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Accelerator-based neutron sources have been developed and installed in recent decades for boron neutron capture therapy (BNCT) in several clinical facilities. Lithium is one of the targets that can produce epithermal neutrons from the Li-7(p,n)Be-7 near-threshold reaction, and accelerator-based BNCT systems employing a Li target are promising for cancer treatment. The accurate evaluation of the characteristics of an accelerator-based neutron source is a key to estimating the therapeutic effects of the accelerator-based BNCT. Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo code, which can simulate a variety of diverse particle types and nuclear reactions. The latest PHITS code enables simulating the generation of neutrons from the Li-7(p,n)Be-7 reactions by using the Japanese Evaluated Nuclear Data Library 4.0 high-energy file. Thus, the PHITS code can be adopted for dose estimation during treatment planning for the accelerator-based BNCT. In this study, we evaluated the neutron fluence using the PHITS code by comparing it to reference data. The subsequent neutron transport simulations were performed to evaluate the boron trifluoride detector responses and the recoiled proton fluence detected by a CR-39 plastic detector. These comparative studies confirmed that the PHITS code can accurately simulate neutrons generated from an accelerator using a Li target. The PHITS code has a significant potential for a detailed evaluation of neutron fields and for predicting the therapeutic effects of the accelerator-based BNCT.

DNA strand breaks are induced in cells mainly composed of liquid water along ionizing radiation tracks. For estimating DNA strand break yields, track structures for electrons in liquid water in Monte Carlo simulations are of great importance; however, detailed simulations to obtain both energy deposition and free radical reaction to DNA are time-consuming processes. Here, we present a simple model for estimating yields of single- and double-strand breaks (SSB, DSB, and DSB/SSB ratio) based only on spatial patterns of inelastic interactions (i.e., ionization and electronic excitation) generated by electrons, which are evaluated by the track structure mode of Particle and Heavy Ion Transport code System without analyzing the production and diffusion of free radicals. In the present model, the number of events per track and that of a pair composed of two events within 3.4 nm (10 base pairs) were stochastically sampled for calculating SSB and DSB yields. The results calculated by this model agree well with other simulations and experimental data on the DSB yield and the DSB/SSB ratio for monoenergetic electron irradiation. This model also demonstrates the relative biological effectiveness at the DSB endpoint for various photon irradiations, indicating that the spatial pattern composed of ionization and electronic excitation without physicochemical and chemical stages is sufficient to obtain the impact of electrons on the initial DNA strand break induction.DNA strand breaks are induced in cells mainly composed of liquid water along ionizing radiation tracks. For estimating DNA strand break yields, track structures for electrons in liquid water in Monte Carlo simulations are of great importance; however, detailed simulations to obtain both energy deposition and free radical reaction to DNA are time-consuming processes. Here, we present a simple model for estimating yields of single- and double-strand breaks (SSB, DSB, and DSB/SSB ratio) based only on spatial patterns of inelastic interactions (i.e., ionization and electronic excitation) generated by electrons, which are evaluated by the track structure mode of Particle and Heavy Ion Transport code System without analyzing the production and diffusion of free radicals. In the present model, the number of events per track and that of a pair composed of two events within 3.4 nm (10 base pairs) were stochastically sampled for calculating SSB and DSB yields. The results calculated by this model agree well with ot...

The transient response of electronegative radio-frequency glow discharges is important for process control, charge free etching, and highly selective etch applications. The step response of typical electronegative process gases (silane at 1 Torr and chlorine at 100 mTorr) is studied using a drift-diffusion model for silane and a three-moment model for chlorine. The silane simulations include a blocking capacitor whereas the chlorine results do not. For the silane results with a blocking capacitor in series with the plasma, it is found that there are three types of transients. Depending on the final steady-state value of the source rf voltage, the step response can be characterized either by smooth transitions in the number densities of species in the discharge from one steady state to the next, temporary extinction of the discharge or a discharge mode characterized by temporary extinction and reignition of the discharge. In the case of silane definite thresholds separate the phenomena. The step response o...

The results of a Monte Carlo simulation study focusing on the spatial characteristics of swarm parameters in an isolated electron swarm and the distribution of the electron density and flux taking into account the anode boundary are presented. The spatial variation of the swarm parameters is interpreted using conventional swarm theory, and potential problems with the measurement of arrival-time spectra of electrons are considered.

Charge damage considerations are prompting the development of neutral beam sources for etching applications. Anisotropic etching with hyperthermal Cl2 and SF6 beams has been demonstrated. We describe a two‐dimensional plasma chemistry fluid model of laser ablation of frozen Cl2 in vacuum as a neutral beam source. In this scheme an externally applied electric field would be used to enhance the dissociation rate of Cl2 potentially providing an enhanced Cl content in the beam for a greater etch rate. Laser ablation generated neutral beams also may contain a desirable and controllable ion content which may be used to further enhance the etch rate. Limitations of the concept are discussed.

The behavior of electron swarms in gases in time‐varying ramp electric fields is investigated using a Monte Carlo simulation. In particular, we consider the case of swarms in chlorine gas. Swarm parameters as a function of instantaneous E/N(E is the electric field and N is the gas number density) for different dE/dt are determined. At higher dE/dt, all the parameters as a function of E/N are shifted to larger E/N when compared to the steady‐state case. The drift velocity curve develops a peak which shifts to higher E/N and increases in magnitude as dE/dt is increased. Next, we pay attention to the definition of the swarm parameters, where the parameters derived from kinetic theory and by analogy to experiment are compared. For the high dE/dt cases, differences in the swarm parameters at the same E/N values are caused by the inertia of the electrons and their transient beam‐like high drift velocity, while discrepancies due to the difference between the definitions in the kinetic theory and in the analogy to experiment appear significantly.