The 41Ca(n,alpha)38Ar reaction cross section has been studied with resonance neutrons at the GELINA neutron facility of the Institute for Reference Materials and Measurements in Geel (Belgium) from a few eV up to 100 keV. A Frisch-gridded ionization chamber with methane as detector gas was installed at a 30 meter long flight path. About 20 resonances have been identified. From the cross section data obtained, the Maxwellian averaged cross section (MACS) as a function of stellar temperature has been calculated by numerical integration.
The 236 U(n,f) cross section has been measured in the neutron energy region from 0.5 eV to 25 keV at the GELINA neutron facility of the IRMM in Geel, Belgium.A highly enriched 236 U sample was mounted back-to-back with a 10 B sample in the centre of a Frisch-gridded ionisation chamber; a control measurement was performed with a 235 U sample in the same configuration.Besides a dominant resonance at 5.45 eV, for which a resonance analysis was performed, the next resonance (cluster) only occurs at about 1.3 keV.It is demonstrated that the fission resonance integral and the thermal fission cross section adopted in all commonly used evaluated data libraries are too large by two orders of magnitude.
Measurements have been performed at the Geel Linear Accelerator from 0.01 eV up to 1000 eV in order to investigate the normalization of 239Pu fission cross-section measurements. Two different experiments were performed using surface barrier detectors and a double ionization chamber, respectively. In both cases, the 10B(n,α) reaction was used as a flux monitor. The results indicate that the Weston and Todd data should be renormalized by ∼3%, resulting in a satisfactory agreement with ENDF/B-VI.
The $^{36}\mathrm{Cl}$($n,p$)$^{36}\mathrm{S}$ and $^{36}\mathrm{Cl}$($n,\ensuremath{\alpha}$)$^{33}\mathrm{P}$ reaction cross sections have been studied with resonance neutrons at the linear accelerator GELINA of the IRMM in Geel (Belgium) and have been determined up to approximately 250 keV using the time-of-flight technique. In this energy region, 17 resonances were observed, whereas eight were identified before. For some resonances the resonance strength, the spin, and the total width could be determined. From the obtained cross section data, the MACS has been calculated by numerical integration. These updated MACS values were used in stellar models to trace the origin of the rare isotope $^{36}\mathrm{S}$.
The fission cross section of 245Cm was measured at the GELINA neutron facility of the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium, as a function of the incident neutron energy. The energy of the neutrons is determined applying the time of flight method using a flight path length of about 9 m. A highly enriched 245Cm sample (98.48%) was mounted back‐to‐back with a 10B sample in the centre of a vacuum chamber together with two surface barrier detectors positioned outside the neutron beam. One detector measured the 10B(n,α)7Li reaction products for the neutron flux determination, while the second one registered the 245Cm(n,f) fragments. A control measurement has been performed replacing the 245Cm sample with a 235U sample in order to check that the well‐known 235U(n,f) cross section can be reproduced. In comparison with previous 245Cm fission cross section measurements, our preliminary results show a nice improvement of the energy resolution, in particular below 20 eV where very few data are available.
The $^{26}\mathrm{Al}$($n,\ensuremath{\alpha}$)$^{23}\mathrm{Na}$ reaction cross section has been studied at the linear accelerator GELINA of the Institute for Reference Materials and Measurements in Geel, Belgium, and has been determined up to a neutron energy of about 100 keV using the time-of-flight technique. Six resonances could be observed in this energy region, whereas before only one had been identified experimentally. For four of them, resonance parameters such as resonance energy, total width, area, and spin of the state could be determined. From the obtained $^{26}\mathrm{Al}$($n,\ensuremath{\alpha}$)$^{23}\mathrm{Na}$ cross section data, Maxwellian averaged cross section (MACS) values were calculated by numerical integration. Since neutron induced reactions are among the major destruction mechanisms of $^{26}\mathrm{Al}$ in our Galaxy, these new MACS values contribute to a better understanding of the observed $^{26}\mathrm{Al}$ abundance.
