Charged particle spectra upon interaction between 50.5 MeV <Superscript>3</Superscript>He ions and <Superscript>27</Superscript>Al nuclei

The inclusive spectra of light charged particles formed upon interaction between 50.5 MeV ³Не ions and ²⁷Al nuclei are studied. The experimental results are analyzed using the exciton model of nucleus decay, with the PRECO-2006 code describing the transition of an excited system to equilibrium state. The contributions from composite, pre-equilibrium, and direct processes of integral cross section formation are calculated. Determination of these mechanisms is of interest to both fundamental nuclear physics and different areas of application, particularly the nuclear transmutation of long-lived radioactive contamination.     

A new cross-section measurement of reactions induced by <Superscript>3</Superscript>He particles on a carbon target

The production of intense beams of light radioactive nuclei can be achieved at the SPIRAL2 facility using intense stable beams accelerated by the driver accelerator and impinging on light targets. The isotope ¹⁴O is identified to be of high interest for future experiments. The excitation function of the production reaction ¹²C(³He, n)¹⁴O was measured between 7 and 35MeV. Results are compared with literature data. As an additional result, we report the first cross-section measurement for the ¹²C(³He,a alpha + n)¹⁰C reaction. Based on this new result, the potential in-target ¹⁴O yield at SPIRAL2 was estimated: 2.4×10¹¹ pps, for 1mA of ³He at 35MeV. This is a factor 140 higher than the in-target yield at SPIRAL1.     

Near-barrier neutron transfer in reactions with <Superscript>3</Superscript>He nucleus

Experimental cross sections for the formation of ^196,198Au isotopes in the ³He + ¹⁹⁷Au reaction and ^44,46Sc isotopes in the ³He + ⁴⁵Sc reaction are analyzed. To calculate transfer probabilities and cross sections, the time-dependent Schrödinger equation is numerically solved for the external neutrons of the ³He, ⁴⁵Sc, and ¹⁹⁷Au nuclei. It is shown that the contribution from the fusion channel with subsequent evaporation is important for the ³He + ⁴⁵Sc reaction and negligibly small for the ³He + ¹⁹⁷Au reaction. Fusion–evaporation is taken into account using the NRV and PACE codes. Calculation results demonstrate overall satisfactory agreement with experimental data.     

Phase analysis of <Superscript>4</Superscript>He-<Superscript>4</Superscript>He scattering at energies of 40–50 MeV

A phase analysis of ⁴He-⁴He elastic scattering is performed for energies of 40–50 MeV. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 74–79, June, 2007.     

Partial-wave analysis of elastic <Superscript>4</Superscript>He<Superscript>4</Superscript>He scattering in the energy range 40–50 MeV

A partial-wave analysis of elastic ⁴He⁴He scattering is performed in the energy range 40–50 MeV.     

Kinetics of the sorption of <Superscript>3</Superscript>He by C<Subscript>60</Subscript> fullerite. The quantum diffusion of <Superscript>3</Superscript>He and <Superscript>4</Superscript>He in fullerite

The kinetics of the sorption and subsequent desorption of gaseous ³He in a C₆₀ fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of ³He and ⁴He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C₆₀ fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of ³He and ⁴He atoms at the same temperatures.     

Cross section of the <Superscript>3</Superscript>H(d, <Superscript>3</Superscript>He)nn reaction at a deuteron beam energy of 37 MeV

Inclusive spectra and differential cross sections of the ³H(d, ³He)nn reaction, measured at E _d = 36.9 MeV are presented. The shape of ³He spectra was reconstructed by modeling amplitudes of the neutron-neutron final state interaction (Watson-Migdal amplitudes), sequential decay via the ⁴He* resonance (E* = 21.2 MeV, Γ = 0.7 MeV), and their interferences. The model allowed the determination of the angular dependence of the differential cross section of the ³H(d, ³He)nn reaction accompanied by singlet nn-pair production. The results are compared to the supermultiplet potential model of the lightest nuclei interaction.     

Different formulations of <Superscript>3</Superscript>He and <Superscript>3</Superscript>H photodisintegration

Different momentum space Faddeev-like equations and their solutions for the radiative pd-capture and the three-nucleon photodisintegration of ³He are presented. Applications are based on the AV18 nucleon-nucleon and the Urbana IX three-nucleon forces. Meson exchange currents are included using the Siegert theorem. A very good agreement has been found in all cases indicating the reliability of the used numerical methods. Predictions for cross-sections and polarization observables in the pd-capture and the complete three-nucleon breakup of ³He at different incoming-deuteron/photon energies are presented.     

Structure of the <Superscript>6</Superscript>He nucleus in the three-particle model

The properties of the ⁶He nucleus were investigated in a three-particle approximation (a alpha-particle cluster plus two neutrons) on the basis of the variational approach by using a Gaussian basis. For nn and nα interactions, potentials that make it possible to describe S-wave phase shifts for elastic scattering and, simultaneously, to reproduce faithfully the energy and the size of the ⁶He nucleus were proposed. Characteristic structural features of this nucleus that are manifested in the density distributions, elastic form factor, pair correlation functions, and momentum distributions of particles constituting the ⁶He nucleus in the three-particle model were revealed.     

Applications of <Superscript>3</Superscript>He neutron detectors

Neutron detectors with ³He-filled proportional counters are described. The use of these detectors in measuring the probability of neutron emission (in particular, multiparticle neutron emission) after the β decay of neutron-rich nuclei and in studying rare events of spontaneous fission of superheavy nuclei is considered.     

