The (p,t) reaction on 12C, 54Fe and 208Pb at 80 MeV

Angular distributions have been measured for the low-lying levels of the residual nuclei for the ¹²C, ⁵⁴Fe and ²⁰⁸Pb(p, t) reactions at E_p = 80 MeV. The shapes of these angular distributions are generally well reproduced by the zero-range distorted-wave Born approximation (DWBA). Enhancement factors extracted from the data show that the DWBA predicts relative strengths consistent with those observed at lower bombarding energies. However, the overall empirical DWBA normalization at E_p = 80 MeV is observed to be $\text{1}\text{12}$ ($\text{1}\text{4}$) of that required at 40 MeV for ²⁰⁸Pb (⁵⁴Fe).     

Study of spin-orbit interaction of13C and15N nuclei in14C induced transfer reactions on138Ba

Angular distributions of single nucleon transfer reactions populating single particle states in the reactions¹³⁸Ba(¹⁵C,¹⁴N)¹³⁷Cs and¹³⁸Ba(¹⁴C,¹³C)¹³⁹Ba have been studied. The shapes of the angular distributions show differences for different final configurations. Using the reaction asymmetry it is possible to describe these differences consistently for all transitions by a spin-orbit potential. The polarisation of the outgoing fragments is discussed and its dependence on final configurations is explained. The spin-orbit potentials deduced from the reaction asymmetry are large, as compared to predictions of folding potentials. They are, however, consistent with measurements of spin-flip probabilities. The origin of theL-S interaction is to be found in coupling effects of second order in the heavy ion reaction.     

Messung der Winkelverteilung der α-Teilchen der Kern-Reaktion11B (p, α1)8Be (2,9 MeV)

It is not possible to measure the angular distribution of the α-particles from¹¹B(p, α₁)⁸Be*(2,9 MeV) with a simple one-detector arrangement, because the back-ground α-particle spectrum from⁸Be* will change shape and contents with angle. Therefore a coincidence method is employed. Two detectors are arranged in such a way that with any angle in thelaboratory system the angle between the detectors is 180 degrees in the center ofmass system. By this method angular correlations are eliminated and the angular distribution of α₁ can be measured as long as the two coincident lines, recorded by each detector, are separable. Since this is not always the case the angular distributions are determined only for reactions proceeding through the two excited states in¹²C that are reached with 1.39 and 2.64 MeV proton energy. Angular distributions of the α_o radiation have been remeasured.     

9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.     

Five-nucleon transfer in the12C(d,7Li)7be reaction atE lab=78.0 MeV

Angular distributions of the¹²C(d,⁷Li)⁷Be reaction to the ground and to the unresolved first excited states of⁷Li or⁷Be nuclei were measured in the entire angular region in the centre of mass system atE _lab=78.0 MeV. Both the one-step five-nucleon cluster transfer as well as two-step sequential transfers were considered in the theoretical analysis. The former mechanism was found to dominate, but the latter is also not negligible.     

The15N(p,α 0)12C reaction at stellar energies

The¹⁵N(ρ, α₀)¹²C reaction has been investigated in the energy range ofE _p (lab)=78-810keV. The measurement of the excitation functions and α-particle angular distributions involved solid targets as well as a quasi-point supersonic jet gas target. The determination of absolute cross sections has been carried out with the gas target. The observed energy dependence of the total cross sections can be described in terms of two-level Breit-Wigner shapes including the resonances atE _p (J ^π)=335(1^?) and 1,028(1^?)keV. The data lead to a zero-energy intercept of the astrophysicalS(E) factor ofS(0)= 65±4MeV-b. The angular distributions are asymmetric around 90° and require an additional amplitude in the reaction mechanism, which interferes predominantly with the 335 keV resonance. The origin of this background amplitude is discussed.     

Measurement of proton polarization in the 208Pb(d,p)209Pb reaction at an incident energy of 20 MeV

Angular distribution measurements of proton polarization in the ²⁰⁸Pb(d, p)²⁰⁹Pb reaction to the ground g_9/2 state were made at an incident deuteron energy of 20 MeV using a high efficiency proton polarimeter. Distorted wave Born approximation analysis and continuum discretized coupled channel analysis were performed on the data and compared with measurements of the angular distribution of the vector analyzing power for the same reaction. The result of the calculations predict that the angular distribution of the vector analyzing power should be similar to that of the polarization. However, the experimental data gives different angular distributions. The measured vector analyzing power is well reproduced by the calculations, while the polarization is not well reproduced.     

A study of the reaction 12C(α, α′)12C exciting the 1+T = 0 level at 12.71 MeV

The differential cross section for the excitation in the inelastic scattering of 36 MeV α-particles of the 1⁺T = 0 level in ¹²C has been measured. Calculated angular distributions suggest that the transition proceeds primarily by two-step reactions rather than by the one-step reaction involving the two-body alpha-nucleon spin-orbit potential.     

