Satoshi Kurashima

Japan Atomic Energy Agency, Muramatsu, Niigata, Japan

Are you Satoshi Kurashima?

Claim your profile

Publications (49)32.79 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We measured temporal profiles of the scintillation of Ce-doped LiCaAlF6 scintillator crystals at different linear energy transfers (LETs). Based on the comparison of high-LET temporal profiles with those at low LET, a fast component was observed only at low LET. The disappearance of the fast component at high LET is tentatively ascribed to the quenching of excited states at crystal defects owing to the interaction between excited states via the Auger process. In addition, the rise and the initial decay behavior were dependent on the LET. This LET-dependent behavior is explained by an acceleration process and a deceleration process in energy transfer at high LET. The LET-dependent temporal profiles provide the basis for a discrimination technique of gamma-ray and neutron detection events using these scintillators based on the nuclear reaction, 6Li(n,α)t.
    No preview · Article · Jul 2015 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
  • [Show abstract] [Hide abstract]
    ABSTRACT: The single-pulse formation technique using a beam chopping system consisting of two types of high-voltage beam kickers was improved to enhance the quality and intensity of the single-pulse beam with a pulse interval over 1 μs at the Japan Atomic Energy Agency cyclotron facility. A contamination rate of neighboring beam bunches in the single-pulse beam was reduced to less than 0.1%. Long-term purification of the single pulse beam was guaranteed by the well-controlled magnetic field stabilization system for the cyclotron magnet. Reduction of the multi-turn extraction number for suppressing the neighboring beam bunch contamination was achieved by restriction of a beam phase width and precise optimization of a particle acceleration phase. In addition, the single-pulse beam intensity was increased by a factor of two or more by a combination of two types of beam bunchers using sinusoidal and saw-tooth voltage waveforms. Provision of the high quality intense single-pulse beam contributed to improve the accuracy of experiments for investigation of scintillation light time-profile and for neutron energy measurement by a time-of-flight method.
    No preview · Article · Jul 2015 · The Review of scientific instruments
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We analyzed the effects of linear energy transfer (LET) on the scintillation properties of a Li glass scintillator, GS20. The temporal profiles of scintillation were measured by using pulsed ion beams with different LETs. The rise in the temporal profiles of scintillation was faster for higher LET, whereas the decay part did not vary significantly for different LETs. The LET effects in the rise were ascribed to excited state interactions during the energy transfer process from the host glass to the luminescent centers, Ce3+ ions. If the light yield decreases with LET, the fast rise at high LET could be explained by the competition between energy transfer and quenching due to the excited state interactions.
    Full-text · Article · Apr 2015 · Journal of Luminescence
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a system for measuring the temporal profiles of scintillation at high linear energy transfer (LET) by using pulsed ion beams from a cyclotron. The half width at half maximum time resolution was estimated to be 1.5-2.2 ns, which we attributed mainly to the duration of the pulsed ion beam and timing jitter between the trigger signal and the arrival of the ion pulse. The temporal profiles of scintillation of BaF2 at different LETs were successfully observed. These results indicate that the proposed system is a powerful tool for analyzing the LET effects in temporal profiles of scintillation.
    No preview · Article · Feb 2015 · Review of Scientific Instruments
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new technique for evaluating the phase bunching performance in the central region of a cyclotron was developed. A newly-developed radial probe with a 6-mm-wide, 5-mm-height plastic scintillator was applied to analysis of the correlation between the internal beam phase distribution and the initial beam phase, defined by adjusting the relative RF phase of the beam buncher. The phase distribution measurement system, comprising the radial probe equipped with a plastic scintillator and the signal-processing modules, had a sufficiently good time resolution of 45 ps full-width at half-maximum for the phase bunching evaluation. The correlations between the buncher phase and the measured phase distribution for the acceleration harmonic number h=1 and 2 were consistent with the calculation result of the geometric trajectory analysis. For h=1 case of a 107 MeV 4He2+ beam, the internal beam phase region spread over 71 RF degrees full-width at quarter-maximum (FWQM) for the acceptable buncher phase region of 48 RF degrees, and no evidence of the phase bunching effect was observed. For h=2 case of a 260 MeV 20Ne7+ beam, the internal beam phase region for the acceptable buncher phase region of 59 RF degrees was compressed into 21 RF degrees FWQM. The phase bunching effect was sharply evident for h=2, and contributed to increase of the acceptable beam phase region and the beam intensity per phase width.
