Masaharu Kawanishi

High-Current Single Bunch Electron Linear Accelerator

An injector of an electron linear accelerator has been modified at ISIR of Osaka University in order to increase a single bunch charge from 14 nC to 60 nC. A 6th subharmonic prebuncher has been replaced with two 12th subharmonic prebunchers and a 6th subharmonic prebuncher which are newly constructed. A one-dimensional disk model has been used to calculate the bunching of the beam and to decide the optimum location of the subharmonic prebunchers. The subharmonic prebunchers are immersed in a solenoidal magnetic field so that the electron beam is confined during the travel through the drift region. The single bunch of 16 - 20 ps duration and up to 67 nC in charge, with the energy spread of 0.7 - 2.5 % over the range of 24 - 34 MeV, and a repetition rate from a single shot to 720 pps can be obtained. The energy spread depends on the charge and the minimum spread is 0.7 % at 33 nC. The single bunch of 25 - 45 nC in charge is used for the experiments in routine work.

Fast decay of the visible band electron in e-irradiated crystalline ice at low temperature: The isotope effects and the role of a mobile proton in the decay

The trapped electron which absorbs in the visible region in crystalline ice e−vis has been studied by pulse radiolysis in the low temperature range 6 to 77 K using 2 μs pulses, and above 77 K using pulses of 40 ps to 6 ns width. The half‐life of e−vis in ice around 77 K is unusually short, 8 ns in H2O ice and 120 ns in D2O ice. The decay of e−vis in ice is found to fit Hummel’s empirical equation for the decay by geminate ion recombination in a spur. Several other pieces of evidence indicate that the decay occurs in a spur. Electron tunneling from e−vis to the OD radical does not occur in D2O ice. It is concluded that a proton (H3O+) or a deuteron (D3O+) produced in a spur by the irradiation migrates through ice to react with immobile e−vis in the same spur, and that the half‐life of e−vis is determined by the mobility of the proton or deuteron. The Arrhenius plot of the half‐life in the range 100 to 6 K is nonlinear and shows an activation energy of 20 meV at higher temperatures and much smaller values a...

Collection efficiency of a parallel-plate ionization chamber exposed to pulsed X-rays

Abstract The collection efficiency of an ionization chamber exposed to a pulsed X-ray field has been discussed. Numerical calculations have been carried out under some idealized conditions to ascertain the fact that the collection efficiency depends on the respective value of the exposure rate and the pulse duration even though the total exposure per single pulse remains constant. One method has been proposed to determine the exact collection efficiency of the chamber in an unknown pulsed X-ray field, although the pulse duration should be found beforehand by some other method.

The Scintillation Process of NaI (Tl)

The scintillation process of NaI(Tl) crystal was studied, and explained according to the model of Hadley et al. The scintillation pulse above room temperature could be expressed by the solution of rate equations for Tl0, excited Tl+, Tl++ centers and conduction electrons, assuming the decay time of the Vk center to be negligible. From the temperature dependence of the decay time, the energy difference between the energy level of Tl0 center and the bottom of the conduction band was obtained to be 0.29 eV, which almost coincided with the value estimated from the thermal glow curve after UV or X ray irradiation. However, the pulse shape below room temperature could not be explained satisfactorily. Therefore another process, i.e. contribution from the self-trapped exciton or the perturbed exciton, had to be introduced.

Dosimetry of pulsed X-rays of high exposure rate generated by an electron linear accelerator with an ionization chamber

Abstract Evaluation of the ionic charges liberated in an air-equivalent, parallel-plate ionization chamber placed in the pulsed, high-energy X-ray field of extremely high-exposure rate around an electron linear accelerator is carried out in order to measure the exposure or the absorbed dose absolutely by applying the correction method previously reported to the observed results. For three typical operation modes of the linear accelerator, i.e. single, transient and steady, ionic charge densities liberated per pulse in air by the X-rays emitted from a tungsten target, which correspond to the exposure per pulse, are determined with the method and both observed and corrected results are reported.

Collective Field Acceleration of Heavy Ions with Intense Relativistic Electron Beam

Experimental study on ion acceleration in a vacuum diode has been performed. The spatial distribution and the energy spectrum of the accelerated ions have been measured. The maximum energy of Fe ions is estimated to be 18 MeV, and is independent of their charge state. The total number of ions is estimated to be of the order of 109 per shot. An acceleration mechanism is proposed by introducing a slow space-charge wave generated by beam-plasma interaction.

The Progress of Research on Exoelectron Emission and Applications in Japan

This is the first time that the International Symposium on Exoelectron Emission and Applications has been held in Osaka, Japan. Japanese research on exoelectron emission has certainly been spreading and growing from the standpoint not only of basic solid-state or surface science but also of technical applications. A brief review of this progress is presented.

TSEE from Ion-Implanted LiF Crystals

TSEE glow curves were studied for ion-implanted LiF single-crystals and for crystals irradiated by X-rays as well as those thermally annealed and irradiated by X-rays (afterward). It was found that the TSEE glow curve for Mg+ implanted LiF is influenced by the implantation energy and dose. Also, the annealed Mg+ implanted LiF (100 kV ×1012 Mg+/cm2) showed a greater response upon X-rays irradiation (compared with non-implanted LiF). Variations in the TSEE glow curves are qualitatively discussed.

Evaluation of average quality factor in a mixed radiation field with an ionization chamber

Abstract The recombination between positive and negative ions inan ionization chamber exposed to n-γ mixed radiation fields has been discussed. The average recombination coefficient is introduced as a parameter which characterizes a nonhomogeneous distribution of the density of ion pairs liberated by secondary electrons and recoil protons. It is pointed out that there exists some relation between the average recombination coefficient and the average quality factor in the mixed radiation field. A method has been proposed for determining the dose equivalent in a single-burst radiation field with an abreast-type ionization chamber. A practical application of the method has been carried out in a pulsed-mixed field generated by an electron linear accelerator.

Experimental observation of radiation loss of a single bunch electron beam in a linear accelerator

Abstract An experimental study on radiation loss of a single bunch caused by beam—cavity interaction has been carried out. The single bunch with up to 14 nC is accelerated by the 35 MeV Osaka University Single Bunch Electron Linear Accelerator. The average energy of electrons in a single bunch decreases in proportion to the charge. The radiation loss is evaluated to be 0.77–0.87 MeV/16 nC in 39 cavities of the accelerating waveguide. A theoretical estimation performed with a diffraction model is compared with the experimental results.