More about neutron–mirror neutron oscillation

It was pointed out recently that oscillation of the neutron n into a mirror neutron n′, a sterile twin of the neutron with exactly the same mass, could be a very fast process with baryon number violation, even faster than the neutron decay itself. This process is sensitive to magnetic fields and it could be observed by comparing the neutron loss rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of the n−n′ oscillation in the case when a mirror magnetic field B′ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field B, depending on its strength and on its orientation with respect to B′. The recent experimental data, under this hypothesis, still allow for an n−n′ oscillation time of order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation of the magnetic field. If these hints will be confirmed in future experiments, this would point to the presence of a mirror magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of other origin that makes a difference between the neutron and mirror neutron states.     

Trajectory of neutron–neutron–C excited three-body state

The trajectory of the first excited Efimov state is investigated by using a renormalized zero-range three-body model for a system with two bound and one virtual two-body subsystems. The approach is applied to n–n–¹⁸C, where the n–n$n\text{–}n$ virtual energy and the three-body ground state are kept fixed. It is shown that such three-body excited state goes from a bound to a virtual state when the n–¹⁸C binding energy is increased. Results obtained for the n–¹⁹C elastic cross-section at low energies also show dominance of an S-matrix pole corresponding to a bound or virtual Efimov state. It is also presented a brief discussion of these findings in the context of ultracold atom physics with tunable scattering lengths.     

β-delayed neutron emission studies

The study of β-delayed neutron emission plays a major role in different fields such as nuclear technology, nuclear astrophysics and nuclear structure. However the quality of the existing experimental data nowadays is not sufficient for the various technical and scientific applications and new high precision measurements are necessary to improve the data bases. One key aspect to the success of these high precission measurements is the use of a very pure ion beam that ensures that only the ion of interest is produced. The combination of the IGISOL mass separator with the JYFLTRAP Penning trap is an excellent tool for this type of measurement because of the ability to deliver isobarically and even isomerically clean beams. Another key feature of the installation is the non-chemical selectivity of the IGISOL ion source which allows measurements in the important region of refractory elements. This paper summarises the β-delayed neutron emission studies that have been carried out at the IGISOL facility with two different neutron detectors based on ³He counters in a polyethylene moderator: the Mainz neutron detector and the BEta deLayEd Neutron detector.     

Two-mirror spin–wave neutron interferometer

The characteristics of a spin-wave neutron interferometer comprising two parallel magnetic mirrors located in noncollinear to the magnetizations of the mirrors are investigated. The device can be used to study the properties of the neutron wave packet and measure the time and spatial correlations of material densities in the medium and on the surface. The interferometer’s sensitivity and the observed neutron coherence length are estimated using experimental data. The possible applications of neutron spin-echo spectrometry based on the two-mirror interferometer are discussed.     

Nano-structured Fabry–Pérot resonators in neutron optics & tunneling of neutron wave-particles

Correlated to the quantum mechanics wave-particle duality, the optical analogy between electromagnetic waves and cold neutrons manifests itself through several interference phenomena particularly the so called Frustrated Total Reflection i.e., the tunneling process in Fabry–Pérot nano-structured cavities. Prominent resonant situations offered by this configuration allow the attainment of numerous fundamental investigations and surface-interface studies as well as to devise new kinds of neutron optics devices. This review contribution reports such possibilities in addition to the recently observed peculiar Goos–Hänchen longitudinal shift of neutron wave-particles which was predicted by Sir Isaac Newton as early as 1730.     

