New experiment on the observation of the effect of accelerating matter in neutron optics

The results of a new experiment on the observation of the effect of accelerating matter in neutron optics are reported. It has been shown that the velocity of neutrons periodically varies when they pass through a harmonically moving refractive sample. The idea of the experiment is based on time focusing, i.e., on the fact that the periodic modulation of the velocity of neutrons leads to the oscillation of the flux density at the observation point. The magnitude of the effect is in reasonable agreement with the theoretical predictions. The experiment has been carried out with ultracold neutrons and a change of ±1 cm/s has been detected in the neutron velocity.     

Potential of the neutron lloyd’s mirror interferometer for the search for new interactions

We discuss the potential of the neutron Lloyd’s mirror interferometer in a search for new interactions at small scales. We consider three hypothetical interactions that may be tested using the interferometer. The chameleon scalar field proposed to solve the enigma of accelerating expansion of the Universe produces interaction between particles and matter. The axion-like spin-dependent coupling between a neutron and nuclei or/and electrons may result in a P- and T-noninvariant interaction with matter. Hypothetical non-Newtonian gravitational interactions mediates an additional short-range potential between neutrons and bulk matter. These interactions between the neutron and the mirror of a Lloyd-type neutron interferometer cause a phase shift of neutron waves. We estimate the sensitivity and systematic effects of possible experiments.     

Effect of accelerating matter in neutron optics

The results of an experiment on the observation of a new neutron-optical effect are reported. It has been experimentally shown that the energy of a neutron passing through a refracting sample moving with acceleration changes. The magnitude of the effect is in qualitative agreement with theoretical predictions. The experiment was carried out with ultracold neutrons and the energy transform is equal to ±2 × 10^?10 eV.     

Dynamic reflection and refraction of neutrons at the boundaries of matter characterized by a variable magnetic induction

Optical phenomena that arise in the interaction of a neutron wave with matter characterized by a variable interaction potential are considered. The time dependence of the potential is assumed to be due to a change in the magnetization vector in matter with time. Since the interaction in question is time-dependent, the neutron energy is not conserved. If a neutron interacts with a sample that has a plane boundary, only the neutron-velocity component orthogonal to the matter boundary changes. Thus, reflected waves are characterized by a reflection angle that is different from the angle of incidence. Waves transmitted through a plane sample can also change direction. The changes in the neutron energy and in the neutron-velocity direction are closely related to the reversal of the neutron-spin projection. The question of whether a slab featuring a rotating magnetization vector can be used as a spin flipper or as a coherent wave splitter is considered.     

The crystal acceleration effect for cold neutrons

A new mechanism of neutron acceleration is discussed and studied experimentally in detail for cold neutrons passing through the accelerated perfect crystal with the energies close to the Bragg one. The effect arises due to the following reason. The crystal refraction index (neutron-crystal interaction potential) for neutron in the vicinity of the Bragg resonance sharply depends on the parameter of deviation from the exact Bragg condition, i.e. on the crystal-neutron relative velocity. Therefore the neutrons enter into accelerated crystal with one neutron-crystal interaction potential and exit with the other. Neutron kinetic energy cannot vary inside the crystal due to its homogeneity. So after passage through such a crystal neutrons will be accelerated or decelerated because of the different energy change at the entrance and exit crystal boundaries.     

Ether drift experiments and electromagnetic momentum

Propagation of Aharonov-Bohm matter waves and light waves in moving media is characterized by the interaction electromagnetic momentum. Thus, recent models of light propagation in moving rarefied media justify and call for an optical experiment of the Mascart-Jamin type, capable of testing the modern interpretations of ether drift experiments.     

Interaction of waves with a birefringent medium moving with acceleration

Recent experiments demonstrated that the energy of a neutron traversing an accelerated sample of a refractive medium changes. Later, it was realized that such an accelerated-medium effect (AME) is quite a general phenomenon characteristic of waves and particles of different nature. This paper discusses some special features of the effect for a birefringent medium. In this case, AME shows quite new features. In neutron optics, where birefringence is due to the spin dependence of the refractive index, AME results in a nonstationary state with a precessing spin. In the case of the propagation of a two-flavor neutrino through an accelerated layer of matter, AME affects substantially the ensuing evolution of a neutrino flavor state as it propagates through a free space.     

Phase transition to the state with nonzero average helicity in dense neutron matter

The possibility of the appearance of the states with a nonzero average helicity in neutron matter is studied in the model with the Skyrme effective interaction. By providing the analysis of the self-consistent equations at zero temperature, it is shown that neutron matter with the Skyrme BSk18 effective force undergoes at high densities a phase transition to the state in which the degeneracy with respect to helicity of neutrons is spontaneously removed.     