    No preview · Article · Nov 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • [Show abstract] [Hide abstract]
    ABSTRACT: The JAEA AVF cyclotron accelerates various kinds of high-energy ion beams for research in biotechnology and materials science. Beam intensities of an ion species of the order of 10(-9)-10(-6) ampere are often required for various experiments performed sequentially over a day. To provide ion beams with sufficient intensity and stability, an operator has to retune an ion source in a short time. However, the beam intensity downstream of the cyclotron rarely increases in proportion to the intensity at the ion source. To understand the cause of this beam behavior, transmission efficiencies of a (12)C(5+) beam from an electron cyclotron resonance ion source to the cyclotron were measured for various conditions of the ion source. Moreover, a feasible region for acceleration in the emittance of the injection beam was clarified using a transverse-acceptance measuring system. We confirmed that the beam emittance and profile were changed depending on the condition of the ion source and that matching between the beam emittance and the acceptance of the cyclotron was degraded. However, after fine-tuning to improve the matching, beam intensity downstream of the cyclotron increased.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • H Kashiwagi · N Miyawaki · S Kurashima · S Okumura
    [Show abstract] [Hide abstract]
    ABSTRACT: A transverse beam emittance and acceptance measurement system has been developed to visualize the relationship between the injected beam emittance and the acceptance of a cyclotron. The system is composed of a steering magnet, two pairs of slits to limit the horizontal and vertical phase-space, a beam intensity detector just behind the slits for the emittance measurement, and a beam intensity detector in the cyclotron for the acceptance measurement. The emittance is obtained by scanning the slits and measuring the beam intensity distribution. The acceptance is obtained by measuring the distribution of relative beam transmission by injecting small emittance beams at various positions in a transverse phase-space using the slits. In the acceptance measurement, the beam from an ion source is deflected to the defined region by the slits using the steering magnet so that measurable acceptance area covers a region outside the injection beam emittance. Measurement tests were carried out under the condition of accelerating a beam of (16)O(6+) from 50.2 keV to 160 MeV. The emittance of the injected beam and the acceptance for accelerating and transporting the beam to the entrance of the extraction deflector were successfully measured. The relationship between the emittance and acceptance is visualized by displaying the results in the same phase-plane.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • [Show abstract] [Hide abstract]
    ABSTRACT: An optimum condition for realizing phase bunching in the central region of a cyclotron was quantitatively clarified by a simplified geometric trajectory analysis of charged particles from the first to the second acceleration gap. The phase bunching performance was evaluated for a general case of a cyclotron. The phase difference of incident particles at the second acceleration gap depends on the combination of four parameters: the acceleration harmonic number h, the span angle θD of the dee electrode, the span angle θF from the first to the second acceleration gap, the ratio RV of the peak acceleration voltage between the cyclotron and ion source. Optimum values of θF for phase bunching were limited by the relationship between h and θD, which is 90°/h+θD/2≤θF≤180°/h+θD/2, and sin θF>0. The phase difference with respect to the reference particle at the second acceleration gap is minimized for voltage-ratios between two and four for an initial phase difference within 40 RF degrees. Although the slope of the first acceleration gap contributes to the RF phase at which the particles reach the second acceleration gap, phase bunching was not affected. An orbit simulation of the AVF cyclotron at the Japan Atomic Energy Agency verifies the evaluation based on geometric analysis.
    No preview · Article · Jul 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • [Show abstract] [Hide abstract]
    ABSTRACT: The JAEA AVF cyclotron provides heavy-ion beams covering a wide range of linear-energy-transfers for microbeam formation. Two types of microbeam formation systems, one using a micro-aperture and the other focusing lenses, are installed on two vertical beam lines of the cyclotron. The average beam time for an experiment using the former system is usually less than 3 h, that is comparable to the time for cyclotron tuning. The time ratio between experiment and tuning determines the usage efficiency of the facility. In order to reduce the tuning time, a scaling method has been introduced to change the ion species with various mass to charge ratios (M/Q) in a shorter total time. The principle of the scaling method is to keep the magnetic rigidity of ion beams constant. This requirement is easily achieved by adjusting the extraction voltage of an ion source proportionally to the M/Q in the beam injection line. Although some cyclotron adjustments, other than the magnetic field strength at the extraction radius, are required, the tuning can be completed within 20 min, and no change is basically required in the beam transport line downstream of the cyclotron. Using the scaling method, 255 MeV 20Ne7+, 335 MeV 20Ne8+, and 440 MeV 40Ar13+ beams were extracted from the cyclotron in sequence after the usual tuning of a 220 MeV 12C5+. As a result, we have succeeded in changing the ion species of the heavy-ion microbeam within a total of 30 min.
