Bond-Breaking Efficiency of High-Energy Ions in Ultrathin Polymer Films.

Thin films of poly(methyl methacrylate) and poly(vinyl chloride) of different thickness are used to investigate the effect of spatial confinement on the efficiency of bond breaking induced by 2 MeV H^{+} and 2.1 GeV Bi ions. Effective cross sections for oxygen and chlorine loss are extracted for films down to a thickness of about 5 nm and are compared to theoretical estimations based on radial energy density profiles simulated with geant-dna. The cross sections are to a large extent thickness independent, indicating that bond breaking is dominated by short-range processes. This is in contrast to the strongly reduced efficiencies found recently for cratering induced by high-energy ions in similar ultrathin polymer films [Phys. Rev. Lett. 114, 118302 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.118302].

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.

All about FAX: a Female Adult voXel phantom for Monte Carlo calculation in radiation protection dosimetry.

The International Commission on Radiological Protection (ICRP) has created a task group on dose calculations, which, among other objectives, should replace the currently used mathematical MIRD phantoms by voxel phantoms. Voxel phantoms are based on digital images recorded from scanning of real persons by computed tomography or magnetic resonance imaging (MRI). Compared to the mathematical MIRD phantoms, voxel phantoms are true to the natural representations of a human body. Connected to a radiation transport code, voxel phantoms serve as virtual humans for which equivalent dose to organs and tissues from exposure to ionizing radiation can be calculated. The principal database for the construction of the FAX (Female Adult voXel) phantom consisted of 151 CT images recorded from scanning of trunk and head of a female patient, whose body weight and height were close to the corresponding data recommended by the ICRP in Publication 89. All 22 organs and tissues at risk, except for the red bone marrow and the osteogenic cells on the endosteal surface of bone ('bone surface'), have been segmented manually with a technique recently developed at the Departamento de Energia Nuclear of the UFPE in Recife, Brazil. After segmentation the volumes of the organs and tissues have been adjusted to agree with the organ and tissue masses recommended by ICRP for the Reference Adult Female in Publication 89. Comparisons have been made with the organ and tissue masses of the mathematical EVA phantom, as well as with the corresponding data for other female voxel phantoms. The three-dimensional matrix of the segmented images has eventually been connected to the EGS4 Monte Carlo code. Effective dose conversion coefficients have been calculated for exposures to photons, and compared to data determined for the mathematical MIRD-type phantoms, as well as for other voxel phantoms.

Análise das doses efetivas recebidas por trabalhadores em radiologia médica / Analysis of effective doses received by workers in medical radiology

Pesquisou-se as doses recebidas por uma fração de trabalhadores ocupacionalmente expostos à radiação ionizante na área de radiologia médica que utilizam dosímetros individuais. A heterogeneidade dos dados, garantia pelo tratameno estatístico adotado, possibilitou verificar que nenhum usuário de dosímetro atingiu o limite de dose de 50 mSv/ano, estabelecido pela Norma da CNEN-NE-3.01. No entanto, no local em que os funcionários não recebem treinamento freqüente em radioproteção, encontraram-se as maiores doses individuais mensais e anuais, e os maiores índices percentuais de doses de investigação e dosímetros não devolvidos.

High measles mortality in infancy related to intensity of exposure.

In a West African urban community, measles infection in infants was examined over 5 years (1979-1983). In the age group 0 to 11 months, measles mortality was higher among secondary cases (infected in the house) than among index cases (infected outside the house), and the proportion of secondary cases was significantly higher for this age group than for older children. Intensive exposure related to the social pattern of disease transmission may be important in explaining the high infant mortality observed with measles in developing countries. Mortality during the first 12 months of life increased with age, presumably because of the decrease of maternally derived measles antibodies. In children younger than 6 months of age, who are usually considered to be protected by maternal antibody, intensive exposure may lead to infection, as demonstrated by a high level of measles-specific antibodies in some children exposed to an older sibling with measles. The aim of public health policies should be to change conditions of exposure.