Interaction Of Ultracold Neutrons Research Articles

Superfluid helium film may greatly increase the storage time of ultracold neutrons in material traps

We propose a method to increase both the neutron storage time and the precision of its lifetime measurements by at least tenfold. The storage of ultracold neutrons (UCN) in material traps now provides the most accurate measurements of neutron lifetime and is used in many other experiments. The precision of these measurements is limited by the interaction of UCN with the trap walls. We show that covering trap walls with liquid helium may strongly decrease the UCN losses from material traps. $^4$He does not absorb neutrons at all. Superfluid He covers the trap walls as a thin film, $\sim 10$ nm thick, due to the van der Waals attraction. However, this He film on a flat wall is too thin to protect the UCN from their absorption inside a trap material. By combining the van der Waals attraction with capillary effects we show that surface roughness may increase the thickness of this film much beyond the neutron penetration depth $\sim 33$nm. Using liquid He for UCN storage requires low temperature $T<0.5$ K to avoid neutron interaction with He vapor, while the neutron losses because of the interaction with surface waves are small and can be accounted for using their linear temperature dependence.

CONDENSATION OF COLD NEUTRONS – IDEA OF G.A.GAMOW. CHEMICAL PROPERTIES OF THE NEUTRON MATTER AND ITS PLACE IN THE PERIODIC SYSTEM OF ELEMENTS

Today, the neutron matter and neutron stars are already substantially rooted in the nuclear physics and astrophysics, and it is logical to have their consideration of them in terms of properties and principles of general chemistry. The formation of a neutron substance, in addition to gravitational neutronization, is considered, other mechanisms, such as the condensation of ultracold neutrons (UCN) and neutronization due to a critical increase in the atomic number in the periodic table (PS). The stability of the neutron substance is substantiated already at the micro level due to Tamm interaction and not only at the macro level due to the gravitational interaction, as it is now considered in astrophysics. A neutron substance is a very concrete physical reality, urgently demanding its rightful place in the PS and studying not only physical, but also chemical, and possibly even in the near future, engineering and technical properties. We also consider the possibility of a chemical interaction of UCN with molecules of substances with an odd number of electrons. It is proposed to extend the PS beyond the limits of classical substances and to cover a much wider range of matter in the universe, based on the forgotten ideas of D.I. Mendeleev. Moreover, PS begins with neutron and its isotopes (dineutron, tetraneutrone, etc.) and ends the neutron stellar substance.

PENTrack—a simulation tool for ultracold neutrons, protons, and electrons in complex electromagnetic fields and geometries

Modern precision experiments trapping low-energy particles require detailed simulations of particle trajectories and spin precession to determine systematic measurement limitations and apparatus deficiencies. We developed PENTrack, a tool that allows to simulate trajectories of ultracold neutrons and their decay products—protons and electrons—and the precession of their spins in complex geometries and electromagnetic fields. The interaction of ultracold neutrons with matter is implemented with the Fermi-potential formalism and diffuse scattering using Lambert and microroughness models. The results of several benchmark simulations agree with STARucn v1.2, uncovered several flaws in Geant4 v10.2.2, and agree with experimental data. Experiment geometry and electromagnetic fields can be imported from commercial computer-aided-design and finite-element software. All simulation parameters are defined in simple text files allowing quick changes. The simulation code is written in C++ and is freely available at github.com/wschreyer/PENTrack.git.

НЕЙТРОННОЕ ВЕЩЕСТВО КАК «НАЧАЛО» И «КОНЕЦ» ПЕРИОДИЧЕСКОЙ СИСТЕМЫ ЭЛЕМЕНТОВ Д.И. МЕНДЕЛЕЕВА

Currently, neutron matter and neutron stars as subjects of research are firmly established in physics and astrophysics. It is logical to consider their chemical properties, based on the principles of general chemistry. The paper shows how neutron matter is formed; besides gravitational neutronization, other mechanisms, such as condensation of ultracold neutrons (UCN) and neutronization by critically increasing the sequence number of elements in the Periodic System (PS) are considered. Thus, arises the question of a possible “end” of the PS. Proceeding from the initial D.I. Mendeleev’s premise concerning his PS, the neutron matter must inevitably be placed in a group of rare gases and at the “beginning” of the System. The possibility of a chemical interaction of UCN with the substances with an odd number of electrons is also considered. A planned experiment to study the chemical properties of UCN is discussed. We offer to expand PS beyond classical chemical substances and use it to cover much wider universe matter, based on the forgotten ideas of D.I. Mendeleev. As a result, neutron and its isotopes (dineutron, tetraneutron, etc.) will begin and the neutron star matter will end the PS.

Quantum levitation of nanoparticles seen with ultracold neutrons

Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nano-droplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing small heating of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there.

Quasielastic scattering in the interaction of ultracold neutrons with a liquid wall and application in a reanalysis of the Mambo I neutron-lifetime experiment

We develop a theory of ultracold and very cold neutron scattering on viscoelastic surface waves up to second-order perturbation theory. The results are applied to reanalyze the 1989 neutron-lifetime experiment using ultracold neutron storage in a Fomblin-coated vessel by Mampe et al. [Phys. Rev. Lett. 63, 593 (1989)]. Inclusion of this theory of the quasielastic scattering process in the data analysis shifts the neutron lifetime value from $887.6\ifmmode\pm\else\textpm\fi{}3$ to $882.5\ifmmode\pm\else\textpm\fi{}2.1$ s.

Search for long-range forces by means of ultracold neutrons (1)

A method of using a gravitational spectrometer to search for long-range forces between neutrons and atoms is proposed. The constraints on the strength of long range forces within the range of 10−10–10−4 cm can be obtained from the experiments on measurements of the total cross section of interaction of ultracold neutrons with atoms of noble gases (He, Ne, Ar, 86Kr) and the data on the coherent neutron scattering length of the nucleus. The first result of such type analysis is presented.

Interaction of ultra-cold neutrons with condensed matter

A general theory of neutron scattering (elastic and inelastic) is presented. It is applicable to the whole domain of slow neutrons and includes, as limiting cases, existing theories for thermal and cold neutrons and for the elastic scattering of UCN. A new expression for the inelastic scattering cross section for UCN is proposed. It differs from the one usually used by consistently taking into account re-scattering processes. Evidence for slight heating and cooling of UCN is given.

Interaction of ultracold neutrons with liquid surface modes as a possible reason for neutron energy spread during long storage in fluid wall traps

Interaction of ultracold neutrons with surface liquid modes is considered in connection with recent possible observation of small ultracold neutron cooling and heating during long storage in closed traps covered with Fomblin grease.

The total cross sections of the interaction of ultracold neutrons with H2O and D2O

The total cross sections of the interaction of ultracold neutrons with H2O and D2O

Interaction of ultracold neutrons with natural uranium and its isotope235U

This paper examines the energy dependence of the total cross sections for the reactions of ultracold neutrons with natural uranium and uranium 235. The cross sections were measured on an ultracold-neutron time-of-flight spectrometer at the reactor of the Reactor Engineering Institute in Moscow. A full description of the data acquisition spectrometer system is provided. Cross sections and spectra for the reactions are tabulated. The total cross sections were found to be determined mainly by capture and fission reactions.

The interaction of Ultra-Cold Neutrons (UCN) with liquid helium and a superthermal UCN source

We discuss the interaction of Ultra-Cold and Cold Neutrons with superfluid 4He and show that this interaction has all the characteristics which are necessary for the achievement of extremely high densities of UCN.