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1. Neutron Elastic Scattering Differential Cross Sections on ¹³ C

   https://doi.org/10.1051/epjconf/202532905004  

   Vanhoy, JR; Perkoff, AS; Hicks, SF; Vajdic, S; Araya, DS; Crider, BP; Marsh, JC; Peters, EE; Xiao, Y; Yates, SW (January 2025, EPJ Web of Conferences)

   Jentschel, M (Ed.)

   Neutron elastic scattering cross sections on natural carbon serve as a reference standard in the incident energy range 10 eV to 1.8 MeV. The 2017 standards evaluation [1, 2] is 0.5 to 2.0% higher in that energy range than the 2006 standards evaluation [3]. In addition the ENDF/B-VIII.0 release split the natural carbon cross sections into the isotopes¹²C,¹³C, and¹⁴C for the first time. These details call for the re-measurement of the¹³C cross sections in sensitive regions. Ten elastic scattering angular distributions were recently measured for incident neutron energies between 0.5 and 3.25 MeV at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator/) using nanosecond pulsed beams and time-of-flight techniques. An overview of neutron production and detection, the new digital data acquisition system, and data analysis will be presented. Results are compared with data from previous measurements and database evaluations. 

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2. Variational inference of effective range parameters for ³ He− ⁴ He scattering

   https://doi.org/10.1088/1361-6471/ad9296  

   Burnelis, Andrius; Kejzlar, Vojtech; Phillips, Daniel R (December 2024, Journal of Physics G: Nuclear and Particle Physics)

   Abstract We use two different methods, Monte Carlo sampling and variational inference (VI), to perform a Bayesian calibration of the effective-range parameters in³He–⁴He elastic scattering. The parameters are calibrated to data from a recent set of³He–⁴He elastic scattering differential cross section measurements. Analysis of these data forE_lab≤ 4.3 MeV yields a unimodal posterior for which both methods obtain the same structure. However, the effective-range expansion amplitude does not account for the 7/2⁻state of⁷Be so, even after calibration, the description of data at the upper end of this energy range is poor. The data up toE_lab = 2.6 MeV can be well described, but calibration to this lower-energy subset of the data yields a bimodal posterior. After adapting VI to treat such a multi-modal posterior we find good agreement between the VI results and those obtained with parallel-tempered Monte Carlo sampling. 

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3. Effective field theory analysis of ³ He–α scattering data

   https://doi.org/10.1088/1361-6471/ac4da6  

   Poudel, Maheshwor; Phillips, Daniel R (March 2022, Journal of Physics G: Nuclear and Particle Physics)

   Abstract We treat low-energy 3 He– α elastic scattering in an effective field theory (EFT) that exploits the separation of scales in this reaction. We compute the amplitude up to next-to-next-to-leading order, developing a hierarchy of the effective-range parameters (ERPs) that contribute at various orders. We use the resulting formalism to analyse data for recent measurements at center-of-mass energies of 0.38–3.12 MeV using the scattering of nuclei in inverse kinematics (SONIK) gas target at TRIUMF as well as older data in this energy regime. We employ a likelihood function that incorporates the theoretical uncertainty due to truncation of the EFT and use Markov chain Monte Carlo sampling to obtain the resulting posterior probability distribution. We find that the inclusion of a small amount of data on the analysing power A y is crucial to determine the sign of the p-wave splitting in such an analysis. The combination of A y and SONIK data constrains all ERPs up to O ( p 4 ) in both s- and p-waves quite well. The asymptotic normalisation coefficients and s-wave scattering length are consistent with a recent EFT analysis of the capture reaction 3 He( α , γ ) 7 Be. 

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4. Experimental study of ⁶ He Coulomb breakup as an indirect measurement of ⁴ He(2n, γ ) ⁶ He reaction rate for the astrophysical r-process

   https://doi.org/10.1051/epjconf/202430402003  

   Godos, D; Acosta, L; Fernández-García, J P; O’Malley, P; Sánchez-Benítez, A M; Di_Pietro, A; Tumino, A; Vicente, A; Boomershine, C; Dembski, C; et al (January 2024, EPJ Web of Conferences)

   Pakou, A; Souliotis, G; Moustakidis, C (Ed.)

   In this work, we report the measurement of elastic and Coulomb break-up channels in⁶He+²⁰⁸Pb collisions at E_lab= 19.3 MeV, close to the Coulomb barrier of this system ∼ 19 MeV. In the context of the astrophysical r-process, the reaction⁴He(2n,γ)⁶He has been proposed to be a key reaction in the path of synthesizing seed nuclei for the r-process, as¹²C, in an environment composed mainly of alpha particles and neutrons. Based on a theoretical approach for treating three body reactions by means of which its reaction rate can be inferred, our experimental approach aims to obtain an indirect measurement of the reaction rate of⁴He(2n,γ)⁶He by measuring the Coulomb breakup of⁶He under the intense electric field produced by a²⁰⁸Pb target nucleus. The experiment was carried out at the TriSol facility operated in the Nuclear Science Laboratory of the University of Notre Dame, USA, which delivered a⁶He beam together with other contaminants. Particular care must be taken for the alpha particles produced in the production reaction. 

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5. Experimental study of the proton-transfer reaction C + H ₂ ⁺ → CH ⁺ + H and its isotopic variant (D ₂ ⁺ )

   https://doi.org/10.1039/D0CP04810K  

   Hillenbrand, Pierre-Michel; Bowen, Kyle P.; Dayou, Fabrice; Miller, Kenneth A.; de Ruette, Nathalie; Urbain, Xavier; Savin, Daniel W. (December 2020, Physical Chemistry Chemical Physics)

   We report absolute integral cross section (ICS) measurements using a dual-source merged-fast-beams apparatus to study the titular reactions over the relative translational energy range of E r ∼ 0.01–10 eV. We used photodetachment of C − to produce a pure beam of atomic C in the ground electronic 3 P term, with statistically populated fine-structure levels. The H 2 + and D 2 + were formed in an electron impact ionization source, with well known vibrational and rotational distributions. The experimental work is complemented by a theoretical study of the CH 2 + electronic system in the reactant and product channels, which helps to clarify the possible reaction mechanisms underlying the ICS measurements. Our measurements provide evidence that the reactions are barrierless and exoergic. They also indicate the apparent absence of an intermolecular isotope effect, to within the total experimental uncertainties. Capture models, taking into account either the charge-induced dipole interaction potential or the combined charge-quadrupole and charge-induced dipole interaction potentials, produce reaction cross sections that lie a factor of ∼4 above the experimental results. Based on our theoretical study, we hypothesize that the reaction is most likely to proceed adiabatically through the 1 4 A′ and 1 4 A′′ states of CH 2 + via the reaction C( 3 P) + H 2 + ( 2 Σ+g) → CH + ( 3 Π) + H( 2 S). We also hypothesize that at low collision energies only H 2 + ( v ≤ 2) and D 2 + ( v ≤ 3) contribute to the titular reactions, due to the onset of dissociative charge transfer for higher vibrational v levels. Incorporating these assumptions into the capture models brings them into better agreement with the experimental results. Still, for energies ≲0.1 eV where capture models are most relevant, the modified charge-induced dipole model yields reaction cross sections with an incorrect energy dependence and lying ∼10% below the experimental results. The capture cross section obtained from the combined charge-quadrupole and charge-induced dipole model better matches the measured energy dependence but lies ∼30–50% above the experimental results. These findings provide important guidance for future quasiclassical trajectory and quantum mechanical treatments of this reaction. 

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