3He Nuclei Research Articles

An Update of the Hypothetical X17 Particle

Recently, when examining the differential internal pair creation coefficients of 8Be, 4He and 12C nuclei, we observed peak-like anomalies in the angular correlation of the e+e− pairs. This was interpreted as the creation and immediate decay of an intermediate bosonic particle with a mass of mXc2≈ 17 MeV, receiving the name X17 in subsequent publications. In this paper, our latest results obtained for the X17 particle are presented by investigating the e+e− pair correlations in the decay of the Giant Dipole Resonance (GDR) of 8Be. Our results initiated a significant number of new experiments all over the world to detect the X17 particle and determine its properties. In this paper, we will also conduct a mini-review of the experiments whose results are already published, as well as the ones closest to being published.

Dark matter scattering off H2 and He4 nuclei within chiral effective field theory

We study dark matter, assumed to be composed of weak interacting massive particles (WIMPs), scattering off H2 and He4 nuclei. In order to parametrize the WIMP-nucleon interaction, the chiral effective field theory approach is used. Considering only interactions invariant under parity, charge conjugation, and time reversal, we examine five interaction types: scalar, pseudoscalar, vector, axial, and tensor. Scattering amplitudes between two nucleons and a WIMP are determined up to second order of chiral perturbation theory. We apply this program to calculate the interaction rate as a function of the WIMP mass and of the magnitude of the WIMP-quark coupling constants. From our study, we conclude that the scalar nuclear response functions is much greater than the others due to their large combination of low energy constants. We verify that the leading order contributions are dominant in these low energy processes. We also provide an estimate for the background due to atmospheric neutrinos. Published by the American Physical Society 2024

Study of magnetic phase transitions by helium-3 in DyF3 nanoparticles

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.7 %) and DyF3 (0.3 %) powders at temperatures of 1.5–3 K was studied by pulsed nuclear magnetic resonance. DyF3 particles have ellipsoidal shape and average size 225 × 153 nm with the magnetic phase transition at temperature Tc = 2.45 K. The temperature dependence of the longitudinal and transverse magnetization relaxation rates of 3He nuclei with a mixture of LaF3 and DyF3 powders has a broad maximum near Tc, which is related to the magnetic phase transition. It is shown that the adsorbed layer of 3He is extremely sensitive to magnetic phase transitions. Preplating the particles surface with adsorbed nitrogen layers allowed to vary the distance from 3He nuclei to the surface of particles in a controlled way. Calculations of the nuclear magnetic relaxation rates with a change in the distance of helium-3 from the particle surface have been carried out, which is in good agreement with experimental data. It was shown that helium-3 is extremely sensitive to surface magnetism and can be used to study surface effects and surface magnetism.

Ab initio framework for nuclear scattering and reactions induced by light projectiles

A quantitative and predictive microscopic theoretical framework that can describe reactions induced by α particles (4He nuclei) and heavier projectiles is currently lacking. Such a framework would contribute to reducing uncertainty in the modeling of stellar evolution and nucleosynthesis and provide the basis for achieving a comprehensive understanding of the phenomenon of nuclear clustering (the organization of protons and neutrons into distinct substructures within a nucleus). We have developed an efficient and general configuration-interaction framework for the description of low-energy reactions and clustering in light nuclei. The new formalism takes full advantage of powerful second-quantization techniques, enabling the description of α-α scattering and an exploration of clustering in the exotic 12Be nucleus. We find that the 4He(α,α)4He differential cross section computed with non-locally regulated chiral interactions is in good agreement with experimental data. Our results for 12Be indicate the presence of strongly mixed helium-cluster states consistent with a molecular-like picture surviving far above the 6He+6He threshold, and reveal the strong influence of neutron decay in both the 12Be spectrum and in the 6He(6He,α)8He cross section. We expect that this approach will enable the description of helium burning cross sections and provide insight on how three-nucleon forces influence the emergence of clustering in nuclei.

