A. K. Petukhov

Search for quantum states of the neutron in a gravitational field: gravitational levels

Abstract The neutron could occupy quantum stationary states if it is trapped between the Earths gravitational field on one side and the Fermi quasi-potential of a mirror on the other side. The quantum states cause a strong variation in neutron density, both for separate energy levels and for a mixture of low-energy states. The use of a position sensitive UCN (ultracold neutron) detector allows simultaneous measurement of the position probability density distribution in the total range of interest and increases significantly the statistics, making possible such an experiment. In this article we describe a specially developed neutron spectrometer and a method of measurement of such quantum states.

New observation of space-parity violation in neutron-induced fission of 229Th, 241Pu and 241Am

Abstract The space-parity violating effect of the asymmetry of light fragment angular distributions relative to the polarization of cold neutrons inducing 229 Th, 241 Pu and 241 Am fission has been observed for the first time with the following values for the P -odd asymmetry coefficients: −(5.6 ± 0.2) × 10 −4 , −(0.89 ± 0.04) × 10 −4 and −(1.0 ± 0.25) × 10 −4 , respectively. In addition the following P -odd asymmetry coefficients have been obtained for 233 U (used as a standard) and for the subbarier fission of 237 Np: (3.67 ± 0.06) × 10 −4 and −(3.3 ± 3.7) × 10 −4 , respectively. For all fissile targets studied, except 237 Np, P -odd asymmetry coefficients for three separate intervals of the heavy fragment kinetic energy have been evaluated and found to be equal to the average values for each target.

Discovery of a P-odd effect in triton emission from the reaction 6Li(n, α)3H

The results of measuring the P-odd asymmetry (Sn · Pt) for triton emission from the reaction 6Li(n, α)3H are presented. Here, Sn is the neutron spin and Pt is the triton momentum. Three series of measurements were performed, one at the Petersburg Nuclear Physics Institute (Gatchina, Russia) in a vertical neutron beam from the PWR reactor and two in the PF1B beam from the reactor at the Institute Laue-Langevin (Grenoble, France). On the basis of all three experiments, the P-odd asymmetry coefficient was found to be αPN = −(8.6 ± 2.0) × 10−8. The results of zero experiments and calculations give every reason to believe that the above P-odd asymmetry is due to the reaction being studied.

Investigations of parity violation and interference effects in 235U fission induced by resonance neutrons

Abstract These investigations were performed to test the modern theory and to obtain first estimates of nuclear matrix elements of weak interaction and the main parameters of p -resonances. Combined investigations of the space parity non-conservation effect of 235 U fission fragment emission and the interference effects of the forward-backward and left-right asymmetries were carried out over the range of neutron energies from 0.02 eV to 90 eV. The experimental results are found to be in good agreement with the theory. The first estimates of the nuclear matrix element of the weak interaction for three p -resonances and the main parameters of some low energy p -wave resonances are obtained from a combined theoretical description of all experimental data.

Investigation of parity violation and interference effects in the angular distributions of fragments originating from 233U fission induced by resonance neutrons

Three interference asymmetry effects in the angular distributions of fragments originating from 233U fission induced by resonance neutrons were measured. The energy dependences of the asymmetry factors being studied show sizable irregularities that are associated, according to modern theory, with the interference of s and p resonances at the stage of a compound nucleus. The basic features of weak p-wave resonances in the low-energy region were obtained from a global theoretical analysis of the asymmetry factors as functions of energy. The first estimates of nuclear matrix elements of weak interaction were derived for a few p-wave resonances.

Investigations of the Space Parity Violation and Interference Effects in the Fragment Angular Distributions of 235U, 233U, and 239Pu Fission by Resonance Neutrons

Investigations of the space parity nonconserving (PNC) asymmetry of 233U, 235U, and 239Pu fission fragment emission and parity conserving (PC) interference effects of left‐right and forward‐backward asymmetries were carried out on the neutron beams of the reactor IBR‐30 (JINR, Dubna) over the range of neutron energies from 0.02 eV to about 100 eV. All experimental results obtained have been found to be in a good mutual accordance within the frames of modern theoretical conceptions about the mechanisms of PNC and PC effects forming in fission process induced by slow neutrons. In case of the P‐even interference effects of asymmetry the evident mutual well‐marked irregularities in their neutron energy dependencies up to about 100 eV were observed. It is connected with the interference of s, p‐resonances at fission compound stage according to modern theory. As a remarkable result of the PNC effect measurements the resonance behavior of the PNC asymmetry coefficients in the low neutron energy region (En < 2 eV...

Investigation of the P-Resonance Properties in Slow Neutron Fission of U-235

A new method to obtain information about the properties of low energy p-resonances in heavy fissile nuclei is described. It is based on a study of neutron energy dependence of the forward-backward asymmetry of angular distribution of fission. fragments. which is the result of s- and p-wave interference in neutron capture. The investigations of this effect for U-235 have been carried out using the neutron TOF-spectrometer GNEIS in Gatchina. The irregular energy behavior of the asymmetry coefficient α nf fb was observed in accordance with theory predictions. For some strong p-resonances the positions and effective widths have been determined at first.