N. Stevanovic

Room model with three modal distributions of attached radon progeny

In this paper a room model with three modal distributions of attached radon progeny is developed. Recoil factors are recalculated for each of the modes, and different recoil factors than usually used are obtained. Dependence of progeny concentration in various modes on ventilation and attachment rate is presented. Unattached 214Pb is overestimated up to 15% if one modal distribution is used, which can lead to the overestimation of lung dose.

Determination of the soil-to-grass transfer of 137Cs and its relation to several soil properties at various locations in Serbia

Transfer coefficients of 137Cs from soil to grass were determined for the terrain around the city of Kragujevac in central Serbia. Mass activity concentrations of 137Cs in soil and grass samples were determined with a high-purity Ge-detector (HPGe). The activity concentration at the depth of 20 cm was found to be in the range of 14.92–124.05 Bq kg−1, whereas the activity in grass for the same location was in the range of 4.60–84.95 Bq kg−1. Transfer factors (TFs) were in the range of 0.07 up to 1.94. Dependences of TFs on different soil characteristics were presented graphically. Weak dependences were determined between them. Absaloms model was used to predict TFs based on soil characteristics: pH value, contents of clay, exchangeable potassium and humus. A comparison of measured and predicted values from Absaloms model is shown graphically. It has been found that Absaloms model might be carefully used for the prediction of 137Cs in grass for specific regions.

Deposition rates of unattached and attached radon progeny in room with turbulent airflow and ventilation.

In this paper deposition rate coefficients for unattached and attached radon progeny were estimated according to a particle deposition model for turbulent indoor airflow described by Zhao and Wu [2006. Modeling particle deposition from fully developed turbulent flow in ventilation duct. Atmos. Environ. 40, 457-466]. The parameter which characterizes turbulent indoor airflow in this model is friction velocity, u*. Indoor ventilation changes indoor airflow and friction velocity and influences deposition rate coefficients. Correlation between deposition and ventilation rate coefficients in the room was determined. It was shown that deposition rate coefficient increases with ventilation rate coefficient and that these parameters of the Jacobi room model cannot be assumed to be independent. The values of deposition rate coefficients were presented as functions of friction velocity and ventilation rate coefficient. If ventilation rate coefficient varies from 0.1 up to 1h(-1), deposition rate coefficients for unattached and attached fractions were estimated to be in the range 3-110 h(-1) and 0.015-0.35 h(-1), respectively.

Computer program Neutron_CR-39 for simulation of neutrons from an Am–Be source and calculation of proton track profiles

Abstract A computer program called Neutron_CR-39.F90 for neutron simulation through a PADC detector and its detection was described and developed. In this work the neutron Am–Be source was considered for simulation. It was shown that the most intensive secondary particles, created in neutron interactions with the detector, are protons. The programming steps are outlined with detailed description of neutron simulation, determination of latent tracks of created protons, as well as, their development after detector etching in the same and opposite direction of particle motion. The outputs of the code are parameters of created protons (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron. Program summary Program title: Neutron_CR-39 Catalogue identifier: AEIU_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEIU_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 140 004 No. of bytes in distributed program, including test data, etc.: 2 213 012 Distribution format: tar.gz Programming language: Fortran 90 Computer: PCs and workstations Operating system: Unix, Linux, Windows 95+ RAM: 256 MB Classification: 17.5, 18 External routines: For the Windows installation the entire code must be linked with the PORTLIB library. Nature of problem: The neutrons do not cause ionizations in the detector, and consequently no tracks are produced directly by them in the PADC. Due to the elastic and nonelastic interaction of neutrons with the atoms of PADC, recoil nuclei and secondary particles are created producing latent intrinsic tracks. After chemical etching in aqueous NaOH solution these tracks become visible under optical microscope and usually density of visible tracks is measured. Optical microscopes are often used for this purpose but the process is relatively tedious and time consuming. The present computer program has been written for neutron simulation through PADC detector; determination of parameters of secondary particles; calculation track profiles of secondary particles emitted in the same and opposite direction as etchant progression. The outputs of the code are parameters of secondary particles (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron. Solution method: A computer program is prepared to simulate neutronʼs interactions in a PADC by the Monte Carlo method using the Neutron data library ENDF/B-VII [B. Milenkovic, D. Nikezic, N. Stevanovic, Radiat. Meas. 45 (2010) 1338]. The parameters of the emitted secondary particles (emission angle, initial energy, deposited energy and starting and stopping coordinates) were stored in an enclosed file. The subroutine for calculation of track profiles by a finite difference method for particles emitted in the same direction was developed [D. Nikezic, N. Stevanovic, D. Kostic, S. Savovic, K.C.C. Tse, K.N. Yu, Radiat. Meas. 43 (2008) S76]. It was shown that there are many tracks formed in the opposite direction than the etchant progression. The method for calculation of track profiles for these particles is developed in [B. Milenkovic, N. Stevanovic, D. Krstic, D. Nikezic, Radiat. Meas. 44 (2009) 57]. It is very different than the method for track in the same direction. The separate subroutine for this purpose was developed here. Additional comments: The program distribution file contains an executable which enables the program to be run on a Windows machine. The source code is also provided, but in order to build an executable the PORTLIB must be available. Running time: Running time depends mainly on the neutron number for simulation, source and detector geometry and removed layer required by the user. Running time is several minutes.

