Neutron Momentum Research Articles

Riptide: a proton-recoil track imaging detector for fast neutrons

Riptide is a detector concept aiming to track fast neutrons. It is based on neutron-proton elastic collisions inside a plastic scintillator, where the neutron momentum can be measured by imaging the scintillation light. More specifically, by stereoscopically imaging the recoil proton tracks, the proposed apparatus provides neutron spectrometry capability and enable the online analysis of the specific energy loss along the track. In principle, the spatial and topological event reconstruction enables particle discrimination, which is a crucial property for neutron detectors. In this contribution, we report the advances on the Riptide detector concept. In particular, we have developed a Geant4 optical simulation to demonstrate the possibility of reconstructing with sufficient precision the tracks and the vertices of neutron interactions inside a plastic scintillator. To realistically model the optics of the scintillation detector, mono-energetic protons were generated inside a 6 × 6 × 6 cm3 cubic BC-408 scintillator, and the produced optical photons were propagated and then recorded on a scoring plane corresponding to the surfaces of the cube. The photons were then transported through an optical system to a 2 × 2 cm2 photo sensitive area with 1 Megapixel. Moreover, we have developed two different analysis procedures to reconstruct 3D tracks: one based on data fitting and one on Principal Component Analysis. The main results of this study will be presented with a particular focus on the role of the optical system and the attainable spatial and energy resolution.

Angular distribution of γ rays from a neutron-induced p -wave resonance of Xe132

A neutron-energy dependent angular distribution was measured for individual $\gamma$-rays from the 3.2 eV $p$-wave resonance of $^{131}$Xe+$n$, that shows enhanced parity violation owing to a mixing between $s$- and $p$-wave amplitudes. The $\gamma$-ray transitions from the $p$-wave resonance were identified, and the angular distribution with respect to the neutron momentum was evaluated as a function of the neutron energy for 7132 keV $\gamma$-rays, which correspond to a transition to the 1807 keV excited state of $^{132}$Xe. The angular distribution is considered to originate from the interference between $s$- and $p$-wave amplitudes, and will provide a basis for a quantitative understanding of the enhancement mechanism of the fundamental parity violation in compound nuclei.

Neural network model of neutral beam injection in the EAST tokamak to enable fast transport simulations

The neutral beam injection (NBI) system in EAST produces energetic neutral particles, which collide with electrons and ions in tokamak plasmas and heat the plasmas through Coulomb collisions. Moreover, it drives a non-inductive source of current, due to the charge-exchange collision between neutral particles and ions, and injects toroidal torque, which generates a toroidal rotation of the plasma. The effect caused by the NBI system, such as plasma heating, current drive, total neutron rate, momentum transfer, and shine-through, are modeled by a comprehensive module called NUBEAM. However, NUBEAM is computationally intensive since it relies on Monte Carlo methods. In this work, a neural network model has been developed as a surrogate model for NUBEAM in EAST. The database for neural-network model training, validation and testing is generated by running TRANSP for experimental discharges from recent EAST campaigns (after the latest NBI upgrade) while using the NUBEAM module. Simulation results illustrate that the trained neural network has the capability of replicating the predictions made by NUBEAM while demanding a significantly shorter execution time. These results indicate that surrogate models like the one proposed in this work could enable fast transport simulations for EAST after integrating them into a control-oriented predictive code such as COTSIM.

Dineutron correlations in knockout reactions with Borromean halo nuclei

We study dineutron correlations in proton-target knockout reactions induced by Borromean two-neutron halo nuclei. Using a core + n + n three-body model for the projectile and a quasifree sudden reaction framework, we focus on the correlation angle as a function of the intrinsic neutron momentum. Our results indicate that the correlations are strong in a range of neutron momenta associated to the nuclear surface. We also discuss on the role of core excitations for such correlations.