Investigation of (3He,3He)- and (3He,t)-reactions on10B,11B and13C

The³He-elastic scattering and the (³He,t)-reactions on¹⁰B,¹¹B and¹³C were studied. Excitation functions for the reactions¹⁰B(³He,t)¹⁰C and¹¹B(³He,t)¹¹C were measured at incident energies between 11 and 17 MeV. All angular distributions were taken at 14 MeV³He-energy. From an optical model analysis of the³He-elastic scattering data the parameters of the optical potentials were determined. Best fits were obtained using surface peaked potentials. The (³He,t)-reactions were interpreted in terms of a microscopic model, which, in general, gave a good account of the data. Corrections due to nonlocality effects were included in the calculations. A satisfactory agreement of the predicted and the measured cross sections required an effective nucleon-nucleon interaction of the Yukawa form (α^?1=1.2 fm). Using a Serber exchange mixture the isospindependent- and the spin-isopin-dependent strength parameters of the potential were deduced to beVτ=21.4±2.3 MeV andV _{σ τ}=19.5 ± 2.7 MeV, respectively.     

Neutron polarizations from the9Be(d,n)10B and11B(d,n)12C reactions

Neutron polarization angular distributions were measured for the⁹Be(d,n)¹⁰B and¹¹B(d,n)¹²C reactions for deuteron energies of 5.47 and 5.34 MeV, respectively. Using neutron time-of-flight techniques, polarizations to eight states in¹⁰B and to six states in¹²C have been measured. Neutron polarization energy excitation functions for both reactions were measured for deuteron energies from 3.0 to 5.5 MeV in 0.25 MeV steps at 30° (lab). Distorted wave method calculations carried out to compare theoretical calculations against experimental results were not in good agreement with the data.     

Angular distributions of photoneutrons from the 207, 208Pb(γ, n0) reactions

Angular distributions of photoneutrons from the ^{207, 208}Pb(γ, n₀) reactions were measured at 11 angles around θ = 90°. The γ-source, E_γ = 7–11.4 MeV, contained discrete lines (ΔE ? 30 eV) obtained from n-capture and was used in conjunction with a high-resolution ³He spectrometer. Strong evidence for an E2 contribution and for E2-E1 and possibly E1-M1 interference was obtained in both ²⁰⁷Pb and ²⁰⁸Pb. The results are compared with calculations using a direct-semidirect model which involved an E1 and isoscalar E2 giant resonances. The results indicate that this model could explain only certain features of the data while most of the other features remain unexplained.     

Polarization of protons in C12(d,p)C13 reaction

The angular distributions of the polarization of protons from C¹²(d,p)C¹³(g.s) reaction were measured at 200 keV intervals for deuteron energies from 1.40 to 2.40 MeV. Elastic scattering on C¹² at 45 ° (lab) was used to analyze the polarization. Positive sign of the polarization corresponds to the vector productK _d ×K _p . The maximum polarization observed is about 30%. The results are not similar to those obtained from the mirror reaction C¹²(d,n)N¹³ in the same deuteron energy range.     

A study of the 11B(3He,p)13C reaction at 12, 10, 8, 6 and 4 MeV

Angular distributions for eight proton groups corresponding to states in ¹³C have been measured at incident ³He energies of 4, 6, 8, 10 and 12 MeV. These states are p₀(ground state), P₁(3.09), p₁(3.68), p₃(3.85), p₄(6.86), p₇(7.68), pio(9.50) and p₁₁ (9.90). The angular distributions have been fitted with DWBA analyses using a zero-range approximation. No radial cut-offs were used. In general the data are reasonably well fit at incident energies of 10 and 12 MeV.     

Elastic scattering and fusion cross sections of 13C+13C

The ¹³C+¹³C total fusion cross section has been determined in the range 3.26⩽E_c.m.⩽8.0 MeV using Ge(Li) detector measurements of low-lying transitions in the residual nuclei and a statistical model calculation of excited state populations. The six most abundantly produced residual nuclei have been observed and their yields are given. To constrain the parameters in fusion models for these reactions, we have also taken elastic scattering data at θ_c.m.=60°, 70°, 80°, and 90° for 4.5⩽E_c.m.⩽8.5 MeV, as well as angular distributions at E_c.m.=7.0 and 8.0 MeV. The IWBC model and an optical model with a “shallow” potential have been used for parametrizing the nucleus-nucleus interaction.     

Study of the structure of16O above 25 Mev by the reaction13C(τ, α)12C*(γ15.1)

The nucleus¹⁶O has been investigated within the excitation range of 25–32 MeV by means of the reaction¹³C(τ, α)¹²C^* _15.1(γ)¹²C. Excitation functions for the 15.1 MeVγ-rays, taken for bombarding energiesE _τ=2.6–12 MeV at 0? and 90?, exhibit some marked structures with widths of 0.5 to 1 MeV. As the (τ, α)-reaction leads to the 15.1 MeV,T=1 state, levels in¹⁶O underlying these structures should have largeT=1 components. Angular distributions of theα-particles coincident to the 15.1 MeVγ-rays show patterns typical for a direct process and are, therefore, compared with DWBA calculations.     

