Determination of thermal neutron flux distribution at the rotary rack served for elemental concentration analysis using the k0-INAA method

The accuracy of elements concentration determination using the k0-standardization method directly depends on irradiation and measurement parameters including Non-1/E epithermal neutron flux distribution shape α (ϕ epi ≈1/E1+α ) , thermal-to-epithermal neutron flux ratio f, efficiency ε, peak area… In the case of the irradiation position at the rotary rack of the Dalat Nuclear Research Reactor (DNRR), the difference of thermal neutron flux between the bottom (3.54x1012 n.cm-2.s-1) and the top (1.93x1012 n.cm-2.s-1) of the 15 cm aluminum container is up to 45%. Therefore, it is necessary to accurately determine above-mentioned parameters in the sample irradiation position. The present paper deals with the determination of the distribution of thermal neutron flux along the sample irradiation container by using 0.1% Au–Al wire activation technique. The thermal neutron flux was then used to calculate the concentration of elements in the Standard Reference Material 2711a and SMELS type III using k0-INAA method at different positions in the container. The obtained results with the neutron flux correction were found to be in good agreement with the certified values. In conclusion, the proposed technique can be applied for activation analyses without sandwiching flux monitors between samples during irradiations.

Evaluating the Therapeutic Potential and the Suitability of Neutron Beams Designed for Clinical BNCT

The standard of neutron beam quality for Boron Neutron Capture Therapy (BNCT) of deep-seated tumours is currently defined by its physical characteristics in air: the epithermal neutron flux, the ratio of thermal and epithermal neutron flux, the fast neutron and photon dose contamination, and the beam collimation. Traditionally, the beam design consists in tailoring a Beam Shaping Assembly (BSA) able to deliver a neutron beam with the recommended values of these figures of merit (FOMs). This work investigated the possibility to produce an epithermal neutron beam able to guarantee the best clinical performance for deep-seated tumours, starting from a 5 MeV, 30 mA proton beam coupled to a beryllium target. Different Beam Shaping Assemblies were designed using those physical FOMs which, however, were not enough to establish a clear ranking of the different beams, nor to describe their clinical relevance. To go beyond this traditional approach, beams were then evaluated employing new criteria based on the dose distributions obtained in-phantom and on the calculation of the Uncomplicated Tumour Control Probability (UTCP). Such radiobiological FOM allows establishing the therapeutic potential of the beams. Moreover, we included the concept of suitability as a criterion to select the safest BSA design, calculating the in-patient out-of-beam dosimetry. The clinical relevance of the selected beam was finally tested in the treatment planning of a clinical case treated at the FiR 1 beam in Finland, where several patients have safely and successfully received BNCT in the last years. Despite the selected beam does not comply with all the standard physical recommendations, it shows a therapeutic potential comparable and even better than that of FiR 1. This confirms that establishing the performance of a beam cannot rely only on its physical characteristics, but requires additional criteria able to predict the clinical outcome of a BNCT treatment.

Characteristics of Thermal Neutron Flux Distribution in a Phantom Irradiated by Epithermal Neutron Beam from Double Layer Beam Shaping Assembly (DBSA)

A simulation study on the Double-layer Beam Shaping Assembly (DBSA) system has been carried out. This study used fast neutron beam resulting from reactions of 30 MeV protons with beryllium target. The MCNPX code was utilized to design the DBSA and the phantom as well as to calculate neutron flux on the phantom. The distribution of epithermal neutron flux and gamma in the DBSA and phantom were computed using the PHITS code. The spectrum of radiation beams generated by the DBSA shows the characteristics that the typical epithermal neutron flux of 1.0 x109 n/(cm2.s), the ratio of epithermal to the thermal and fast neutron flux of 344 and 85, respectively and the ratio of gamma dose to the epithermal neutron flux of 1.82 x 10-13 Gy.cm2. The test of epithermal neutron beams irradiation on the water phantom shows that epithermal neutrons are thermalized and penetrate the phantom up to 12 cm in depth. The maximum value of neutron flux is 1.1 x 109 n/(cm2.s) at a depth of 2 cm in phantom.

Beam Shaping Assembly Optimization for Boron Neutron Capture Therapy Facility Based on Cyclotron 30 MeV as Neutron Source

A design of beam shaping assembly (BSA) installed on cyclotron 30 MeV model neutron source for boron neutron capture therapy (BNCT) has been optimized using simulator software of Monte Carlo N-Particle Extended (MCNPX). The Beryllium target with thickness of 0.55 cm is simulated to be bombarded with 30 MeV of proton beam. In this design, the parameter regarding beam characteristics for BNCT treatment has been improved, which is ratio of fast neutron dose and epithermal neutron flux. TiF3 is replaced to 30 cm of 27Al as moderator, and 1.5 cm of 32S is combined with 28 cm of 60Ni as neutron filter. Eventually, this design produces epithermal neutron flux of 2.33 × 109, ratio between fast neutron dose and epithermal neutron flux of 2.12 × 10-13,ratio between gamma dose and epithermal neutron flux of 1.00 × 10-13, ratio between thermal neutron flux and epithermal neutron flux is 0.047, and ration between particle current and total neutron flux is 0.56.

Double Layer Collimator for BNCT Neutron Source Based on 30 MeV Cyclotron

<span>A research of design of double layer collimator using </span>⁹<span>Be(p,n) neutron source has been conducted. The research objective is to design a double layer collimator to obtain neutron sources that are compliant with the IAEA standards. The approach to the design of double layer collimator used the MCNPX code. From the research, it was found that the optimum dimensions of a beryllium target are 0.01 mm in length and 9.5 cm in radius. Collimator consists of a D</span>₂<span>O and Al moderator, Pb and Ni as a reflector, and Cd and Fe as a thermal and fast neutron filter. The gamma filter used Bi and Pb. The quality neutron beams emitted from the double layer collimator is specified by five parameters: epithermal neutron flux 1 ×10</span>⁹<span> n/cm</span>²<span>s; fast neutron dose per epithermal neutron flux 5 ×10</span>¹³<span> Gy cm</span>²<span>s; gamma dose per epithermal neutron flux 1×10</span>¹³<span> Gy cm</span>²<span>s; ratio of the thermal neutron flux of epithermal neutron flux 0; and the ratio of epithermal neutron current to total epithermal neutron 0.54.</span>