Measurement of neutron capture onCa48at thermal and thermonuclear energies

Abstract

At the Karlsruhe pulsed 3.75 MV Van de Graaff accelerator the thermonuclear 48 Ca(n,γ) 49 Ca(8.72 min) cross section was measured by the fast cyclic activation technique via the 3084.5 keV γ-ray line of the 49 Ca-decay. Samples of CaCO3 enriched in 48 Ca by 77.87 % were irradiated between two gold foils which served as capture standards. The capture cross-section was measured at the neutron energies 25, 151, 176, and 218 keV, respectively. Additionally, the thermal capture cross-section was measured at the reactor BR1 in Mol, Belgium, via the prompt and decay γ-ray lines using the same target material. The 48 Ca(n,γ) 49 Ca cross-section in the thermonuclear and thermal energy range has been calculated using the direct-capture model combined with folding potentials. The potential strengths are adjusted to the scattering length and the binding energies of the final states in 49 Ca. The small coherent elastic cross section of 48 Ca+n is explained through the nuclear Ramsauer effect. Spectroscopic factors of 49 Ca have been extracted from the thermal capture cross-section with better accuracy than from a recent (d,p) experiment. Within the uncertainties both results are in agreement. The non-resonant thermal and thermonuclear experimental data for this reaction can be reproduced using the direct-capture model. A possible interference with a resonant contribution is discussed. The neutron spectroscopic factors of 49 Ca determined from shell-model calculations are compared with the values extracted from the experimental cross sections for 48 Ca(d,p) 49 Ca and 48 Ca(n,γ) 49 Ca.

Thermal neutron activation cross section for 48Ca

“…In this work the thermal neutron absorption cross section for 48 Ca was determined as 0.979(20) b; this result, while in perfect agreement with the values found on reference [7,8], was determined with a much better accuracy, resulting in an uncertainty about 2.0% (which is 16% of the uncertainty of the compiled value and 44% of uncertainty of the best value so far), and thus should allow much more precise results for the determination of Calcium using the ANAA technique.…”

“…Table 2 compares the value obtained in this work and the values from references [7,8], and figure 1 compares the individual results obtained in this work to the previously available values, an also to the weighted average from this work and its uncertainty, showing that the present measurements are very reproductible and the value found for the 48 Ca cross section, while compatible with the previous data, presents a lower uncertainty.…”

“…One measurement was found in the literature [8] that used 77.87% enriched 48 CaCO 3 samples, resulting in a value of (0.982 ± 0.046) b. Thus, in order to both confirm this value and possibly reduce even further the uncertainty, a new measurement was performed, using natural Calcium.…”

“…[7] 1.09 ± 0.14 12.8 ref. [8] 0.982 ± 0.046 4.68 Present Work 0.979 ± 0.020 2.01 is the atomic mass, λ is the decay constant, N A is Avogadro's number, φ is the thermal neutron flux, F m is the mass fraction of the interest element in the sample, m is the sample mass, I γ is the intensity of the chosen γ-ray, is the system's detection efficiency for the energy of that γ-ray, F I is the isotopic abundance of the interest isotope, T i is the irradiation time, T e is the time elapsed between the end of the irradiation and the start of the counting and T c is the counting time.…”

Exploration of direct neutron capture with covariant density functional theory inputs

“…3 along with experimental data [28,45]. Since the CH89 OMP was developed for masses greater than 40, we compared FRESCO calculations with CH89 and KD optical model parameters.…”