Neutron Drop Research Articles

Neutron drop trapped in axially deformed external fields

The neutron drop is firstly investigated in an axially symmetric harmonic oscillator (ASHO) field, whose potential strengths of different directions can be controlled artificially. The shape of the neutron drop will change from spherical to oblate or prolate according to the anisotropy of the external field. With the potential strength increasing in the axial direction, the neutron prefers to occupy the orbital perpendicular to the symmetry axis. On the contrary, the neutron likes to stay in the orbital parallel to the symmetry axis when the potential strength increases in the radial direction. Meanwhile, when the potential strength of one direction disappears, the neutron drop cannot bind together. These investigations are not only helpful to simulate the properties of neutrons in finite nuclei but also provide the theoretical predictions to the future artificial operations on the nuclei like the ultracold atom system, for a deeper realization of quantum many-body systems.

Impact of tensor forces on spin-orbit splittings in neutron-proton drops

A systematic study of the tensor-force impact in neutron-proton drops has been reported using the relativistic Hartree-Fock (RHF) theory with the $\ensuremath{\pi}\text{\ensuremath{-}}N$ coupling strength optimized to the relativistic Brueckner-Hartree-Fock (RBHF) results for neutron drops. The evolutions of the neutron spin-orbit splittings as a function of the neutron number for neutron-proton drops with one proton behave similarly to the pure neutron drops, which show the tensor-force effect. By adding one more proton or neutron in the neutron drop with $N=20$, it is found that the tensor-force effect is more prominent between neutrons and protons than between neutrons. This can be attributed to the isospin factor in the tensor term of the $\ensuremath{\pi}\text{\ensuremath{-}}N$ interaction in the RHF density functional theory, which reflects the fact that the neutron-proton tensor force is stronger than the neutron-neutron one. Similar behavior for the spin-orbit splitting evolutions has also been found for the neutron-proton drops with 20 protons, where the tensor-force strength $\ensuremath{\lambda}$ is redetermined according to the RBHF results due to the large central densities of the systems.

Symmetry energy at supra-saturation densities via the gravitational waves from GW170817

Motivated by the historical detection of gravitational waves from GW170817, the neutron star and the neutron drop, i.e., a certain number of neutrons confined in an external field, are systematically investigated by ab initio calculations as well as the nonrelativistic and relativistic state-of-art density functional theories. Strong correlations are found among the neutron star tidal deformability, the neutron star radius, the root-mean-square radii of neutron drops, and the symmetry energies of nuclear matter at supra-saturation densities. From these correlations and the upper limit on the tidal deformability extracted from GW170817, the neutron star radii, the neutron drop radii, and the symmetry energy at twice saturation density are respectively constrained as $R_{1.4M_{\odot}}\leqslant 12.94$ km, $R_{\rm nd} \leqslant 2.36$ fm, and $E_{\mathrm{sym}}(2\rho_0) \leqslant 53.2$ MeV.

Effects of pairing correlation on neutron drop

In this work, the effects of the pairing correlation on the properties of neutron drops $N$=6-50 trapped in a harmonic oscillator potential with $\hbar\omega=10$ MeV are investigated by comparing the results given by the Skyrme Hartree-Fock and Hartree-Fock-Bogoliubov theories with the density-dependent delta interaction (DDDI) pairing force. The results showed that the pairing correlation slightly made the neutron drops more bound, and increased the central neutron density, the spin-orbit and pseudo spin-orbit splittings. Thus, the pairing correlation must be accounted for to improve the Skyrme functional compared with the ab initio calculations. Furthermore, although the single-particle energy gaps with or without pairing were similar, the shell closures varied due to pair scattering. Here, the shell closures in neutron drops using the SkM* parameter set and DDDI pairing force were found at $N$=8, 16, and 32.

An impact of inherent neutron source on subcriticality measurement in a highly enriched uranium core of Kyoto University Critical Assembly

ABSTRACT In a variety of highly enriched uranium cores of Kyoto University Critical Assembly, many different subcriticality measurements have been strenuously performed. However, any influence of neutron source inherent in the highly enriched uranium fuels on these measurements has hardly been studied. This is because the influence has been expected to be negligible in the fuels. In this study, we revaluated the influence on pulsed neutron, accelerator-beam trip and rod drop measurements to reveal an unexpected impact of the weak inherent source. Especially, the inherent source was injurious to most of the beam trip and the rod drop measurements based on the integral count method. The least-squares inverse kinetics analysis also had a significant influence on the inherent source. In the area ratio analysis for a pulsed neutron measurement, a considerable number of neutrons from the inherent source was mixed into delayed-neutron area. When the influence was considered in these data analyses, the subcritical reactivity of the above measurements was in good agreement with that calculated by the continuous-energy Monte Carlo code MVP.

