Search

Aiming to provide critical information in the fields of heavy ion therapy, radiation shielding in space, and facility design for heavy-ion research accelerators, the physics models in three Monte Carlo simulation codes – PHITS, FLUKA, and MCNP6, were systematically benchmarked with comparisons to fifteen sets of experimental data for neutron production cross sections, which include various combinations of 12C, 20Ne, 40Ar, 84Kr and 132Xe projectiles and natLi, natC, natAl, natCu, and natPb target nuclides at incident energies between 135 MeV/nucleon and 600 MeV/nucleon. For neutron energies above 60% of the specific projectile energy per nucleon, the LAQGMS03.03 in MCNP6, the JQMD/JQMD-2.0 in PHITS, and the RQMD-2.4 in FLUKA all show a better agreement with data in heavy-projectile systems than with light-projectile systems, suggesting that the collective properties of projectile nuclei and nucleon interactions in the nucleus should be considered for light projectiles. For intermediate-energy neutrons whose energies are below the 60% projectile energy per nucleon and above 20 MeV, FLUKA is likely to overestimate the secondary neutron production, while MCNP6 tends towards underestimation. PHITS with JQMD shows a mild tendency for underestimation, but the JQMD-2.0 model with a modified physics description for central collisions generally improves the agreement between data and calculations. For low-energy neutrons (below 20 MeV), which are dominated by the evaporation mechanism, PHITS (which uses GEM linked with JQMD and JQMD-2.0) and FLUKA both tend to overestimate the production cross section, whereas MCNP6 tends to underestimate more systems than to overestimate. For total neutron production cross sections, the trends of the benchmark results over the entire energy range are similar to the trends seen in the dominate energy region. Also, the comparison of GEM coupled with either JQMD or JQMD-2.0 in the PHITS code indicates that the model used to describe the first stage of a nucleus-nucleus collision also affects the low-energy neutron production. Thus, in this case, a proper combination of two physics models is desired to reproduce the measured results. In addition, code users should be aware that certain models consistently produce secondary neutrons within a constant fraction of another model in certain energy regions, which might be correlated to different physics treatments in different models.

We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and released the new version as PHITS3.02. The accuracy and the applicable energy ranges of the code were ...

Stopping target measurements with energetic ion beams are important for building and validating physics models used to predict nuclear fragmentation fields created by interactions between incoming ...

With the aim of providing critical nuclear data of primary knock-on atoms (PKAs) created from proton-induced spallation reactions, a new detection system was designed and dedicated to the PKA measurement that requires lower measurement threshold energies and superior mass resolution than the conventional experimental setups. Such requirements can be fulfilled by employing the TOF-E and dE-E methods, and this new PKA detection system, which consists of two fast timing detectors and one dE-E gas ionization detector. The design of the detectors and the experimental setup, along with the estimated system performed are briefly described in this paper.

The dose distributions from proton pencil beam scanning were calculated by FLUKA, GEANT4, MCNP, and PHITS, in order to investigate their applicability in proton radiotherapy. The first studied case was the integrated depth dose curves (IDDCs), respectively from a 100 and a 226-MeV proton pencil beam impinging a water phantom. The calculated IDDCs agree with each other as long as each code employs 75 eV for the ionization potential of water. The second case considered a similar condition of the first case but with proton energies in a Gaussian distribution. The comparison to the measurement indicates the inter-code differences might not only due to different stopping power but also the nuclear physics models. How the physics parameter setting affect the computation time was also discussed. In the third case, the applicability of each code for pencil beam scanning was confirmed by delivering a uniform volumetric dose distribution based on the treatment plan, and the results showed general agreement between each codes, the treatment plan, and the measurement, except that some deviations were found in the penumbra region. This study has demonstrated that the selected codes are all capable of performing dose calculations for therapeutic scanning proton beams with proper physics settings.

This study aims to measure the neutronic characteristics of the 14-cm diameter boron neutron capture therapy beam at the Tsing Hua Open-pool Reactor and to provide essential information for the neutron source adjustment and validation. The measurements were performed both in air and inside a cubic PMMA phantom at the beam, with and without an 18-cm long extended PE collimator. The neutron intensity was determined by neutron activation analysis; the indirect neutron radiography and the cadmium difference method were coupled to provide the two-dimensional neutron flux distributions. According to the measurements, the angular distribution is highly forward for epithermal neutrons but much more divergent for thermal ones. A PE extended collimator will modify the beam characteristics and could benefit the treatment for head and neck tumors, which often needs higher therapeutical boron dose at the shallow region.