New level of precision in study of neutron beta-decay. Theoretical basics and experimental backgrounds

The article provides a theoretical substantiation for a significant increase in the level of accuracy in determining the neutron lifetime using an alternative concept of neutron beta decay. Neutrons are distributed among different subsets depending on the sign of the scalar product of the neutron spin vector and momentum of the emitted electron during decay. Therefore, the neutron lifetime can be determined separately for each of the subsets as the inverse frequency of its decay, which is to be averaged over the number of neutrons in this subset. The total neutron lifetime on the total set of neutrons is calculated by averaging the partial (basic) lifetimes, considering their weights. The weights of the basic lifetimes are calculated for two weighing methods, leading, respectively, to the so-called lifetime of "nonpolarized" neutrons, the weighted average lifetime of neutrons and the central lifetime, i.e. the arithmetic mean for the basic lifetimes of neutrons. The dependence between different average neutron lifetimes through the integral asymmetry parameter calculated by using known experimental data leads to simple analytical expressions. The numerical estimate of the weighted average neutron lifetime gives a value that is in good agreement with the results of well-known experiments, which proves the validity of the proposed concept of neutron beta decay. This article includes necessary conditions for a new experiment to bring the neutron lifetime determination to a new level of accuracy.

“RIPTIDE” — an innovative recoil-proton track imaging detector

Neutron detectors perform key tasks in many research fields as nuclear, particle and astroparticle physics as well as neutron dosimetry, radiotherapy, and radiation protection. Neutron detectors exhibiting tracking capability are still missing, although several approaches to neutron momentum reconstruction have been proposed. In this context, we aim at developing a novel RecoIl-Proton Track Imaging DEtection system “RIPTIDE”, in which the light output of a fast scintillation signal is used to perform a complete reconstruction in space and time of the neutron-proton elastic scattering. The 3D track reconstruction is going to be implemented by state-of-the-art high-sensitivity imaging detector (CMOS, MCP-Timepix). Preliminary Geant4 simulations of the proposed set-up show up a good detection efficiency in a compact active volume. The envisaged electronic readout can be easily adapted according to a specific application (event-by-event mode or integration mode). The system can be rescaled by increasing the detection volume or by combining several detection modules. Further developments of the basic detection technique can be adapted for fast charged particle detection tracking as well.

Efficiency Studies of Fast Neutron Tracking Using MCNP

Fast neutron identification and spectroscopy is of great interest to nuclear physics experiments. Using the neutron elastic scattering, the fast neutron momentum can be measured. Wang and Morris introduced the theoretical concept that the initial fast neutron momentum can be derived from up to three consecutive elastic collisions between the neutron and the target, including the information of two consecutive recoil ion tracks and the vertex position of the third collision or two consecutive elastic collisions with the timing information. Here, we also include the additional possibility of measuring the deposited energies from the recoil ions. In this paper, we simulate the neutron elastic scattering using the Monte Carlo N-Particle Transport Code (MCNP) and study the corresponding neutron detection and tracking efficiency. The corresponding efficiency and the scattering distances are simulated with different target materials, especially natural silicon (92.23%28Si, 4.67%29Si, and 3.1%30Si) and helium-4 (4He). The timing of collision and the recoil ion energy are also investigated, which are important characters for the detector design. We also calculate the ion traveling range for different energies using the software, “The Stopping and Range of Ions in Matter (SRIM)”, showing that the ion track can be most conveniently observed in 4He unless sub-micron spatial resolution can be obtained in silicon.

Nucleon momentum gap in asymmetric nuclear matter

For more than half a century, nucleons were considered to move continuously in the nuclei. Recent electron-scattering experiments indicate about 20--25% of nucleons in heavier nuclei are involved in the neutron-proton short-range correlations. Nucleons in the nuclei thus have abnormal behavior unlike those in the noninteraction fermi gas. In the neutron-rich nuclei, around the Fermi momentum, the neutron-proton short-range correlations lead to a momentum gap in the proton momentum distribution, which is circumstantially supported by the pionic experimental data. Likewise, there should also be a neutron momentum gap in the proton-rich nuclei. Nucleon momentum gap is thought to have profound and extensive implications in the studies ranging from particle physics to neutron stars as well as ultracold atomic gases.

