"Study of the T-odd effects for gamma-rays and neutrons in the fission of uranium nuclei induced by polarized neutrons"

Berikov Daniyar


T-odd angular correlations in ternary nuclear fission (TRI and ROT asymmetries) were studied with the aim of finding a violation of Time Reversal Invariance (TRI) in neutron-nuclear interactions. A nonzero T-odd effect was discovered in an experiment to measure asymmetry in the emission of light charged particles in the 233U ternary fission (TRI effect), which was performed at a high-flux ILL nuclear reactor in Grenoble by the collaboration of Russian and European institutions. As it turned out, the effect is not associated with violation of T-invariance, but can be explained by a complex mechanism of the fission process. Later, the ROT effect was observed in the emission of prompt gamma-rays and neutrons in fission of 235U and 233U, although its magnitude was an order of magnitude smaller than in the emission of α-particles in ternary fission. All experiments up to now were performed with cold polarized neutrons, which suggests a mixture of several spin states of the compound nucleus, the relative contributions of which are not well known. Our work presents the results of the first experiments to measure the ROT effect in the fission of 235U by hot polarized neutrons at the POLI facility of the FRM II reactor in Garching with neutron energies of 0.06 and 0.3 eV. The latter energy corresponds to the position of the first isolated resonance of 235U.