Monte Carlo simulation of thermal neutron flux of americium–beryllium source used in neutron activation analysis

The neutron activation analysis is a method of exclusively elemental analysis. Its implementation of irradiates the sample which can be analyzed by a high neutron flux, this method is widely used in developed countries with nuclear reactors or accelerators of particle. The purpose of this study is to develop a prototype to increase the neutron flux such as americium–beryllium and have the opportunity to produce radioisotopes. Americium–beryllium is a mobile source of neutron activity of 20 curie, and gives a thermal neutron flux of (1.8 ± 0.0007) × 10⁶ n/cm² s when using water as moderator, when using the paraffin, the thermal neutron flux increases to (2.2 ± 0.0008) × 10⁶ n/cm² s, in the case of adding two solid beryllium barriers, the distance between them is 24 cm, parallel and symmetrical about the source, the thermal flux is increased to (2.5 ± 0.0008) × 10⁶ n/cm² s and in the case of multi-source (6 sources), with-out barriers, increases to (1.17 ± 0.0008) × 10⁷ n/cm² s with a rate of increase equal to 4.3 and with the both barriers flux increased to (1.37 ± 0.0008) × 10⁷ n/cm² s.     

μCF based 14 MeV intense neutron source

Results of a design study for an advanced scheme of a μCF based 14 MeV intense neutron source for test material irradiation including the liquid lithium primary target and a low temperature liquid deuterium-tritium (D–T) mixture as a secondary target are presented. According to this scheme negative pions are produced inside a 150-cm-long 0.75-cm-radius lithium target. Pions and muons resulting from the pion decay in flight are collected in the backward direction and stopped in the D–T mixture. The fusion chamber has the shape of a 10-cm-radius sphere surrounded by two 0.03-cm-thickness titanium shells. Assuming 100 fusions per muon in this scheme one can produce 14-MeV neutrons with a source strength up to 10¹⁷ n/s. A neutron flux of up to 10¹⁴ n/cm²/s can be achieved in a test volume of about 2.5 l and on the surface of about 350 cm². The results of the thermophysical and thermomechanical analysis show that the technological limits are not exceeded. This source has the advantage of producing the original 14 MeV fusion spectrum without tails, isotropically into a 4π solid angle, contrary to the d-Li stripping neutron source. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Accelerated oxygen precipitation in fast neutron irradiated Czochralski silicon

Annealing effect of the oxygen precipitation and the induced defects have been investigated on the fast neutron irradiated Czochralski silicon （CZ-Si） by infrared absorption spectrum and the optical microscopy. It is found that the fast neutron irradiation greatly accelerates the oxygen precipitation that leads to a sharp decrease of the interstitial oxygen with the annealing time. At room temperature （RT）, the 1107cm^-1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. At low temperature, the infrared absorption peaks appear at 1078cm^-1, 1096cm^-1, and 1182cm^-1, related to different shapes of the oxygen precipitates. The bulk microdefects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self-interstitial atoms are created and aggregate with oxygen precipitation.     

Possibility of ~5He emission in neutron induced reactions

There are some statistical model codes[1—4] as the evaluation tool that have been long and widely used to set up neutron data library below 20 MeV, which is the most important energy region in the application of nuclear engineering. The emitted particles considered in these codes mentioned above are neutrons, protons, as well as the compos-ite particles, such as deuterons, tritons, 3He and alpha particles. These emitted particles and nuclei can be treated as the nucleon or stable clusters. H…     

Does a neutron know that the earth is rotating?

In 1979 we observed the quantum mechanical phase shift of neutron deBroglie waves due to the Earth’s rotation. After the result was published, a number of very nice theoretical papers on the experiment appeared. I have two favorites: The one by M. Dresden and C. N. Yang in which they view the effect as due to the Doppler shift created by reflection from moving mirrors; and the other one by J. J. Sakurai in which he views the origin of the effect as being due to a flux of rotation threading the neutron interferometer loop, in much the same way that magnetic flux threads the electron interferometer loop to create the topological Aharonov-Bohm effect. Here, I would like to place their explanations of the physics of this experiment in juxtaposition with my own understanding of it. This paper is part of the 60th birthday Festschrift for Prof. Bahram Mashhoon.     

Is the nuclear spin-orbit interaction changing with neutron excess?

