The rate of the astrophysical 48Cr(p,γ)49Mn reaction and its influence on the potential A = 48 waiting point in the rp process
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Engineering topics
Pain, S. D.
Publications and source records attributed to Pain, S. D..
Investigation of the \(\gamma \)-ray Properties of the \(2^+\) States in \(^{14}\)C
The properties of the 2$^+_1$ and 2$^+_2$ excited states in 14 C were studied in an experiment conducted at Argonne National Laboratory. A 9 Be( 6 Li,pγ) fusion-evaporation reaction and the GRETINA-ORRUBA setup were employed to populate states of 14 C and detect γ-particle coincidence events. Finally, the precise determination of the 2$^+_1$ level energy, complemented by the estimation of the γ-ray branch of the 2$^+_2$ near-threshold state, will serve as a benchmark to test the Shell Model Embedded in the Continuum calculations.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Structure studies of 13 Be from the 12 Be (𝑑,𝑝) reaction in inverse kinematics on a solid deuteron target
The low-lying structure of 13 Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound and one neutron away from 14 Be, the heaviest bound beryllium nucleus, 13 Be is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the 12 Be (𝑑,𝑝) 13 Be reaction in inverse kinematics using a 9.5 MeV per nucleon 12 Be beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The 𝑄-value spectrum below −4.4 MeV was analyzed using a Bayesian method with geant4 simulations. A three-point angular distribution with the same 𝑄-value gate was fit with a mixture of 𝑠- and 𝑝-wave, 𝑠- and 𝑑-wave, or pure 𝑝-wave transfer. The 𝑄-value spectrum was also compared with geant simulations obtained using the energies and widths of states reported in four previous works. As a result, it was found that our results are incompatible with works that revealed a wide 5/2 + resonance but shows better agreement with ones that reported a narrower width.
6 ≤ A ≤ 19↗
First Direct Measurement Constraining the Ar 34 ( α , p ) K 37 Reaction Cross Section for Mixed Hydrogen and Helium Burning in Accreting Neutron Stars
The rate of the final step in the astrophysical αp process, the 34 Ar(α,p) 37 K reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. Here, we present the first direct measurement constraining the 34Ar(α,p)37K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the 34 Ar,Cl(α,p) 37 K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The 34 Ar(α,2p) 36 Ar cross section, which can be exclusively attributed to the 34 Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical (α,p) reaction rates in this part of the αp process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
{sup 58}Ni({sup 3}He,t){sup 58}Cu*({gamma}) Measurements with GODDESS to Constrain the Astrophysical Rate of {sup 57}Ni(p,{gamma}){sup 58}Cu
The observation of γ rays from the decay of 44Ti in the remnants of core-collapse supernovae (CCSNe) provides crucial information regarding the nucleosynthesis occurring in these events, as 44Ti production is sensitive to CCSNe conditions. The final abundance of 44Ti is also sensitive to specific nuclear input parameters, one of which is the 57Ni(p,γ) 58Cu reaction rate. A precise rate for 57Ni(p,γ) 58Cu is thus critical if 44Ti production is to be an effective probe into CCSNe. To experimentally constrain the 57Ni(p,γ) 58Cu rate, the structure properties of 58Cu were measured via the 58Ni(3He,t)58Cu*(γ) reaction using GODDESS (GRETINA ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory’s ATLAS facility. Details of the experiment, ongoing analysis, and plans are presented.
