A. M. Gagarski

Study of the neutron quantum states in the gravity field

We have studied neutron quantum states in the potential well formed by the earths gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in the two lowest quantum states correspond to expectations with an experimental accuracy. A position-sensitive neutron detector with an extra-high spatial resolution of ~2 microns was developed and tested for this particular experiment, to be used to measure the spatial density distribution in a standing neutron wave above a mirror for a set of some of the lowest quantum states. The present experiment can be used to set an upper limit for an additional short-range fundamental force. We studied methodological uncertainties as well as the feasibility of improving further the accuracy of this experiment.

Observation of a triple correlation in ternary fission: is time reversal invariance violated?

Abstract In ternary fission, besides the two main fission fragments, a third (usually light) charged particle is emitted. A triple correlation has been studied involving the momenta for a specific fission fragment p f , the momenta of the ternary particle p t and the spin of the polarized cold neutron inducing fission σ . The correlation observable B= σ ·[ p f × p t ] reverses sign upon time reversal and thus a non-vanishing value for the expectation value 〈 B 〉 could possibly be due to TRI being violated. However, final-state interactions or specific properties of the emission mechanism for ternary particles could equally well lead to a non-zero 〈 B 〉 with TRI being perfectly conserved. The reaction chosen was 233 U(n,f). An unexpectedly large correlation was observed. From the raw data the value for 〈 B 〉 is 〈 B 〉=−(0.78±0.02)×10 −3 with the sign corresponding to light fragments. Corrections for neutron polarization, geometric efficiency, resolution of detectors and background increase this figure by a factor of (1.5±0.3).

Rotation of the compound nucleus 236U∗ in the fission reaction 235U( n , f ) induced by cold polarised neutrons

A model for ternary fission is discussed in which a third particle (α-particle) is emitted due to non-adiabatic change of the nuclear potential at neck rapture. An expression for energy and angular distribution of α-particles is proposed. It is shown that an interaction between spin of fissioning system and orbital momentum of α-particle (spin-orbit interaction in the final state) results in recently observed asymmetry of α-particle emission, which can be formally related to T-odd correlation. No strong dependence of the asymmetry on the angle of α-particle emission with respect to the fission axis is predicted by the model in accordance with the experimental data.

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.

A method to measure the resonance transitions between the gravitationally bound quantum states of neutrons in the GRANIT spectrometer

We present a method to measure the resonance transitions between the gravitationally bound quantum states of neutrons in the GRANIT spectrometer. The purpose of GRANIT is to improve the accuracy of measurement of the quantum states parameters by several orders of magnitude, taking advantage of long storage of ultracold neutrons at specular trajectories. The transitions could be excited using a periodic spatial variation of a magnetic field gradient. If the frequency of such a perturbation (in the frame of a moving neutron) coincides with a resonance frequency defined by the energy difference of two quantum states, the transition probability will sharply increase. The GRANIT experiment is motivated by searches for short-range interactions (in particular spin-dependent interactions), by studying the interaction of a quantum system with a gravitational field, by searches for extensions of the Standard model, by the unique possibility to check the equivalence principle for an object in a quantum state and by studying various quantum optics phenomena.

Angular correlations in ternary fission induced by polarized neutrons

Ternary fission induced by cold polarized neutrons was studied for the two isotopes 233U and 235U at the Institut Laue-Langevin in Grenoble, France. In particular two types of angular correlations between the spin of the incoming neutrons and the emission directions of both, the fission fragments (FF) and the ternary particles (TP), were investigated. For FF and TP detectors facing the target at right angles to the neutron beam, first, for longitudinally polarized neutrons a triple correlation between spin and the emission of outgoing particles was explored and, second, for transversally polarized neutrons parity violating asymmetries in the emission of FFs and TPs were analyzed. Nonzero expectation values for the triple correlation were oberserved in the present experiments for the first time.

Search for Scission Neutrons Emitted in Low Energy Fission of Heavy Nucleus

In accordance with the PNPI Program of the fast neutron emission mechanism investigations in low excitation energy fission of heavy nucleus, the energy and angular distributions of neutron emission and angular dependence of (n‐n)‐ coincidences for different thresholds of neutron energy recording have been investigated in 252Cf(sf), 233,235U(n,f), and 239Pu(nf) fission. As a result of experimental data analysis performed on the assumption that the main part of neutrons are evaporated from the fully accelerated fragments with a big oriented angular momenta, the following figures for the yields of neutrons emitted before appearance of the fragments had been obtained for 252Cf(sf) and thermal neutron induced fission of 233,235U, and 239Pu: (10±2)%, (5±2)%, (7±2)%, and (10±2)% respectively.

Gravitationally bound quantum states of neutrons: applications and perspectives

Gravitationally bound quantum states of matter were observed recently due to unique properties of ultracold neutrons. We discuss here the actual status and possible improvements in this experiment. This phenomenon could be useful for various domains ranging from the physics of elementary particles and fields, to surface studies, or to foundations of quantum mechanics.

Tri And Rot Effects In Ternary Fission: What Can Be Learned?

Inducing fission by polarized neutrons allows studying subtle effects of the dynamics of the process. In the present experiments ternary fission of 235U and 239Pu was investigated with cold neutrons in the (n,f) reaction at the Institut Laue‐Langevin, Grenoble. Asymmetries in the emission of ternary particles were discovered by making use of the neutron spin flipping. It was found that two effects are interfering. There is first an asymmetry in the total yields of ternary particles having been called the TRI‐effect. Second, it was observed that the angular distributions of ternary particles are shifted back and forth when flipping the neutron spin. This shift was named ROT effect. Guided by trajectory calculations of the three‐body decay, the signs and sizes of the ROT effect are interpreted in terms of the K‐numbers of the transition states at the saddle point of fission.

Rotation of scissioning nuclei observed in ternary fission induced by polarized neutrons

Angular distributions of light charged particles relative to the momentum of the light fission fragment were studied in ternary fission induced by cold polarized neutrons. It was discovered that the angular distribution is asymmetric with respect to a plane determined by the direction of incident neutron spin and the light fragment momentum. The violation of the mirrorlike symmetry was established at the level of ∼10−2–10−4 for three reactions studied: 233U(n,f), 235U(n,f) and 239Pu(n,f). In spite of the smallness of the effects the neutron spin flip method allowed to make reliable measurements. The current status of the experimental studies of the effect and its interpretation are presented. Perspectives for further studies of the new phenomenon are discussed.