obtained up to the neutron
number .Comment: 12 pages, 9 figures, submitted to Physical Review
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