Search

A scheme for spot scanning using11C beams has been developed in order to form and verify a three-dimensionally conformal irradiation field for cancer radiotherapy. By selecting the momentum spread of a11C beam, we could considerably decrease the distal falloff of the irradiation field, thus conserving the beam quality. To estimate and optimize the dose distribution in the irradiation field, it is essential to evaluate the precise dose distribution of spot beams. The coupling of the lateral dose and depth-dose distributions originating from a wide momentum spread should be taken into account to calculate the dose distribution of11C beams. The reconstructed dose distribution of the irradiation field was in good agreement with the experimental results, i.e., within ±0.2%. An irradiation field of 35×35×43 mm3was optimized and spot scanning using11C beams was carried out. The flatness was within ±2.3% with an error of 1% in the detector resolution.

For medical irradiation, beams with a uniform distribution have been required. We have proposed a method to control the beam profile using an octupole magnet. We have installed an octupole magnet and confirmed its effectiveness at the Heavy Ion Medical Accelerator in Chiba (HIMAC) beam-transport line. A beam efficiency of 91% can be realized with a flatness of ±4% over the range of ±15 mm. The beam offset at the position of the octupole magnet is required to be within ±0.2 mm to realize this condition. This method is expected to have a beam efficiency higher than that of the ordinary method using wobbler magnets and a scatterer system.

The energy levels of 109 Pd have been studied from the decay of 109 Rh by using high-resolution γ-detector systems. A total of 35 γ-transitions were observed. From various coincidence studies on these transition, it is concluded that excited levels are populated at 113.4, 245.0, 266.3, 276.3, 291.4, 325.4, 326.8, 426.1, 491.7, 540.7, 597.3, 667.3, 983.4 and 1318.0 keV. The half-life of 113.4 keV level was determined as 380±50 ns. K conversion coefficients for a few low-energy transitions were determined. Spins and parties of most of the levels were deduced from β- and γ-transition properties combined with the previous studied on the ( d , p ) and ( d , t ) reactions.

The decay of 99m Nb to the levels in 99 Mo has been studied using β- and γ-spectroscopic techniques in singles and coincidence modes. A total of 143 γ rays were observed. Ninety-eight γ rays have been placed into the decay scheme involving 31 excited levels in 99 Mo. Spin and parity assignments for the levels have been deduced using β-decay logft values, γ-ray transition rates and reaction data in the literature.

Differential cross sections of the reaction γp→ηp have been measured by using a tagged photon beam in the energy range from 808 MeV to 1008 MeV at θ * η =45°C, 80°C, 100°C and 110°C. Photon couplings of nucleon resonances with masses below 1700 MeV are determined by a partial wave analysis of the reaction γp→ηp based on the isobar model. Results are compared with photon-couplings obtained by the analysis of the reaction γN→πN and by the quark model calculation.

A high field gradient cavity (HGC) which has been developed for high intensity proton synchrotrons is suitable to generate multi-harmonic voltage on the accelerating gap because of the broad band impedance of the cavity. In this paper, the experimental results on the dual harmonic RF, saw-tooth RF, and bunch compression by barrier bucket are described.

The momentum distributions of projectile-like fragments produced in the 40 Ar+ 9 Be reaction at E / A =90 MeV and the 16 O+ 12 C reaction at E / A =290 MeV were observed. A correlation between the width of the transverse momentum distribution and the velocity was found at E / A =90 MeV. Coulomb final-state interaction and AMD calculation cannot explain this correlation. A good agreement between EPAX2 and the production cross sections derived from observed momentum distribution of the fragments was found.

Over 3000 cancer patients have already been treated with 140- to 400-MeV/n carbon beams produced by the heavy ion medical accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIRS) since 1994. These clinical results have clearly verified the advantages of carbon ions. Based on our experience at HIMAC, a hospital-specific facility optimized for carbon-ion therapy has been designed. The prototype developments of an electron cyclotron resonance (ECR) ion source, a radio frequency quadruple (RFQ) linac, an inter digital H (IH) linac, an acceleration system of synchrotron, a beam-delivery system and other key-technology parts have been successfully finished. Thus, in co-operation with NIRS, Gunma University has been constructing a carbon-therapy facility since April, 2006. If the present clinical results are to be improved, it is necessary to create a more accurate dose distribution on tumors without an undesired dose being deposited in normal tissue. Beam-scanning methods with respiration-gated irradiation are especially important to treat a cancer tumor located in the trunk of a patient.