Abstract
Constraints on the beam diagnostics available in real-time and time-varying beam source conditions make it difficult to provide users with high-quality beams for long periods without ...interrupting experiments. Although surrogate model-based inference is useful for inferring the unmeasurable, the system states can be incorrectly inferred due to manufacturing errors and neglected higher-order effects when creating the surrogate model. In this paper, we propose to adaptively assimilate the surrogate model for reconstructing the transverse beam distribution with uncertainty and underspecification using a sequential Monte Carlo from the measurements of quadrant beam loss monitors. The proposed method enables sample-efficient and training-free inference and control of the time-varying transverse beam distribution.
Abstract
NC-FG (nanocomposite Fricke gel) dosimeter is a 3D dosimeter for heavy ion beam without LET dependence. In this study, we evaluate the effects of silver perchlorate, a radical scavenger, on ...NC-FG. We find that radiological properties of NC-FG are changed by small amounts of silver perchlorate. Especially, dose response at high LET enhanced.
In this research, we used a 135 MeV/nucleon carbon-ion beam to irradiate a biological sample composed of fresh chicken meat and bones, which was placed in front of a PAGAT gel dosimeter, and compared ...the measured and simulated transverse-relaxation-rate (R2) distributions in the gel dosimeter. We experimentally measured the three-dimensional R2 distribution, which records the dose induced by particles penetrating the sample, by using magnetic resonance imaging. The obtained R2 distribution reflected the heterogeneity of the biological sample. We also conducted Monte Carlo simulations using the PHITS code by reconstructing the elemental composition of the biological sample from its computed tomography images while taking into account the dependence of the gel response on the linear energy transfer. The simulation reproduced the experimental distal edge structure of the R2 distribution with an accuracy under about 2 mm, which is approximately the same as the voxel size currently used in treatment planning.
We report a new magnetic-resonance-imaging (MRI) based nanocomposite Fricke gel (NC-FG) dosimeter system, which is free from two main drawbacks of conventional Fricke gel dosimeters, namely, the ...diffusion of the radiation products and the linear-energy-transfer (LET) dependence of the radiation sensitivity when used for ion beams. The NC-FG dosimeter was prepared by incorporating 1% (w/w) clay nanoparticles into deaerated Fricke gel. We have dosimetrically characterized the NC-FG by using MRI measurements after irradiation with a monoenergetic 290MeV/nucleon carbon beam. No diffusion of the radiation products was observed during nine days after the irradiation. Moreover, its response faithfully reproduced the depth-dose distribution measured by an ionization chamber, which indicates the absence of the LET dependence. Also, the NC-FG dosimeter exhibited a good linearity up to 800Gy.
•We report a new magnetic-resonance-imaging based nanocomposite Fricke gel dosimeter.•No diffusion of the radiation products was observed during nine days after the irradiation.•Gel response faithfully reproduced the carbon beam depth-dose distribution.•The NC-FG dosimeter exhibited a good linearity up to 800Gy and suppression of LET effects.
We study the radiological characteristics of VIP polymer gel dosimeters under carbon beam irradiation with energy of 135 and 290AMeV. To evaluate dose response of VIP polymer gels, the transverse (or ...spin–spin) relaxation rate R2 of the dosimeters measured by magnetic resonance imaging (MRI) as a function of linear energy transfer (LET), rather than penetration depth, as is usually done in previous reports. LET is evaluated by use of the particle transport simulation code PHITS. Our results reveal that the dose response decreases with increasing dose-averaged LET and that the dose response–LET relation also varies with incident carbon beam energy. The latter can be explained by taking into account the contribution from fragmentation products.
•We study the radiological characteristics of VIP gel dosimeters under carbon beam irradiation.•Linear energy transfer dependence was evaluated and discussed with simulation code PHITS.•Contribution from secondly ion can explain results with different incident beam energy.