    No preview · Article · Jul 2013 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39’s detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical openings are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method is applied to laser-driven ion acceleration experiments using cluster-gas targets, and ion signals with energies up to 50 MeV per nucleon are identified.
    Full-text · Article · May 2013 · Radiation Measurements
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate a new ion diagnosis method for high energy ions by utilizing a combination of a single CR-39 detector and plastic plates, which enables to detect high energy ions beyond the detection threshold limit of the CR-39. This detection method coupled with a magnetic spectrometer is applied to identify high energy ions of 50 MeV per nucleon in laser-driven ion acceleration experiments using cluster-gas targets.
    Full-text · Article · May 2013 · Proceedings of SPIE - The International Society for Optical Engineering
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new diagnosis method has been developed utilizing back scattered particles for high energy intense ion beams. The CR-39 detector mounted on the uniform back-scatterer was irradiated with 4 He 2+ ions with an energy 25 MeV/n, which is never recorded as etchable track in CR-39. We found that it is possible to diagnose by analyzing the etch pits on the rear surface of CR-39 that directly contacted on the back-scatterers. It turns out that most of etch pits in the rear surface are made by the backscattered particles by investigating the growth pattern of each etch pit with multi-step etching technique. This method allows simple diagnosis of the ion beam profile and intensity distribution in mixed radiation field such as laser-driven ion acceleration experiments.
    No preview · Article · Jul 2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A single CR-39 detector mounted on plastic plates is irradiated with a 100 MeV He ion beam. Although the beam energy is much greater than the detection threshold limit of the CR-39 detector, a large number of etch pits having elliptical openings are observed on the rear surface. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This method allows a simple diagnosis of the ion beam profile and the presence of the high-energy component beyond the detection threshold limit of the CR-39 detector, especially in mixed-radiation fields such as laser-driven ion acceleration experiments. # 2012 The Japan Society of Applied Physics
    Full-text · Article · Apr 2012 · Japanese Journal of Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: A phase bunching effect has been achieved for the first time using a rising slope of the dee voltage waveform produced at the first acceleration gap between the RF shielding cover of the inflector and the puller in the new central region of the JAEA AVF cyclotron. The feasibility of the phase bunching effect in the central region for a two-dee system with a span angle of 86° in three acceleration harmonic modes was assessed by a simple geometrical analysis of particle trajectories and a three-dimensional beam orbit simulation using the calculated electric field and a measured magnetic field. The simulation indicated that the initial beam phase width of 40 RF degrees is compressed to 11 RF degrees (about 28% of the initial phase width) in the second harmonic mode. A phase width of 1.5 RF degrees FWHM for a 260MeV 20Ne7+ beam accelerated in the second harmonic mode was observed when using a 4mm phase slit gap. The phase width reduction was considerably enhanced by the bunching effect, compared with the beam phase width of 7.3 RF degrees FWHM in the same harmonic mode for a 10MeV H+ beam accelerated in the original central region. The ratio of the beam current for the 1.5 RF degrees FWHM phase width with 4mm phase slit gap restriction to the full beam current without the phase slit was drastically improved to 80%, while the beam current was less than 1% of the full beam when narrowing the phase slit gap to obtain the 7.3 RF degrees FWHM phase width in the original central region.
    No preview · Article · Apr 2011 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • Source
    K. Iwamatsu · M. Taguchi · Y. Sugo · S. Kurashima · Y. Katsumura
    [Show abstract] [Hide abstract]
    ABSTRACT: The concentration and incident energy dependence of transient species Br2●– were obtained for aqueous NaBr solutions irradiated with pulsed H+ ion with energies of 20 MeV. The formation and decomposition of Br2●– were observed by transient absorbance method at 375 nm. Dose in irradiation pulse was evaluated by using GAF film dosimeter for the quantitative analysis of reactive species. The formation yield of Br2●– slightly increased from 0.73 to 0.85 (number of reactive species per absorbed energy of 100 eV) with the increase in the concentration of NaBr from 1 to 1000 mM. The formation yield of Br2●– for 1000 mM NaBr aqueous solution decreased from 0.85 to 0.27 with the decrease in the incident energy from 19.4 to 8.8 MeV, in other words, the increase in LET value from 4.79 to 8.81 eV/nm.