This paper presents a way to determine the angular and spatial distributions of the thermal neutron source strength of a boron neutron capture therapy (BNCT) beam. The experiments applied 1) the indirect neutron radiography, 2) the cadmium difference method, and 3) the instrumental neutron activation analysis. The measured data were processed by the spectrum deconvolution technique to resolve into a proper set of angular and spatial distributions. This paper took the epithermal neutron beam of the BNCT facility at the Tsing Hua Open-pool Reactor as an example.

This study is a part of the beam comparison campaign, inter-center dose comparison, between boron neutron capture therapy facilities at the Tsing Hua Open-pool Reactor and the High Flux Reactor. The clinical information exchange can improve the dosimetry uncertainty for medical physics in a mixed field. The method of paired Mg(Ar) and TE(TE) ionization chambers was used to determine the gamma-ray and neutron dose rates. Furthermore, activation foils, including gold, copper, and manganese, were employed to estimate the thermal and epithermal neutron fluxes. Measurements were performed free in air and also in a PMMA phantom. All the chambers were calibrated using a 60Co primary standard source at the Institute of Nuclear Energy Research, Taiwan. Spectrum dependent neutron sensitivity of TE(TE) chamber is one of the important parameters to evaluate dose components. The requested neutron spectra were calculated by the Monte Carlo code MCNP. The measured thermal neutron fluxes, gamma-ray and neutron dose rates of the THOR beam in the phantom were 2.6, 2.2, and 2.1 times of the HFR beam at 2.5-cm depth, respectively. The higher thermal neutron flux and neutron and gamma-ray dose rates are due to the higher epithermal neutron beam intensity of the THOR.

This study aims to determine the activation contamination in the metal-based ionization chambers, i.e. Mg(Ar)- and Al(Ar)-chambers. The contamination was estimated by directly measuring the signal caused by the radioactive nuclides after the irradiation. The INAA gamma ray spectra clearly showed that the ionization chambers were activated. The activation contamination could comprise more than 2% of the total measured current of the Mg(Ar)-chamber, and more than 50% of the Al(Ar)-chamber, both irradiated free-in-air at the THOR epithermal neutron beam. The activation contamination provides concrete evidence of the necessity of the thermal neutron sensitivity correction.

This paper aims to measure the neutron flux distribution over the cross section of the boron neutron capture therapy epithermal neutron beam at the Tsing Hua Open-pool Reactor (THOR) by using indir...

In this article, we will consider several core configurations and run the core calculation with MCNP to obtain the neutrons distribution at THOR. The thermal neutron flux inside the vertical tubes (VT-B-VT-E) and the fast neutron flux in the first row facing to the boron neutron capture therapy (BNCT) facility (I3-I5) were tallied for indication. Based on these simulation results, the fuel elements were rearranged during the annual repair period in 2007. The epithermal neutron flux at the center of BNCT beam exit in air was measured again, and the results showed that the beam intensity increased by 50%. Comparing the neutron intensities both in reactor core and at the BNCT beam exit for several core configurations, the results show that the BNCT beam intensity can be increased without decreasing the neutron intensity in core.

This paper aims to measure the spectra of HB11 (high flux reactor, HFR) and the Tsing Hua open-pool reactor (THOR) boron neutron capture therapy (BNCT) beams by multiple activation foils. The self-shielding corrections were made with the aid of MCNP calculations. The initial spectra were adjusted by a sophisticated process named coarse-scaling adjustment using SAND-EX, which can adjust a given coarse-group spectrum into a fine-group structure, i.e. 640 groups, with excellent continuity. The epithermal neutron flux of the THOR beam is about three times of HB11. The thermal neutron flux, boron and gold reaction rates along the central axis of a PMMA phantom are calculated for both adjusted spectra for comparison.

In order to provide an improved and reliable neutron source description for treatment planning in boron neutron capture therapy (BNCT), a spectrum adjustment procedure named coarse-scaling adjustment has been developed and applied to the neutron spectrum measurements of both the Tsing Hua Open-pool Reactor (THOR) epithermal neutron beam in Taiwan and the High Flux Reactor (HFR) in The Netherlands, using multiple activation detectors. The coarse-scaling adjustment utilizes a similar idea as the well-known two-foil method, which adjusts the thermal and epithermal neutron fluxes according to the Maxwellian distribution for thermal neutrons and 1/ E distribution over the epithermal neutron energy region. The coarse-scaling adjustment can effectively suppress the number of oscillations appearing in the adjusted spectrum and provide better smoothness. This paper also presents a sophisticated 9-step process utilizing twice the coarse-scaling adjustment which can adjust a given coarse-group spectrum into a fine-group structure, i.e. 640 groups, with satisfactory continuity and excellently matched reaction rates between measurements and calculation. The spectrum adjustment algorithm applied in this study is the same as the well-known SAND-II.

