H.R. Schelin

Comparison of SRIM, MCNPX and GEANT simulations with experimental data for thick Al absorbers

Proton computerized tomography deals with relatively thick targets like the human head or trunk. In this case precise analytical calculation of the proton final energy is a rather complicated task, thus the Monte Carlo simulation stands out as a solution. We used the GEANT4.8.2 code to calculate the proton final energy spectra after passing a thick Al absorber and compared it with the same conditions of the experimental data. The ICRU49, Ziegler85 and Ziegler2000 models from the low energy extension pack were used. The results were also compared with the SRIM2008 and MCNPX2.4 simulations, and with solutions of the Boltzmann transport equation in the Fokker-Planck approximation.

Excitation of discrete levels of 63Cu and 65Cu nuclei in (e, e′) reactions

Inelastic electron scattering on 63Cu and 65Cu nuclei at excitation energies of up to 5 MeV was studied. Information about the reduced probability and multipolarity of transitions was obtained for 11 low-lying levels and groups of levels of the 63Cu nucleus and for 17 such levels and groups of levels of the 65Cu nucleus. It was shown that the experimental form factors for inelastic scattering accompanied by the excitation of discrete levels and group of levels of these nuclei with a nonzero spin can be described in terms of a single multipolarity, even though the law of angular-momentum conservation admits the existence of several more multipolarities yielding the same parity of an excited state.

GEANT4 simulations for low energy proton computerized tomography

This work presents the recent results of computer simulations for the low energy proton beam tomographic scanner installed at the cyclotron CV-28 of IEN/CNEN. New computer simulations were performed in order to adjust the parameters of previous simulation within the first experimental results and to understand some specific effects that affected the form of the final proton energy spectra. To do this, the energy and angular spread of the initial proton beam were added, and the virtual phantom geometry was specified more accurately in relation to the real one. As a result, a more realistic view on the measurements was achieved.

Activity measurements of radon from construction materials

This work presents the results of radon concentration measurements of construction materials used in the Brazilian industry, such as clay (red) bricks and concrete blocks. The measurements focused on the detection of indoor radon activity during different construction stages and the analysis of radionuclides present in the construction materials. For this purpose, sealed chambers with internal dimensions of approximately 60×60×60 cm3 were built within a protected and isolated laboratory environment, and stable air humidity and temperature levels were maintained. These chambers were also used for radon emanation reduction tests. The chambers were built in four major stages: (1) assembly of the walls using clay (red) bricks, concrete blocks, and mortar; (2) installation of plaster; (3) finishing of wall surface using lime; and (4) insulation of wall surface and finishing using paint. Radon measurements were performed using polycarbonate etched track detectors. By comparing the three layers applied to the masonry walls, it was concluded that only the last step (wall painting using acrylic varnish) reduced the radon emanation, by a factor of approximately 2. Samples of the construction materials (clay bricks and concrete blocks) were ground, homogenized, and subjected to gamma-ray spectrometry analysis to evaluate the activity concentrations of 226Ra, 232Th and 40K. The values for the index of the activity concentration (I), radium equivalent activity (Raeq), and external hazard index (Hext) showed that these construction materials could be used without restrictions or concern about the equivalent dose limit (1 mSv/year).

Dose Energy Dependence in Proton Imaging Near the Bragg Peak

Since the earliest work, the main advantage of proton imaging as compared to X‐rays was expected to be based on the specific property of the proton flux to drop off very steeply at the end of the particle range. However, this conclusion was based on the stopping power dependence on the path length and was experimentally verified only with thin detectors, such as photographic films. Such detectors register only part of the energy flux of exit protons. An alternative method is based on the measurement of the total exit energy of protons. In this case one must consider two other effects that act in opposite ways: they increase the necessary irradiation dose with decreasing energy of the protons. First of all, the energy loss of a proton in an object becomes higher at lower initial energies. At the same time, the decrease in energy of protons results in the increase of the energy straggling, which increases the number of protons needed to determine the exit energy of protons with a predetermined precision. Ou...