Finding signatures of the nuclear symmetry energy in heavy-ion collisions with deep learning

A deep convolutional neural network (CNN) is developed to study symmetry energy (Esym(ρ)) effects by learning the mapping between the symmetry energy and the two-dimensional (transverse momentum and rapidity) distributions of protons and neutrons in heavy-ion collisions. Supervised training is performed with labeled data-set from the ultrarelativistic quantum molecular dynamics (UrQMD) model simulation. It is found that, by using proton spectra on event-by-event basis as input, the accuracy for classifying the soft and stiff Esym(ρ) is about 60% due to large event-by-event fluctuations, while by setting event-summed proton spectra as input, the classification accuracy increases to 98%. The accuracies for 5-label (5 different Esym(ρ)) classification task are about 58% and 72% by using proton and neutron spectra, respectively. For the regression task, the mean absolute errors (MAE) which measure the average magnitude of the absolute differences between the predicted and actual L (the slope parameter of Esym(ρ)) are about 20.4 and 14.8 MeV by using proton and neutron spectra, respectively. Fingerprints of the density-dependent nuclear symmetry energy on the transverse momentum and rapidity distributions of protons and neutrons can be identified by convolutional neural network algorithm.

Opening angle and dineutron correlations in knockout reactions with Borromean two-neutron halo nuclei

Background: Knockout reactions with proton targets provide an invaluable tool to access the properties of two-neutron halo nuclei. Recently, experimental results for the average opening angle as a function of the intrinsic neutron momentum in $^{11}\mathrm{Li}$ have shown a localization of dineutron correlations on the nucleus surface.Purpose: Study the model dependence and the effect of distortion and absorption on the opening angle distributions to assess the reliability of this observable to extract properties of Borromean two-neutron halo nuclei.Method: A quasifree sudden model is used to describe the knockout process, where absorption effects are modeled by the eikonal $S$ matrix between the proton target and the core of the Borromean nucleus. Final states in momentum space are built within a three-body model for the projectile, which enables the description of momenta and opening angle distributions.Results: A strong dependence on absorption effects is found for the opening angle at large intrinsic momenta, while the region of lower momenta is mostly insensitive to them. Reasonable agreement with the available data is obtained for $^{11}\mathrm{Li}$ at low momenta with weights for $s$ and $p$ waves different from those previously reported, showing a model dependence in their extraction. For $^{19}\mathrm{B}$, test calculations show marked sensitivity to small $p$-wave components.Conclusions: The opening angle for $(p,pn)$ knockout reactions on Borromean nuclei at small intrinsic momenta is a reliable observable mostly sensitive to the structure of the Borromean nucleus. For larger momenta, the reaction mechanism leads to a larger distortion of the distribution. In the case of nuclei with small components of opposite parity to the dominant ones, this observable can be used to explore them. The relation between dineutron in coordinate space and opening angle in momentum space is found to be model dependent.

Surface Localization of the Dineutron in ^{11}Li.

The formation of a dineutron in the ^{11}Li nucleus is found to be localized to the surface region. The experiment measured the intrinsic momentum of the struck neutron in ^{11}Li via the (p,pn) knockout reaction at 246 MeV/nucleon. The correlation angle between the two neutrons is, for the first time, measured as a function of the intrinsic neutron momentum. A comparison with reaction calculations reveals the localization of the dineutron at r∼3.6 fm. The results also support the density dependence of dineutron formation as deduced from Hartree-Fock-Bogoliubov calculations for nuclear matter.

The CLAS12 Backward Angle Neutron Detector (BAND)

The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted at backward angles of 155° to 175°, with momenta between 200 and 600 MeV/c0. It is positioned 3-m upstream of the target, consists of 18 rows and 5 layers of 7.2-cm by 7.2-cm scintillator bars, and read out on both ends by PMTs to measure time and energy deposition in the scintillator layers. Between the target and BAND there is a 2-cm thick lead wall followed by a 2-cm veto layer to suppress gammas and reject charged particles. This paper discusses the component-selection tests and the detector assembly. Timing calibrations (including offsets and time-walk) were performed using a novel pulsed-laser calibration system, resulting in time resolutions better than 250 ps (150 ps) for energy depositions above 2 MeV (5 MeV). Cosmic rays and a variety of radioactive sources were used to calibration the energy response of the detector. Scintillator bar attenuation lengths were measured. The time resolution results in a neutron momentum reconstruction resolution, δp/p<1.5% for neutron momentum 200≤p≤600 MeV/c. Final performance of the BAND with CLAS12 is shown, including electron–neutral particle timing spectra and a discussion of the off-time neutral contamination as a function of energy deposition threshold.

