n_TOF Collaboration(Torres-Sanchez, P. et al), Babiano-Suarez, V., Caballero, L., Domingo-Pardo, C., Ladarescu, I., & Tain, J. L. (2023). Measurement of the 14N(n, p) 14C cross section at the CERN n_TOF facility from subthermal energy to 800 keV. Phys. Rev. C, 107(6), 064617–15pp.
Abstract: Background: The 14N(n, p) 14C reaction is of interest in neutron capture therapy, where nitrogen-related dose is the main component due to low-energy neutrons, and in astrophysics, where 14N acts as a neutron poison in the s process. Several discrepancies remain between the existing data obtained in partial energy ranges: thermal energy, keV region, and resonance region. Purpose: We aim to measure the 14N(n, p) 14C cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and provide calculations of Maxwellian averaged cross sections (MACS). Method: We apply the time-of-flight technique at Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. 10B(n, & alpha;) 7Li and 235U(n, f ) reactions are used as references. Two detection systems are run simultaneously, one on beam and another off beam. Resonances are described with the R-matrix code SAMMY. Results: The cross section was measured from subthermal energy to 800 keV, resolving the first two resonances (at 492.7 and 644 keV). A thermal cross section was obtained (1.809 & PLUSMN; 0.045 b) that is lower than the two most recent measurements by slightly more than one standard deviation, but in line with the ENDF/B-VIII.0 and JEFF-3.3 evaluations. A 1/v energy dependence of the cross section was confirmed up to tens of keV neutron energy. The low energy tail of the first resonance at 492.7 keV is lower than suggested by evaluated values, while the overall resonance strength agrees with evaluations. Conclusions: Our measurement has allowed determination of the 14N(n, p) cross section over a wide energy range for the first time. We have obtained cross sections with high accuracy (2.5%) from subthermal energy to 800 keV and used these data to calculate the MACS for kT = 5 to kT = 100 keV.
|
Montesinos, V., Albaladejo, M., Nieves, J., & Tolos, L. (2023). Properties of the Tcc(3875)+ and Tcbar,cbar(3875)- and their heavy-quark spin partners in nuclear matter. Phys. Rev. C, 108(3), 035205–15pp.
Abstract: We discuss the modification of the properties of the tetraquark-like Tcc(3875)+ and Tc over bar c over bar (3875)- states in dense nuclear matter. We consider the Tcc+ and Tc over bar c over bar – in vacuum as purely isoscalar D*D and D*D S-wave bound states, respectively, dynamically generated from a heavy-quark effective interaction between the charmed mesons. We compute the D, D, D*, and D* spectral functions embedded in a nuclear medium and use them to determine the corresponding Tcc+ and Tc over bar c over bar – self-energies and spectral functions. We find important modifications of the D*D and D*D scattering amplitudes and of the pole position of these exotic states already for p0/2, with p0 the normal nuclear density. We also discuss the dependence of these results on the D*D (D*D) molecular component in the Tcc+ (Tc over bar c- over bar ) wave function. Owing to the different nature of the D(*)N and D(*)N interactions, we find characteristic changes of the in-medium properties of the Tcc(3875)+ and Tc over bar c over bar (3875)-, which become increasingly visible as the density increases. The experimental confirmation of the found distinctive density pattern will give support to the existence of molecular components in these tetraquark-like states, since in the case they were mostly colorless compact quark structures (cct over bar t over bar and c over bar c over bar tt, with t = u, d), the density behaviors of the Tcc(3875)+ and Tc over bar c over bar (3875)- nuclear medium spectral functions, though different, would not likely be the same as those found in this work for molecular scenarios. Finally, we perform similar analyses for the isoscalar JP = 1+ heavy-quark spin symmetry partners of the Tcc+ (T cc *+ ) and the T c over bar c- over bar (T*- c over bar c over bar ) by considering the D*0D*+ and D*0D*- scattering T matrices.
|
Davesne, D., Holt, J. W., Navarro, J., & Pastore, A. (2023). Landau sum rules with noncentral quasiparticle interactions. Phys. Rev. C, 108(3), 034003–7pp.
Abstract: We derive explicit expressions for the Landau sum rules for the case of the most general spin-dependent quasiparticle interaction including all possible tensor interactions. For pure neutron matter, we investigate the convergence of the sum rules at different orders of approximation. Employing modern nuclear Hamiltonians based on chiral effective field theory, we find that the inclusion of noncentral interactions improves the convergence of the sum rules only for low densities (n <= 0.1 fm-3). Around nuclear matter saturation density, we find that even ostensibly perturbative nuclear interactions violate the sum rules considerably. By artificially weakening the strength of the nuclear Hamiltonian, the convergence can be improved.
|
Xu, Z. Y. et al, Algora, A., & Morales, A. I. (2023). Beta-delayed neutron spectroscopy of 133In. Phys. Rev. C, 108(1), 014314–9pp.
Abstract: The decay properties of 133In were studied in detail at the ISOLDE Decay Station. The implementation of the Resonance Ionization Laser Ion Source allowed separate measurements of its 9/2+ ground state (133gIn) and 1/2- isomer (133mIn). With the use of & beta;-delayed neutron and & gamma; spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition 9/2+ & RARR; 7/2+ was located at 5.93 MeV in the 133gIn decay with a log ft = 4.7(1). In addition, several neutron-unbound states were populated at lower excitation energies by the first-forbidden decays of 133g,mIn. We assigned spins and parities to those neutron-unbound states based on the & beta;-decay selection rules, the log ft values, and systematics.
|
Yokoyama, R. et al, Tain, J. L., Algora, A., Agramunt, J., Domingo-Pardo, C., Morales, A. I., et al. (2023). β-delayed neutron emissions from N > 50 gallium isotopes. Phys. Rev. C, 108(6), 064307–15pp.
Abstract: beta-delayed gamma-neutron spectroscopy has been performed on the decay of A=84 to 87 gallium isotopes at the RI-beam Factory at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). beta-2n-gamma events were measured in the decays of all of the four isotopes for the first time, which is direct evidence for populating the excited states of two-neutron daughter nuclei. Detailed decay schemes with the gamma branching ratios were obtained for these isotopes, and the neutron emission probabilities (P-xn) were updated from the previous study. Hauser-Feshbach statistical model calculations were performed to understand the experimental branching ratios. We found that the P-1n and P-2n values are sensitive to the nuclear level densities of 1n daughter nuclei and showed that the statistical model reproduced the P-2n/P-1n ratio better when experimental levels plus shell-model level densities fit by the Gilbert-Cameron formula were used as the level-density input. We also showed the neutron and gamma branching ratios are sensitive to the ground-state spin of the parent nucleus. Our statistical model analysis suggested J <= 3 for the unknown ground-state spin of the odd-odd nucleus Ga-86, from the I gamma(4(+)-> 2(+))/I-gamma(2(+)-> 0(+)) ratio of Ga-84 and the P-2n/P-1n ratio. These results show the necessity of detailed understanding of the decay scheme, including data from neutron spectroscopy, in addition to gamma measurements of the multineutron emitters.
|
