A study of the 59Co(n,n′γ)59Co reaction

The ⁵⁹Co(n, n'γ)⁵⁹Co reaction has been studied for incident neutron energies ranging from 1.3 to 3.9 MeV. The pulsed-beam time-of-flight technique was employed to discriminate between the inelastically scattered neutrons and the de-excitation γ-rays, which were detected by means of a true-coaxial Ge(Li) detector. Thirty-five levels were identified in this way, and their excitation functions have been extensively compared with the predictions of the statistical theory of the compound nucleus. Possible spin assignements to the levels of ⁵⁹Co are discussed and compared with the results available from previous works.     

7Li(p,n)7Be reaction with polarized protons from the threshold to 3.0 MeV

A polarized beam was used to measure angular distributions of the proton analyzing power of the ⁷Li(p,n)⁷Be reaction at 11 energies from 2.05 to 3.00 MeV. The analyzing power is generally large and positive. The analyzing power can be fitted with associated Legendre polynomials. The coefficient of P₁¹ rises rapidly from threshold to a maximum near the 3⁺ state at 2.25 MeV from which it drops to a minimum at 2.42 MeV, whence it gently rises to 3.00 MeV; the coefficient of P₂¹ has small values that increase with energy. The data were measured typically to an accuracy of 0.02 with a target 20 keV thick at 2 MeV bombarding energy. Polarization contour maps are given. Comparison of these analyzing power measurements with previous data for the neutron polarization induced with unpolarized protons shows equality at some energies and slightly higher values at others.     

Further study of the reaction 2H(n,p2n) near 120 MeV

A kinematically complete experiment on the reaction ²H(n, p2n) is described, in which both outgoing neutrons were detected at a lab angle of 30° so as to enhance their final state interaction in a region far from interfering reaction mechanisms. The data were analysed in terms of the Watson-Migdal model to obtain two independent values for the neutron-neutron scattering length. We find a_nn to be ?13.3^+3.8_?3.1 fm (from a comparison with measurements of p-d breakup), and ? 17.5_?4.5^+4.0 fm (from the shape of the relative neutron energy spectrum), thus validating the Watson-Migdal model in this kinematic region.     

The low energy 2H(α, αp)n reaction

An investigation of the breakup reaction ²H(α, αp)n with incident energies of α-particles between 9.847 and 13.991 MeV has been performed. Results from kinematically complete measurements at 21 different kinematical configurations are presented. Final-state interaction enhancements have been experimentally observed. The energy is sufficiently low that the A = 6 system should be reasonably well described as a three-body system. The experimental data were compared with predictions based on Faddeev equations. Taking into account that no adjustable parameter is used, the quality of agreement is in general acceptable.     

Initial-state distortion and final-state interactions in the 2H(3He, 3He p)n and 2H(3He, 3H p)p reactions

The predictions of two fully antisymmetrized reaction theories (DWBA and PWBA-FSI) are compared with absolute coincidence cross sections for the ²H(³He, ³He p)n and ²H(³He, ³H p)p reactions exhibiting final-state interactions (FSI) and quasi-elastic scattering (QES) both with and without charge exchange. The DWBA theory takes into account both the initial ³He-d and the final N-N interactions, while the PWBA-FSI theory includes only the latter. New QES data at E_He = 35.9 MeV, as well as previously reported 26.8 and 35.9 MeV data, are fitted. The DWBA theory gives good fits, both in shape and magnitude, to spectra showing N-N final-state interactions but gives somewhat poorer fits to QES spectra whose predicted magnitudes are two to ten times too large. The PWBA-FSI theory always predicts cross sections that are too large; however the predicted shapes are about as good as those from the DWBA. The initial-state interaction is shown to affect both the width and position of QES peaks from these reactions.     

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.     

Effects of exchange and final-state interactions in the reactions 2H(3He, 3H p)p and 2H(3He, 3He p)n

Absolute coincidence cross sections for the ²H(³He, ³He p)n and ²H(³He,³H p)p reactions were measured at E_He = 35.9 MeV. Spectra dominated by the nucleon-nucleon final-state interaction (FSI) are fitted by a fully antisymmetrized PWBA theory which includes the effects of FSI in all its matrix elements. Previously reported 26.8 MeV data showing both FSI and quasi-elastic scattering (both with and without charge exchange) are also fitted by the theory, which qualitatively describes the shapes of all these spectra and the ratios of the cross sections for the various processes. Predictions of Watson-Migdal theory are fitted to the FSI spectra and differences between the two theories are analyzed.     

