C. Borcea

High precision neutron inelastic cross section measurements

High precision neutron inelastic scattering cross section data are very important for the development of the new generation of nuclear reactors (Gen IV). Our experiments, performed using the GELINA neutron source and the GAINS spectrometer of the European Commission Joint Research Center, Geel, produce highly reliable and precise cross section data. We will present the details of the setup and the data analysis technique allowing production of such unique results, and we will show examples of two experimental results.

Neutron inelastic cross section measurements for natTi

A neutron inelastic scattering experiment was performed at the GELINA (Geel Electron LINear Accelerator) neutron source of the European Commission Joint Research Centre Geel (EC-JRC Geel) with the aim of determining the reaction cross sections for the stable isotopes of natural titanium. A 235 U fission chamber was used to monitor neutrons with energies up to 20 MeV. The GAINS (Gamma Array for Inelastic Neutron Scattering) spectrometer was employed to detect the γ rays resulting from the decay of the excited nuclei. We determined the γ-ray production cross sections of the first transitions in the 46,48,49,50 Ti isotopes. The experimental values were compared with previous reported results and also with theoretical calculations performed with the TALYS 1.8 code using the default input parameters. Uncertainties of around 5% were obtained for the strongest observed transitions.

GRAPhEME: A setup to measure (n, xnγ) reaction cross sections

Most of nuclear reactor developments are using evaluated data base for numerical simulations. However, the considered databases present still large uncertainties and disagreements. To improve their level of precision, new measurements are needed, in particular for (n, xnγ) reactions, which are of great importance as they modify the neutron spectrum, the neutron population, and produce radioactive species. In 2003, the IPHC group started an experimental program to measure (n, xnγ) reaction cross sections using prompt gamma spectroscopy and neutron energy determination by time of flight. Measurements of (n, xnγ) cross section have been performed for 235,238U, 232Th, nat,182,183,184,186W, natZr. The experimental setup, consisting of HPGe detectors and a fission chamber, is installed at the neutron beam at GELINA (Institute for Reference Materials and Measurements (IRMM), Geel, Belgium). It has recently been upgraded with the addition of a highly segmented 36 pixels planar HPGe detector. The setup is equipped with a high rate digital acquisition system. The analysis of the segmented detector data requires a specific procedure to account for cross signals between pixels. An overall attention is paid to the precision of the measurement. The setup characteristic and the analysis procedure will be presented along with the acquisition and analysis challenges. Examples of results and their impact on models will be discussed. Finally, the perspectives on complimentary experiments will be presented.

Present status of the MISTRAL mass measurement experiment

The MISTRAL experiment for measuring masses of very short-lived nuclides at ISOLDE has been installed during the summer of 1997 and has had its first radioactive beam in November 1997. Tests are presently been carried out to study all possible systematic effects. This paper recalls the basic principles of the Smith-type radio-frequency spectrometer, gives its present characteristics and limitations, and describes the methods used to improve its performances.

MISTRAL: The beginning of a new mass measurement program at ISOLDE

The MISTRAL* experiment is now on-line at ISOLDE. Installed in May 1997, MISTRAL received its first stable beam in October and first radioactive beam in November 1997. These first tests, with a plasma ion source, resulted in excellent isobaric separation and reasonable transmission. Further testing and development enabled first data taking in July 1998 on neutron-rich Na isotopes having half-lives as short as 31 ms.

STRUCTURE OF THE HEAVY CA ISOTOPES AND EFFECTIVE INTERACTION IN THE SD-FP SHELL

p decays of the neutron-rich nuclei 51,52,53K have been used to populate bound and unbound levels in 50,51,52,53Ca. y r a y spectroscopy as well as P-delayed neutron spectroscopy by time of flight were carried out to obtain a detailed decay scheme to levels in 53Ca, 52Ca, 51Ca and 50Ca. A half-life of 1 1 6 f 6 ms was deduced and new PI, and Pzn delayed neutron emission probabilities have also been determined for 52K. A total of 11 and 3 new y transitions have been observed in the decay of 52K and 53K, respectively. The low-lying level structure of 52Ca is compared to shell-model calculations. Implications of these results on the determination of the Y-Y interaction in the fp shell are discussed.