The RIKEN accelerator complex started feeding the next-generation exotic beam facility radioisotope beam factory (RIBF) with heavy-ion beams from 2007 after the successful commissioning of RIBF at ...the end of 2006. Many improvements made from 2007 to 2010 were instrumental in increasing the intensity of various heavy-ion beams. However, the available beam intensity of very heavy ion beams, especially uranium beams, is far below our goal of 1pμA (6×1012particles/s ). In order to achieve this goal, upgrade programs are already in progress; the programs include the construction of a new 28-GHz superconducting electron cyclotron resonance ion source and a new injector linac. However, the most serious problem, that of a charge stripper for high-power uranium beams, still remains unsolved, despite extensive research and development work using large foils mounted on a rotating cylinder and a N2 gas stripper. A gas stripper is free from problems related to lifetime, though the equilibrium charge state in this stripper is considerably lower than that in a carbon foil, owing to the absence of the density effect. Nevertheless, the merits of gas strippers motivated us to develop a low-Z gas stripper to achieve a higher equilibrium charge state even in gases. We measured the electron-loss and electron-capture cross sections of uranium ions in He gas as a function of their charge state at 11, 14, and 15MeV/nucleon . The equilibrium charge states extracted from the intersection of the lines of the two cross sections were promisingly higher than those in N2 gas by more than 10. Simple simulations of charge development along the stripper thickness were performed by assuming the measured cross sections. The simulation results show that about 1mg/cm2 of He gas should be accumulated to achieve a charge state higher than that of N2 gas, notwithstanding the difficulty in accumulation of this helium amount owing to its fast dispersion. However, we now believe that the following two solutions can overcome this difficulty: a gas cell with a very large differential pumping system and a gas cell with a plasma window. Their merits and demerits are discussed in the paper.
The Radioactive Isotope Beam Factory (RIBF) is a cyclotron-based accelerator facility that is used for nuclear science studies and was completed at the end of 2006. RIBF can produce the most intense ...RI beams using fragmentation or fission of high speed heavy ion beams. Ever since the first beam was produced, effort has focused on increasing the intensity of uranium beams. Ions beams with high intensity and high availability have been used to produce many important scientific achievements. Upgrade programs have been proposed to further expand scientific opportunities. These programs have two goals. The first goal is to find heavier elements than element 118, which is already named. The upgrade program for the heavy ion linac (RILAC), including installation of a superconducting linac, has been funded and is under construction. The second goals is to increase the intensity of uranium ion beams up to 1 pµA, thus facilitating further investigations into the physics of unstable nuclei. This program for uranium beams is still been unfunded. We are pursuing a budget-friendly version without changing the project goals.
We measured resonant coherent excitation of a 2s electron of 83.3MeV/u Fe23+ ions planar-channeling in the (2¯20) plane of the silicon crystal. A silicon surface barrier detector (SSD) was used as a ...crystal target in order to obtain information on the ion trajectory in the channel since the energy deposit (ΔE) to the SSD gives information on the ion trajectories where the resonant transitions occur. For the low ΔE, i.e., near the channel center, optically allowed 2s–3p transitions were much stronger compared with other transitions. Increasing ΔE, i.e., increasing the amplitude of ion trajectory, the optically forbidden 2s–3s transition rapidly became strong. On the other hand, the optically forbidden 2s–3d transitions did not become strong as rapidly as 2s–3s transition. Furthermore, it was found that the transition energies to the n=3 states changed with ΔE. The shifts of the transition energies were consistent with the estimation for the energy levels of the Stark-mixed n=3 states depending on the distance from the channel center.
Development of a nondestructive, efficient electric-charge-stripping method is a key requirement for next-generation high-intensity heavy-ion accelerators such as the RIKEN Radioactive-Isotope Beam ...Factory. A charge stripper employing a low-Z gas is an important candidate applicable to high-intensity uranium beams for replacing carbon-foil strippers. In this study, a high-beam-transmission charge-stripping system employing helium gas for U238 beams injected at 10.8MeV/u was developed and demonstrated for the first time. The charge-state evolution measured using helium in a thickness range of 0.24–1.83mg/cm2 is compared with theoretical predictions. Energy attenuation and energy spread due to the helium stripper are also investigated.
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