Validation of nuclear reaction models for incident α-particles

Two different models allowing the calculation of reaction products are confronted with data from α-particle induced reactions. Both models contain a pre-equilibrium part and an equilibrium or compound nucleus part. The models are the exciton model in form of a code written by the author and TALYS. The other model is the intranuclear cascade model in form of the Liege-Saclay formulation incorporated in the PHITS code. The data are angle-integrated proton spectra from reactions with α-particle energies below 720 MeV and excitation functions from multi neutron emission with α-particle energies below 200 MeV.

Comparison between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT): a monte carlo study

The aim of this study is to compare between proton boron fusion therapy (PBFT) and boron neutron capture therapy (BNCT) and to analyze dose escalation using a Monte Carlo simulation. We simulated a proton beam passing through the water with a boron uptake region (BUR) in MCNPX. To estimate the interaction between neutrons/protons and borons by the alpha particle, the simulation yielded with a variation of the center of the BUR location and proton energies. The variation and influence about the alpha particle were observed from the percent depth dose (PDD) and cross-plane dose profile of both the neutron and proton beams. The peak value of the maximum dose level when the boron particle was accurately labeled at the region was 192.4% among the energies. In all, we confirmed that prompt gamma rays of 478 keV and 719 keV were generated by the nuclear reactions in PBFT and BNCT, respectively. We validated the dramatic effectiveness of the alpha particle, especially in PBFT. The utility of PBFT was verified using the simulation and it has a potential for application in radiotherapy.

Production of 4He and 3He from tantalum and tungsten irradiated with nucleons at energies up to 1 GeV

The comparison of different methods of calculation and computer codes used to obtain helium isotope production cross-sections for nuclear reactions induced by nucleons at energies up to 1 GeV was performed. The cross-sections were calculated using the GNASH code, the modified ALICE code, the DISCA code and the CASCADE/INPE code. The evaluation of the helium production cross-section for tantalum and tungsten was performed using the results of model calculations, available experimental data and systematics predictions. The cross-sections were obtained for nuclear reactions induced by neutrons and protons at energies up to 1 GeV

Excitation energy division in 51V+197Au collisions 75 MeV above the barrier

We have previously determined the excitation energy division in 51V+197Au collisions at a bombarding energy corresponding exactly to the Bass-model barrier, E cm=B, and at E cm=B+25 MeV. At the barrier, the average excitation energies as a function of Z showed an extreme acceptor-donor asymmetry ("sawtooth" phenomenon) suggesting that the excitation energy division depends on how the neck nucleons are shared at scission. At the 25 MeV higher bombarding energy, a rapid change toward equipartition of the excitation energy was observed. We report here on the determination of the excitation energy division in the same system, using the same experimental technique, at E cm=B+75 MeV. At this bombarding energy, the average excitation energies indicate that a temperature equilibrium has been reached for most partitions except for the - on the average - incompletely damped events near the entrance channel charges, where some remnant of the "sawtooth" phenomenon is still visible.

Measurement and calculation of radioactivities of spallation products by high-energy heavy ions

Irradiation experiments were performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba) facility, National Institute of Radiological Sciences, Japan. The radioactivity distributions of spallation products in a thick Cu target were obtained by irradiating 230 and 100MeV/nucleon Ne, C, He, p and 230MeV/nucleon Ar ions. The gamma-ray spectra from thin irradiated samples of C, Al and Cu inserted into a Cu target were measured with a HPGe detector. From the gamma-ray spectra, we obtained the spatial distribution of radioactive yields of spallation products of about 40 nuclides in Cu sample in the Cu target. Our results agree with other experimental data. We also calculated the spatial distribution of residual radioactivities in the Cu target by the PHITS (Particle and Heavy-Ion Transport code System) code and compared with measured results. The PHITS code provides good results on residual activity calculations.

Analytical shielding calculations for a proton therapy facility

The University of Pennsylvania is building a proton therapy facility in collaboration with Walter Reed Army Medical Center. The proposed facility has four gantry rooms, a fixed beam room and a research room, and will use a cyclotron as the source of protons. In this study, neutron shielding considerations for the proposed proton therapy facility were investigated using analytical techniques and Monte Carlo simulated neutron spectra. Neutron spectra calculations were done using the GEANT4 (v6.2) simulation code for various materials: water, carbon, iron, nickel and tantalum to estimate the neutron production at proton beam energies of 100, 175 and 250 MeV. Dose equivalent calculations were performed using analytical methods at various critical points within the facility, by folding the GEANT4 produced neutron spectra with dose equivalent rate data from the National Council on Radiation Protection and Measurements (NCRP) Report #144.

Nuclear model calculations and their role in space radiation research

Proper assessments of spacecraft shielding requirements and concomitant estimates of risk to spacecraft crews from energetic space radiation requires accurate, quantitative methods of characterizing the compositional changes in these radiation fields as they pass through thick absorbers. These quantitative methods are also needed for characterizing accelerator beams used in space radiobiology studies. Because of the impracticality/impossibility of measuring these altered radiation fields inside critical internal body organs of biological test specimens and humans, computational methods rather than direct measurements must be used. Since composition changes in the fields arise from nuclear interaction processes (elastic, inelastic and breakup), knowledge of the appropriate cross sections and spectra must be available. Experiments alone cannot provide the necessary cross section and secondary particle (neutron and charged particle) spectral data because of the large number of nuclear species and wide range of energies involved in space radiation research. Hence, nuclear models are needed. In this paper current methods of predicting total and absorption cross sections and secondary particle (neutrons and ions) yields and spectra for space radiation protection analyses are reviewed. Model shortcomings are discussed and future needs presented.

Abrasion-ablation model for neutron production in heavy ion collisions

In intermediate energy nucleus-nucleus collisions, neutron production at forward angles is observed to occur with a Gaussian shape that is centered near the beam energy and extends to energies well above that of the beam. This paper presents an abrasion-ablation model for making quantitative predictions of the neutron spectrum. To describe neutrons produced from the abrasion step of the reaction where the projectile and target overlap, we use the Glauber model and include effects of final-state interactions. We then use the prefragment mass distribution from abrasion with a statistical evaporation model to estimate the neutron spectrum resulting from ablation. Measurements of neutron production from Ne and Nb beams are compared with calculations, and good agreement is found.

Secondary radiations in spacecraft shieldings

Some problems are discussed which relate to the generation of secondary radiation under the effects of heavy charged cosmic ray particles in spacecraft shielding and in biological tissue. Methods for obtaining the total and differential inelastic interaction cross sections are recommended for use in the calculation of heavy charged particle transport in the shielding. The most extensively used methods for calculating heavy charged particle passage through matter are appraised. The results of calculating cosmic ray doses in biological tissue behind shielding, which allow for the secondary particle contribution, are presented. All the calculations have been made using the set of radiation protection standards approved by the Russian State Committee for Standards. The set of standards has been verified experimentally on board satellites of the Cosmos series.