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IntroductionBoron Neutron Capture Therapy (BNCT) is a promising cancer therapy. At present, development of accelerator based neutron source (ABNS) is underway to be utilized as a neutron source instead of nuclear reactor. However, it is known that the neutron field formed with accelerators have different characteristics depending on kinds of accelerators. We thus have to characterize the field before practical use.MethodIn the authors’ group, various neutronics characterization devices have been developed for our p-Li based BNCT machine named CSePT. In this paper, three neutron intensity monitor foils with an isomer production reaction for several tens to 800 keV of the p-Li neutrons were proposed, i.e., 107Ag, 115In and 189Os.Result and DiscussionFrom the experimental test results, two activation foils of 107Ag and 115In were confirmed to be a possible candidate as the monitor. However, the isomer production cross sections of them should be examined for practical use.

Over the years, Maxwellian Averaged Cross Sections (MACS) have been measured by neutron activation, providing a neutron energy spectrum resembling the one found inside the stars. Recently, a new method has been proposed to produce stellar spectra at different stellar temperatures (a Maxwell–Boltzmann neutron energy distribution), employing the 7 Li(p,n) 7 Be reaction. The method is based on the idea of shaping the proton beam energy to shape the neutron beam spectrum. This method was applied to obtain a well-reproduced Maxwell–Boltzmann neutron spectrum (MBNS) at k T = 28 keV. An initial proton energy of 3170 keV and an aluminum foil as a proton energy shaper were employed. Differential angular neutron energy distributions from 0 to 90 degrees in 10 ∘ steps were measured to obtain the 0 ∘ –90 ∘ integrated neutron spectrum over a neutron flight path of 50 cm. This manuscript reports on the measurement results, confirming the method's capability, and suggests the approach for producing a high-quality MBNS at k T = 28 keV. [ABSTRACT FROM AUTHOR]

The radio frequency structure design of the radio frequency quadrupole (RFQ) for the front end of China Material Irradiation Facility (CMIF), which is an accelerator based neutron irradiation facility for fusion reactor material qualification, has been completed. The RFQ is specified to accelerate 10 mA continuous deuteron beams from the energies of 20 keV/u to 1.5 MeV/u within the vane length of 5250 mm. The working frequency of the RFQ is selected to 162.5 MHz and the inter-vane voltage is set to 65 kV. Four-vane cavity type is selected and the cavity structure is designed drawing on the experience of China Initiative Accelerator Driven System (CIADS) Injector II RFQ. In order to reduce the azimuthal asymmetry of the field caused from errors in fabrication and assembly, a frequency separation between the working mode and its nearest dipole mode is reached to 17.66 MHz by utilizing 20 pairs of π -mode stabilizing loops (PISLs) distributed along the longitudinal direction with equal intervals. For the purpose of tuning, 100 slug tuners were introduced to compensate the errors caused by machining and assembly. In order to obtain a homogeneous electrical field distribution along cavity, vane cutbacks are introduced and output endplate is modified. Multi-physics study of the cavity with radio frequency power and water cooling is performed to obtain the water temperature tuning coefficients. Through comparing to the worldwide CW RFQs, it is indicated that the power density of the designed structure is moderate for operation under continuous wave (CW) mode. [ABSTRACT FROM AUTHOR]

A new target station that generates a thermal neutron field based on a 30-MeV proton accelerator was designed for the basic study of boron neutron capture therapy (BNCT). The calculated thermal neutron fluxes at the sample regions under free air conditions reached 2.84 × 109 [n/cm2/s]. The fast neutron and gamma ray dose rates per thermal neutron flux in several regions were on the order of 10−13 [ Gy ⋅ cm 2 ]. The beam characteristics were found to be closer to those of the heavy-water neutron irradiation facility of Kyoto University Research Reactor, which is an established facility in BNCT research. In addition, the shielding size for the new target station was realistically estimated for long-term beam operation. [ABSTRACT FROM AUTHOR]

Abstract: The T(D,n)4He and 7Li(p,n)7Be neutron sources have been used for decades in nuclear physics research, stellar nucleosynthesis research and neutron therapy research. In this work, the neutron characterization including neutron yield, spectra, and angular distribution for D–T and p-7Li sources have been studied with our new binary collision approximation (BCA) based direct collision coupling method. Distinguished from the traditional path integration method for getting the neutron weight, the new model establishes a relationship between the scattering cross section and the impact parameter, which allows the secondary neutron generation carrying out jointly with ions BCA tracking. The experimental measurements of neutron characterizations have been employed for these two reactions, and the new algorithm is validated. [Copyright &y& Elsevier]

Abstract: A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ)+Drift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8MeV and average current was 10mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80kW proton beam. Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012. In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient׳s position during irradiation. [Copyright &y& Elsevier]

