Possible mechanisms of fragmentation of 16O nuclei with a momentum of 4.5 GeV/c per nucleon in track emulsions

The angular distributions of doubly charged fragments of ¹⁶O nuclei having a momentum of 4.5 GeV/c per nucleon and interacting with track-emulsion nuclei were studied. The experimental angular distributions of doubly charged fragments of a ¹⁶O nucleus are not described by the statistical model of the fragmentation of nuclei. The possible channels of fragmentation of ¹⁶O nuclei may include ¹⁶O → 2⁸Be → 4α, ¹⁶O → ⁸Be +⁸ Be* → 4α, ¹⁶O → 2⁸Be* → 4α, ¹⁶O → α+¹²C, ¹⁶O → α +¹²C* → α + 3α, ¹⁶O → α +¹²C* → α + pα ⁷Li, ¹⁶O → α +¹²C* → α + 2⁶Li, ¹⁶O → α +¹²C* → α + pt2α, ¹⁶O → Li + B, and ¹⁶O → Li* + B*.     

The pole peripheral model for (α, 2α) reactions

The peripheral-model approach proposed previously for binary and quasi-binary direct reactions is extended to quasi-elastic (α, 2α) reactions. The calculated angular correlations functions are compared with the experimental ones for (α, 2α) reactions on ⁶Li, ⁹Be and ¹²C and the values of the A → B + α vertex constants are extracted from the analyses. On the whole, the peripheral-model calculations agree with experiment much better than do calculations based on the pure pole knock-out Feynman graph.     

The 6Li(α, 2α)2H reaction at 700 MeV and the α-d momentum distribution

The results of an experimental study of the reaction ⁶Li(α, 2α)²H at 700 MeV are given. A comparison with the data from seven other reactions pertaining to the α⁺d cluster structure of ⁶Li is presented. The amplitude for the virtual transition ⁶Li→α+d obtained three of these experiments and the present one are comparable. The internal momentum distributions extracted with the plane-wave impulse approximation in four of the experiments are compatible with a pole form, the width parameter being given by the α-separation energy in ⁶Li. The remarkable consistency among these results is seen as evidence for the validity of the simple models used for both the reaction mechanism (PWIA) and to describe the α d-vertex (pole approximation) in ⁶Li.     

Alpha-deuteron structure of 6Li as predicted by a separable-potential three-body model

Schroedinger's equation with separable n-p (³S₁) and $\text{n}\text{-α (}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}$ potentials solved to obtain a three-body model of the ⁶Li ground-state wave function. This model predicts the α-n-p binding energy of ⁶Li to be 4.67 MeV [Exp.: 4.53 MeV = 3.697 + 0.834 (Coulomb)], the asymptotic normalization constant of the d-α tail to be 2.39, and the amount of d+α component to be 65%. The ⁶Li→α+d vertex function is slightly more momentum dependent than present experiments suggest.     

Multibody final states of the 6Li + 6Li reaction AT 97 MeV

Absolute coincidence cross sections were measured for the reactions ⁶Li + ⁶Li → 3α, ⁶Li(⁶Li, 2α), and ⁶Li (⁶Li, 2d), where the latter two represent $\text{N-}\text{body}\text{(N ≧ 4)}$ final states. Broad peaks from the ⁶Li (⁶Li, 2α) reaction are well described by a double spectator pole (DSP) model utilizing a Hulthén wave function, whereas near 40 MeV the DSP peaks are much narrower than predicted. A broad peak in the 3α final-state spectrum, attributed to a single-spectator pole (SSP) process, is well described with the same wave function. The SSP is the principal mechanism for the 3α reaction, in contrast to data near 40 MeV which show that sequential decay from ⁸Be levels is dominant.     

Excitation function of quasi-free processes in the6Li+6Li → 3α reaction

The⁶Li+⁶Li → 3α reaction was studied at energies around the Coulomb barrier. Excitation functions of the quasi-free processes⁶Li(d,α)⁴ He with an α-particle spectator either in the target or in the beam were measured.     

Production of 6He and 9Be by radiative capture and four-body recombination

In this work we estimate the production rates for the three-body radiative capture processes α + n + n → ⁶He + γ and α + α + n → ⁹Be + γ, as well as the four-body recombination reactions α + α + n + n → ⁶He + α, ^α + n + n + n → ⁶He + n, α + α + n + n → ⁹Be + n and α + α + α + n → ^BeBe + α. These processes compete as a source of ⁶He and ⁹Be. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. Both sequential and direct capture are included. The production rates for the radiative and the four-body recombination processes are found to be comparable for a mass density of about 10⁷g/cm³ ( ～ 10³⁰ neutrons/cm³) and temperatures of a few GK.     

