Milan Štefánik

Hybrid detectors of neutrons based on 3D silicon sensors with PolySiloxane converter

We report on the first prototypes of hybrid detectors for neutrons from the INFN HYDE project. Devices consist of 3D silicon sensors coupled to PolySiloxane-based converters. The sensor design and fabrication technology are presented, along with initial results from the functional characterization of the devices in response to radioactive sources and neutron beams of different energies.

NEUTRON FIELD MEASUREMENT OF P(35)+Be SOURCE USING THE MULTI-FOIL ACTIVATION METHOD

Neutron field from the p+Be interaction was investigated at the NPI CAS for a proton beam energy of 35 MeV and thick beryllium target. Broad neutron spectra at close source-to-sample distances were determined using the multi-foil activation technique. Two large sets of dosimetry foils containing the Ni, Co, Au, In, Ti, Al, Y, Lu, Nb and Fe were irradiated at a distance of 74 mm at direct neutron beam axis and at a distance of 34 mm from beam axis. Supporting Monte-Carlo MCNPX calculations of the irradiation system were performed as well. From measured reaction rates, the neutron energy spectra at both positions were reconstructed employing the modified version of the SAND-II unfolding code and activation cross-section data from the EAF-2010 library. At the position of irradiated samples, the total fast neutron flux reaches the value up to 1010 cm-2 s-1, and the neutron field is utilizable for radiation hardness study and integral benchmark experiments within the International Fusion Material Irradiation Facility (IFMIF) program.

On similarity of various reactor spectra and 235 U prompt fission neutron spectrum

A well-defined neutron spectrum is an essential tool not only for calibration and testing of neutron detectors used in dosimetry and spectroscopy but also for validation and verification of evaluated cross sections. A new evaluation of thermal-neutron induced 235U PFNS was performed by the International Atomic Energy Agency (IAEA) in the CIELO (Collaborative International Evaluated Library Organisation Project) project; new measurements of Spectral Averaged Cross sections averaged in the evaluated spectrum are to be obtained. In general, a neutron spectrum in the core is not identical to the pure fission one because fission neutrons undergo many scattering reactions, but it can be shown that PFNS and reactor spectra become undistinguishable from a certain energy boundary. This limit is important for experiments, because when the studied reaction threshold is over this limit, the spectral averaged cross sections in PFNS can be derived from the measured reactions in the reactor core. The evaluation of the neutron spectrum measurements in three different thermal-reactor cores shows that this lower limit is around the energy of 5.5 - 6 MeV. Above this energy the reactor spectra becomes identical with the 235U PFNS. IAEA CIELO PFNS is within 5% of the measured PFNS from 10 to 14 MeV in a LR-0 reactor, while ENDF/B-VII evaluated PFNS underestimated measured neutron spectra.

CROSS SECTIONS MEASURED BY QUASI-MONOENERGETIC NEUTRONS

197Au, 209Bi, 59Co, natFe and 169Tm samples were irradiated several times with quasi-monoenergetic neutrons from the p+7Li reaction in the energy range of 18-34 MeV. The activities of the samples were measured with the HPGe detector and the reaction rates were calculated. The cross sections were extracted using the SAND-II code with the reference cross sections from the IRDFF database.

Mössbauer spectrometry of LC 200N steel

The long-term reliability of construction materials operating in nuclear facilities under harsh conditions such as intense irradiation, high temperature, and in the presence of corrosion agents is a serious technologic, economic, and environmental demand. In this work, we elucidate the structural features of advanced corrosion-resistant LC 200N steel. High Cr and N contents provide high hardness and wear resistance of this perspective material which can be considered for possible applications in nuclear installations. Structural arrangement was checked by scanning electron microscopy and transmission electron microscopy. Chemical composition was inspected by X-ray fluorescence technique, spark optical emission spectroscopy, and neutron activation analysis. Mossbauer spectrometry was chosen as the principal method of investigation. Conversion Electron Mossbauer Spectrometry and transmission techniques were applied.

Investigation of corrosion-resistant LC200N steel by back scattering Mössbauer spectrometry

In this work we focus on characterization of LC200N steel by back-scattering Mossbauer spectrometry (MS). This geometry was used due to high sample thickness (0.5 mm). MS is a method suitable for determination of iron compounds and their properties in steels. We investigated samples with three different thermal treatments: non-hardened, hardened, and hardened with subsequent rapid quenching. Disk-shaped samples were cut off from original rods and polished from one side. The effect of surface treatment was investigated, too. Variations in microstructure imposed by different thermal and surface treatments were unveiled by Mossbauer parameters of backscattering spectra taken from both sides of the investigated samples. In this way, differences between the original as-cut and polished surfaces of the disks were unveiled.

Iron meteorite fragment studied by atomic and nuclear analytical methods

Chemical and structural compositions of a fragment of Sikhote-Alin iron meteorite were investigated by X-ray fluorescence analysis (XRF), neutron activation analysis (NAA) and Mossbauer spectroscopy (MS). XRF and NAA revealed the presence of chemical elements which are characteristic for iron meteorites. XRF also showed a significant amount of Si and Al on the surface of the fragment. MS spectra revealed possible presence of α-Fe(Ni, Co) phase with different local Ni concentration. Furthermore, paramagnetic singlet was detected in Mossbauer spectra recorded at room temperature and at 4.2 K.

Study of cross-sections of yttrium (n,xn) threshold reactions

Currently the development of the nuclear systems is heading to systems with fast neutrons instead of thermal ones. Such systems are mainly fast reactors of gen eration IV family and accelerator driven systems. Unfortunately the possibilities of monito ring fast neutrons are limited. One of the possible principles is to use activation detectors. It h as shown up that yttrium is very good candidate to act as the activation detector of the fast neutr ons. The advantages of yttrium are namely its (n, xn) threshold reactions and the fact that its only one natural ly occurring isotope. To be possible to use yttrium as the activation detector it is ne cessary to know the cross-sections of the (n,xn) reactions sufficiently good. This condition is fulfilled o nly in case of the89Y(n,2n)88Y reaction. For higher orders of reactions there are almost no experimental data. For this reason a series of experiment were made using quasi m ono-energetic neutron source based on the reaction of protons with 7Li target at Nuclear Physics Institute of ASCR in Rez. Special attention was paid to the 89Y(n,3n)87Y reaction. In this case the nuclei are produced both in the ground state and in the isomeric state. The half-lives ar 79.8 hours for the ground state and 13.38 hours for the isomeric state. The isomeric state decay s m inly through the gamma transition to the ground state. The beta decay of the isomeric state is wi thin our accuracy negligible. The cross-sections of both cases of products were analyzed and c ompared with existing experimental data, calculated models and evaluated values.

Accelerator driven p(37)-D 2 O fast neutron source at NPI Řeř

In the article, the fundamental information on the neutron production in the D(p,n)2p reaction is summarized, and the measurements at research facilities dealing with such types of source are described. The details about the experimental study of p + D2 and p + D2O reactions and corresponding neutron source development at the NPI in Řež are provided. The accelerator driven fast neutron generator NG-2 based on p(37) + D2O source reaction with a broad neutron spectrum up to 34 MeV is characterized, and the neutron field determined by the multi-foil activation technique validated against the Monte Carlo MCNPX calculations is presented. The research programs realized in this neutron field, commonly used for experimental simulation of the IFMIF (International Fusion Material Irradiation Facility) spectrum, are outlined.