The Periodic Table Possible Coincided with an Unfolded Shape of Atomic Nuclei

The periodic table seems to correspond to folding nuclei, a visible proton (nucleon) distribution, that can grow vertical 4 a (representative), 4 b (transition), and 8 c (inner transition) axes (alpha-clusters) bound with valence neutrons standing a core (1st period) of likely expanding in Co, Ni, Rh, and Pd, which was naturally within proton and neutron drop lines, and roughly able to fit in with nuclear fission phenomena, including alpha-cluster decay. It was observed in analysis molecular structures that crosses nuclear, atomic, and molecular three levels, which provides a convenient way that will enable the nature of the periodic table promisingly to become easier understanding.

Properties of trapped neutrons interacting with realistic nuclear Hamiltonians

We calculate properties of neutron drops in external potentials using both quantum Monte Carlo and no-core full configuration techniques. The properties of the external wells are varied to examine different density profiles. We compare neutron drop results given by a selection of nuclear Hamiltonians, including realistic two-body interactions as well as several three-body forces. We compute a range of properties for the neutron drops: ground-state energies, spin-orbit splittings, excitation energies, radial densities and rms radii. We compare the equations of state for neutron matter for several of these Hamiltonians. Our results can be used as benchmarks to test other many-body techniques, and to constrain properties of energy-density functionals.

Study of fast-ion transport induced by fishbones on JET

The impact of fishbone oscillations onto a confined fast-ion population is simulated for a JET plasma and benchmarked against experiment quantitatively with the help of neutron rate measurements. The transient drops in volume integrated neutron emission are found to be mainly caused by the spatial redistribution of the (neutral beam injected) fast-ion population confined in the plasma rather than by fast-ion loss. The simulations yield a quadratic dependence of the neutron drop on the fishbone amplitude. It is found that the simulations are able to correctly reproduce the magnitude of the experimentally observed drop in volume integrated neutron emission to within a factor 2. Furthermore, frequency chirping is found to be important. Omitting the fishbone frequency chirp in the simulations reduces the magnitude of the neutron rate drop (and hence fast-ion redistribution) to about half its original value.

Testing the density matrix expansion againstab initiocalculations of trapped neutron drops

Microscopic input to a universal nuclear energy density functional can be provided through the density matrix expansion (DME), which has recently been revived and improved. Several DME implementation strategies are tested for neutron drop systems in harmonic traps by comparing to Hartree-Fock (HF) and ab initio no-core full configuration (NCFC) calculations with a model interaction (Minnesota potential). The new DME with exact treatment of Hartree contributions is found to best reproduce HF results and supplementing the functional with fit Skyrme-like contact terms shows systematic improvement toward the full NCFC results.

Neutron reflection and small-angle neutron scattering studies of a fluorocarbon telomer surfactant

Dilute aqueous phase behavior of a novel tris(hydroxymethyl)acrylamidomethane (THAM)-derived telomer bearing a perfluorohexyl hydrophobic chain, F6THAM6, has been investigated. Fluorinated polyhydroxy surfactants of this kind find use in emerging biomedical applications. Neutron reflection (NR) and drop volume surface tension (DVT) methods have been used to determine the critical micelle concentration ( cmc=4.7×10 −4 mol dm −3) and surface adsorption parameters (at the cmc NR gives a molecular area a cmc=67.4 and 62 A ̊ 2 and surface excess Γ cmc =2.46×10 −6 mol m −2) . The aggregation structures were determined by small-angle neutron scattering (SANS), indicating globular (polydisperse spheres) micelles of radius ∼30 Å are present. These findings are compared with literature on surfactants with related structures, to identify how the unusual molecular structure of F6THAM6 affects surfactant properties.

A directional dose equivalent monitor for neutrons.

A directional dose equivalent monitor is introduced which consists of a 30 cm diameter spherical phantom hosting a superheated drop detector embedded at a depth of 10 mm. The device relies on the similarity between the fluence response of neutron superheated drop detectors based on halocarbon-12 and the quality-factor-weighted kerma factor. This implies that these detectors can be used for in-phantom dosimetry and provide a direct reading of dose equivalent at depth. The directional dose equivalent monitor was characterised experimentally with fast neutron calibrations and numerically with Monte Carlo simulations. The fluence response was determined at angles of 0, 45, 90, 135 and 180 degrees for thermal to 20 MeV neutrons. The response of the device is closely proportional to the fluence-to-directional dose equivalent conversion coefficient, h'phi (10; alpha, E). Therefore, our monitor is suitable for a direct measurement of neutron directional dose equivalent, H'(10), regardless of angle and energy distribution of the neutron fluence.

