Li(p,pd)He reaction at 100 MeV

An angular correlation experiment of the ⁶Li(p, pd)⁴He reaction at 100 MeV has been performed using a symmetric and coplanar geometry and covering an angular range from 45.5 to 57°. In addition to the conventional ΔE-E telescope systems for the detection of both protons and deuterons, a 14° analyzing magnet was employed to select deuterons of a given momentum range. The results for the ground state transition are consistent with those obtained at other incident energies. The angular distribution for the transition to the 20 MeV excited state of the recoiling α-particle was also obtained and the overall magnitude of the differential cross section is at least an order of magnitude smaller than that of the ground state transition. The plane wave impulse approximation (PWIA) was used to analyze the experimental results. A form factor was generated using the Saxon-Woods potential as the d-α inter-cluster potential. Satisfactory agreement between theory and experiment was obtained. A value of 0.45 ±0.08 was extracted for the deuteron clustering probability on ⁶Li. The exchange and the optical distortion effects were also discussed.     

Investigation of the 60Ni(n,p) reaction mechanism at 18.5 MeV

The differential cross sections of the ⁶⁰Ni(n, p) reaction are measured at 18.5 MeV. The reaction mechanism has been discussed in the framework of the Geramb model and of the FKK statistical multistep emission theory. Special attention is paid to the excitation of the GDR as a doorway state in ⁶⁰Ni and as a parent analog in ⁶⁰Co. The total proton emission cross section is estimated.     

A study of reaction mechanisms for the Li(p, 2d)He reaction at 45 MeV

The first kinematically complete experiment involving a (p, 2d) reaction is reported. It is found that at 45 MeV bombarding energy a significant part of the ⁷Li(p, 2d)⁴He reaction cross section arises from contributions from sequential decay processes through excited states of ⁶Li. A new three-body break-up mechanism involving the quasi-free interaction of the proton with the bound triton is discussed.     

The (p,d) reaction at 65 MeV

The (p, d) reaction on ¹²C, ¹⁴N, ¹⁶O, ⁴⁰Ca and ⁹⁰Zr has been studied with 65 MeV incident protons. DWBA calculations have been carried out to investigate the importance of finite range and non-locality effects. The experimental angular distributions for the strong transitions have been compared to DWBA calculations to study the effect of the deuteron optical potential. This comparison supports the use of the adiabatic deuteron potential which includes the effect of deuteron breakup.     

The C(Li, t)O reaction at 20 MeV

States in ¹⁶O op to an excitation energy of 16.9 MeV were observed from the ¹³C(⁶Li, t)¹⁶O reaction at 20 MeV. Differential cross sections were obtained from θ_lab = 15° to 105° for the triton groups corresponding to the states in ¹⁶O at 6.13, 6.92, 7.12, 8.87, 9.85, 10.35 and 11.09 MeV.     

The reactions 6, 7Li, 9Be, 10B(e,e′p) at 700 MeV and DWIA analysis

The proton spectral functions of ⁶Li, ⁷Li, ⁹Be and ¹⁰B obtained from the (e, e′p) reactions at 700 MeV are presented. The results were analyzed in the distorted-wave impulse approximation, using the shell-model single-particle wave functions consistent with the elastic electron scattering results. The observed Ip proton momentum distributions for the nuclei ⁶Li, ⁷Li and ⁹Be show significant disagreement with the shell-model momentum distributions. The occupation probabilities of the proton single-particle states are around 0.7, with a few exceptions.     

Measurement of (p,n) and (n,p) reactions on 6Li and 7Li at 800 MeV

The measured ⁷Li(p,n), and ⁶Li(n,p) cross sections at 0° show a high-energy peak (≈25 MeV/c FWHM) which we attribute primarily to nuclear charge exchange leading to final states in ⁷Be, ⁶Be, and ⁶He, respectively. By contrast, the ⁷Li(n,p) cross section at O° shows a broad weak high-energy peak believed due mostly to break-up processes. At 16°, the ^6,7Li(n,p) cross sections are dominated by quasi-elastic scattering.     

Investigation of7Be(n,p)7Li reaction

The⁷Be(n, p)⁷Li nuclear reaction with thermal and 2 keV neutrons was studied. For thermal neutrons the total cross section of (46 800± 4 000) b was obtained and the proton branching ratio to the first excited and ground states of⁷Li was determined to be ₁/₀ = (2±1) %. For 2 keV neutrons the upper limit of the cross section of 540 b was estimated.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The autors thank Mr. A. Dvoák and Mrs. B. Michalcová for their manufacturing the⁶Li standards, Dr. J. Frána for his help in determining the number of⁷Be atoms and Ing. J. Hoffmann, Mr. J. Novotný and Mr. J. Badura for their careful preparation of electronics.     

The24Mg(p,t) reaction at 50 MeV

Angular distributions are given for tritons from the ground and first two excited states of the²⁴Mg(p, t)²²Mg reaction. Excitation energies, spins and parities of these levels are given, and a new level also reported.     