Determination of parameters of the Jacobi room model using the Brownian motion model.

Parameters of the Jacobi room model were estimated with simulation of Brownian motion. Deposition on internal room surfaces and attachment of progeny atoms to three modally distributed aerosols were taken into account. The values of parameters were presented as functions of aerosol concentrations. The deposition rate of an unattached progeny was estimated in the range 30-47 h−1; the deposition rate of an attached progeny was very small and its range is 0.0007-0.004 h−1; the attachment rate of a progeny is in range 40-170 h−1. The statistical uncertainty was lower than 1%. The ranges of parameters were similar to those reported in literature.

Relationship between deposition and attachment rates in Jacobi room model

It is shown in this work that parameters of the Jacobi model, which describes behavior of short-lived radon progeny, are not independent. The relationship between deposition rate of attached radon progeny and attachment rate of their unattached fraction was determined in this paper. It was found that deposition rate increases when the attachment rate is smaller; this effect is more pronounced for larger friction velocity. The deposition rate of attached radon progeny is presented here as a function of friction velocity, ventilation and attachment rate. Deposition rate of attached fraction was estimated in the range 0.012-0.46 h(-1), when attachment rate varies from 10 h(-1) to 100 h(-1).

NEUTRON DETECTION BY A CR-39 DETECTOR AND ANALYSIS OF PROTON TRACKS ETCHED IN THE SAME AND OPPOSITE DIRECTIONS

A program code to simulate neutron interactions with a CR-39 detector and calculate parameters describing the induced etched proton tracks in the CR-39 material was previously developed(( 1)). This code was used to understand the mechanisms involved during interactions with neutrons in the CR-39 material and the influence of the etching process, enabling an improvement in the efficiency of the CR-39 detector. Due to neutron interaction with atoms of the detector material, the created protons are emitted in different directions and their latent tracks are oriented randomly within the detector. The aim of this paper is to show differences between the number of visible tracks etched in the same and opposite directions from both sides of the detector. The efficiency of neutron detection was analysed as a function of the removed layer and neutron energy for both sides of detector.

Determination of a CR-39 detector response to neutrons from an Am-Be source.

A comparison of experimental and calculated responses of a CR-39 detector to neutron spectra from an Am-Be source is presented. Code named Neutron_CR-39.F90 has been used to calculate the neutron dose equivalent as well as the track density. Conversion coefficient (sensitivity), between track density in track/cm(2) and neutron dose equivalent in mSv, was calculated and good agreement with experimental data was found. Sensitivity increases linearly with removed layer in the range between 6 μm and 24 μm.

Photon albedo for water, concrete, and iron at normal incidence, and dependence on the thickness of reflecting material

Total number and angular albedo were calculated for commonly used shielding materials, water, concrete, and iron, for photons with initial energies from 10 keV up to 10 MeV and normal incident angle. Influence of material thickness on total number albedo was also investigated. Double differential albedo was determined from simulation of photon transport through materials by using PENELOPE and MCNP software. Backscattered photons were scored and grouped in equal intervals of energy and angle. Analytical expressions for angular and total number albedo as a function of initial energy were obtained. It was shown that angular albedo can be determined with the same formula for three examined materials. Corresponding analytical expressions for number albedo as a function of material thickness were presented in this paper. [Projekat Ministarstva nauke Republike Srbije, br. 171021]

Influence of electron motion in target atom on stopping power for low-energetic ions

In this paper the stopping power was calculated, representing the electrons of the target atom as an assembly of quantum oscillators. It was considered that the electrons in the atoms have some velocity before interaction with the projectile, which is the main contribution of this paper. The influence of electron velocity on stopping power for different projectiles and targets was investigated. It was found that the velocity of the electron stopping power has the greatest influence at low energies of the projectile.