The investigation of the radiation field around the thick lead target irradiated by the 650 MeV protons. Part 1. The neutron spectra measurement around the target

The experimental investigation of the characteristics of the neutron and hadron yield from the thick lead target (50 cm lengthwise and 8.2 cm in diameter) bombarded by the protons with energy of 650 MeV was carried out at the JINR Phasotron. This work was done in the frame of the project SAD (MOX subcritical assembling in Dubna). The target imitates the core of the subcritical assembling. Two different methods were applied: 1) the multisphere neutron spectrometer for the study of the double differential (on angle and energy) distributions of the neutron fluence around the target; 2) the threshold activation detectors for the study of the angular and the spatial distributions of the hadron yield (with energy above 6, 20 and 40 MeV) and the total hadron yield from the target. The corresponding techniques and the experimental results are described in two parts of the paper. The general conditions of the experiment and the technique of the neutron spectra measurement are described in Part 1 of the paper. The experimental data on the angular and the spatial distributions of the hadrons from the target are presented in Part 2. The comparisons between the experimental data and the results of the calculations performed under real conditions of the experiments are given in Part 3