C. Wagemans

A double ΔE-E detection set-up for ternary fission

Abstract A double ΔE-E detection set-up was constructed to measure the yield and energy characteristics of α-particles and tritons emitted in ternary fission processes. The binary fission fragments can also be measured in the same geometrical conditions. A methane filled, back-to-back ionization chamber with common cathode is used for the ΔE-sections. The ternary particles are stopped in two surface barrier detectors situated inside the gas chamber. The detection set-up has been tested with the spontaneous ternary fission of 252Cf and the neutron induced ternary fission of 235U at the GELINA facility of the IRMM at Geel. The results have been compared with a computer simulation of the expected energy signals for the applied configurations.

Preparation and characterisation of an 39Ar sample and study of the 39Ar(nth, α)36S reaction

Abstract The 39 Ar ( n th , α ) 36 S reaction has been studied for the first time. A sample containing 2.85×10 14 39 Ar atoms was produced at the ISOLDE facility at CERN. The number of 39 Ar atoms in the layer was determined by measuring the 39 Ar β -activity using a primary standardisation method. Subsequently, the sample was irradiated with thermal neutrons at the High Flux Reactor of the Institut Laue–Langevin. An upper limit of 0.29 b was obtained for the 39 Ar ( n th , α ) 36 S reaction cross-section.

NORMALIZATION OF THE 239PU FISSION CROSS SECTION

Measurements have been performed at the Geel Linear Accelerator from 0.01 eV up to 1,000 eV in order to investigate the normalization of [sup 239]Pu fission cross-section measurements. Two different experiments were performed using surface barrier detectors and a double ionization chamber, respectively. In both cases, the [sup 10]B(n, [alpha]) reaction was used as a flux monitor. The results indicate that the Weston and Todd data should be renormalized by [approximately]3%, resulting in a satisfactory agreement with ENDF/B-VI.

Cross-Section Measurement of Thermal Neutron-Induced Fission on 243Cm

Abstract An experimental program was set up at SCK·CEN to determine the thermal neutron-induced fission cross section of curium isotopes. These transuranium nuclei are produced in nuclear reactors and are candidates for transmutation. This paper presents our 243Cm(n,f) measurement, yielding a cross-section value of (667 ± 26) b. A detailed analysis of the experimental results published by previous groups is performed, and the renormalized values are compared with our result. In general, a good agreement with old data is observed, questioning the values adopted by different nuclear data libraries.

Measurement of the 236U(n,f) Cross Section in the Neutron Energy Range from 0.5 eV up to 25 keV

Abstract The 236U(n,f) cross section has been measured in the energy range from 0.5 eV to 25 keV at the Geel Electron Linear Accelerator neutron time-of-flight facility of the Institute for Reference Materials and Measurements in Geel, Belgium. A highly enriched 236U sample was mounted back-to-back with a 10B sample in the center of a Frisch-gridded ionization chamber, hence realizing a 2π detection geometry. A 235U(n,f) cross-section control measurement was performed in the same experimental conditions. Special attention has been given to the fission resonance integral If and to the strongest resonance at 5.45 eV, for which a resonance analysis has been performed yielding Γf = 1.7 μeV. Both values are highly overestimated in the literature.

Determination of the 243,246,248Cm thermal neutron induced fission cross sections

The minor actinide waste produced in nuclear power plants contains various Cm‐isotopes, and transmutation scenarios require improved fission cross section data. The available thermal neutron induced fission cross section data for 243Cm, 246Cm and 248Cm are not very accurate, so new cross section measurements have been performed at the high flux reactor of the ILL in Grenoble (France) under better experimental conditions (highly enriched samples, very intense and clean neutron beam). The measurements were performed at a neutron energy of 5.38 meV, yielding fission cross section values of (1240±28)b for 243Cm, (25±47)mb for 246Cm and (685±84)mb for 248Cm. From these results, thermal fission cross section values of (572±14)b; (12±25)mb and (316±43)mb have been deduced for 243Cm, 246Cm and 248Cm, respectively.

New results on the ternary fission of 243Cm

Ternary fission is an important source of He and tritium gas in nuclear reactors and used fuel elements. Therefore a systematic study of the ternary fission yields for 4He and tritons (t) is being performed. In recent years the influence of the excitation energy of the fissioning nucleus on the triton emission probability (t/B) has been investigated for different Cm and Cf isotopes. In this paper we report on new results on the neutron induced fission of 243Cm.

Experimental determination of the

The 41Ca(n,α)38Ar reaction cross section has been studied with resonance neutrons at the linear accelerator GELINA of the IRMM in Geel (Belgium) and has been determined up to 45 keV using the time-of-flight technique. A dozen resonances have been identified and for most of them the area, the total width, and a value for Γn/Γp could be determined. From the obtained cross section data the Maxwellian averaged cross section (MACS) has been calculated by numerical integration.

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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 ver...

Ca

The {sup 36}Cl(n,p){sup 36}S and {sup 36}Cl(n,{alpha}){sup 33}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 {sup 36}S.