The (p, t) and (p, τ) reactions on O at 39.8 MeV

Differential cross sections have been measured at forward angles for (p, t) and (p, τ) transitions from ¹⁷O to the ⁻ ground states and lowest-energy ⁻ states in the ¹⁵O and ¹⁵N mirror nuclei. The data are compared with DWBA calculations using simple single-particle and single-hole wave functions. When the (p, t) and (p, τ) transitions are considered separately, the calculated and experimental ratios of the ⁻ integrated cross sections to the ⁻ integrated cross sections agree to within 30 %; however, the ratios of (p, τ) cross sections to the mirror state (p, t) cross sections are calculated to be about twice as large as actually measured. This experimentally observed reduction of the (p, τ) cross section relative to the (p, t) cross section can possibly be attributed to interference between the S = 0 and S = 1 components of the (p, τ) transitions.     

The 206, 204Pb(p, α)203, 201Tl reactions at 35 MeV

The ²⁰⁶Pb(p, α)²⁰³Tl and ²⁰⁴Pb(p, α)²⁰¹Tl reactions have been studied using 35 MeV protons. For both ²⁰³Tl and ²⁰¹Tl approximately 50 levels with excitation energies up to 4.0 MeV were identified and angular distributions of most of these states were measured. Cluster-model DWBA calculations were shown to produce excellent fits to the measured angular distributions. Using these calculations high-spin $\text{(j ≧}\text{15}\text{2}\text{)}$ states were found in both nuclei. The strengths, energies, and number of high-spin states excited in ²⁰¹Tl and ²⁰³Tl are compared with those observed in ²⁰⁵Tl in a previous study.     

The 90,92Zrd(p,p′) reactions at Ep = 800 MeV+

Angular distributions of analyzing powers and differential cross sections have been measured for elastic and inelastic scattering of 800 MeV protons from ⁹⁰Zr and ⁹²Zr. The data have been interpreted using both the collective-model distorted-wave Born approximation and the semimicroscopic distorted-wave impulse approximation with the Love and Franey t-matrix. Clear differences in the data for transitions to both the 2⁺₁ and the 4⁺ states in the two nuclei, attributable to differences in the microscopic structures of the states, have been observed. These differences are only partially explained by the semimicroscopic analyses. Interpreting the A_y data with the help of recent data-to-data relations suggests that the free L · S interaction used at 800 MeV is incorrect.     

A study of the Li(π, pp)He reaction within the three-body problem

The differential cross section for the ⁶Li(π⁺, pp)⁴He reaction for symmetrical coplanar kinematics has been calculated at the incident pion energy E_π = 70 MeV within the three-body problem + 2N taking into account the Pauli exclusion principle in each N subsystem. Three-body distortions in the final state have been taken into account in the eikonal approximation. The treatment is based on the superposition of the single-particle and two-particle mechanisms of absorption leading to the rescattering of the π- and ρ-mesons through the Δ-isobar. The analytical character of the adopted wave function for the ⁶Li nucleus (the multidimensional gaussian basis) makes it possible to ascertain clearly that the reaction amplitude of the type under study is insensitive to short-range NN correlations both in the initial and final states. The calculated momentum distribution of recoil -particles is in good agreement with the experimental data available, but the experimental accuracy should be improved in order to see the contribution of a specific three-body part of the ⁶Li wave function orthogonal to the ad channel. Some problems to be solved in future are discussed.     

Proton-proton bremsstrahlung and the 2H(p, 2p)n reaction at 51.8 MeV

Proton-proton bremsstrahlung cross sections were measured at 33°-33° and 8.5°-8.5° with a coplanar symmetric geometry. A comparison between experimental cross sections and theoretical predictions was made. The ²H(p, 2p)n reaction was also investigated at 12.5°–12.5° and 8.5°–8.5°. The cross sections were compared with the values calculated by existing theories.     

Isomeric cross-section ratios in (n,t) reactions on some medium- and heavy-mass nuclei at 14.6 MeV

Cross sections were measured for the first time for the reactions ⁷⁹Br(n, t)^77mSe, ⁸⁸Sr(n, t)(^86mRb, ¹¹³In(n, t)^111mCd, ¹²⁷I(n, t)^125mTe, ¹⁴¹Pr(n, t) ^139mCe, ¹⁶⁹Tm(n, t)^167mEr and ¹⁸¹Ta(n, t)^179mHf at 14.6±0.4 MeV using the activation technique, wherever necessary radiochemical separations, and high-resolution γ-ray spectroscopy. The data lie between 10 and 120 μb. A brief review of isomeric cross-section ratios measured in (n, t) reactions is given, and the ratios are compared qualitatively with those obtained in low-energy (n, γ) reactions as well as in high-energy (n, 2n) processes. The isomeric cross-section ratios are influenced by the reaction energy available and are dependent on the spin of the isomeric state. In (n, t) reactions nuclear states with spins between $\text{3}\text{2}$ and 3 seem to be preferentially populated.     