Neutron-neutron effective range from quasifree scattering 2H(n,nn)p at 25 MeV

A neutron coincidence spectrum from the deuteron breakup ²H(n, nn)p was measured at the kinematical condition of quasifree neutron-neutron scattering with 25 MeV neutrons in the entrance channel. The efficiencies of both scintillation detectors were calibrated in the same experimental arrangement as the breakup measurement was performed. The neutron flux was monitored by a proton recoil telescope. Absorption, double scattering and geometric conditions have been simulated by the Monte Carlo technique. From a fit based on the Ebenhöh-Bruinsma-Stuivenberg code with the neutron-neutron scattering length a_nn = ?16.6 fm for the effective range, the value r_{nn = 2.69 ± 0.27 fm} was determined.     

Study of 94Mo through the (n,n′γ) reaction

The ⁹⁴Mo(n, n′γ) reaction has been studied in the neutron energy range 1.5–4.0 MeV. Neutron inelastic scattering cross sections for levels up to an excitation energy of 2.6 MeV have been measured from 1.5 to 3.0 MeV. The results have been analyzed with the optical-statistical and coupled-channels theories. The 1.74 MeV level has been observed and has been assigned to be 0⁺. The branching ratios for the γ-rays deexciting the levels below the 3.5 MeV excitation have also been obtained.     

The neutron-neutron scattering length from a complete experiment on the 3H(d, 2n)3He reaction at 8.45 MeV

The spectrum of the time-differences between the two neutrons from the ³H(d, 2n)³He reaction detected by two plastic scintillators situated at 0.2 and 2.0 m from the target was measured at 0°. The spectrum was compared with a Jost-function final-state interaction enhancement factor and yielded a value of 16.2 ± 1.2 fm for a_n?n, the neutron-neutron scattering length.     

A study of the 2H(d,p)3H AND 2H(d,n)3He reactions and the excited state of 4He at 23.9 MeV

The relative differential cross sections have been measured for the ²H(d, p)³H and the ²H(d, n)³He reactions from 300 keV to 700 keV in 50 keV steps. Angular distributions of all charged particles from the reactions were taken from 20° to 160° in the laboratory system. Energy-dependent asymmetry coefficients from the expansion of the centre-of-mass angular distributions in terms of even powers of cos θ were obtained as were the branching ratios between the two reaction modes. The different energy dependences of the moments of the two cross sections were used to test the need for the existence of a recently reported T = 0 state in ⁴He.     

Experiment and theory for the 2H(e,p)e′n reaction

Differential cross sections and angular distributions of protons from the ²H(e, p)e′n reaction have been measured at four incident electron energies. The proton angular distributions were measured with the neutron-proton relative energy approximately constant, and an 85° differential cross section was measured as a function of the incident electron energy. The electrodisintegration cross section was calculated using the Hulthén wave function for the ground state with a plane wave for the final state. Reasonable agreement between experiment and theory is found.     

Neutron-neutron quasifree scattering in the 2H(n,nn)p reaction at En = 14.1 MeV

Neutron-neutron quasifree scattering has been studied in the deuteron break-up reaction ²H(n, nn)p at E_n = 14.1 MeV. Two coplanar and symmetric configurations have been investigated in a kinematically complete experiment where the detection of the spectator particle was not possible. The experimental cross sections are compared with “exact” calculations derived from Faddeev-type equations solved with S- and P-wave nucleon-nucleon separable interactions. These calculations agree both in shape and magnitude with the differential cross section for the θ₁ = ? θ₂ = 40° configuration (E_p^min = 0). At θ₁ = ? θ₂ = 30° (E_p^min = 180 keV). however, the absolute value of the measured cross section is too high and an observed structure in the shape of the differential cross section is in sharp conflict with the now available “exact” calculations.     