<Superscript>6</Superscript>He + <Superscript>6</Superscript>He Clustering of <Superscript>12</Superscript>Be in a Microscopic Algebraic Approach

The norm kernel of the A=12 system composed of two ⁶He clusters, and the L=0 basis functions (in the SU(3) and angular momentum-coupled schemes) are analytically obtained in the Fock-Bargmann space. The norm kernel has a diagonal form in the former basis, but the asymptotic conditions are naturally defined in the latter one. The system is a good illustration for the method of projection of the norm kernel to the basis functions in the presence of SU(3) degeneracy that was proposed by the authors. The coupled-channel problem is considered in the algebraic version of the resonating-group method, with the multiple decay thresholds being properly accounted for. The structure of the ground state of ¹²Be obtained in the approximation of zero-range nuclear force is compared with the shell-model predictions. In the continuum part of the spectrum, the S-matrix is constructed, the asymptotic normalization coefficients are deduced and their energy dependence is analyzed.     

Mechanism of <Superscript>238</Superscript>U disintegration induced by relativistic particles

In heavy-nucleus disintegration induced by a relativistic projectile particle, the production of collinear massive fragments accompanied by numerous charged particles and neutrons is explained in terms of the mechanism of projectile-momentum compensation due to the emission of a particle whose mass is greater than the projectile mass.     

Appearance of anomalous phase in <Superscript>4</Superscript>He crystal in the presence of small <Superscript>3</Superscript>He impurity

The kinetics of formation of an anomalous phase from a solution with a small ³He impurity was studied in the temperature range 0.2–0.7 K up to a supersaturation of ～30 mbar. The phase diagram was determined for normal and anomalous growths. It is found that, in the presence of impurities, the formation of a fast-growing state is retarded. This experimental fact indicates that the dissipative processes in fluids have an appreciable effect on the phase formation kinetics. The retardation is, possibly, caused by the direct interaction of an impurity with the crystal surface.     

Role of the nuclear and electromagnetic interactions in the coherent dissociation of the relativistic <Superscript>7</Superscript>Li nucleus into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

The differential cross section in the transverse momentum Q and a total cross section of (31 ± 4) mb for the coherent dissociation of a 3-A-Ge V/c ⁷Li nucleus through the ³H + ⁴He channel have been measured on emulsion nuclei. The observed Q dependence of the cross section is explained by the predominant supposition of the nuclear diffraction patterns on light (C, N, O) and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from nuclear diffraction (Q ≤ 400 Me V/c) and Coulomb (Q ≤ 50 Me V/c) dissociations are calculated to be 40.7 and 4 mb, respectively.     

Momentum distributions of <Superscript>4</Superscript>He nuclei from the <Superscript>6</Superscript>He and <Superscript>6</Superscript>Li breakup

Experimental data on the momentum distributions of ⁴He nuclei originating from ⁶He and ⁶Li breakup on various targets are presented over a wide beam energy range. The experiment with ⁶He was performed at the DRIBs accelerator complex for radioactive beams at the Joint Institute for Nuclear Research (JINR, Dubna). The intensity of the ⁶He beam used was 5 × 10⁶ particles per second and its energy was 10 MeV per nucleon. The momentum distributions of breakup products were measured by means of the MSP-144 magnetic spectrometer. The distribution width was shown to be virtually independent of the target mass. A small value of this width, σ ～ 28 MeV/c, confirms the presence of a halo in ⁶He. The measurements performed with ⁶Li beams of energy 18 and 46 MeV per nucleon at the U-400M accelerator yielded a width value of σ ～ 50 MeV/c for the momentum distributions of ⁴He nuclei, which is intermediate between that for ⁶He and those for stable nuclei. A compilation of the widths of the momentum distributions of fragments originating from the breakup of various nuclei is presented versus the binding energy of one or two neutrons in these nuclei, the target mass and the projectile energy.     

Fragmentation of <Superscript>7</Superscript>Li relativistic nuclei on a proton into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

In a track nuclear photoemulsion exposed to a beam of ⁷Li nuclei accelerated to a momentum of 3 GeV/c per nucleon at the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna), 13 events in which ⁷Li nuclei interacting with protons break up into ³H and ⁴He fragments were detected among 3730 inelastic-interaction events. For this fragmentation channel, the cross section was found to be 8 ± 2 mb. The average value of the fragment total transverse momentum was 214 ± 5 MeV/c. This value exceeds markedly the average value of the transverse-momentum transfer in the coherent dissociation of ⁷Li nuclei on track-emulsion nuclei (166±5MeV/c). The recoil-proton transverse momentum was on average 98% of the total proton momentum. The longitudinal-momentum distribution of protons was characterized by a variance of 16 MeV/c and a mean value of 37 ± 2MeV/c.     

<Superscript>4</Superscript>He<Superscript>3</Superscript>H<Superscript>2</Superscript>H three-body model of the <Superscript>9</Superscript>Be nucleus

Within the framework of the single-channel approximation, an {αtd} model of the ⁹ Be nucleus is presented. A comparative analysis of the t ⁶ Li wave functions describing relative motion of bound states constructed in {ααn} and {αtd} cluster representations is carried out on the example of calculations of the ⁹ Be(γ,t₀)⁶ Li process characteristics. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 85–89, January, 2008.     

Phase shift analysis of the <Superscript>6</Superscript>He+<Superscript>208</Superscript>Pb and the <Superscript>6</Superscript>He+<Superscript>197</Superscript>Au systems

We present the elastic scattering of the ⁶He+²⁰⁸Pb and the ⁶He+¹⁹⁷Au systems at the laboratory energy of E _lab=27 MeV within the framework of the McIntyre parametrization, and systematically investigate χ ²/N analysis of both systems to obtain an excellent agreement between the theoretical results and the experimental data. We find large diffusivity parameters indicating long range absorption mechanisms. We also show that both systems lack both the nuclear and the Coulomb rainbow scattering for obtained S-matrix parameters.