The 6Li(e,e′α) and 6Li(e,e′d) reactions at 520 MeV

The reactions ⁶Li(e,e′α) and ⁶Li(e,e′d) have been studied at T₀ ≈ 520 MeV and q ≈ 1.4 fm^?1, by coincidence measurements. The angular dependence of the cross sections is interpreted in the plane wave impulse approximation to obtain the momentum distribution of α-particle and deuteron clusters in ⁶Li. The amount of clustering of ⁶Li is also discussed.     

Analytic continuation of the effective-range expansion as a method for determining the features of bound states: Application to the 6Li nucleus

The scattering function (effective-range function) for the two-channel elastic scattering of charged particles is used to analyze dα scattering at low energies. In order to construct this function, use is made of various sets of phase shifts and mixing parameter, both those that were obtained by solving Faddeev equations in the three-body (n, p, α) model and those that were deduced from available phaseshift analyses. By means of an analytic continuation of the scattering function to the point of the pole corresponding to the bound state of the ⁶Li nucleus, the values of the vertex constants and asymptotic normalization coefficients are found for the process ⁶Li → α + d. Possible means for refining these results are discussed.     

The tensor polarization of 5Li (32−) in the reaction α + d → α + p + n

At the Hamburger Isochronous Cyclotron the formation of the particle unstable ground state of ${}^5\text{Li(}\text{3}\text{2}{}^{\mathrm{?}}$ has been investigated in the reaction α + d → α + p + n at E_α = 28.3 MeV. The neutrons were detected in two liquid scintillation counters, while a large Si (Li) detector was used to observe the α-particles. In a first analysis, the tensor polarization parameters of the five-nucleon system ⁵Li are determined from the experimental data. The results are in quite good agreement with theoretical predictions of Hackenbroich et al.     

Quasi-free contributions in the d + 6Li reactions at low energies

The ⁶Li(d, dd)α, ⁶Li(d, dα)d and ⁶Li(d, tp)α reactions were investigated at low bombarding energies with the purpose to determine the importance of quasi-free processes relative to sequential reactions.     

Die Breite des 4+(11,4 MeV)-Zustandes von8Be aus7Li(d,n) 2α

With the reaction⁷Li+“d→n+⁸Be→n+2α the location and width of the⁸Be(4,+) level is redetermined. While the location at 11.4±0.05 MeV is found in agreement with known values, the width is found to be onlyΓ=2.8±0.2 MeV thereby disagreeing with data fromα-α-scattering but being close to a recent determination from the reaction¹⁰B(d,α)⁸Be (Γ=2.6 MeV). — No indication for participation of an excited state of⁵He in the simultaneously possible reaction via⁵He is found.     

Angular correlations from 6Li break-up near the Coulomb barrier of 118Sn and 208Pb

Absolute coincidence cross sections for three-particle final states have been measured inplane in the ⁶Li + ¹¹⁸Sn and ⁶Li +²⁰⁸Pb reactions at incident energies of 22.2 and 23.0 MeV, respectively. Most strongly populated is the α + d branch, proceeding sequentially through the first excited state (E_x = 2.18 MeV, J^π = 3⁺) of ⁶Li. The angular distributions are fitted by DWBA calculations including Coulomb interaction in the excitation of the projectile. The main competing reaction channels above and at the Coulomb barrier (¹¹⁸Sn: E/E_c ≈ 1.3; ²⁰⁸Pb: E/E_c ≈ 0.9) are: neutron transfer (⁶Li, αp) and the non-sequential α + d break-up of ⁶Li. The latter spectra are consistent with a quasi-free break-up mechanism. No ³He or tritons have been found in the coincidence spectra, as well as no evidence for a three-particle dissociation of ⁶Li into α + p + n.     

Application of the method of integral equations for calculating the vertex constants for an α-particle

The vertex constants G²_αTN and G²_αdd for the virtual decays α → t(τ) + p(n) and α → d + d are calculated by solving the Faddeev-Yakubovsky equations for four nucleons. A spin-dependent separable potential with the Hulthén form factor is used as the NN interaction. The resonant Hilbert-Schmidt expansion is applied to solve the integral equations. The values obtained G²_αTN = 17.9 ± 1.7 fm and G²_αdd = 18.1 ± 1.3 fm are compared with the phenomenological values extracted from data on nuclear reactions.     