3H(p,n)3He reaction with polarized protons from threshold to 2.9 MeV

A polarized beam was used to measure angular distributions of the analyzing power of the ³H($\text{p}$, n)³He reaction at 9 energies from 1.30 to 2.90 MeV. The data were measured typically to an accuracy of 0.02 with a target 25 keV thick at 2 MeV bombarding energy. The analyzing power can be fitted with associated Legendre polynomials. The coefficient of P₁¹ is small, near zero at the upper and lower energies and negative in between; the coefficient of P₂¹ is much larger and positive, rising to a maximum at 2.2 MeV. Comparison of the analyzing power A with earlier data for the neutron polarization P induced with unpolarized protons shows the coefficients of P₁¹ to be equal and those of P₂¹ to have a similar energy dependence but with larger values for A than for P. Theoretical treatment elsewhere of the inequality of P and A infers that transitions between ³P₂ and ³F₂ are responsible. Polarization contour maps are given.     

New highly excited 4He levels found by the 2H(d,p)3H reaction

The differential cross section, the vector- and the tensor-analyzing powers of the reaction ²H($\text{d}$, p)³H have been measured. The polarization data were obtained at 11 energies between 1.0 and 13 MeV at lab angles between 5° and 160°. The data were fitted with Legendre polynomials and the resulting coefficients analyzed for resonances in ⁴He. Overwhelming evidence for a 1^? level at 24.1 MeV and a strong indication of a 4⁺ level at 24.6 MeV excitation energy have been found.     

A particle-gamma correlation study in the 52Cr(d,pγ) reaction

Particle-gamma angular correlations for states populated in the ⁵²Cr(d, p) reaction have been measured. States in ⁵³Cr for which data are presented are the $\text{5}\text{2}$^?, 1.01 MeV, the $\text{7}\text{2}$^?, 1.29 MeV, the $\text{7}\text{2}$^?, 1.54 MeV, and the $\text{3}\text{2}$^?, 2.32 MeV levels. The DWBA is found to give a good representation of the data for strongly populated levels when the particle detector is located near the stripping peak. The data for the 1.29 MeV level confirm the previously suggested particle-excited core wave function.     

A study of the reaction 2H(π±, p)X

We have studied the excitation function of the reaction ²H(π^±, p)X at a fixed proton angle of 90° for several fixed proton momenta of the detected proton as a function of the incident pion energy. No signal was found for a previous candidate for a dibaryon resonance around a mass of 2.23 GeV. The general trend of the data is reproduced by a multiple scattering theory     

The 3H(t, α)2n reaction at 40 keV

The two-dimensional energy spectrum of the α-particle and the neutron of the ³H(t, α)2n reaction was measured with a small single-gap accelerator at 90 keV. The mean energy of the ³H ions initiating the reaction was estimated to be about 40 keV, i.e. small against the Q-value of 11.3 Me V. It was found that the n-α interaction plays a strong part in the reaction so that no unambiguous determination of a_n-n, the n-n scattering length, was possible. The addition of an n-α final-state interaction to the n-n Jost-function enhancement factor in the analysis greatly improves the agreement with the experimental results, but it was not possible to distinguish between various forms of the n-α enhancement factors nor between different combinations of the n-α and the n-n interactions. The failure to obtain a well established n-n interaction peak is attributed to the absence of a direct reaction mechanism.     

Quasi-free scattering in the 6Li(d,dα)2H reaction at 52 MeV

In order to study the momentum distribution of an α-cluster in ⁶Li we have investigated the quasi-free scattering of deuterons in the ⁶Li(d, dα)²H reaction, using 52 MeV deuterons. The α-particle detector was kept at a fixed position of 30° and the second detector scanned over a range of coplanar angles. The α-cluster momentum distribution has been extracted by means of the plane-wave impulse approximation, using both the energy-sharing method and the angular correlation method. The momentum distributions so obtained are in good agreement with those obtained from other reactions such as (p, pα) and (α, 2α), and are compared with the spectator model. The reasons why the model works well are discussed. For the first time, to our knowledge, quasi-free scattering of deuterons on an α-cluster of a nucleus has been measured and analysed.     

On the mechanism of the 27Al(α, d)29Si reaction

The ²⁷Al(α, d)²⁷Si reaction has been studied at three bombarding energies: 26.2, 26.45 and 26.7 MeV. The energy-averaged angular distributions for states populated in ²⁹Si have been compared with the microscopic and macroscopic DWBA calculations and Hauser-Feshbach theory. Spectroscopic amplitudes were calculated using the available shell-model wave functions.