Analyzing powers for the (p, α) reactions on 58, 60, 62Ni at Ep = 22 MeV

Measurements of both the analyzing power and cross section were made for the (p, α) reactions on ^58,60,62Ni at an incident energy of 22 MeV. Data were taken for the strongly populated proton-hole states (0f_{$\text{7}\text{2}$}, 1s_{$\text{1}\text{2}$} and 0d_{$\text{3}\text{2}$}) in the residual cobalt isotopes and for 8 weakly populated low-lying states in ⁵⁵Co and ⁵⁹Co. Angular distributions were taken between θ_lab = 10° and 140° for the ground state and θ_lab = 10° and 80° for the excited states. Both the cross sections and analyzing powers exhibit a similar angular distribution for states having the same J^π values except in the transition to the $\text{3}\text{2}$^? state in ⁵⁹Co at 1.099 MeV. Using the observed J-dependence of the analyzing power, the unknown J^π values for the states at 2.982 MeV in ⁵⁵Co and 3.090 MeV in ⁵⁹Co are assigned to be $\text{9}\text{2}$^?. The shapes of the differential cross sections were well reproduced by the zero-range DWBA calculations using a triton-cluster form factor. However, all the measured analyzing powers could not be reproduced within the framework of such a simple DWBA calculation.     

Observation of two-hole states at high excitation energy in (p,t) reactions

Bumps of two-hole states at high excitation energies were observed systematically in the triton spectra from (p, t) reactions with 52 MeV protons on nuclei in a broad range of masses. The cross sections of the bumps are almost equal for various targets with the same deep major shells. These cross sections vary discontinuously with variation of the corresponding deep major shell. About 20 to 50 % of the total expected strength is observed experimentally, if the bumps are assumed to arise from two-neutron pickup from the deep major shells. The centres of gravity of the bumps are located at excitation energies of about 7 to 9 MeV in all cases. On the other hand, the widths of the bumps change from about 3 MeV for ⁶⁶Zn to about 9 MeV for ²³⁰Th.     

18O(p,p)18O and18O(p,p′)18O1for E = 6.1−16.6 MeV

Angular distributions of cross sections and analyzing powers have been measured for ¹⁸O(p, p)¹⁸O and ¹⁸O(p, p₁)¹⁸O¹(1.98 MeV) for proton energies between 6.1 and 16.6 MeV. The measurement were crarried out in 25 keV intervals between 6.1 and 8.0 MeV, and in 100 keV intervals between 8.0 and 16.6 MeV. Although the general appearance of the angular distributions changes quite smoothly with energy above about 8 MeV, structure is evident in the backangle excitation functions up to 14 MeV. A phase-shift analysis of the elastic scattering data yielded resonance parameters for 25 levels in ¹⁹F in the excitation enrgy region 13.8?21.4 MeV. A large fraction of these levels have odd parity, and the energies of the $\text{1}\text{2}{}^{\mathrm{?}}$ and $\text{3}\text{2}{}^{\mathrm{?}}$ levels coincide closely with peaks seen in the ¹⁹F photonuclear yield curves. A simple model involving proton single-particle states coupled to the 2₁^+; and 3₁^? levels of ¹⁸O is able to account for some features of the observed structure. The energy-averaged elastic and inelastic scattering data for E_p > 12 MeV agree reasonably well with the spherical optical model and the DWBA, respectively, as well as with coupled-channels calculations.     

Investigation of 91Zr by high resolution (d,p), (p,p′) and (p,d) reactions

Energy spectra and angular distributions of light particles (Z = 3–8) produced in the reactions ¹³C+^{58, 60, 64}Ni have been measured at 105 MeV. Coincidence events between light outgoing particles Li, Be, B and α, p have been observed for the first time in the ¹³C+⁵⁸Ni and ¹³C+⁶⁴Ni reactions. The results show that at least part of the ‘deep-inelastic’ events are due to many-particle reactions.     

The 93Nb(p,d)92Nb reaction at 26.3 MeV

The ⁹³Nb(p, d)⁹²Nb reaction was studied at a proton energy of 26.3 MeV. Angular distributions were obtained for outgoing deuterons to 37 states in ⁹²Nb up to an excitation energy of 4.2 MeV. The results were compared with DWBA calculations to extract l-values and spectroscopic factors. Fourteen previously unobserved l = 1 transitions were measured.     

Investigation of (n,t) reactions at 14.6 MeV and an analysis of some systematic trends in the cross-section data

Cross sections for (n, t) reactions at 14.6 ±0.4 MeV on ⁴⁶Ti, ⁵⁶Fe, ^58,60Ni, ⁸⁸Sr, ⁹⁰Zr, ¹⁴¹Pr and ²⁰⁴Pb have been measured by the activation technique in combination with specific radiochemical methods. Some systematic trends in the cross-section data have been observed. An analysis of the gross trend and isotope effect is given.     

