Toshihiro Honma

Response Functions of Phoswich-Type Neutron Detector for High-Energy Cosmic Ray Neutron Measurement

A phoswich-type neutron detector was developed in order to measure high-energy cosmic ray neutron spectra in aircraft. The neutron detector consists of an EJ309 organic liquid scintillator that is 121.7mm in diameter and 121.7mm in length and is covered with a 15mm thick EJ299-13 outer plastic scintillator. The neutron response functions of the detector are required for the unfolding method to obtain the energy spectrum. The neutron response functions were created based on MCNPX simulations using an anticoincidence mode with the experimental light-output correlations with particle energies, uniformity of light collection and energy resolutions. The light-output correlation with particle energy, the uniformity of light collection and the energy resolutions were evaluated based on experiments. Measurements of neutron response functions were performed using four quasi-monoenergetic neutron beams from 40 to 80 MeV p-Li reactions to verify the calculated results. The calculated response functions show good agreement with the measurements. The angular response of the phoswich detector was confirmed to be isotropic from the calculation. The photon response functions of the detector were also calculated and agreed well with the measurements for 6.129MeV photons. Neutron and photon response matrices were created up to 300 and 50 MeV, respectively, over a wide energy range for experimental flights.

11CH4 molecule production using a NaBH4 target for 11C ion accelerationa)

Solid-state materials suitable for use as proton irradiation targets were investigated for producing high-purity (11)CH4 molecules for heavy-ion cancer therapy. The radioactivity of gas produced by proton irradiation was measured for several target materials. Also, the radioactive molecular species of the produced gas were analyzed by radio gas chromatography. We found that 5 × 10(12) (11)C molecules could be collected by proton irradiation on a NaBH4 target. We also found that the (11)CH4 molecules were produced and collected directly from the irradiated target, owing to the hydrogen atoms bound in the solid-state NaBH4.

Development of gas pulsing system for electron cyclotron resonance ion source

A gas-pulsing system for an electron cyclotron resonance ion source with all permanent magnets (Kei2 source) at NIRS has been developed and tested. The system consists of a small vessel (30 ml) to reserve CH(4) gas and two fast solenoid valves that are installed at both sides of the vessel. They are connected to each other and to the Kei2 source by using a stainless-steel pipe (4 mm inner diameter), where the length of the pipe from the valve to the source is 60 cm and the conductance is 1.2 l/s. From the results of the test, almost 300 e microA for a pulsed (12)C(4+) beam was obtained at a Faraday cup in an extraction-beam channel with a pressure range of 4000 Pa in the vessel. At this time, the valve has an open time of 10 ms and the delay time between the valve open time and the application of microwave power is 100 ms. In experiments, the conversion efficiency for input CH(4) molecules to the quantity of extracted (12)C(4+) ions in one beam pulse was found to be around 3% and the ratio of the total amount of the gas requirement was only 10% compared with the case of continuous gas provided in 3.3 s of repetition in HIMAC.

A simple algorithm for beam profile diagnostics using a thermographic camera.

A new algorithm for digital image processing apparatuses is developed to evaluate profiles of high-intensity DC beams from temperature images of irradiated thin foils. Numerical analyses are performed to examine the reliability of the algorithm. To simulate the temperature images acquired by a thermographic camera, temperature distributions are numerically calculated for 20 MeV proton beams with different parameters. Noise in the temperature images which is added by the camera sensor is also simulated to account for its effect. Using the algorithm, beam profiles are evaluated from the simulated temperature images and compared with exact solutions. We find that niobium is an appropriate material for the thin foil used in the diagnostic system. We also confirm that the algorithm is adaptable over a wide beam current range of 0.11-214 μA, even when employing a general-purpose thermographic camera with rather high noise (ΔT(NETD) ≃ 0.3 K; NETD: noise equivalent temperature difference).

Low-energy ion decelerator for an external injection line at the NIRS-930 cyclotron

A low-energy ion decelerator for the acceleration-deceleration system has been designed and installed in the beam-injection line of the NIRS-930 cyclotron in an attempt to increase the beam intensity from the cyclotron. With this acceleration-deceleration system, the beam intensity of C4+12 ions at the cyclotron exit has been increased by about five times. The system has an advantage in that it allows us to extract a high-current ion beam from an electron cyclotron resonance ion source because, independently of the injection-energy matching to the cyclotron, a large potential difference can be applied between the source and the extractor. The voltage applied to the extractor is about −12kV, which is reduced to the ground potential by the decelerator. The electric field distributions in the deceleration system were carefully designed using a three-dimensional field simulator. Design studies of the decelerator as well as the result of a beam test are presented.

Effects of ion pumping in a pulsed Penning source

We recently reported on the first observation of ion-pumping phenomenon in a low-duty pulsed Penning source at the heavy-ion medical accelerator (HIMAC) in Chiba and its effectiveness to produce multiply charged ions [Y. Sato et al., Nucl. Instrum Methods Phys. Res. A 450, 231 (2000)]. In the Penning-ionized gauge ion source (PIGIS) of the HIMAC, the gas flow is not being pulsed, but there is a transient pressure response in the source when the arc is pulsed that permits the production of high-charge-state ions under a reasonably low gas pressure obtained by ion pumping. The best record for Ar8+ is 700 eμA in a peak under a constant gas flow of 0.2 cc/min, an extraction voltage of 24 kV, and a pulsed arc power of 1 kV and 5 A with a duty factor of 0.5% (25 W on average). This yield is higher than those of cw PIGISs by a factor of 100–1000 having a similar design and power (peak). This article gives a brief review for the mechanism and effects of ion pumping in a pulsed PIGIS.

Improvements and applications at NIRS cyclotron facility

The NIRS-Chiba isochronous cyclotron has been working in routinely, and providing the stable beams for bio-medical studies and various kind of related experiments since 1975. The clinical trail of eye melanoma has been under continued. Recently two new beam lines were constructed in order to carry out the bio-physical study, and to produce the long-lived R.I.s for SPECT. Some progressive improvements, such as updating the magnetic-channel and development of a floating septum system, were performed for stable operation of the cyclotron. A brief review of the current status of the cyclotron and typical application of latest experiments in the various fields are described.

Status of a compact electron cyclotron resonance ion source for National Institute of Radiological Sciences-930 cyclotron.

The Kei-source is a compact electron cyclotron resonance ion source using only permanent magnets and a frequency of 10 GHz. It was developed at the National Institute of Radiological Sciences (NIRS) for producing C(4+) ions oriented for high-energy carbon therapy. It has also been used as an ion source for the NIRS-930 cyclotron. Its microwave band region for the traveling-wave-tube amplifier and maximum output power are 8-10 GHz and 350 W, respectively. Since 2006, it has provided various ion beams such as proton, deuteron, carbon, oxygen, and neon with sufficient intensity (200 μA for proton and deuteron, 50 μA for C(4+), for example) and good stability for radioisotope production, tests of radiation damage, and basic research experiments. Its horizontal and vertical emittances were measured using a screen monitor and waist-scan. The present paper reports the current status of the Kei-source.