Machine Learning in the Problem of Extrapolating Variational Calculations in Nuclear Physics

A modified machine learning method is proposed, utilizing an ensemble of artificial neural networks for the extrapolation of energies obtained in variational calculations, specifically in the No-core Shell Model (NCSM), to the case of the infinite basis. A new neural network topology is employed, and criteria for selecting both the data used for training and the trained neural networks for statistical analysis of the results are formulated. The approach is tested by extrapolating the deutron ground state energy in calculations with the Nijmegen II NN interaction and provides statistically significant results. This technique is applied to obtain extrapolated ground state energies of 6Li and 6He nuclei based on the NCSM calculations with Daejeon16 NN interaction.

X17: Status and Perspectives

Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the 3H(p,e −e +) 4He, 7Li(p,e −e +) 8Be, and 11B(p,e −e +) 12C processes. Kinematics indicate that this anomaly might be due to the de-excitation of 4He, 8Be, and 12C nuclei with the emission of a boson with a mass of about 17 MeV, rapidly decaying into e −e + pairs. The result of the experiments performed with the singletron accelerator of ATOMKI is reviewed, and the consequences of the so-called X17 boson in particle physics and in cosmology are discussed. Forthcoming experiments designed to shed light on the possible existence of the X17 boson are also reported.

Some of the History Surrounding the Oliphant et al. Discovery of dd Fusion and an Inference of the d(d,p)t Cross Section from This 1934 Paper

A review of the flurry of papers involving deuteron beams in 1933 and 1934 reveals some aspects of historical significance. A team led by Lawrence saw several mega-electron-volt protons and neutrons from deuteron-plus-deuteron (dd) fusion in 1933 before the discovery of this process by Oliphant et al. in 1934. However, Lawrence et al. failed to notice deuteron contamination in their targets, and instead incorrectly concluded that the protons and neutrons were being emitted back to back from the breakup of the deuterons in the relevant center-of-mass frame. By observing disintegrations induced by deuteron beams incident on deuterated targets, Oliphant et al. correctly identified dd fusion proceeding through an intermediate excited 4He nucleus that broke up into either back-to-back protons and tritons or back-to-back neutrons and 3He nuclei. Here we use Oliphant et al.’s proton production rates to infer d(d,p) cross sections that are twice the known modern values. This discrepancy is likely due to our lack of knowledge of some key aspects of Oliphant et al.’s 1934 experimental setup. However, the deuterium beam energy dependence of Oliphant et al.’s d(d,p) proton production rate is clearly consistent with the quantum mechanical tunneling through the Coulomb barrier associated with the fusion of two hydrogen isotopes.

Comparative study for the elastic scattering of the isobar nuclei 6Li and 6He on 64Zn using different nuclear potentials

The available experimental data for the elastic scattering of the isobar nuclei 6Li and 6He on [Formula: see text]Zn have been reanalyzed in the available energy range using the optical model, double folding (DF) (Sao Paulo), and crystal model (CM). Double-folding (DF) and crystal model (CM) have been used to investigate the experimental data as a real part of the optical potential, while the imaginary part was taken in Woods–Saxon (WS) shape. One value of the real part of the optical potential has been applied to the two systems under consideration. The distance of the closest approach of the 6Li (6He) + [Formula: see text]Zn systems has been extracted from the available experimental data using different methods. The extracted potential from the 6Li and 6He elastically scattered by [Formula: see text]Zn data could be used as the basis for the creation of a simple global optical potential for 6Li and 6He. The extracted normalization factor ([Formula: see text]) was equal to the unity during the fitting process avoiding its unfortunate value (in the range 0.5–0.7) exists in the literature. It was observed that interaction distances vary slowly with the energy of the projectile and strongly depend on the projectile properties. The halo properties of 6He have a significant effect on the calculated reaction cross-sections. Different methods have been applied to 6He and 6Li elastically scattered by [Formula: see text]Zn, where fair agreement between them has been observed.

Analysis of fusion reactions induced by weakly bound nuclei on medium and heavy mass targets

Fusion cross section for reactions induced by weakly bound nuclei 6He, 6,7Li 9,11Be and 10B on targets lying in the mass region 64 ≤ A ≤ 238 have been investigated at around Coulomb barrier energies within the coupled channel formalism. Specifically, the effects of coupling to low-lying excited states of reactants and those arises due to the breakup of projectile have been studied by using Broglia and Winther (BW91), Aage Winther (AW95) and fitted potential (FP) parameterization schemes. Among these the FP scheme is found to be most appropriate in the description of fusion excitation functions of various projectile-target combination. Further, it is observed that in the sub barrier energy region there is an enhancement in the fusion cross section due to coupling to excited states while there occurs fusion suppression at above barrier energies because of the breakup of the projectile.