Carmichael, S. R.↗
E2 rotational invariants of 0$^{+}_{1}$ and 2$^{+}_{1}$ states for 106 Cd: The emergence of collective rotation
The collective structure of 106 Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/A beam of 106 Cd on a 1.1 mg/cm 2 208 Pb target using GRETINA-CHICO2 at ATLAS. Fourteen E2 matrix elements were obtained. The nucleus 106 Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of E2 matrix elements. The < 0$^{+}_{2}$ ||E2||2$^{+}_{1}$ > matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, < Q 2 >, of the first-excited 2$^{+}_{1}$ level relative to the 0$^{+}_{1}$ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in 114 Cd by C. Fahlander et al., Nucl. Phys. A485, 327 (1988), which is complicated by low-lying shape coexistence near midshell.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Neutron transfer reactions on the ground state and isomeric state of a 130 Sn beam
The structure of nuclei around the neutron-rich nucleus 132 Sn is of particular interest due to the vicinity of the Z = 50 and N = 82 shell closures and the r-process nucleosynthetic path. Four states in 131 Sn with a strong single-particle-like component have previously been studied via the (d,p) reaction, with limited excitation energy resolution. Here, the 130 Sn( 9 Be, 8 Be) 131 Sn and 130 Sn( 13 C, 12 C) 131 Sn single-neutron transfer reactions were performed in inverse kinematics at the Holifield Radioactive Ion Beam Facility using particle-γ coincidence spectroscopy. The uncertainties in the energies of the single-particle-like states have been reduced by more than an order of magnitude using the energies of γ rays. The previous tentative J π values have been confirmed. Decays from high-spin states in 131 Sn have been observed following transfer on the isomeric component of the 130 Sn beam. The improved energies and confirmed spin-parities of the p-wave states important to the r-process lead to direct-semidirect cross-sections for neutron capture on the ground state of 130 Sn at 30 keV that are in agreement with previous analyses. A similar assessment of the impact of neutron-transfer on the isomer would require significant nuclear structure and reaction theory input. There are few measurements of transfer reaction on isomers, and this is the first on an isomer in the 132 Sn region.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
First measurement of proton decay from a transfer reaction to 21 Na
Decay protons from excited states in Na 21 populated through a previously reported Mg 24 ( p , α ) Na 21 transfer reaction [Cha et al. , Phys. Rev. C 96 , 025810 (2017) ] were analyzed to extract the proton branching ratios of the energy levels. Additionally, by utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched Mg 24 solid targets, the decay protons were detected in coincidence with α particles from the ( p , α ) reaction using a silicon strip detector array. Proton decay branching ratios of several Na 21 levels were deduced for the p 0 and p 1 decay channels to the ground and first excited states in Ne 20 , respectively.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Performance of neutron spectrum unfolding using deuterated liquid scintillator
The performance of the maximum likelihood expectation maximization method for unfolding neutron energy spectra using deuterated liquid scintillator is evaluated for future utilization with rare isotope beams. High-resolution neutron energy spectra as well as the detector response matrix were measured at the Edwards Accelerator Laboratory at Ohio University. Maximum-likelihood expectation maximization (MLEM) unfolded neutron spectra are compared with spectra from neutron time-of-flight. In conclusion, the effects of the MLEM stopping criteria and spectrum statistics are also investigated.
47 OTHER INSTRUMENTATION↗
Proton Decay of 21 Na for 20 Ne Energy Levels
The 24 Mg(p,α) 21 Na transfer reaction has been previously studied for a spectroscopic study of 21 Na. In this follow-up analysis, the proton decays of the excited states of the radionuclide 21 Na, which were measured simultaneously, are reported. By investigating the coincidence between the reaction α-particles and decay protons, we were able to identify three groups of events that are associated with the energy levels in 20 Ne. The 20 Ne excitation energy plot was obtained as a result. Here, the four lowest known energy levels in 20 Ne (the ground state and excited states at E x = 1.633, 4.247 and 4.966 MeV) were clearly observed.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
New 13 C(α,n) 16 O Cross Section with Implications for Neutrino Mixing and Geoneutrino Measurements
Precise antineutrino measurements are very sensitive to proper background characterization. Here, we present an improved measurement of the 13 C(α,n) 16 O reaction cross section which constitutes significant background for large v¯ detectors. We greatly improve the precision and accuracy by utilizing a setup that is sensitive to the neutron energies while making measurements of the excited state transitions via secondary γ-ray detection. Our results shows a 54% reduction in the background contributions from the 16 O(3–, 6.13 MeV) state used in the KamLAND analysis.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurement of the Li 7 ( γ , t ) He 4 ground-state cross section between E γ = 4.4 and 10 MeV
