Neutron-neutron scattering length in the reaction9Be (n,nn)8Be at 10.3 MeV

In a kinematically complete experiment on⁹Be(n, nn)⁸Be_gs at 10.3 MeV, the absolute differential cross section of then-n FSI configuration at _lab=30° has been measured. It was our particular object to determine the singlet scattering length of then-n interaction via its final-state interaction being embedded in a multi-nucleon background. An extended and thorough analysis yielded¹ a _nn =–16.5±1.0 fm which is consistent with the results of the most recent and most precise kinematically complete measurements with three hadrons in the final state. These, however, altogether contradict the values deduced from ^– dnn.     

Polarization in neutron-proton scattering at 16.2 MeV

The polarization in the scattering of neutrons from protons has been measured at a lab neutron energy of 16.2 MeV for the three c.m. angles 70°, 100° and 130°, at which the measured polarizations were (+2.95 ± 0.86) %, (+1.84 ± 0.91)% and (+1.62 ± 0.99) % respectively.     

Neutron-neutron scattering length from the 2H(n,np)n reaction at bombarding energies up to 27 MeV

The n-n interaction has been investigated in a kinematically complete experiment with high statistical accuracy via the ²H(n, np)n reaction at bombarding energies up to 27 MeV, extending previous measurements to higher energies and to a different geometry. The analysis with exact three-body calculations yields ann = ?16.9 ± 0.6 fm.     

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.     

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.     

Low-energy S(E) factor of 9Be(p, α)6Li and 9Be(p,d)8Be

Excitation functions and angular distributions of the ⁹Be(p, α)⁶Li and ⁹Be(p, d)⁸Be reactions have been measured over the energy range E _p = 16 to 390 keV. The data are dominated by one broad resonance including interference effects with a direct process. The effects of electron screening have also been observed, which are however significantly larger than expected. The deduced reaction rates at T₉ ≤ 1 are in excellent agreement with values given in a compilation.     

Multiple scattering effect for quasifree scattering in the 3He(p,pp)2H reaction at 64.8 MeV

For the ³He(p, pp)²H reaction at 64.8 MeV, angular correlations have been measured in the quasifree scattering region. Angular dependence of the ratio of the cross sections measured to those calculated in the plane-wave impulse approximation is well reproduced by a calculation taking account of the double-scattering effect.     

States in Be studied through the reaction B(p, α)Be with 40 MeV protons

Spectroscopy of the α- and τ-particles from 40 MeV proton bombardment of ¹¹B reveals transitions to ⁸Be states up to 19 MeV. The ratio of excitation of the 16.6 MeV state to the 16.9 MeV state is 2.3 ± 0.4. The ⁸Be(4⁺) state is found at 12.5 MeV with a width of 4.0 ± 0.5 MeV.     

Large-angle proton emission in the 9Be(p, 2p) reaction at 300 MeV

A ⁹Be(p, 2p) coincidence experiment performed to further elucidate the reaction mechanism for the production of energetic wide-angle protons in intermediate-energy proton-induced reac- tions is reported. Detectors in a coplanar geometry were used to measure coincidences between trigger protons at 90° to the beam and forward-angle protons on the opposite side of the beam. The incident proton energy was 300 MeV. We report both the inclusive spectra for the trigger protons and the differential mean multiplicities for the coincidence events.The outgoing proton energies were measured using NaI detectors. Trigger protons were grouped into 10 MeV bins covering the kinetic energy range from 55 to 155 MeV. The forward protons were measured over a kinetic energy range of 65–280 MeV and an angular range of 14–60° with respect to the beam.The present results are compared with two previous experiments which covered a more restrictive kinematical range. Calculations are performed with both phase-space and direct knockout models, and compared with experiment. Observation of angle and energy correlation effects suggested by knockout models indicate that such direct mechanisms provide a significant contribution to energetic wide-angle inclusive proton spectra.     

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.     

New attempt to determine the n-n scattering length with the 2H(n, np)n reaction

The n-n final-state interaction (FSI) was investigated via the 2H(n, np)n reaction at 25 MeV, using a geometry which enables the simultaneous observation of n-p quasifree (QFS) scattering. The data were analyzed with Monte Carlo simulations based on rigorous Faddeev calculations with realistic nucleon-nucleon potentials. The value of a(nn) deduced from the absolute yield in the FSI peak is -16.27+/-0. 40 fm while the relative data, normalized in the QFS region, give -16.06+/-0.35 fm. Thus our results differ from the "recommended" value of a(nn) = -18.5+/-0.3 fm by more than 5 standard deviations.     