Effects of inelastic multistep processes on (p,t) reactions in a transition region between rare-earth nuclei and double-magic 208Pb

Effects of inelastic multistep processes on (p, t) reactions in a transition region between well-deformed rare-earth nuclei and the double-magic ²⁰⁸Pb have been investigated by the ¹⁸⁸Os(p, t) ¹⁸⁶0s, ^{194, 196}Pt(p, t)^{192, 194}Pt and ^{200, 202}Hg(p, t)^{198, 200}Hg reactions at E_p = 51.9 MeV. The observed ground 0⁺, first excited 2⁺ and 4⁺ angular distributions together with those for the ^{206, 208}pb(p, t)^{204, 206}pb reactions have been compared with CCBA and DWBA calculations, using transfer form factors based on the Nilsson, vibrational and shell models. It is found that the inelastic multistep processes play a very important role in reproducing both the shapes and magnitudes of the observed first excited 2⁺ angular distributions, contrasting to small contributions in the ground-state 0⁺ transitions. The effects of the inelastic multistep processes on the first excited 4⁺ transitions are also considered to be important.     

Folding model analysis of 10, 11B, 12C + 27Al, 39K and 40Ca

Elastic scattering angular distributions for ^{10, 11}B + ⁴⁰Ca at E_lab = 46.6 and 51.5 MeV and¹²C+³⁹K at E_lab = 54 and 63 MeV have been measured and compared with Woods-Saxon and double-folding optical models. The oscillatory structure observed previously for ¹²C + ⁴⁰Ca disappears when the projectile is changed to ^10,11B or the target is changed to ³⁹K. The angular distributions are adequately reproduced by a double-folding analysis, which employs the nucleon-nucleon potential of Bertsch et al., with a range of real normalizations N_R = 1.0–1.38. This same range of real normalizations was also able to describe previously measured ^10,11B, ¹²C + ²⁷A1 data. The double-folding analysis of ¹²C + ⁴⁰Ca scattering indicates that this system behaves differently from neighboring systems.     

Highly excited 8Be core in the configuration of the 12C and 11B ground states

Angular distributions of the ¹²C(d, ⁶Li)⁸Be reaction at E_lab = 78.0 MeV and the ¹¹B(³He, ⁶Li)⁸Be reaction at E_lab = 71.8 MeV were measured. Transitions leading to ⁸Be in the ground state and the 3.04, 16.63, 16.92, 17.64 and 18.15 MeV excited states were observed. A DWBA analysis was performed regarding the (d, ⁶Li) and (³He, ⁶Li) reactions as direct α particle or triton transfers, respectively.     

Fragmentation of12C nuclei in emulsion at 50 GeV/c

A total of 852¹²C-emulsion nucleus interactions at 4.2 GeV/c per incident nucleon was investigated. At least one charged projectile fragment was observed in 733 events, in which the multiplicity and angular distributions ofZ=1,2, and ≧3 projectile fragments were studied. Five events were observed in which¹²C projectile nuclei were fragmented into twoZ=3 fragments. Thus the cross section of this process is about 6×10^?3 of the inelastic cross section. The angular distribution of projectile fragments becomes narrower as the fragment charge increases. At all values of fragment charges, a pronounced peak in the angular distribution can be observed at zero emission angle. In this paper, only the projectile-fragmentation events possessing no heavily ionizing particle (n _h =0 events) have been investigated. Our sample contains 84 of these events, i.e., about 10% of the total inelastic events. The number of events withZ _max, the charge of the emitted principal fragment, equal to 1, 2, 3, 4, and 5 are 11, 52, 13, 4, and 4, respectively. Of these 84 events, 36 interactions have a total charge of emitted projectile fragmentsZ ^* equal to 6, i.e., as much as the beam chargeZ _p . Of the 36 events, 17 produce no charged pions and of the 17 events, 10 only represent the dissociation of¹²C→3α, i.e., 1.2% of the total inelastic interactions. The number of events withZ ^*=5, 4, 3, 2, and 1 are 27, 14, 4, 2, and 1, respectively. The average number of produced charged pions per one interacting projectile nucleon was estimated to be 1.2±0.1. This value agrees with the corresponding one in elementary interaction at the same energy per nucleon, a result pertaining to the incoherent production model in collision of two nuclei. In this class of events,n _h =0, the number of stars in which H, He, Li, Be, and B isotopes were detected are 59, 58, 13, 4, and 4, respectively. The projected angular distributions ofZ=1 and 2 projectile fragments are Gaussian shaped, narrow, consistent with isotropy, and depend on the fragment. These distributions are consistent with quantum mechanical calculations using the sudden approximation and shell-model functions. From the angular measurements ofα-particle tracks in the dissociation¹²C→3α events, the distribution ofα-particle transverse momentum inside the carbon projectile nucleus was deduced. It seems that the dissociation of¹²C→3α happens via an intermediate⁸Be state.