Here, the Li 7 ( γ , t ) He 4 ground state cross section was measured for the first time using monoenergetic γ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror α -capture reactions H 3 ( α , γ ) Li 7 and He 3 ( α , γ ) Be 7 . Although over the last 30 years most measurements of the H 3 ( α , γ ) Li 7 reaction have concentrated in an energy range below E γ = 3.65 MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the Li 7 ( γ , t ) He 4 reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical S factor of H 3 ( α , γ ) calculated from the present data was fitted using the R -matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated S factor agrees with the potential model calculation and lower energy experimental data.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Spin assignments for $^{23}\hbox {Mg}$ levels and the astrophysical $^{22}\hbox {Na}(p,\gamma )^{23}\hbox {Mg}$ reaction
The 22 Na(p,γ) 23 Mg reaction is responsible for destruction of the long-lived radionuclide 22 Na produced during nova explosions. Since the reaction proceeds through resonances from levels in 23 Mg above the proton threshold at 7.581 MeV, the properties of these levels such as excitation energies, spins, and parities are crucial ingredients to deter- mine the 22 Na(p,γ) 23 Mg reaction rate. Despite recent studies of these levels, their spins are not well constrained in many cases. We have measured the 24 Mg(p,d) 23 Mg transfer reaction to determine spectroscopic properties of these levels at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spin of the E x = 7.788 MeV level in 23 Mg is constrained to be J π = (3/2 + , 5/2 + ) through the present work. Here, the astrophysical 22 Na(p,γ) 23 Mg reaction rate at nova temperatures is updated accordingly. Nova nucleosynthesis model calculations using the newly updated 22 Na(p,γ) 23 Mg reaction rate shows that the final weighted abundance of the radionuclide 22 Na is increased by 42% compared to that obtained by using the previous 22 Na(p,γ) 23 Mg reaction rate of Sallaska et al. for a 1.35 M ⊙ ONeMg white dwarf.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
γ -ray spectroscopy of astrophysically important states in Ca 39
Background: Nova explosions synthesize elements up to A ≃ 40 , and discrepancies exist between calculated and observed abundances of Ar and Ca created in the explosion. The K 38 ( p , γ ) Ca 39 reaction rate has been illustrated to be influential on these isotopic abundances at the endpoint of nova nucleosynthesis. The energies of the three most important resonances, corresponding to J π = 5 / 2 + excited states in the Ca 39 nucleus above the proton separation threshold, are uncertain and one has been measured with conflicting values [ E r = 679 ( 2 ) versus E r = 701 ( 2 ) keV] in previous experiments. Purpose: Reducing the uncertainties on the resonance energies would allow for a better understanding of the reaction rate. To improve these uncertainties, we searched for γ rays from the depopulation of the corresponding excited states in Ca 39 . Methods: We report a new measurement of these resonance energies via the observation of previously unobserved γ -ray transitions. These transitions were observed by studying the Ca 40 ( 3 He , α γ ) Ca 39 reaction with Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS). The updated resonance energies were then used to calculate the K 38 ( p , γ ) Ca 39 reaction rate and assess its uncertainties. Results: In total, 23 new transitions were found, including three γ -ray transitions corresponding to the three J π = 5 / 2 + states of astrophysical interest at energies of 6156.2(16), 6268.8(22), and 6470.8(19) keV. These correspond to resonance energies in the K 38 ( p , γ ) Ca 39 reaction of 386(2), 498(2), and 701(2) keV. Conclusions: Updated K 38 ( p , γ ) Ca 39 reaction rate calculations reflect a reduced upper limit at nova temperatures. However, the lower-than-previously-measured energy of the 498-keV resonance and uncertainty in its resonance strength increases the upper limit of the rate close to previous estimates at 0.4 GK.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Direct neutron capture cross section on Ge 80 and probing shape coexistence in neutron-rich nuclei
Results are presented from the first neutron-transfer measurement on 80 Ge using an exotic beam from the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Newly measured spins and spectroscopic factors of low-lying states of 81 Ge are determined, and the neutron capture cross section on 80 Ge was calculated in a direct-semidirect model to provide a more realistic (n,γ) reaction rate for r-process simulations. Furthermore, a region of shape coexistence around N ≈ 50 is confirmed and implications for the magic nature of 78 Ni are discussed.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Erratum: Informing direct neutron capture on tin isotopes near the N = 82 shell closure [Phys. Rev. C 99 , 041302(R) (2019)]
Erratum to "Informing direct neutron capture on tin isotopes near the N = 82 shell closure [Phys. Rev. C 99, 041302(R) (2019)]
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