Abstract: At present, the clinical trials of Boron Neutron Capture Therapy (BNCT) are being performed at research reactor facilities. However, an accelerator based BNCT has a merit that it can be built in a hospital. So, we just launched a development project for the BNCT based on an accelerator in order to establish and to spread the BNCT as an effective therapy in the near future. In the project, a compact proton linac installed in a hospital will be applied as a neutron source, and energy of the proton beam is planned to be less than about 10 MeV to reduce the radioactivity. The BNCT requires epithermal neutron beam with an intensity of around 1x109 (n/cm2/sec) to deliver the therapeutic dose to a deeper region in a body and to complete the irradiation within an hour. From this condition, the current of the proton beam required is estimated to be a few mA on average. Enormous heat deposition in the target is a big issue. We are aiming at total optimization of the accelerator based BNCT from the linac to the irradiation position. Here, the outline of the project is introduced and the moderator design is presented. [Copyright &y& Elsevier]

Abstract: This study describes the measurement of lineal energy spectra carried out with a 5.1cm (2in.) diameter spherical tissue equivalent proportional counter (TEPC) simulating 2μm tissue equivalent (TE) site diameter in low energy mixed photon–neutron fields with varying dose rates generated by employing the McMaster University 1.25MV double stage Tandetron accelerator. The 7Li (p, n) 7Be reaction was employed to generate a variety of mixed fields of photons and low energy neutrons using proton beam energy ranging 1.89–2.56MeV. The dose rate at a given beam energy was varied by changing the beam current. Dose rates that resulted in dead times as high as 75% were employed to study the effect of dose rate on quality, microdosimetric averages (y¯ F and y¯ D), absorbed dose and dose equivalent. We have observed that high dose rates due to both photons and neutrons in a mixed field of radiation result in pile up of pulses and distort the lineal energy spectrum measured under these conditions. The pile up effect and hence the distortion in the lineal energy spectrum becomes prominent with dose rates, which result in dead times larger than 25% for the high linear energy transfer (LET) radiation component. Intense neutron fields, which may amount to 75% dead time, could result in a 50% or even larger increase in the values of the microsdosimetric averages and the neutron quality factor. This study demonstrates moderate dose rates that do not result in dead times of more than 20–25% due to either of the component radiation or due to both components of mixed field radiation generate results that are acceptable for radiation monitoring. [Copyright &y& Elsevier]

Abstract: This study describes the measurement of lineal energy spectra carried out with a graphite walled proportional counter (GPC) simulating 1μm tissue equivalent (TE) site diameter in low energy neutron fields generated by employing the McMaster University 1.25MV double stage Tandetron accelerator. Experiments were carried out for neutron beams of mean energies extending from 34 to 354keV in direct neutron beams from the 7Li target using proton beam energies ranging from 1.89 to 2.56MeV. We have observed a continuously increasing trend in microdosimetric averages, and , and the ICRP 60 based quality factor, Q, with an increase in neutron energy. It is interesting to note that standard tissue equivalent proportional counters (TEPCs) give rise to a similar trend for these microdosimetric quantities of interest in the same energy range. Quantitatively, these quantities are also comparable to those obtained with standard TEPCs. This implies that at the microdosimetric level in the neutron energy range we employed in this study, the pattern of average energy deposited by ‘starter’ and ‘insider’ proton recoil events in the gas is similar to those generated cumulatively by ‘crosser’ and ‘stopper’ events originating from the counter wall plus ‘starter’ and ‘insider’ recoil events originating in the sensitive volume of a TEPC. This suggests that the average energy deposition per event in the wall of a TEPC counter is the same as in the counting gas itself, which confirms the similarity of the composition and mass stopping power of two media, i.e., TE wall and TE gas, used in neutron dosimetric measurements. [Copyright &y& Elsevier]

Liquid lithium (Li) is a candidate material for a target of intense neutron source, heat transfer medium in space engines and charges stripper. For a medical application of BNCT, epithermal neutrons with least energetic neutrons and γ-ray are required so as to avoid unnecessary doses to a patient. This is enabled by lithium target irradiated by protons at 2.5 MeV range, with utilizing the threshold reaction of 7 Li(p,n) 7 Be at 1.88 MeV. In the system, protons at 2.5 MeV penetrate into Li layer by 0.25 mm with dissipating heat load near the surface. To handle it, thin film flow of high velocity is important for stable operation. For the proton accelerator, electrostatic type of the Schnkel or the tandem is planned to be employed. Neutrons generated at 0.6 MeV are gently moderated to epithermal energy while suppressing accompanying γ-ray minimum by the dedicated moderator assembly. [ABSTRACT FROM AUTHOR]

Mock-up experiment for development of accelerator based neutron source for Osaka University BNCT project was carried out at Birmingham University, UK. In this paper, spatial distribution of neutron flux intensity was evaluated by foil activation method. Validity of the design code system was confirmed by comparing measured gold foil activities with calculations. As a result, it was found that the epi-thermal neutron beam was well collimated by our neutron moderator assembly. Also, the design accuracy was evaluated to have less than 20% error. [ABSTRACT FROM AUTHOR]