Effect of T-Invariance Violation in Scattering of Polarized 3He Nuclei on Tensor-Polarized Deuterons

In the interaction of a transversely polarized nuclear beam with a tensor-polarized deuteron target, a nonzero value of the component of the total cross section corresponding to this combination of polarizations is an unambiguous signal ofT-invariance violation whileP-parity is preserved. The method developed earlier for calculating this component of the total cross section forpdscattering based on the Glauber theory has been generalized by us to the case of3Hedscattering, and its energy dependence in the range of beam energies 0.1–1 GeV/nucleon has been calculated. It is found that in3Hedcollisions, in contrast topdscattering, the contribution of only one type ofT-violating nucleon-nucleon forces dominates, which is essential for extraction of the unknown constant of this interaction from the corresponding data.

Effect of T-Invariance Violation in Scattering of Polarized 3He Nuclei on Tensor-Polarized Deuterons

Effect of T-Invariance Violation in Scattering of Polarized 3He Nuclei on Tensor-Polarized Deuterons

Probing 6He induced reactions with nuclear level density

Abstract In this study, both elastic and inelastic cross sections of the light exotic nucleus 6He on 12C and 4He at energies of 18 MeV, 30 MeV, 3.8 MeV, 4.2 MeV, 4.7 MeV, 5.1 MeV, 5.4 MeV, and 5.8 MeV, as well as the quasi-elastic cross section of 6He on 9Be at 16.2 MeV and 21.3 MeV, are calculated using the coupled-channel method. The deformation parameters of the first excited states of 6He, 9Be and 12C are obtained through the collective nuclear level density. The results align well with the available experimental data. It is demonstrated that the collective nuclear level density is essential to reduce the uncertainty between the deformation parameter and the optical model parameters. Furthermore, it is shown that the first excited state of both the projectile and the target must be considered in calculations 6He + 9Be scattering at increasing energies.

Estimation of Radiation Damping Rates Using 133Cs, 7Li and 31P Solution NMR Spectroscopy and a Theoretical NMR RASER Model

Radio amplification using stimulated emission of radiation (RASER) effects in the NMR can increase NMR signals over time due to a feedback loop between the sample magnetization and the probe coil coupled with radiation damping (RD). Previously, RD rates had been directly observed only for the 1H, 3He, 17O and 129Xe nuclei. We report that experimental direct measurements of an NMR RASER to determine RD time constants for the three heteronuclei (133Cs (I = 7/2), 7Li (I = 3/2) and 31P (I = 1/2)) in a highly concentrated solution from the NMR RASER emissions using a conventional NMR probe. Under conditions where the RD rate exceeds the transverse relaxation rate (i.e., the NMR RASER condition is fulfilled), we recorded both the transverse NMR RASER response to imperfect inversion and the recovery of longitudinal magnetization. The data were directly evaluated based on the well-known Bloom model as estimated RD rate constants of 8.0, 1.8 and 25 Hz for 133Cs, 7Li and 31P, respectively. The proposed method can be applied to observe RD rate constants for the other nuclei as well.

Estimation of the buildup of He-3 and Li-6 poisoning, He-4 and tritium activity in beryllium oxide reflector block in APSARA-U reactor

The Apsara-U research reactor, situated at the Bhabha Atomic Research Center, began its operation in 2018. This facility employs a fuel core configuration employing low-enriched uranium and reflector assemblies made of beryllium oxide. In neutron-rich environment of a nuclear reactor, these beryllium oxide reflector blocks participate in nuclear reactions identified as 9Be(n,α) and 9Be(n,2n). The 9Be(n,α) reaction initiates the formation of isotopes such as 4He, 6Li, 3He, and 3H in the process. The accumulation of gasses like 3He, 4He, and 3H causes the beryllium oxide reflector to swell, ultimately restricting how long it can effectively serve as a reflector or moderator material within the reactor. Extended periods of reactor shutdown result in a significant increase in the concentrations of 3He, mainly due to the radioactive decay of 3H. 6Li and 3He nuclei have significant neutron capture cross-sections, leading to a reduction in the reactor's reactivity, a phenomenon termed "poisoning". This effect varies depending on factors like neutron flux, neutron flux spectrum, and the reactor's operational history. Thorough investigations have been carried out to gain insights into the accumulation of 4He, 3He, 6Li, and 3H within beryllium oxide and their effects on reactivity considering the diverse levels of neutron exposure it encounters.