The difference in the energies of the lowest states corresponding to the two nodeless single-particle orbitals outside the Z=50 closed proton shell, h(11/2) and g(7/2), increases with neutron excess. We have measured the Sn(alpha,t) reaction for all seven stable even Sn isotopes and found that the spectroscopic factors are constant for these two states, confirming their characterization as single-particle states. The trend in energies is consistent with a decrease in the nuclear spin-orbit interaction. A similar trend, also suggesting a decreasing spin-orbit splitting, is seen in the energies of the neutron single-particle states outside the N=82 core, i(13/2) and h(9/2).     

The decay of the neutron–rich nucleus 216Bi

The decay of the neutron–rich isotope ²¹⁶Bi, produced by proton–induced spallation at the PS Booster–ISOLDE facility, was investigated by β-γγ, αγ coincidence and spectrum-multiscaling measurements. A new method for reducing isobaric contamination enabled to cover the unknown region “east” of ²⁰⁸Pb for the isobaric chain A=216. The half-life of the β decay of ²¹⁶Bi was found as T_1/2= 135 ± 5 s. Its decay scheme was extended and the possible shell model configurations are proposed. Received: 13 July 1999 / Revised version: 22 September 1999     

In-beamγ-ray spectroscopy of the neutron deficient100Ag

The neutron deficient nucleus¹⁰⁰Ag, three proton holes below and three neutron particles above the N=Z=50 shell closure at¹⁰⁰Sn, has been identified and studied by in-beam spectroscopy. The reactions⁴⁶Ti(⁵⁸Ni,3pn) at 231 MeV and⁶⁴Zn(⁴⁰Ca,3pn) at 167 MeV of the respective⁵⁸Ni and⁴⁰Ca beams were used, and states up to 8.7 MeV excitation energy and spin I?20 were found in two mainγ-ray cascades forming band-like structures of even and odd parity. Large scale shell model calculations suggest predominantπg ₉ ^2/?3 ν(d_5/2,g_7/2)³ andπg ₉ ^2/?3 ν(d_5/2,g_7/2)²h_11/2 structures with maximum spins I ^π = 19⁺ and I ^π =22^?, respectively, for the two level sequences. The influence ofπp_1/2 vs.νh_11/2 excitations is discussed for low lying odd-parity levels.     

Antikaon condensation in neutron star matter with strong magnetic fields

We study the influence of strong magnetic fields on antikaon condensation in neutron star matter using the quark-meson coupling (QMC) model. The QMC model describes a nuclear many-body system as nonoverlapping MIT bags interacting through the self-consistent exchange of scalar and vector meson mean fields. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly. The results of the QMC model are compared with those obtained in a relativistic mean-field (RMF) model.     

Direct neutron decay of analogue resonances in ^105Rh

A new method, while takes into account the contribution of direct neutron decay of analogue resonances to the isomeric ratio resulting from （p,n） reaction, is used to analyse the published experimental data for the reaction ^104Ru（p,n） ^104Rh and also estimate a minimum probability of direct decay.     

Pair-vibrational states in the presence of neutron–proton pairing

Pair vibrations are studied for a Hamiltonian with neutron–neutron, proton–proton and neutron–proton pairing. The spectrum is found to be rich in strongly correlated, low-lying excited states. Changing the ratio of diagonal to off-diagonal pairing matrix elements is found to have a large impact on the excited-state spectrum. The variational configuration interaction (VCI) method, used to calculate the excitation spectrum, is found to be in very good agreement with exact solutions for systems with large degeneracies having equal T=0$T=0$ and T=1$T=1$ pairing strengths.     

Thermal neutron flux detection near the Earth’s surface

The thermal neutron flux near the Earth’s surface has been measured using large unshielded neutron scintillator detectors of a new type, based on ZnS(Ag) and lithium fluoride, enriched with ⁶Li to 90%. The existence of a gradient of the thermal neutron concentration near the Earth’s surface is shown.