M. Majerle

Comparison between experimental data and Monte-Carlo simulations of neutron production in spallation reactions of 0.7-1.5 GeV protons on a thick, lead target

Relativistic protons with energies 0.7-1.5 GeV interacting with a thick, cylindrical, lead target, surrounded by a uranium blanket and a polyethylene moderator, produced spallation neutrons. The spatial and energetic distributions of the produced neutron field were measured by the Activation Analysis Method using Al, Au, Bi, and Co radio-chemical sensors. The experimental yields of isotopes induced in the sensors were compared with Monte-Carlo calculations performed with the MCNPX 2.4.0 code.

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.

Monte-Carlo Simulations: FLUKA vs. MCNPX

Several experiments were performed at the Phasotron and Nuclotron accelerators in JINR Dubna in which spallation reactions and neutron transport were studied. The experimental results were checked against the predictions of the Monte‐Carlo code MCNPX. The discrepancies at 1.5 GeV and 2 GeV on the “Energy plus Transmutation” setup were observed. Therefore the experimental results were checked with another code–FLUKA.

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.

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.