Angular correlation measurements in the Be9(d,p, γ)Be10 reaction

Thep-γ angular correlations in the Be⁹(d, p, γ)Be¹⁰ reaction have been measured in the reaction plane atE _d =1.3, 1.5, 1.9, 2.3 and 2.45 MeV for proton anglesθ _p =35°, 80° and 120°. The anisotropy of the angular correlations measured forθ _p =35° is independent of deuteron energy. A systematic shift of the symmetry axis from the recoil direction has been observed. The shift is 20.5° at E_d=2.45 MeV. The anisotropy decreases with increasing proton angle and vanishes atθ _p =120°.     

Polarization of protons from the Be(d,p)Be reaction at Ed = 12.0 MeV

The polarization of protons from the ⁹Be(d,p)¹⁰Be reaction at E_d = 12.0 MeV was measured for the ground state and first excited state transitions. The results obtained are compared with the predictions of DWBA theory. It was found that better fits to the experimental data can be obtained using volume absorption in the distorting potential of the deuteron elastic channel. A comparison of the present polarization data with the vector analysing power for the same reaction and the same incident deuteron energy has also been made.     

High-lying excited states in ~(10)Be from the ~9Be(~9Be,~(10)Be)~8Be reaction

A transfer-reaction experiment of ~9Be(~9Be,~(10)Be)~8Be was performed at a beam energy of 45 Me V.Excited states in ~(10)Be up to 18.80 Me V are produced using missing mass and invariant mass methods.Most of the observed high-lying resonant states,reconstructed from theα+~6He and t+~7Li decay channels,agree with the previously reported results.In addition,two new resonances at 15.6 and 18.8 Me V are identified from the present measurement.The 18.55 Me V state is found to decay into both the t + ~7Lig:s: and t + ~7Li?(0.478 MeV) channels, with a relative branching ratio of 0:93 ± 0:33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

Proton polarization and differential cross section for the (3He,p) reaction on 6Li and 9Be at 14 MeV

Angular distributions of the proton polarization and the differential cross section have been measured for the reaction (³He, p) initiated by 14 MeV incident ³He particles and proceeding to the ground and the first excited states of the final nuclei ⁸Be and ¹¹B. Large polarization values were observed, especially for the ⁹Be(³He, p)¹¹B reaction leading to both the ground and the first excited states in ¹¹B. The experimental results have been analysed in terms of a two-nucleon transfer spindependent distorted-waves theory using finite-range formalism and including corrections due to the non-locality of the optical potentials. A proper coherent summation over L and S, whenever necessary was included in the DWBA calculations of the polarization and the differential cross section as implied by the presence of the spin-orbit terms in the optical-model potentials used to generate the distorted waves.     

A survey of the (3He, 7Be) reaction at 70 MeV

A study of the (³He, ⁷Be) reaction has been undertaken using a 70 MeV ³He beam. By surveying a wide range of target nuclides, namely ^{12, 13}C, ¹⁶O, ^{24, 26}Mg, ^{40, 42, 44}Ca, ^{58, 60, 62, 64}Ni, ⁹⁰Zr, ^{120, 124}Sn, ¹⁴⁴Sm and ²⁰⁶Pb, systematics of the α-clustering phenomenon were investigated. In addition, masses and energy levels of ⁶⁰Fe and ¹²⁰Cd were measured. The ⁷Be particles were detected in a single wire proportional counter backed by a plastic scintillator in the focal plane of an Enge spectrometer to ensure adequate particle identification. Total energy resolution as small as 140 keV full width at half maximum was obtained, although in most cases the target thickness limited the energy resolution to larger values. Differential cross sections as low as 20 nb/sr were measured. The finite range programs LOLA and LOLITA were used to calculate differential cross sections for comparison to data, assuming the reaction to proceed by a direct α-transfer. The spectroscopic factors which were extracted show a marked decrease with increasing atomic mass number, implying a decrease in surface α-clustering for heavier nuclei.     

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.