Search

Commercially available radiochromic films are primarily designed for clinical X-ray dosimetry. These films change color upon exposures to radiation as a result of solid-state polymerization (SSP). Built on a previous model developed for SSP upon exposures to ultraviolet (UV) radiation, a new model was developed in the present work for X-ray-induced coloration in Gafchromic EBT3 films. Monte Carlo simulations using the Monte Carlo N-Particle (MCNP) code were employed to model the transport and interaction of photons and the generated secondary electrons within the film active layer. The films were exposed to continuous-energy photon beams. The dose DE in the external radiation detector (i.e., ionization chamber) was determined and the realistic dose DA in the film active layer was then obtained using the calibration coefficient R (=DA/DE). The finite element method (FEM) was used to solve the classical steady-state Helmholtz equation using the multifrontal massively parallel sparse direct solver (MUMPS). An extensive grid independence test was carried out and the numerical stability of the present model was ensured. The reflected light intensity from the film surface was used to theoretically obtain the net reflective optical density of the film exposed to X-ray. Good agreement was obtained between the experimental and theoretical results of the net reflective optical density of the film. For X-ray doses >~600 cGy, due to the already formed densely cross-linked structure in the active layer of the EBT3 film so further bond formation was less likely, the reflected light intensity from the film surface increased at a relatively lower rate when compared to those for dose values <~600 cGy. [ABSTRACT FROM AUTHOR]

Radiochromic films change color upon exposures to radiation doses as a result of solid-state polymerization (SSP). Commercially available radiochromic films are primarily designed for, and have become widely used in, clinical X-ray dosimetry. However, many intriguing properties of radiochromic films are not yet fully understood. The present work aimed at developing a theoretical model at both atomic and macroscopic scales to provide a platform for future works to understand these intriguing properties. Despite the fact that radiochromic films were primarily designed for clinical X-ray dosimetry, dose-response curves for the Gafchromic EBT3 film obtained for ultraviolet (UV) radiation were employed to develop our model in order to avoid complications of ionization, non-uniform energy deposition, as well as dispersed doses caused by secondary electrons set in motion by the indirectly ionizing X-ray photons, which might introduce added uncertainties to the model and overshadow the basic SSP processes. The active layer in the EBT3 film consisted of diacetylene (DA) pentacosa-10,12-diynoate monomers, which were modelled using molecular dynamics (MD). The degrees of SSP in the atomic scale upon different UV exposures were obtained to determine the absorption coefficients of the active layer, which were then input into the finite element method (FEM). The classical steady-state Helmholtz equation was engaged to model the reflection from the active layer using the FEM technique. The multifrontal massively parallel sparse direct solver (MUMPS) was employed to solve the present numerical problem. Very good agreement between experimentally and theoretically obtained coloration in terms of net reflective optical density was achieved for different UV exposures. In particular, for UV exposures larger than ***40 J/cm², the reflected light intensity decreased at a lower rate when compared to other UV exposure values, which was explained by the densely cross-linked structure under near-complete polymerization, and thus the lower efficiency for further bond formation between DA monomer strands. [ABSTRACT FROM AUTHOR]

A calibration method was proposed in the present work to determine the medium-thickness-dependent proton doses absorbed in cellular components (i.e., cellular cytoplasm and nucleus) in radiobiological experiments. Consideration of the dependency on medium thickness was crucial as the linear energy transfer (LET) of protons could rise to a sharp peak (known as the Bragg peak) towards the end of their ranges. Relationships between the calibration coefficient R vs medium-layer thickness were obtained for incident proton energies of 10, 15, 20, 25, 30 and 35 MeV, and for various medium thicknesses up to 5000 μm, where R was defined as the ratio DA/DE, DA was the absorbed proton dose in cellular components, and DE was the absorbed proton dose in a separate radiation detector. In the present work, DA and DE were determined using the MCNPX (Monte Carlo N-Particle eXtended) code version 2.4.0. For lower incident proton energies (i.e., 10, 15 and 20 MeV), formation of Bragg-peak-like features were noticed in their R-vs-medium-layer-thickness relationships, and large R values of >7 and >6 were obtained for cytoplasm and nucleus of cells, respectively, which highlighted the importance of careful consideration of the medium thickness in radiobiological experiments. [ABSTRACT FROM AUTHOR]

EURADOS Working Group 6 has organized an intercomparison exercise on the use of the ICRP Reference Computational Phantoms with radiation transport codes. This paper summarizes the results of a specific task from the intercomparison exercise modelling internal radiation sources. The quantities to be calculated were absorbed fractions and specific absorbed fractions for monoenergetic photon and electron sources as well as S-values for two radionuclides in four source organs. Twelve participants from eleven countries participated in this specific task using the Monte Carlo radiation transport codes FLUKA, Geant4, the MCNP code family, PenEasy, TRIPOLI-4 and VMC. Although some participants provided initial solutions in good agreement with the master solution evaluated by the organizers, differences of factors or even orders of magnitude were also found. Following feedback from the organizer, most participants submitted revised solutions that were mostly in better agreement with the master solution, although this was not always the case. Some initial and revised results are discussed in detail in this paper, and the reasons of mistakes are described as far as they were revealed by the participants. A full account of all results is presented in specific annexes as supplemental material. • EURADOS has organized an intercomparison study on the use of the ICRP/ICRU reference computational phantoms. • This article deals with one task involving internal sources. • Some participants provided solutions in agreement with the master solution, but large differences were also found. • Following feedback from the organizer, most participants submitted revised solutions that were mostly in better agreement. • It has been confirmed that intercomparison exercises are valuable for establishing good practice in computational dosimetry. [ABSTRACT FROM AUTHOR]