Energy acceptance of the St. George recoil separator Meisel, Z.; Moran, M.T.; Gilardy, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2017, Letnik:
850
Journal Article
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Radiative alpha-capture, (α,γ), reactions play a critical role in nucleosynthesis and nuclear energy generation in a variety of astrophysical environments. The St. George recoil separator at the ...University of Notre Dame's Nuclear Science Laboratory was developed to measure (α,γ) reactions in inverse kinematics via recoil detection in order to obtain nuclear reaction cross sections at the low energies of astrophysical interest, while avoiding the γ-background that plagues traditional measurement techniques. Due to the γ ray produced by the nuclear reaction at the target location, recoil nuclei are produced with a variety of energies and angles, all of which must be accepted by St. George in order to accurately determine the reaction cross section. We demonstrate the energy acceptance of the St. George recoil separator using primary beams of helium, hydrogen, neon, and oxygen, spanning the magnetic and electric rigidity phase space populated by recoils of anticipated (α,γ) reaction measurements. We find the performance of St. George meets the design specifications, demonstrating its suitability for (α,γ) reaction measurements of astrophysical interest.
We present new experimental measurements of resonance strengths in the astrophysical 23Al(p,γ)24Si reaction, constraining the pathway of nucleosynthesis beyond 22Mg in X-ray burster scenarios. ...Specifically, we have performed the first measurement of the (d,p) reaction using a radioactive beam of 23Ne to explore levels in 24Ne, the mirror analog of 24Si. Four strong single-particle states were observed and corresponding neutron spectroscopic factors were extracted with a precision of ∼20%. Using these spectroscopic factors, together with mirror state identifications, we have reduced uncertainties in the strength of the key ℓ = 0 resonance at Er = 157 keV, in the astrophysical 23Al(p,γ) reaction, by a factor of 4. Our results show that the 22Mg(p,γ)23Al(p,γ) pathway dominates over the competing 22Mg(α,p) reaction in all but the most energetic X-ray burster events (T>0.85 GK), significantly affecting energy production and the preservation of hydrogen fuel.
The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The ...strength of crust Urca neutrino cooling depends sensitively on the electron-capture and β-decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of A = 61 are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the β decay of 61 V . This Letter reports the first experimental determination of this transition strength, a ground-state branching of 8.1+4.0−3.1% , corresponding to a log f t value of 5.5+0.2−0.2 . This result was achieved through the measurement of the β -delayed γ rays using the total absorption spectrometer SuN and the measurement of the β -delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that A = 61 nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future.
We report the first experimental constraints on spectroscopic factors and strengths of key resonances in the P30(p,γ)S31 reaction critical for determining the production of intermediate-mass elements ...up to Ca in nova ejecta. The P30(d,n)S31 reaction was studied in inverse kinematics using the GRETINA γ-ray array to measure the angle-integrated cross-sections of states above the proton threshold. In general, negative-parity states are found to be most strongly produced but the absolute values of spectroscopic factors are typically an order of magnitude lower than predicted by the shell-model calculations employing WBP Hamiltonian for the negative-parity states. The results clearly indicate the dominance of a single 3/2− resonance state at 196 keV in the region of nova burning T≈0.10–0.17 GK, well within the region of interest for nova nucleosynthesis. Hydrodynamic simulations of nova explosions have been performed to demonstrate the effect on the composition of nova ejecta.
•In our letter, we address the dominant uncertainty regarding the extent of the rp-process flow bypass around Ni56 waiting point for astrophysical conditions relevant to Type-1 X-ray bursts.•We ...removed the final significant uncertainty, the beta-delayed proton branching ratio for Zn57, definitively determining that there is a Ni56 bypass.•In addition, we also identified the second case of the exotic β−γ−p decay mode in the fp-shell.
We measured the Zn57β-delayed proton (βp) and γ emission at the National Superconducting Cyclotron Laboratory. We find a Zn57 half-life of 43.6±0.2 ms, βp branching ratio of (84.7±1.4)%, and identify four transitions corresponding to the exotic β-γ-p decay mode, the second such identification in the fp-shell. The p/γ ratio was used to correct for isospin mixing while determining the Zn57 mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp-process flow could bypass the textbook waiting point Ni56 for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the Ni56 bypass, with 14-17% of the rp-process flow taking this route.
We present results from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. We report the first mass measurements of ...^{48}Ar and ^{49}Ar and find atomic mass excesses of -22.28(31) MeV and -17.8(1.1) MeV, respectively. These masses provide strong evidence for the closed shell nature of neutron number N=28 in argon, which is therefore the lowest even-Z element exhibiting the N=28 closed shell. The resulting trend in binding-energy differences, which probes the strength of the N=28 shell, compares favorably with shell-model calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.
The abundance and distribution of 44Ti tells us about the nature of the core-collapse supernovae explosions. There is a need to understand the nuclear reaction network creating and destroying 44Ti in ...order to use it as a probe for the explosive mechanism. The 44Ti(α, p)47V reaction is a very important reaction and it controls the destruction of 44Ti. Difficulties with direct measurements have led to an attempt to study this reaction indirectly. Here, the first step of the indirect study which is the identification of levels of the compound nucleus 48Cr is presented. A 100-MeV proton beam was incident on a 50Cr target. States in 48Cr were populated in the 50Cr(p, t)48Cr reaction. The tritons were momentum-analysed in the K600 Q2D magnetic spectrometer at iThemba LABS.
Time-of-flight mass measurements of exotic nuclei Matoš, M.; Estradé, A.; Schatz, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2012, Letnik:
696
Journal Article
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Atomic masses play an important role in nuclear physics and astrophysics. The need of experimental mass values for unstable nuclides has triggered the development of a wide range of mass measurement ...techniques, with devices installed at many laboratories around the world. We have implemented a time-of-flight–magnetic-rigidity (TOF-Bρ) technique at the National Superconducting Cyclotron Laboratory (NSCL) that includes a position measurement for magnetic rigidity corrections and uses the A1900 separator and the S800 spectrograph. We performed a successful first experiment measuring masses of neutron-rich isotopes in the region of Z∼ 20–30, important for calculations of processes occurring in the crust of accreting neutron stars. The masses of 16 nuclei were determined, for 61V, 63Cr, 66Mn, and 74Ni for the first time, with atomic mass excesses of −30.510(890)MeV, −35.280(650)MeV, −36.900(790)MeV, and −49.210(990)MeV, respectively. The mass resolution achieved was 1.8×10−4.
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