Metastability exchange optical pumping of 3He at low pressure and high magnetic field

Systematic studies on metastability exchange optical pumping of 3He nuclei have been performed at Jefferson Lab using a 1-torr sealed cell at magnetic fields from 2 to 4T. The effects of the discharge intensity, pump laser power and pumping transition schemes on achievable nuclear polarization and pumping rate have been investigated. A maximum steady-state nuclear polarization of about 75% has been obtained. This work provides a baseline for the development of the novel polarized 3He target for CLAS12 at Jefferson Lab.

Solid-State mathrm {^3He} NMR of the Superconducting Rubidium Endofulleride mathrm {Rb_3(^3He@C_{60})}

A new variant of the superconducting fulleride Rb_3C_{60} is presented, with ^3He atoms encapsulated in the C_{60} cages. The ^3He nuclei act as sensitive NMR probes embedded in the material. The superconducting and normal states are characterized by ^3He NMR. Evidence is found for coexisting vortex liquid and vortex solid phases below the superconducting transition temperature. A strong dependence of the spin–lattice relaxation time constant on spectral frequency is observed in the superconducting state, as revealed by two-dimensional NMR utilizing an inverse Laplace transform. Surprisingly, this phenomenon persists, in attenuated form, at temperatures well above the superconducting transition.

Derivation of transition density from the observed 4He(e, e′)4He(02+) form factor raising the α-particle monopole puzzle

Abstract Recently, the monopole transition form factor of the electron-scattering excitation of the $0^+_2$ state (Ex = 20.21 MeV) of the 4He nucleus was observed over a broad momentum transfer range ($0.5 \le q^2 \le 5.0 \, {\rm fm}^{-2}$) with dramatically improved precision compared with older sets of data; modern nuclear forces, including those derived from the chiral effective field theory, failed to reproduce the form factor, which is called the α-particle monopole puzzle. To resolve this puzzle by improving the study of the spatial structure of the $0^+_2$ state, we derive in this letter a possible $0^+_1\!\rightarrow \! 0^+_2$ transition density ρtr(r) for r ≳ 1 fm from the observed form factor. The shape of the transition density is significantly different from that obtained theoretically in the literature.

Study of the threshold anomaly in the elastic scattering of d+ 197Au

Measurements of the elastic scattering angular distribution for the d+ 197Au system were carried out covering deuteron incident energies in the range from 5 to 16 MeV, i.e. approximately 50% below and above the Coulomb barrier. A critical interaction distance of d I = 2.49 fm was determined from these distributions, which is comparable to that of the radioactive halo nucleus 6He. The experimental angular distributions were systematically analyzed using two alternative models: the semi-microscopic São Paulo and the effective Woods–Saxon optical potentials, for which the best-fitting parameters were determined. These potentials, integrated with the vicinity of the sensitivity radius, were calculated for each energy. For both models, the energy dependence of these integrals presented the breakup threshold anomaly around the coulomb barrier, a typical signature of weakly bound nuclei.

On the Peculiarities of Studying Unbound Excited States of 4He Nucleus by α + 3H Interaction

Due to the alpha-particle beam interaction with tritium, the two-dimensional spectra of tt, t3He, and dd coincidences are obtained using the particle-decay spectroscopy from three-particle 3H(α,tt)p, 3H(α,t 3He)n, and 3H(α,td)d reactions (Eα = 67.2 MeV). Excitation energies and energy widths for seven excited 4He states, as well as the ratio of their different decay modes, namely t + p, n + 3He, and d + d, are obtained by using the Monte Carlo method.

Measurement of Cumulative Cross Sections for 232Th Fission Products upon Irradiation with Medium-Energy 3He Nuclei

Measurement of Cumulative Cross Sections for 232Th Fission Products upon Irradiation with Medium-Energy 3He Nuclei