Generalized contact formalism analysis of the 4He(e,e′pN) reaction

Measurements of short-range correlations in exclusive 4He(e,e′pN) reactions are analyzed using the Generalized Contact Formalism (GCF). We consider both instant-form and light-cone formulations with both the AV18 and local N2LO(1.0) nucleon-nucleon (NN) potentials. We find that kinematic distributions, such as the reconstructed pair opening angle, recoil neutron momentum distribution, and pair center of mass motion, as well as the measured missing energy, missing mass distributions, are all well reproduced by GCF calculations. The missing momentum dependence of the measured 4He(e,e′pN)/4He(e,e′p) cross-section ratios, sensitive to nature of the NN interaction at short-distacnes, are also well reproduced by GCF calculations using either interaction and formulation. This gives credence to the GCF scale-separated factorized description of the short-distance many-body nuclear wave-function.

Quasi-free limit in the deuteron-deuteron three-body break-up process

Detailed measurements of vector and tensor analyzing powers of the ^{2}{\rm H}(\vec d,dp){n} break-up process are presented. The data were obtained using a polarized deuteron-beam with an energy of 65 MeV/nucleon impinging on a liquid-deuterium target. The experiment was conducted at the AGOR facility at KVI using the BINA 4\piπ-detection system. The focus of this contribution is to analyze data of the dddd scattering process in the regime at which the neutron acts as a spectator, which we refer to as the quasi-free (QF) limit. To achieve this, events for which the final-state deuteron and proton are coplanar have been analyzed and the data have been sorted for various reconstructed momenta of the missing neutron. In the limit of vanishing neutron momentum and at small deuteron-proton momentum transfer, the data match very well with measured and predicted spin observables of the elastic deuteron-proton scattering process. The agreement deteriorates rapidly with increasing neutron momentum and deuteron-proton momentum transfer. The results of coplanar configurations in four-body phase space are compared with the results of recent available theoretical calculations based on the Single-Scattering Approximation.

Magnetic Spin Susceptibility of Graphene in Ferromagnetic State: A Tight-Binding Model Study

We report here a tight-binding model study of frequency-dependent ferromagnetic spin susceptibility of the graphene system. The tight-binding Hamiltonian consists of electron hoppings up to third-nearest-neighbors, substrate and impurity effects in the presence of Coulomb interaction of electrons separately at two in-equivalent A and B sub-lattices of graphene. To calculate magnetic susceptibility, we calculate the two-particle electron Green’s functions by using Zubarev’s double time Green’s function technique. The electron occupations at A and B sub-lattices for both up and down spins are computed numerically and self-consistently. The frequency-dependent real part of ferromagnetic susceptibility of the system is computed numerically by taking [Formula: see text] grid points of the electron momentum. The susceptibility displays a sharp peak at the neutron momentum transfer energy at low energies and another higher energy resonance peak appearing at substrate-induced gap. The [Formula: see text]-peak shifts to a higher energy with the increase of momentum [Formula: see text]. The susceptibility shows that the high energy peak shifts to higher energies due to the corresponding increase of substrate-induced gap observed experimentally. It is observed that the Coulomb interaction suppresses the substrate-induced gap, but the impurity doping at A site enhances the substrate-induced gap, while doping at B site suppresses it.