Local coherence, condensation and nuclear reaction of neutrons at crystal boundary of metal hydrides and deuterides

Using a concept of the neutron Bloch wave in the one-body approximation presented previously, possibilities of the following effects in boundary regions of crystals including hydrogen isotopes are pointed out: occurrence of local coherence, formation of a neutron Cooper pair, condensation of neutrons, formation of neutron drop and an effective nuclear reaction of a nucleus with thermal neutrons. It is shown that these new states and reactions will have strong effects on solid state-nuclear physics in metal hydrides (deuterides). The stochastic occurrence of localized nuclear reactions observed in CF experiments is explained by these properties of the trapped neutron. The possible application of the nuclear reactions in metal hydrides is discussed.

Neutron Drop: Condensation of Neutrons in Metal Hydrides and Deuterides

The possible formation of the neutron drop nA-ZpZ composed of Nn = A - Z neutrons and Np = Z protons in metal hydrides and deuterides is discussed on the basis of experimental facts using the evaporation model of the decay of the compound nucleus. Exotic nuclei and the neutron drop will be formed at a region with a high neutron density in crystals including hydrogen isotopes. Successful explanation of the anomalous nuclear reaction phenomenon in solids by models assuming neutrons in a solid lattice is legitimated.

Field Aided Characterization of a Sandstone Reservoir: Arroyo Grande Oil Field, California, USA: ABSTRACT

The Arroyo Grande Oil Field in Central California has been productive since 1905 from the miopliocene Edna member of the Pismo formation. The Edna member is a massive poorly consolidated sandstone unit with an average porosity of 0.2 and a permeability of 1000-5000 md; the producing levels are shallow, 100 to 500 m from the ground surface. Excellent surface exposures of the same formation along road cuts across the field and above the reservoir provide an opportunity to study reservoir rocks at the surface and to relate fracture and permeability distribution obtained from cores to folds and faults observed in outcrops. We mapped in outcrops the major structures of the oil field and determine the statistical distribution and orientation of small faults (deformation bands) that have been observed both in cores and outcrop. The relation between deformation bands and major structures has also been characterized with detailed mapping. By using synthetic logs it is possible to determine the log signature of structural heterogeneities such as deformation bands in sandstone; these faults cause a neutron porosity drop respect to the host rock in the order of 1-4%. Image analysis has been used to determine the petrophysical properties of the sandstone inmore » outcrop and in cores; permeability is three orders of magnitude lower in faults than in the host rock and capillary pressure is 1-2 orders of magnitude larger in faults than in the host rock. Faults with tens of meters offsets are associated with an high density of deformation bands (10 to 250 m{sup -1}) and with zones of cement precipitation up to 30 m from the fault. By combining well and field data, we propose a structural model for the oil field in which high angle reverse faults with localized deformation bands control the distribution of the hydrocarbons on the limb of a syncline, thereby explaining the seemingly unexpected direction of slope of the top surface of the reservoir which was inferred by well data only.« less

Determination of large negative reactivity by integral versions of various experimental methods.

The large negative reactivity is measured in Semi-Homogeneous Experimental facility (SHE). Experimental methods are Sjöstrand's pulsed neutron, source multiplication and rod drop methods beside revised King-Simmons' pulsed neutron methods. Neutron detectors are placed at various points in the core region for multi-points measurement. Usual one-point reactor model analysis resulted in the reactivity values, strongly dependent on the detector position with the increase of subcriticality. In addition, disagreements between the used experimental methods are also pointed out. In order to overcome these difficulties due to the spatial higher harmonics and the kinetic distortion in the neutron flux distribution, an integral version analysis is applied, in which use is made of multi-points reactor model. In the analysis, space integration of the neutron counts obtained throughout the core region is made with weights of the adjoint function of fast neutrons, calculated using the two- or three-dimensional diffusion code. The negative reactivity values determined by the integral version analysis agreed well with each other within the uncertainty of ∼5% in the reactivity range down to ∼50 dollars. It is concluded that all the experimental methods are adequate for precise determination of the large negative reactivity of reactor provided that the integral version analysis is utilized or that correction is made for the change of the neutron generation time using precise calculation.