    Full-text · Article · Jan 2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a new technique for analysis and control of the acceleration beam phase in the cyclotron. In this technique, the beam current pattern at a fixed radius r is measured by slightly scanning the acceleration frequency in the cyclotron. The acceleration beam phase is obtained by analyzing symmetry of the current pattern. Simple procedure to control the acceleration beam phase by changing coil currents of a few trim coils was established. The beam phase width is also obtained by analyzing gradient of the decreasing part of the current pattern. We verified reliability of this technique with 260 MeV (20)Ne(7+) beams which were accelerated on different tuning condition of the cyclotron. When the acceleration beam phase was around 0 degrees, top of the energy gain of cosine wave, and the beam phase width was about 6 degrees in full width at half maximum, a clear turn pattern of the beam was observed with a differential beam probe in the extraction region. Beam phase widths of ion beams at acceleration harmonics of h=1 and h=2 were estimated without beam cutting by phase-defining slits. We also calculated the beam phase widths roughly from the beam current ratio between the injected beam and the accelerated beam in the cyclotron without operating the beam buncher. Both beam phase widths were almost the same for h=1, while phase compressions by a factor of about 3 were confirmed for h=2.
    No preview · Article · Mar 2010 · The Review of scientific instruments
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to supply ion beam stably we have recently constructed an all-permanent-magnet type ion source. Ion beams such as H, O and Ne were produced stably. A beam attenuation system with metal meshes has been improved. By using new meshes with denser hole arrangement and lengthening the space of meshes, beam intensity can be controlled more precisely with maintaining the beam profile. The power supplies of the magnet coils used in the cyclotron were modified to stabilize the coil current with the stability ∆I/I of the order of 10 -6 . In addition, developments of new irradiation techniques such as quick change of microbeam by cocktail beam acceleration technique and large-area uniform beam irradiation using multipole magnets are in progress.
    Preview · Article · Jan 2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An apparatus for transverse acceptance measurement has been developed in JAEA cyclotron facility. The apparatus consists of a phase-space collimator in the injection beam line and a beam current monitor after the cyclotron. The collimator consists of two pairs of position-defining slits and angle-defining slits to inject an arbitrarily small portion of transverse phase-space into the cyclotron. Measurement of the acceptance is made by injecting every portion in the whole phase-space which should be large enough to cover the acceptance. The acceptance can be estimated from the sum of the portions of the beam which pass through the system. The beam is measured by an uncooled Faraday cup or a scintillator because of the low beam current from a few picoampere to a few hundred picoampere in HEBT for acceptance measurement.
    Preview · Article · Jan 2010
  • Source
    S Kurashima · M Taguchi · I Ishibori · T Nara · W Yokota
    [Show abstract] [Hide abstract]
    ABSTRACT: The intervals of beam pulses from a cyclotron are generally tens of ns and they are too short for pulse radiolysis experiments which require beam pulses at intervals over 1 μs (single-pulse beam). A chopping system, consisting of two types of high voltage kickers, is used at the JAEA AVF cyclotron to form single-pulse beam. However, we could not provide single-pulse beam stably over 30 min since the magnetic field of the cyclotron gradually decreased and the number of multi-turn extraction increased. The magnetic field is stabilized at present by keeping temperature of the cyclotron magnet constant. In addition, a new technique to measure and control an acceleration beam phase has enabled us to reduce the number of multi-turn extraction easier than before. The single-pulse beam of a 320 MeV 12 C 6+ is successfully provided without retuning of the cyclotron over 4 h, as a result.
    Preview · Article · Jan 2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This article reports a highly sensitive transient absorbance measurement system using pulsed energetic ions. The ions were pulsed by a beam chopper, which was synchronized with the cyclotron, and accelerated to the desired energy around 18MeV/u. H, He, C and Ne ions can be used for the transient absorption measurement. The optical system can measure an absorbance smaller than 1.0×10−4 in the wavelength range of 400–740nm.
    Full-text · Article · Dec 2009 · Radiation Physics and Chemistry