Excitation functions of191+193Ir,197Au(6Li,xn+yp) compound nuclear reactions at ELi=48–156 MeV

Excitation functions of the compound nuclear reactions^191+193Ir,¹⁹⁷Au(⁶Li,xn+yp) forx =3–13 andy=0–2 have been investigated by means of in-beamγ-ray spectroscopy at the 156 MeV⁶Li beam of the Karlsruhe Isochronous Cyclotron. The beam energy has been varied in the range of 48 to 156 MeV in steps of about 10 MeV by Be-absorber foils in the external beam line. Absolute cross sections have been determined by normalizing the measuredγ-ray intensities to the production cross sections ofK- X-rays in the target. The experimental excitation functions are discussed on the basis of predictions of the preequilibrium (hybrid) model. While in most cases the theoretical calculations fairly well reproduce energy position and shapes of the curves, strong discrepancies in the absolute scale of the cross sections are observed. The theoretical predictions overestimate the (⁶Li,xn) cross sections by a factor of about 6. Conspicuous anomalies have been detected when comparing the (⁶Li, xn+1(2)p) reactions with (⁶Li,xn) reactions. The reactions with emission of one or two protons are considerably enhanced. The discrepancies and anomalies observed are tentatively explained by the influence of direct reaction channels as the⁶Li break-up, which experimentally proved to be the dominant contribution to the total reaction cross section. The enhancement of the reactions with emission of protons may be a consequence of transfer reactions into highly excited states combined with compound nucleus formation thus implying a cluster effect in preequilibrium emission process.     

He+和He2+离子与碱金属原子Li碰撞中的靶激发

本文在q×(20—150)keV的能量范围内,通过光学测量,对He⁺和He²⁺离子与碱余属原子Li碰撞过程中的靶激发过程进行了研究。由光学多道分析系统(OMA),测得LiI 670.8nm(2p→2s),LiI610.4nm(3d→2p),LiI460.3nm(4d→2p)和LiI812.6nm(3s→2p)谱线。给出所观察到的谱线的发射截面和相立的Li(2p)激发截面。对He⁺与Li碰撞过程,LiI670.8nm谱线发射截面与Aumayr 关键词：     

Medium energy cluster knock-out reactions on 6Li and their interpretation in terms of distorted waves

The ⁶Li(d, 2d)⁴He and ⁶Li(d, dα)²H reactions were performed at 27 MeV. Analyses of these and the 42.8 and 55 MeV ⁶Li(α, 2α)²H reactions were performed using distorted wave and plane wave impulse approximations. The kinematic and potential coupling approximations to final state three-body Schrödinger equation and the post and prior form approximations to off-shell scattering cross section were studied for the three reactions. It was found that only the kinematic coupling and post form approximations could be used for the consistent analyses of the three reactions. The effects of distortions and localization of the reactions were investigated. Manifestations of deuteron cluster deformation were noticed in the analyses of the three reactions.     

Study of the missing-mass spectra in the reactions π−d → K+ + MM and K−d → π+ + MM at 1.4 GeV/c to search for strange dibaryon states

The reactions π^?d → K⁺ + MM and K^?d → π⁺ + MM have been studied at 1.4 GeV/c to search for strange dibaryon states with quantum numbers Q = ?1, and S = ?1. No structures are found which could indicate the production of such states and upper limits for the cross sections are established.     

Study of the spectra of fast deuterons produced in the interaction of 670 MeV protons with nuclei

The spectra of deuterons emitted at angles of 6.5°, 9.5°, 13.5° and 16° (lab system) in the interaction of protons with the nuclei ¹H, ²H, ⁶Li, ⁷Li, C, Al, Cu, Rh and Pb have been measured in the momentum range 700–1700 MeV/c. The secondary particles were analyzed with the help of magnetic and time-of-flight spectrometers. The differential cross sections for deuteron production in the reactions p + 〈2N〉 → N + d and p + 〈N〉 → d + π have been measured for selected nuclei and angles. The effective numbers of nucleons and of two-nucleon clusters for the investigated nuclei were determined. The results obtained are discussed in terms of the dispersion theory of direct nuclear reactions.