双中子集团结构研究进展

回顾了晕核发现以来双中子集团结构的研究进展,分析了可能的发展方向。系统的理论研究表明, 在原子核的表面和低密度核物质中, 空间紧密关联的2n集团的出现是一个普遍的现象。 但在较重原子核表面出现2n集团的机制与核物质或轻晕核中的机制很不一样, 前者是由有限核的平均场造成的尺度效应（size effect）,而后者主要是由低密度下对相互作用（或对能隙）的增强造成的。另外,在轻晕核或有限核表面,2n集团的均方根半径与它们到核芯的距离（或背景密度）有关,最小值普遍可以达到2～3 fm,然而在核物质中2n集团最小只能到～5 fm。 实验方面,在重靶上的库仑激发强度, 能够比较准确地给出2n系统到核芯的平均距离。 但到目前为止尚没有有效的实验方法给出基态中两个中子之间的间距, 主要原因是中子发射过程中末态相互作用（共振态或虚粒子态）造成的两步过程的干扰, 这个问题在库仑激发破碎（重靶）或核作用破碎（轻靶）中都出现。“拖出”反应和敲出核芯反应是下一步可以考虑的路径。 双中子的关联测量通常效率比较低,尤其是需要有效排除中子串扰(CT)事件。为此, 需要发展特殊设计的中子关联测量装置, 在提高探测效率的同时,能够通过运动学关系以及其他方法有效排除中子CT信号。 在数据处理阶段,通过反复迭代给出的双中子关联函数, 经验证明是比较有效的关联状态表达方式, 从中可以直接提取出双中子分布均方根半径。 This article outlines the progress in the study of the di neutron structure in various systems. Systematic theoretical investigations reveal that di neutron structure is a general phenomenon appeared at nucleus surface and in low density nuclear matter. But the underline mechanism of forming di neutron clusters at the surface of heavier nuclei is quite different to that for light halo nuclei or at the low density nuclear matter, with the former being basically due to the so called “size effect” and the latter due to the enhanced pairing interaction. It is also realized that the RMS radii of the di neutron cluster at the surface of light halo nuclei or heavier finite nuclei varies with the distance from the center of nuclei (or background density) and may attain a minimum of about 2～3 fm, whereas that in the low density nuclear matter may only attain about 5 fm. From experimental side, Coulomb excitation caused by heavy targets provides a good way to extract the mean distance from the center of the neutron pair to the center of nucleus. But up to now it is still difficult to experimentally determine the distance between the two valence neutrons, due primarily to the final state interactions which lead to two step emission of neutrons via resonances or virtual intermediate states. This problem happens in both Coulomb and nuclear breakup processes. Possible ways to avoid this problem might come from experiments based on “towing mode” or core knockout reactions. Detection of two neutrons in coincidence often suffers from low efficiencies and the need to reject the cross talk events. Therefore it is important to develop specially designed multi neutron detection array to achieve high efficiency as well as good cross talk rejection performance using kinematics conditions. For data analysis, it was found that two neutron correlation function generated by iteration method is a good expression of the correlation situation, from which the RMS radii of the two neutron distribution may be deduced.     

Experimental verification of the 1/v law for the absorption cross section of ultracold neutrons in natural gadolinium

The results of a new experiment on the transmission of ultracold neutrons through a natural gadolinium film are reported. The results indicate that the transmission of the sample is unchanged when the sample moves parallel to its surface. The neutron velocity in the sample coordinate system varies in a range of 6–35 m/s. It follows from the constancy of the sample transmission that the imaginary part of the scattering length is constant; i.e., the law 1/v is valid for the capture cross section of the free nucleus with an accuracy of about 0.5%.     

Ultra low momentum neutron catalyzed nuclear reactions on metallic hydride surfaces

Ultra low momentum neutron catalyzed nuclear reactions in metallic hydride system surfaces are discussed. Weak interaction catalysis initially occurs when neutrons (along with neutrinos) are produced from the protons that capture “heavy” electrons. Surface electron masses are shifted upwards by localized condensed matter electromagnetic fields. Condensed matter quantum electrodynamic processes may also shift the densities of final states, allowing an appreciable production of extremely low momentum neutrons, which are thereby efficiently absorbed by nearby nuclei. No Coulomb barriers exist for the weak interaction neutron production or other resulting catalytic processes. PACS 24.60.-k, 23.20.Nx     

Neutron optics and weak currents

The weak interaction can produce two small but striking effects with low energy neutrons. With a transversely polarized neutron beam the polarization rotates in passing through matter; and with an unpolarized beam a longitudinal polarization develops. These effects are of first order in the weak coupling and can only be produced by parity violating forces. With the conventional weak interaction only the nucleons in the material contribute, with “neutral currents” electrons also interact weakly. Thus, if experiments on different materials are performed, “neutral currents” may be observed by detecting an electron contribution to the effect and furthermore the isotopic structure of the weak interaction between nucleons may be determined.     

