Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the ...initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.
Charge-exchange (d,2He) reactions in inverse kinematics at intermediate energies are a very promising method to investigate the Gamow–Teller transition strength in unstable nuclei. A simulation and ...analysis software based on the attpcroot package was developed to study this type of reactions with the active-target time projection chamber (AT-TPC). The simulation routines provide a realistic detector response that can be used to understand and benchmark experimental data. Analysis tools and correction routines can be developed and tested from simulations in attpcroot, because they are processed in the same way as the real data. In particular, we study the feasibility of using coincidences with beam-like particles to unambiguously identify the (d,2He) reaction channel, and to develop a kinematic fitting routine for future applications. More technically, the impact of space-charge effects in the track reconstruction, and a possible correction method are investigated in detail. This analysis and simulation package constitutes an essential part of the software development for the fast-beams program with the AT-TPC.
The discrepancy between observations from γ-ray astronomy of the 60Fe/26Al γ-ray flux ratio and recent calculations is an unresolved puzzle in nuclear astrophysics. The stellar β-decay rate of 59Fe ...is one of the major nuclear uncertainties impeding us from a precise prediction. The important Gamow-Teller strengths from the low-lying states in 59Fe to the 59Co ground state are measured for the first time using the exclusive measurement of the 59Co(t,3He+γ)59Fe charge-exchange reaction. The new stellar decay rate of 59Fe is a factor of 3.5±1.1 larger than the currently adopted rate at T=1.2 GK. Stellar evolution calculations show that the 60Fe production yield of an 18 solar mass star is decreased significantly by 40% when using the new rate. Our result eliminates one of the major nuclear uncertainties in the predicted yield of 60Fe and alleviates the existing discrepancy of the 60Fe/26Al ratio.
A comparative study of the nuclear Gamow–Teller response (GTR) within conceptually different state-of-the-art approaches is presented. Three nuclear microscopic models are considered: (i) the ...recently developed charge-exchange relativistic time blocking approximation (RTBA) based on the covariant density functional theory, (ii) the shell model (SM) with an extended “jj77” model space and (iii) the non-relativistic quasiparticle random-phase approximation (QRPA) with a Brueckner G-matrix effective interaction. We study the physics cases where two or all three of these models can be applied. The Gamow–Teller response functions are calculated for 208Pb, 132Sn and 78Ni within both RTBA and QRPA. The strengths obtained for 208Pb are compared to data that enable a firm model benchmarking. For the nucleus 132Sn, also SM calculations are performed within the model space truncated at the level of a particle–hole (ph) coupled to vibration configurations. This allows a consistent comparison to the RTBA where ph⊗phonon coupling is responsible for the spreading width and considerable quenching of the GTR. Differences between the models and perspectives of their future developments are discussed.
Design of the High Rigidity Spectrometer at FRIB Noji, S.; Zegers, R.G.T.; Berg, G.P.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2023, Letnik:
1045
Journal Article
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A High Rigidity Spectrometer (HRS) has been designed for experiments at the Facility for Rare-Isotope Beams (FRIB) at Michigan State University (MSU). The HRS will allow experiments to be performed ...with the most exotic neutron-rich isotopes at high beam energies (≳100MeV/u). The HRS consists of an analysis beamline called the High-Transmission Beamline (HTBL) and the spectrometer proper called the Spectrometer Section. The maximum magnetic rigidity of the HRS is 8Tm, which corresponds to the rigidities at which rare-isotope beams are optimally produced at FRIB. The resolving power, angular acceptance, and momentum acceptance are set to match the anticipated scientific program. An ion-optical design developed for the HRS is described in detail, along with the specifications of the associated magnet and detector systems.
The Active Target Time Projection Chamber (AT-TPC) project at the National Superconducting Cyclotron Laboratory (NSCL) is a novel Active Target designed to study nuclear reactions induced by ...low-intensity exotic beams. The AT-TPC acts as a tracking medium and target at the same time, providing excellent angular (1°) and energy resolution (3% FWHM) and high luminosity. The AT-TPC offers a broad range of applications within the low-energy nuclear physics domain. Resonant scattering and transfer reactions are typically performed with Active Targets using beams with energies spanning from 1 to 10AMeV and with intensities as low as 100 pps. The AT-TPC is also a promising tool for experiments where the observables of interest require higher beam energies (above 100AMeV). In particular, inelastic scattering reactions on light targets, where the recoil particle has a very low kinetic energy (less than 1 MeV), can be performed with such a device. In this work, we discuss aspects of the AT-TPC experimental program, focusing on experiments that leverage the outstanding capabilities this detector offers. In addition, we introduce a conceptual design for a new Time Projection Chamber detector for specific measurements of reactions using special gases as targets.
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