Proton CT setup at CV-28 of IEN/CNEN

Although the idea of proton Computed Tomography (pCT) is not new, it is currently not available. It is still unknown if the image quality of pCT is sufficient for localizing tumors and if the accuracy of proton range calculations surpass that of X-ray CT based range calculations without significantly increasing the patient exposure. The spatial resolution of pCT is limited mainly by multiple Coulomb scattering, while the contrast resolution is affected principally by the statistical nature of the proton energy loss mechanism. Both effects are more pronounced and thus easier to study at the low proton energies available at CV-28. An experimental setup for pCT at CV-28 was elaborated by our team. The first-generation CT scheme was assumed as the most adequate for the existing CV-28 proton pencil beam. All equipment, which includes the collimators for the initial and outgoing proton beam, the tomographic turntable, and the ORTEC L-035-025-5 proton detector, was assembled onto the support bar of the ORTEC vacuum chamber. A water-filled glass tube of 5 mm external diameter with a 1 mm diameter polyethylene rod on the central axis was chosen as the first sample to be studied. Later, the water will be substituted by tissue-equivalent solutions of different densities to study the contrast resolution. A Monte Carlo simulation of the experiment, assuming 25 MeV monochromatic proton beam, was made using the SRIM-2003.20 code. The simulation permitted to choose the critical parameters for the setup, such as the beam collimation, the steps of translation and rotation of the turntable, and the required statistics for an accurate measurement of proton energy.

Linear polarization of photons produced by the electron plane channeling in a silicon crystal

We present the results of the polarization and intensity measurements versus photon energy MeV for the photon beam produced by the electron plane channeling with the energies 1.2 and 1.5 GeV in silicon crystals 500 m and 290 m thick along the (110) plane. The comparison with results of another research group and theoretical calculations indicate a qualitative agreement. The correlation between the shape of the radiation intensity spectrum and its polarization energy dependence is observed.

Monte Carlo Simulation Used to Calculate Energy Correction Factor for Thermoluminescent Dosimeters Used by Occupational Workers on Pediatric Exams

The main objective of this work is to simulate the X-ray scattered spectra by different pediatric phantoms (simulation of children subjected to barium meal procedures) to calculate an energy correction factor (ECF) to the reading of thermoluminescent dosimeters (TLDs). To perform this evaluation, the TLDs were positioned over three areas in two occupational workers: eyes, thyroid and hands. The Geant4 toolkit was used to define the spectra collected by TLDs, making possible to calculate the ECF. This work was developed in two stages: (1) evaluation of scattered spectra by different standard phantoms (newborn, 1, 5 and 10 years old); (2) definition of the ECF to the absorbed energy by each TLD. Geant4 shows to be a good toolkit to calculate the ECF and among the different characteristics evaluated, in this work, the TLD position and acceleration voltages are the most significant parameters that may influence the ECF calculated.

Dose energy dependence in proton imaging with thin detector

Since the earliest works proposing the use of protons for imaging, the main advantage of protons over X-rays was expected to be a result of the specific property of the proton flux dropping off very steeply at the end of the particle range. This idea was declared but was not checked. In the present work, this assumption was investigated using the Monte Carlo simulation for the case of registration of protons with a thin detector.

Comparison of the GEANT4 releases 8.2 and 9.2 in terms of a pCT reduced calibration curve

The GEANT4 simulations are essential for the development of medical tomography with proton beams — pCT. In the case of thin absorbers the latest releases of GEANT4 generate very similar final spectra which agree well with the results of other popular Monte Carlo codes like TRIM/SRIM, or MCNPX. For thick absorbers, however, the disagreements became evident. In a part, these disagreements are due to the known contradictions in the NIST PSTAR and SRIM reference data. Therefore, it is interesting to compare the GEANT4 results with each other, with experiment, and with diverse code results in a reduced form, which is free from this kind of doubts. In this work such comparison is done within the Reduced Calibration Curve concept elaborated for the proton beam tomography.