A. Sakaguchi

Four-nucleon pickup reaction on 12 ⩽ A ⩽ 94 nuclei

Abstract The differential cross sections for the (d, 6 Li) reaction on targets of 12 C, 16 O, 24 Mg, 40 Ca, 58 Ni and 94 Mo have been measured at E d = 54.2 MeV. The measured angular distributions have been analyzed by finite-range DWBA calculations, and spectroscopic factors for an α-cluster transfer have been extracted. In the DWBA analysis using an optical model with a phenomenological Woods-Saxon potential, the spin-orbit part of the deuteron optical potential played a significant role in reproducing the measured angular distributions but the spin-orbit part of the 6 Li optical potential had a minor effect. Relative spectroscopic factors extracted from the present data were compared with theoretical predictions together with the results from the (p, pα) reaction. The relative spectroscopic factors for 1p-shell nuclei were in quantitative agreement with theoretical predictions. However, there were certain discrepancies between the spectroscopic factors extracted from the (d, 6 Li) reaction and those from the (p, pα) reaction, and the discrepancies increased with target mass number.

Zero degree neutron time-of-flight facility at RCNP

Abstract An outline of the 0° neutron time-of-flight facility at RCNP is briefly described. A technique has been developed for obtaining a narrow beam burst width by detuning the isochronous cyclotron magnetic field. An overall subnanosecond time resolution has been achieved for 50–80 MeV proton beams. Applications have been made to polarization transfer experiments for the (p, n) reaction at 0°.

Various intermediate channels in the 12C + 12C → 12Cg.s. + α + 8Beg.s. reaction

Abstract The 12 C + 12 C → 12 C g. s. + α + 8 Be g.s. reaction has been investigated by 12 C-α coincidence measurements at incident energies of 90, 110 and 140 MeV. Cross sections of three kinds of intermediate channels ( 12 C + 12 C ∗ , 16 O ∗ + 8 Be and α + 20 Ne ∗ ) and of non-resonant parts (breakup, etc.) leading to the same 12 C g.s. + α + 8 Be g.s. final channel have been deduced. Among them the 16 O ∗ + 8 Be and 12 C + 12 C ∗ channels had dominant cross sections, whereas massive-cluster transfer (α + 20 Ne ∗ ) and non-resonant reactions contributed only a few percent. For the 16 O ∗ + 8 Be and 12 C + 12 C ∗ channels, states in 16 O(4 + 1 , 5 − 1 , 6 1 + and 7 1 − ) and in 12 C(3 1 − and 4 1 + ) were populated selectively. Coincidence cross sections for these channels were reproduced by DWBA calculations. In the present reaction, there are kinematical regions where two intermediate channels 16 O ∗ + 8 Be and 12 C + 12 C ∗ can participate at the same time, since these intermediate channels lead to the same final channel, 12 C g.s. + α + 8 Be g.s. . Cross sections obtained experimentally at such regions could not be explained by a simple sum of the cross sections estimated individually for these two intermediate channels. This shows evidence of interference between two different intermediate channels. The interference effect is discussed in terms of DWBA calculations taking into account interference between T -matrices of the two channels.

The response function of organic scintillator NE213 to 59.5 MeV neutrons

Abstract The response function of a 12.7 cm diameter × 12.7 cm cell of an organic liquid scintillator NE213 has been studied at E n = 59.5 MeV. In the pulse shape spectra bands due to deuterons, besides protons and alpha particles produced by neutron interactions are identified. In order to discriminate the contribution from the 12 C (n, np) reaction, a coincidence experiment between the protons in the scintillator and the escaping neutrons from the scintillator was made. To confirm the deuteron band further, a liquid scintillator cell was directly bombarded by a faint deuteron beam with an energy of 56 MeV. The response functions for individual bands are very different from the calculated response using the Monte Carlo method.

A neutron polarimeter for the (p,n) reaction at Ep=50–80 MeV

A conventional type of neutron polarimeter consisting of three 12.5 × 12.5 cm cylindrical liquid scintillators and two 12.5 × 12.5 cm cylindrical plastic scintillators has been used to measure the transverse polarization transfer coefficient Kyy in the (p, n) reaction in the energy range 50 < Ep < 80 MeV. The effective analyzing powers of this polarimeter have been obtained empirically by observing neutrons from the 6Li(p, n)6Be reaction at θ = 0° and Ep = 50,65 and 80 MeV whose polarizations are deduced from the Kyy values of the 6Li(p,p′)6Be∗ (0+ reaction by utilizing the analogue relation. Observed effective analyzing powers are significantly reduced particularly at high energy, most likely due to the 12C(n,np)11B reaction process. The double scattering efficiencies are 6 × 10−4 and 3 × 10−4 with effective analyzing powers of 0.14 and 0.11 at En = 45 and 75 MeV, respectively.

High-energy gamma ray spectrometer for heavy-ion induced experiments

Abstract A gamma-ray detector system of large NaI(Tl) crystals has been constructed to investigated heavy ion reaction mechanisms and highly excited nuclear structure with heavy ion beams. The NaI(Tl) crystals have as a whole a cross section of hexagonal shape of 30 cm between the parallel sides and a length of 20 cm, and are composed of seven substructures based on a honeycomb shape. This is designed for detection of high energy gamma rays with high resolution, and also for use as an anti-Compton spectrometer for a Germanium detector. A good energy resolution of 2.7 (3.2)% fwhm was obtained for 22.3 MeV gamma rays with 18 (39)% detection effeciency of the full-energy-loss peak with anti-Compton mode (sum mode) operation of the trapezoidal NaI(Tl) crystals. Compton scattering background in a spectrum by a Ge detector was successfully reduced by about 60% in applying the trapezoidal NaI(Tl) crystals for Compton suppression. The performance of the spectrometer is discussed.

Excitation of spin- and isospin-flip states with the (d, ds=0) reaction*

The (d, d s =0 ) reaction has been studied for the first time at E d = 56 MeV and 70 MeV. It is demonstrated that the reaction is a useful tool for the study of the inelastic excitation of the spin- and isospin-flip mode. Several states in 12 C with T = 1 and S = 1 are strongly excited. The differential cross sections and vector analyzing powers are reasonably reproduced by the distorted-wave Born-approximation calculation.