Study of the W(t, p)W reaction at 20 MeV

The ¹⁸²W(t, p)¹⁸⁴W reaction has been studied at 20 MeV. The outgoing protons were detected in an Elbek broad range magnetic spectrograph. Absolute cross sections and angular distributions were measured. Evidence for inelastic effects in the reaction mechanism was observed for the first excited 2⁺ state, the 3⁻ level at 1221 keV and the 5⁺ state at 1295 keV. The 0⁺ level at 1002 keV was populated with ≈ 2% the ground state cross section. A 4⁺ level at 1536 keV was observed with ≈ 50% the ground state cross section. Calculations of the absolute (t, p) cross sections to this and other states with known structure resulted in excellent agreement with the measured values.     

208Pb(p, α)205Tl reaction at 16.475 MeV

The (p, α) reaction was studied on a²⁰⁸Pb target at 16.475 MeV. Nineteen states were observed in²⁰⁵Tl, up to 3.6 MeV in excitation. Angular distributions were obtained for five strong proton-hole transitions, and DWBA fits made to determinelj values. Results are compared with previous²⁰⁶Pb(t, α)²⁰⁵Tl,²⁰⁶Pb(d,³He)²⁰⁵Tl,²⁰⁵Tl(p, p′), and²⁰⁵Tl(n, n′) work.     

2H(e,e(')p)n reaction at high recoil momenta

The 2H(e,e(')p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (x(Bj)=0.964) at a four-momentum transfer squared, Q(2)=0.665 (GeV/c) (2) (omega=0.368 GeV, W=2.057 GeV), and for recoil momenta up to 550 MeV/c. The measured cross section deviates by 1-2sigma from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations.     

Pre-equilibrium emission effect in (n,p) reaction cross-sections at 14.8 MeV

The influence of pre-equilibrium emission on (n, p) reaction cross-sections at 14.8 MeV has been studied. Cross-sections for (n, p) reactions have been measured by the activation technique at 14.8 .1; 0.5 MeV neutron energy. The experimental cross-section values have been compared with the calculated values at 14.8 MeV with and without considering the pre-equilibrium emission. Equilibrium calculations have been performed according to the statistical model of Hauser and Feshbach while the hybrid model has been used to include the pre-equilibrium contribution. Pre-equilibrium emission has been considered only in the first emission step. The comparison of experimental and calculated values clearly indicates the presence of pre-equilibrium emission.     

On the Li(p,pt)He reaction

Using a cluster model, the reaction ⁷Li(p, pt)⁴He has been analysed in the distorted-wave impulse approximation. All exchange terms arising from antisymmetrization of the target wave function have been calculated. When the correct asymptotic form for the intercluster wave function is used, the magnitude and shape of the measured angular correlation are reproduced both at 156 and 55 MeV. The analysis indicates that ⁷Li in its ground state is strongly clustered.     

Study of the 90Zr(p,α)87Y reaction at 22 MeV

The (p,α) reaction on ⁹⁰Zr has been studied in a high resolution experiment at an incident proton energy of 22 MeV. The cross section and asymmetry angular distributions for transitions to 36 levels of ⁸⁷Y with an excitation energy up to 3 MeV have been measured. DWBA analyses of experimental angular distributions, using either Woods-Saxon or Double Folded potentials for the exit channel, have been done, allowing either the confirmation of previous spin and parity values or the assignment of new spin and parity to a large number of states. The structure of low lying states of ⁸⁷Y has been studied in the framework of the shell model, using the OXBASH code. With the interaction PMM90 reasonable agreement is obtained for part of the negative parity spectrum. Received: 17 November 1997     

Study of the 182W(t,p)184W reaction at 20 MeV

The ¹⁸²W(t, p)¹⁸⁴W reaction has been studied at 20 MeV. The outgoing protons were detected in an Elbek broad range magnetic spectrograph. Absolute cross sections and angular distributions were measured. Evidence for inelastic effects in the reaction mechanism was observed for the first excited 2⁺ state, the 3^? level at 1221 keV and the 5⁺ state at 1295 keV. The 0⁺ level at 1002 keV was populated with ≈ 2% the ground state cross section. A 4⁺ level at 1536 keV was observed with ≈ 50% the ground state cross section. Calculations of the absolute (t, p) cross sections to this and other states with known structure resulted in excellent agreement with the measured values.     

The 28Si(7Li, 7Be)28Al reaction at 36 MeV

The ²⁸Si(⁷Li, ⁷Be)²⁸Al reaction has been investigated at E_7Li = 36 MeV. States and groups of states were observed up to 5.3 MeV excitation in the ²⁸Al+⁷Be system. Experimental angular distribution for unresolved doublets of states at ≈ 0.0 and 0.44 MeV excitation, corresponding to ⁷Be in its ground state (⁷Be₀) and first excited states (⁷Be₁) with ²⁸Al in its ground state (3⁺) and first excited state (0.031 MeV, 2⁺) are compared with microscopic distorted wave approximation calculations.