Extended Relativistic Invariance, Quantization of the Kinetic Momentum

The aim of this research is a better understanding of the quantization in physics. The true origin of the quantization is the existence of the quantized kinetic momentum of electrons, neutrinos, protons and neutrons with the value. It is a consequence of the extended relativistic invariance of the wave of fundamental particles with spin 1/2. This logical link is due to properties of the quantum waves of fermions, which are functions of space-time with value into the and End(Cl3) Lie groups. Space-time is a manifold forming the auto-adjoint part of . The Lagrangian densities are the real parts of the waves. The equivalence between the invariant form and the Dirac form of the wave equation takes the form of Lagrange's equations. The momentum-energy tensor linked by Noether's theorem to the invariance under space-time translations has components which are directly linked to the electromagnetic tensor. The invariance under of the kinetic momentum tensor gives eight vectors. One of these vectors has a time component with value . Resulting aspects of the standard model of quantum physics and of the relativistic theory of gravitation are discussed.

Signature of Λ(1405) resonance in K− +6Li reaction

We investigate whether the mass and momentum spectra of emitted particles in [Formula: see text] reaction can be used for disentangling the nature of [Formula: see text](1405) and how the signature of the [Formula: see text](1405) resonance appears in the cross-sections of the kaon-lithium reaction on the physical real energy. We used different types of [Formula: see text] potentials to study the dependence of the results to the fundamental kaon-nucleon interaction. The momentum spectra are calculated for final pions and neutrons. The possibility of the observation of the [Formula: see text](1405) resonance in the mass spectra is studied. It was demonstrated that the [Formula: see text] mass and neutron momentum spectra are more suitable than the pion momentum spectra to see the trace of the [Formula: see text](1405) resonance and it is a useful tool for investigating the subthreshold behavior of the [Formula: see text] interaction.

Neutron spin rotation measurements

The neutron spin rotation (NSR) collaboration used parity-violating spin rotation of transversely polarized neutrons transmitted through a 0.5 m liquid helium target to constrain weak coupling constants between nucleons. While consistent with theoretical expectation, the upper limit set by this measurement on the rotation angle is limited by statistical uncertainties. The NSR collaboration is preparing a new measurement to improve this statistically-limited result by about an order of magnitude. In addition to using the new high-flux NG-C beam at the NIST Center for Neutron Research, the apparatus was upgraded to take advantage of the larger-area and more divergent NG-C beam. Significant improvements are also being made to the cryogenic design. Details of these improvements and readiness of the upgraded apparatus are presented. We also comment on how recent theoretical work combining effective field theory techniques with the 1/Nc expansion of QCD along with previous NN weak measurements can be used to make a prediction for dϕ/dz in 4He. An experiment using the same apparatus with a room-temperature target was carried out at LANSCE to place limits on parity-conserving rotations from possible fifth-force interactions to complement previous studies. We sought this interaction using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The results of this measurement and its impact on the neutron-matter coupling gA2 from such an interaction are presented. The NSR collaboration is also preparing a new measurement that uses an upgraded version of the room-temperature target to be run on the NG-C beamline; and it is expected to constrain gA2 by at least two additional orders of magnitude for λc between 1 cm and 1 μm.

A search for deviations from the inverse square law of gravity at nm range using a pulsed neutron beam

Recently published results and ongoing experimental efforts to search for deviations from the inverse square law of gravity at the nanometer length scale using slow neutron scattering from the noble gases are discussed. Using the pulsed slow neutron beamline BL05 at the Materials and Life Sciences Facility at J-PARC, we measured the neutron momentum transfer (q) dependence of the differential scattering cross section for the noble gases He, Ne, Ar, Kr, and Xe. By comparing to the distributions obtained using pseudo-experimental Monte Carlo simulations and forming ratios between Xe and He, we placed an upper bound on the strength of a new interaction as a function of interaction length λ which improved upon previous results in the region λ &lt; 0.1 nm, and remains competitive in the larger λ region. Additionally we describe how we are using our technique to extract relative values of the total neutron scattering cross sections of the noble gases, as well as how we plan to measure the neutron-electron scattering length using the NOVA instrument on BL21 at J-PARC.

A search for possible long range spin dependent interactions of the neutron from exotic vector boson exchange

We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that interactions would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, ϕ′=[2.8±4.6(stat.)±4.0(sys.)]×10−5 rad/m is consistent with zero. This result improves the upper bounds on the neutron-matter coupling gA2 by about three orders of magnitude for force ranges in the mm– μm regime.