Low energy transmission measurements of ^240,242Pu at GELINA and their impact on the capture width

Abstract

Abstract. We present an approach to account for sample inhomogeneities as observed in thin powder samples. To test this model a series of transmission measurements on enriched 240 Pu and 242 Pu oxide samples was carried out. These measurements were performed at GELINA, the pulsed, white neutron source at the Institute for Reference Materials and Measurements in Geel. For all samples a mixture of PuO 2 and graphite powder was used. To reduce the influence of the models for Doppler broadening on the extracted resonance parameters, measurements were performed with sample temperatures of approximately 12 K, 77 K and 300 K. To describe the variation in the sample thickness, caused by the particle distribution in a thin powder sample, a Monte Carlo and an analytical description were used in the resonance shape analysis. The values and uncertainties of the extracted resonance parameters are discussed, and suggestion for future measurements are given.

Determination of Resonance Parameters and their Covariances from Neutron Induced Reaction Cross Section Data

“…The constraints for an optimum transmission geometry require homogeneous samples without holes. In case of non-ideal samples the resonance parameters will be biased, unless the sample characteristics, in particular sample inhomogeneities, are taken into account in the data analysis [90]. This is illustrated in Fig.…”

“…16, showing the transmission around the 2.65 eV resonance of 242 Pu as a function of neu-tron energy. The data are the result of transmission measurements using a PuO 2 powder sample enriched to 99.93 wt% in 242 Pu, mixed with carbon powder and canned in a copper container [90]. The average area density of 242 Pu was 2.51 10 −5 at/b.…”

“…To account for the powder grain size, a special model was implemented in REFIT, as discussed in section VIII B. This model [90] includes a log-normal distribution describing the variation in the area density and a parameter reflecting the fraction of holes in the sample. Table II shows that there is a strong difference between the parameters (Γ n and Γ γ ) which are derived from a fit with and without accounting for sample inhomogeneities.…”

Recent Developments in the CONRAD Code regarding Experimental Corrections

“…In Ref. [5], S. Kopecky detailed a model to describe the thickness in the sample using a log-normal distribution. This model is available in the REFIT code to account for powder sample inhomogeneities and it has been implemented in CONRAD as well for transmission experiments.…”

Neutron resonance analysis for nuclear safeguards and security applications

“…The impact of the diversity in shape and size of the samples was investigated by means of simulations by Becker et al [9]. Various analytical methods were studied in terms of their capability to take into account the powder characteristics and the best results were obtained using an empirical model proposed by Kopecky et al [10] and the Levermore-Pomraning model [11]. Both models were implemented in the resonance shape analysis code REFIT [12] and validated with transmission experiments at GELINA [13].…”