Experimental results on the deuteron-beam-induced high-energy neutron fission of the uranium isotopes at the massive uranium target

The massive uranium target QUINTA [1] represents an experimental setup of the international collaboration "Energy and Transmutation of Radioactive Waste" (E&T-RAW) at the Joint Institute for Nuclear Research (JINR). The setup is composed of 500 kg of natural uranium and the biological lead shielding without any integrated moderator. The target is systematically irradiated with the high-energy particle beams of the JINR Nuclotron accelerator. There is generated a neutron spectrum with a hard component via the spallation reaction inside the target. A response of the experimental samples to the considered neutron field has been investigated. The uranium setup was irradiated with the deuteron beams of energy up to 8 GeV during the recent experimental performances. The maximum total intensity of the beam reached 3·10¹³ particles per irradiation lasting no longer than 20 hours. The main emphasis of this work is put on the experimental determination of the reaction rates of the radioisotopes widely produced in uranium samples due to (n,f), (n,γ), and (n,2n) reactions. A proper knowledge of the number of produced nuclei in ²³³U, ²³⁵U, and ^natU samples can one help to understand the basic physics behavior within the whole QUINTA target. For this reason, the diminutive uranium cylinders (∼1 g) were situated in some measurement positions inside the target. Gamma-ray spectrometry with HPGe detectors was used in order to obtain the experimental results. An increase in the number of fissions as a function of the beam energy has been proved. The results on (n,f), (n,γ), and (n,2n) reactions were compared with the Monte Carlo calculations performed by the MCNPX 2.7 code [2]. The comparison, as well as a brief review of the experimental results regarding the neutron spectra inside the target, including the obtained spectral indices, is presented further in this paper.