Direct reactions to many-channel, many-level final states : (II). (d, p)n and (He, d)p

In an earlier paper, the cross section for a direct reaction to a generalised positive-energy final state, described by an R-matrix wave function, was derived. Here a distinction is emphasised between two classes of such a reaction, depending on whether it can or cannot decay back to the target state. A major contribution in the latter case can be via direct break-up. This is computed for the reaction ⁷Li(³He, d)⁸Be(p)⁷Li, treated by a stripping mechanism. The dependence of the cross section on the final-state (⁸Be) channel energy is discussed. The present work uses shell-model wave functions for R-matrix basis states, and this is shown to be appropriate and useful for direct reactions.     

Volume form of coupling interaction in semi-direct (n, γ) and (p, γ) reactions

A coupling interaction between the nucleon and the nuclear E1 mode having a volume radial form instead of the usual surface one is used in the semi-direct nucleon radiative-capture theory. The calculated cross sections for the ²⁰⁸Pb(n,γ) and ¹⁴²Ce(p,γ) reactions in the giantresonance region reproduce the measured ones both in shape and magnitude. Satisfactory agreement is achieved in comparing the predicted and detected γ-ray spectra following neutron capture by ²⁰⁸Pb. A detailed analysis of the energy and angular-momentum dependence of the matrix elements when the volume and surface form factors are used, is performed.     

Proton-neutron final-state interaction in the reaction 2H(p,pp)n at 6.4, 10.0, 15.9, 19.85 and 25.8 MeV

This paper presents and analyzes the results of measurements of the proton-neutron final-state interaction (FSI) at 6.4, 10.0, 15.9, 19.85 and 25.8 MeV. At each energy nine angular combinations were measured and for each experiment the cross section was measured along the whole kinematic curve. The data are compared with the predictions of S-wave rank-one and rank-two separable potential models. The potentials used in one of the models reproduce the experimental S-wave N-N phase shifts. Fairly large differences between experiment and theory are found in the FSI regions and in the other regions of the kinematic curves. These disagreements cannot be attributed to off-shell effects. The inclusion of the tensor force and the P-wave N-N interaction in the calculations reduces the disagreements considerably at the higher energies. However, systematic differences of 10% to 20% remain.     

Alpha-cluster break-up and reaction mechanism in (p, α) reactions on light nuclei

The differential cross sections for the ¹¹B(p, α)⁸Be and ²³Na(p, α)²⁰Ne reactions were measured at bombarding energies between 6 and 24 MeV. The observed angular distributions can be divided into two domains: at low energies the shapes vary rapidly with incident energy indicating a compound nucleus reaction ; at higher energies rather stable diffraction patterns are seen exhibiting a direct reaction mechanism and DWBA calculations are able to describe the shapes. The change from one region to the other is rather abrupt and this behaviour seems typical for reactions having an α-like compound nucleus. The energy at which this change occurs corresponds to an excitation energy in the compound nucleus of about 20 MeV above the α-threshold.     

The reaction 3He + p → p + p + d studied with BOL at 69 MeV 3He incoming energy

The proton-induced ³He breakup into p and d has been studied in a kinematically complete way at 69 MeV ³He-incoming (23 MeV p-incoming) lab energy, using the spherical multi-detector array BOL.The four-dimensional cross-section data cover most of the three-body final-state phase space. By slicing and integrating the data, they have been brought into suitable one- and two-dimensional representations to reveal different aspects of the reaction process. Based on these, this paper presents information on the interplay between the different reaction modes occurring in the p³He breakup process. In particular, pp final-state interaction, pp and pd quasi-free scattering and nucléon transfer have been studied here.Anomalous effects, probably due to interference between these processes, show up in the data.     

Quasi-free (p,pα) scattering on 24Mg, 28Si, 40Ca and 58Ni at 157 MeV

Sixfold energy spectra have been measured for the (p, pα) reaction at 157 MeV on ²⁴Mg, ²⁸Si, ⁴⁰Ca and ⁵⁸Ni around quasi-free kinematic conditions. For the three s-d shell nuclei the experiment covered a map ranging from 0 to 220 MeV/c in recoil momentum and from 0 to 20 MeV in excitation energy of the final nucleus. Recoil momentum distributions have been obtained for the 0⁺ ground state and the 2⁺ first excited state of ²⁰Ne, ²⁴Mg and ³⁶Ar, and also for the states around 4.4 MeV (mainly 4⁺) of ³⁶Ar. The a spectroscopic factors extracted by a DWIA analysis are about three times larger than those predicted by the SU(3) model; however, they agree quite well in relative magnitude for a number of cases. The disagreement in shape between experiment and theory observed at low recoil momentum for the 2⁺ states might result from another reaction mechanism. The cross sections for ⁵⁸Ni are about a factor often smaller than those for ⁴⁰Ca. The ⁵⁸Ni(p, pα)⁵⁴Fe reaction seems to lead mainly to excited states of the final nucleus.