One of the most important sources of systematic uncertainties in the evaluation of measured cross sections is the absolute normalization of every dataset, which were often performed by measuring simultaneously the reference cross-section of the standard isotope. In other experiments the shape of the cross-section spectrum is normalized using as reference the integral value in a certain energy interval taken from an evaluated library. The choice of the energy interval used as reference has been often left up to the experimentalist criteria, leading to inconsistent normalizations and hardly assessable uncertainties. In this work the experimental datasets of the (n,f) cross section of many actinides are reviewed looking for the best suited energy interval to be recommended for renormalization purposes. Using standard integration intervals, wide enough to get very low statistical uncertainties, should improve the normalization of every experimental dataset, reducing so the associated total uncertainty when making the evaluation. A common integration range from 8 to 10 MeV is proposed for the whole set of actinides needed in fission applications. This energy range, which falls between the second and the third fission-chance thresholds, is characterized by a flat behaviour of the fission cross sections.

The experimental setup of the new measurement of 239Pu fission and capture cross-section in the n_TOF time-of-flight facility at CERN is presented. The measurement aims to address the needs and demands of nuclear data users. The experiment incorporates an innovative fast Fission Fragment Detector and the n_TOF Total Absorption Calorimeter, enabling the implementation of the fission tagging technique. Preliminary results exhibit the robust performance of the detector systems, along with the high quality of the new 239Pu samples. These samples were exclusively produced for this measurement by the European Commission’s Joint Research Centre in Geel.

Neutron cross section measurements are often made relative to a neutron cross section standard. Thus, the accuracy of the neutron standards determines the best possible accuracy of the neutron measurements. The 235U(n,f) cross section is widely used as reference, while it is considered a standard at thermal point and between 0.15 to 200 MeV. For this reason, additional cross section data for the 235U(n,f) reaction are useful in order to improve the accuracy and to extend the energy range of the standard. In this work, preliminary results of the measurement of the 235U(n,f) cross-section relative to the standard 10B(n,a) reaction are presented. The high accuracy measurement was performed at the experimental area EAR-1 of the n_TOF facility at CERN, aiming at covering the energy range from the thermal region up to approximately 100 keV. The samples were produced at JRC-Geel in Belgium, while the experimental setup was based on Micromegas detectors.

An accurate measurement of the 140Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged cross-section.

An international effort has produced evaluations of the neutron data standards. Evaluations were obtained for the cross section standards: the H(n,n), 6Li(n,t), 10B(n,αγ), 10B(n,α), natC(n,n), Au(n,γ), 235U(n,f), and 238U(n,f) reactions. Also in the evaluation process, the 238U(n,γ) and 239Pu(n,f) nonstandard cross sections were evaluated. Many of these are dosimetry cross sections. Evaluations were also obtained for data that are not traditional standards: Maxwellian spectrum averaged cross section for the Au(n,γ) cross section at 30 keV, reference cross sections for prompt γ-ray production in fast neutron-induced reactions, reference cross sections for very high-energy fission cross sections, the 252Cf spontaneous fission neutron spectrum and the 235U thermal fission neutron spectrum, and the thermal constants. The data and covariances were obtained directly from this evaluation procedure as is required by the dosimetry community.

A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235U interaction the only value in agreement with the standard is the thermal fission cross section. A resonance re-evaluation of the n + 235U interaction has been performed to address the issues regarding standard values in the energy range from 10−5 eV to 2250 eV. Recently, 235U fission cross-section measurements have been performed at the CERN Neutron Time-of-Flight facility (TOF), known as n_TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n_TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n_TOF data were included in the 235U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. This paper presents the procedure used for re-evaluating the 235U resonance parameters including the recommended standard values as well as new cross section measurements.

Neutron-induced fission cross sections of Pb-nat and Bi-209 between threshold and 1 GeV have been measured at the CERN neutron Time-Of-Flight (n_TOF) facility. The cross section ratios of these subactinides were determined relative to U-235 and U-238 using PPAC detectors for coincident detection of both fission fragments. There is good agreement with previous experimental results below 200 MeV. Around 1 GeV, the results are compared with the cross sections obtained in proton-induced fission.

Several studies with different Large Area Avalanche Photo-Diodes (LAAPDs) coupled to ad-hoc bi-frustum shaped CsI(Tl) crystals have been carried out as a part of the R&D program for the CALIFA R(3)/FAIR calorimeter. CALIFA, which is designed for the detection of light charged particles and gamma-rays in a wide energetic domain, has very stringent requirements. We report in this work our studies on the energy resolution for gamma-rays using LAAPDs as photosensors. One of the factors affecting the energy resolution is the matching between the APD active area and the crystal exit face. We present in this paper a procedure for characterizing APDs based on the measurement of their contribution to the energy resolution. The results obtained are very promising and suggest that a solution based on CsI(Tl) crystals coupled to LAAPDs could be suitable for, at least, part of the CALIFA calorimeter.

Studies with different bi-frustum CsI(Tl) crystal samples from several providers, coupled to large area avalanche photodiodes (Hamamatsu S8664-1010 2CH), specifically developed for this project, were performed as part of the R&D program for the design of the R3B calorimeter (CALIFA). Particular attention is given to the energy resolution optimization for CsI(Tl) crystal samples with realistic dimensions. The results obtained with Large Area Avalanche Photo-Diode (LAAPD) are very promising and suggest CsI(Tl) as a suitable candidate for the barrel of the calorimeter.

Studies with different CsI(TI) crystals coupled to avalanche photodiodes were performed in the frame of the R+D programme for the design of the R3B calorimeter (CALIFA [1]). The study of the energy resolution has been performed for crystals with lengths varying from 1 to 10 cm and square section (1 x 1 cm(2)), attending to different optimization of parameters (i.e., crystal wrapping, optical coupling to the avalanche photodiode and the electronic chain). The obtained results with Avalanche Photo-Diodes are very promising and suggest CsI(Tl) as a suitable candidate for at least part of the calorimeter. EDICS Category: 3-BBND.