An official website of the United States government
Abstract The resonant scattering of 10 B+ p reaction was measured at θ c.m. = 180°, 170°, 160°, 150° and 140° using a 35.93 MeV 10 B beam to investigate the spectroscopy of 11 C with the thick target inverse kinematic method at RIBRAS facility, IFUSP, São Paulo. Influence of the stopping power uncertainty on the resonant scattering cross section values for 11 C in the 10 B( p, p ) 10 B reaction is shown. The data measured for the reaction channels p ( 10 B, α ) and p ( 10 B, 3 He) is also presented. Interestingly, the cross sections for the 3 He channel are observed upto 2 MeV below the lowest energy measurement available in literature.
more »
« less
Performing Bayesian Analyses With AZURE2 Using BRICK: An Application to the 7Be System
Phenomenological R -matrix has been a standard framework for the evaluation of resolved resonance cross section data in nuclear physics for many years. It is a powerful method for comparing different types of experimental nuclear data and combining the results of many different experimental measurements in order to gain a better estimation of the true underlying cross sections. Yet a practical challenge has always been the estimation of the uncertainty on both the cross sections at the energies of interest and the fit parameters, which can take the form of standard level parameters. Frequentist ( χ 2 -based) estimation has been the norm. In this work, a Markov Chain Monte Carlo sampler, emcee , has been implemented for the R -matrix code AZURE2 , creating the Bayesian R -matrix Inference Code Kit ( BRICK ). Bayesian uncertainty estimation has then been carried out for a simultaneous R -matrix fit of the 3 He ( α , γ ) 7 Be and 3 He ( α , α ) 3 He reactions in order to gain further insight into the fitting of capture and scattering data. Both data sets constrain the values of the bound state α -particle asymptotic normalization coefficients in 7 Be. The analysis highlights the need for low-energy scattering data with well-documented uncertainty information and shows how misleading results can be obtained in its absence.
more »
« less
- PAR ID:
- 10332828
- Date Published:
- Journal Name:
- Frontiers in Physics
- Volume:
- 10
- ISSN:
- 2296-424X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Cross sections for the vibrational excitation and dissociative recombination (DR) of the C F 3 + ion in collisions with electrons at low scattering energies are computed using a previously-developed approach combining the normal mode approximation for the vibrational states of the target ion and the UK R -matrix code for the evaluation of the scattering matrices at fixed geometries. The obtained cross section for the DR shows excellent agreement with the experimental data from the ASTRID storage ring. Thermally-averaged rate coefficients are obtained from the cross sections for temperatures 10–3000 K.more » « less
-
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.more » « less
-
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 forElab≤ 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 toElab = 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.more » « less
-
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fphy.2022.888476