In order to define the ranges of relevant neutron energies for the purposes of measurement and dosimetry in space, we have performed a series of Monte Carlo transport model calculations that predict the neutron field created by Galactic Cosmic Ray interactions inside a variety of simple shielding configurations. These predictions indicate that a significant fraction of the neutron fluence and neutron effective dose lies in the region above 20 MeV up to several hundred MeV. These results are consistent over thicknesses of shielding that range from very thin (2.7 g/cm(2)) to thick (54 g/cm(2)), and over both shielding materials considered (aluminum and water). In addition to these results, we have also investigated whether simplified Galactic Cosmic Ray source terms can yield predictions that are equivalent to simulations run with a full GCR source term. We found that a source using a GCR proton and helium spectrum together with a scaled oxygen spectrum yielded nearly identical results to a full GCR spectrum, and that the scaling factor used for the oxygen spectrum was independent of shielding material and thickness. Good results were also obtained using a GCR proton spectrum together with a scaled helium spectrum, with the helium scaling factor also independent of shielding material and thickness. Using a proton spectrum alone was unable to reproduce the full GCR results.

The GAFCHROMIC(®) EBT2 dosimetry film has been studied as a rapid QC/QA tool for 2D dose profile mapping in the BNCT beam at THOR. The pixel values of the EBT2 film image were converted to the 2D dose profile using a dose calibration curve obtained by 6-MV X-ray. The reproducibility of the 2D dose profile measured using the EBT2 film in the PMMA phantom was preliminarily found to be acceptable with uncertainties within about ±2 to ±3.5%. It is found that the EBT2 measured dose profile consisted of both gamma-ray components and neutron contributions. Therefore, the dose profile measured using the EBT2 film is significantly different from the neutron flux profile measured using the indirect neutron radiography method. Further study of the influence of neutrons to the response of the EBT2 film is indispensible for the absolute dose profile determination in a BNCT beam.

Transport code calculations with the code PHITS have been performed to determine the nature of the secondary neutron field produced by galactic cosmic ray (GCR) interactions in aluminum and water shielding. The neutron production from each elemental component of the GCR spectrum was calculated separately, and the total neutron spectrum from the entire incident GCR field was determined from the weighted sum of the individual GCR components. Analysis was then performed on those results to determine the relative importance of specific ranges of neutrons energies in regards to the total neutron fluence and total neutron effective dose. Results indicate that high energy neutrons (above 20 MeV) contribute a significant fraction to both fluence and effective dose. Thus, any new detectors or methodologies being developed for the purpose of neutron detection or neutron dosimetry in space must develop a reliable means of accounting for neutrons above 20 MeV.

This paper aims to evaluate the performance of the source description of the THOR BNCT beam via different measurement techniques in different phantoms. The measurement included (1) the absolute reaction rate measurement of a set of triple activation foils, (2) the neutron and gamma-ray dose rates measured using the paired ionization chamber method, and (3) the relative reaction rate distributions obtained using the indirect neutron radiography. Three source descriptions, THOR-Y09, surface source file RSSA, and THOR-50C, were tested. The comparison results concluded that THOR-Y09 is a well-tested source description not only for neutron components, but also for gamma-ray component.

Various quality control (QC) and quality assurance (QA) procedures of the boron neutron capture therapy (BNCT) beam at the Tsing Hua Open-pool Reactor (THOR) are established to ensure beam availability and quality. The QC/QA methods mainly employ foil activation and paired ionization chambers, respectively, for beam intensity check and dose assessment. Beam intensity is monitored on-line by using three dead-time corrected fission chambers. In addition to the periodic QC/QA activities regarding beam quality and the monitoring system, the quick QC/QA performed in an all-in-one phantom will be executed less than 70 min before the clinical treatment to guarantee beam quality. The QC/QA procedures have been gradually established and the actual performance satisfied the preset criteria defined for the BNCT facility at THOR.

This study aims to measure the two-dimensional (2D) neutron spatial distribution inside a cubic and a head PMMA phantom for the purpose of further comparison with the treatment planning. The measurements were made by using the indirect neutron radiography (INR), which utilized a thin copper foil and the imaging plate. The developed image provides satisfactory spatial resolution and very low statistical error (< 1%). As to the time cost, the whole procedure normally takes less than 3 h. The result shows that the indirect neutron radiography can be a quick and reliable method to provide a 2D neutron spatial distribution inside a phantom.