Neutron storage in a magnetic field

The motion of neutrons in magnetic traps is considered for various cases of neutron polarization. The results of implementing such traps in practice and special features of experiments studying magnetic neutron storage are discussed. The problem of neutron losses during injection via magnetic valves can be solved by conjoining a magnetic trap with a converter of cold neutrons into ultracold ones or with a source of ultracold neutrons. Prospects for expanding neutron-storage experiments by invoking a correlation analysis of neutron decay and by using the transport properties of charged particles in a nonuniform magnetic field are analyzed. In such an investigation, the recording of the storage time of neutrons proper can be supplemented with the detection of decay protons and electrons and with a parallel measurement of the asymmetries of proton and electron emission with respect to the magnetic field. A set of relative measurements permits improving the accuracy of an experimental determination of the neutron lifetime and combining this determination with the determination of correlation coefficients. On this basis, it is possible to find directly the ratio of the weak-interaction constants and the constants themselves. The application of the most advanced reactor and accelerator technologies to subcritical electric nuclear devices optimized for generating cold and ultracold neutrons, along with the use of solid deuterium and superfluid helium, creates preconditions for developing a neutron plant and for launching neutron studies at accelerators. Thus, the work that has been done as a development of V.V. Vladimirsky's proposals on magnetic neutron storage is analyzed, and the potential of a further use of ultracold neutrons and magnetic devices for deploying a full-scale precision experiment to study the beta decay of polarized neutrons is demonstrated.     

Cosmic Ray Electrons and Protons,and Their Antiparticles

Cosmic rays are a sample of solar, galactic, and extragalactic matter. Their origin, acceleration mechanisms, and subsequent propagation toward Earth have intrigued scientists since their discovery. These issues can be studied via analysis of the energy spectra and composition of cosmic rays. Protons are the most abundant component of the cosmic radiation, and many experiments have been dedicated to the accurate measurement of their spectra. Complementary information is provided by electrons, which comprise about 1 % of the cosmic radiation. Because of their low mass, electrons experience severe energy losses through synchrotron emission in the galactic magnetic field and inverse Compton scattering of radiation fields. Electrons therefore provide information on the local galactic environment that is not accessible from the study of the cosmic ray nuclei. Antiparticles, namely antiprotons and positrons, are produced in the interaction between cosmic ray nuclei and the interstellar matter. They are therefore intimately linked to the propagation mechanisms of the parent nuclei. Novel sources of primary cosmic ray antiparticles of either astrophysical (e.g., positrons from pulsars) or exotic origin (e.g., annihilation of dark matter particles) may exist. The nature of dark matter is one of the most prominent open questions in science today. An observation of positrons from pulsars would open a new observation window on these sources. Several experiments equipped with state-of-the art detector systems have recently presented results on the energy spectra of electrons, protons, and their antiparticles with a significant improvement in statistics and better control of systematics. The status of the field will be reviewed, with a focus on these recent scientific results.     

New gravitational experiment with ultracold neutrons

The results of a new neutron gravitation experiment are reported. The change in the energy of a neutron falling to a known height in the Earth’s gravitational field is compensated by an energy quantum ?Θ transferred to the neutron as a result of the phase modulation of the neutron wave. A phase diffraction grating moving across the direction of the propagation of the neutron wave is used as a modulator. The experiment has been carried out with ultracold neutrons Interference filters, neutron analogues of Fabry-Perot interferometers, are used for the spectrometry of ultracold neutrons. The force m _g g _n acting on the neutron in the Earth’s gravitational field has been measured with an accuracy of about 0.2%.     

2.5-MeV neutron source controlled by high-intensity pulsed laser generating plasma

A laptop neutron source suited for the most demanding field or laboratory applications is presented. It is based on laser ablation of CD₂ primary targets, plasma acceleration of the D⁺ ions, and their irradiation of secondary CD₂ targets. The deuterium–deuterium (D-D) fusion reaction is induced in the secondary target, according to the values of fusion cross-section versus deuteron energy, which show a significant probability also at relatively low ion energies. The experiments were completed in the PALS laboratory, Prague, detecting monoenergetic neutrons at 2.45 MeV with an emission flux of about 10⁹ neutrons per laser shot. Other experiments demonstrating the possibility to induce D-D events were performed at IPPLM, Warsaw, and at INFN-LNS, Catania, where the deuterons were accelerated at about 4 MeV and 50 keV, respectively. In the last case, a low laser intensity and a post-ion acceleration system were employed. A special interaction chamber, under vacuum, is proposed to develop a new source of monochromatic neutrons or thermalized distribution of neutrons     

On the question of possible experimental observation of Anderson localization of the neutron

A possible experiment is discussed, for the observation of Anderson localization of the neutron. The localized state may be formed in the process of inelastic downscattering of thermal or cold neutrons in a highly disordered substance with low neutron capture and upscattering cross sections. The lifetime of trapped (localized) neutrons in the sample is measured by counting the upscattered neutrons with a neutron counter surrounding the sample. Estimations of experimental parameters relevant to such an experiment are given. Received: 12 May 1997 / Revised: 12 September 1997 / Accepted: 16 September 1997