Measurement of the ROT effect in the neutron induced fission of ²³⁵U in the 0.3 eV resonance at a hot source of polarized neutrons

Abstract

Abstract. The TRI and ROT asymmetries in fission of heavy nuclei have been extensively studied during more than a decade. The effects were first discovered in the ternary fission in a series of experiments performed at the ILL reactor (Grenoble) by a collaboration of Russian and European institutes, and were carefully measured for a number of fissioning nuclei. Later on, the ROT effect has been observed in the emission of prompt gamma rays and neutrons in fission of 235 U and 233 U, although its value was an order of magnitude smaller than in the α-particle emission from ternary fission. All experiments performed so far are done with cold polarized neutrons, what assumes a mixture of several spin states, the weights of these states being not well known. The present paper describes the first attempt to get "clean" data by performing the measurement of gamma and neutron asymmetries in an isolated resonance of 235 U at the POLI instrument of the FRM2 reactor in Garching.

An instrument for measuring T-odd asymmetries in the fission of heavy nuclei

“…The latter was a more important consideration during the experiment, as the main goal was to observe the effect, but not to measure its absolute value. This approach has been successfully proved in our last measurement on the ROT effect [8].…”

“…The schematic view of the experimental setup at the POLI instrument is depicted in figure 1. Details of these measurements may be found elsewhere [8]. The focus of this article is on the description of the instrumental setup.…”

Magnetic system for controlling the spin of polarized neutrons

“…The schematic view of the experimental setup at the POLI instrument is depicted in figure 3. A more detailed description of these experiments are given in [11][12][13]. Three identical spin-control devices were used in the experiment: two correction devices and one test device.…”

Searches for Exotic Interactions Using Neutrons

“…More speculative experiments include performing pendellösung interferometry on a wider set of crystal types, as well as spin-resonant pendellösung, where a resonance effect occurs when the Larmor precession distance from a laboratory magnetic field matches the pendellösung length. Because both interactions have the same dependence on neutron energy, the resonance field depends only on the momentum transfer of the Bragg reflection; the resonant field for the (111) reflection is silicon is about 6 kG [54]. Alternatively, tuning the Larmor precession distance to the width of a channel-cut multi-bounce crystal may be sensitive to exotic spin-dependent interactions, even in crystal species that are centrosymmetric [55].…”

“…Extensive work led primarily by Soviet/Russian groups over several decades discovered many parity-odd and parity-even asymmetries in polarized neutron-induced fission resonances in several fissionable nuclei [104][105][106]. Later work in this field shifted mainly to measurement of formally T-odd correlations in fission product angular distributions to try to understand subtle features of fission dynamics by looking at various angular correlations in both binary and ternary fission [107][108][109][110][111].…”