N. Ikeda

Strong-focusing in tandem accelerator with alternating voltage gradient

Abstract A new method to obtain low-energy high-intensity beams from a tandem accelerator of a high design-voltage is presented. In this method, the beam undergoes repeated actions of acceleration and deceleration from alternating voltage gradient along the beam axis, so that the beam divergence is minimized. The practical test was carried out at the 10 MV tandem accelerator at Kyushu University, and the beam transmission efficiency at a low operation voltage of 1 MV was found to be an order of magnitude increased. The method also enables the accelerator to stand a high beam load. The necessary changes in the accelerator configuration are quite simple and easily achievable at a low cost.

A ray-trace-type counter telescope for neutron spectrometry

A compact recoil proton counter telescope with two position sensitive proportional counters (PSPCs) for neutron spectrometry has been developed. This counter telescope consists of a radiator (a thin polyethylene film), two PSPCs used as /spl Delta/E detector and a Si-SSD used as E detector. Using the position information extracted from two PSPCs, the three-dimensional trajectory of the recoil proton and the recoil angle can be determined event by event. The performance of this counter telescope was tested by the measurement of 7.2 MeV neutrons produced from D-D reactions, and it was shown that the energy spectra of neutrons could be obtained by determining the energy of each incident neutron using a recoil angle.

Low-Level Radiation Measurement System With Magnetically Levitated Electrode Ionization Chamber Detector

An automatic system was developed for the measurement of radiation using a magnetically levitated electrode ionization chamber. The system was used to measure background and 40K gamma ray dose rates. The background dose rate measurement demonstrated high sensitivity and reliability of the system, and a low-level 40K gamma ray dose rate was successfully measured. For the case of a 30-minute measurement, the detection limit of the system is 13 nGy/h. This measurement system will be useful as an area monitor to measure space dose rates

Development of FFAG Accelerator at KEK

The 150MeV proton FFAG accelerator is constructed and a beam is extracted at the final energy. This is the prototype FFAG for various applications such as proton beam therapy. We are now in preparation for using an extracted beam in the practical applications.

Continuum spectra in one-nucleon transfer reactions —(p→, d) reactions at medium energy region—

The continuum spectra up to about 20 MeV of the (p→, d) reactions induced by 65 and 21 MeV polarized protons have been analyzed using such an approach as proposed by Lewis. An asymmetry Lorentzian form strength function was employed in the analysis, in set with empirical spreading widths. The cross sections were estimated as an incoherent sum of many shell-orbits constituents based on the distorted-wave Bom approximation (DWBA). The comparisons between the theoretical and experimental results of cross section angular distribution indicate a systematic relation between the distribution of strength and the target mass number, in isotopes.

Light Output Response of GSO(Ce) Crystals to Relativistic Carbon Ions

We have investigated the light output response of a GSO(Ce) crystal to carbon ions of energy up to 3.34 GeV. An experiment was carried out with HIMAC at National Institute of Radiological Sciences in Chiba, Japan. The incident energy of carbon beam was changed by inserting target materials with different thicknesses as degraders. Experimental results were consistent with the calculated curve by Birks equation, and the light output plotted as a function of deposited energy in the GSO(Ce) crystal showed a slight non-linearity in the low energy region and a good linearity in the higher energy region above around 1.5 GeV.

The Mo 96 ( p ⃗ , d ) Mo 95 reaction at 50 MeV

The {sup 96}Mo(p,d){sup 95}Mo reaction has been studied with a 50 MeV polarized beam. Differential cross sections and analyzing powers have been measured for investigating the level structure in {sup 95}Mo up to the excitation energy of 5.8 MeV. The standard distorted-wave Born approximation theory provides transfer angular momentum values and spectroscopic factors for the excited states. Furthermore, the theoretical analysis is extended also for the continuum region with a direct reaction model. Experimental double differential cross sections for continuum spectra are predicted well by adopting an asymmetric Lorentzian form for the response function in the distorted wave Born approximation based cross section calculations.

Facilities for direct measurement of 4He(12C,16O)γ reaction cross section at KUTL

Abstract A recoil mass separator designed to achieve a highest possible capability of the background rejection in the condition of inverse kinematics has been developed at Kyushu University tandem accelerator laboratory. Developments at accelerator have also been carried out to obtain a pulsed beam of high current and good emittance. With the mass separator and the pulsed heavy-ion beam, we are about to start the investigation of the 4 He( 12 C, 16 O)γ reaction of astrophysical interest.

Measurements of Radiative Capture Reaction by Recoil Detection in Inverse Kinematics

The analyzing powers of the 1H(d,3He)γ reaction at 17.5 MeV have been measured with enough accuracy to discuss the details of nuclear force. The 12C-α radiative capture reaction of astrophysical interest is planned to be investigated at center-of-mass energies down to 0.7 MeV. Both experiments take advantage of the recoiled particle detection in inverse kinematics to realize the high-efficiency measurement.

Tensor polarization of 12C[2+1] in the 16O(13C,12C)17O reaction at 50 MeV

Abstract: The 16O(13C,12C)17O reaction at 50 MeV has been investigated using the kinematical coincidence method. Polarization tensors t20 and t40 of 12C[2+1] for the quantization axis taken along the direction of propagation have been measured by analyzing the energy spectrum of 12C[2+1], modulated by the effect of γ ray emission. The deduced t40 values significantly deviate from zero, contrary to the prediction of the distorted-wave Born approximation theory based on one-step p shell neutron stripping without spin-dependent interactions. The phenomenological spin–orbit interaction necessary to reproduce the magnitude of measured t40 is found to be much larger than the folding model prediction. It is shown that the experimental polarization tensors as well as the cross sections can be reproduced by introducing multi-step processes involving excitations in 12C and 13C without introducing spin-dependent interactions.