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Biological polymeric shielding design for an X-ray laboratory using Monte Carlo codes

Tajudin SM, Tabbakh F

Radiol Phys Technol, 2019 Sep;12(3):299-304.
PMID: 31302871 DOI: 10.1007/s12194-019-00522-w

Photon irradiation facilities are often shielded using lead despite its toxicity and high cost. In this study, three Monte Carlo codes, EGS5, MCNPX, and Geant4, were utilized to investigate the efficiency of a relatively new polymeric base compound (CnH2n), as a radiation shielding material for photons with energies below 150 keV. The proposed compound with the densities of 6 and 8 g cm-3 were doped with the weight percentages of 8.0 and 15.0% gadolinium. The probabilities of photoelectric effect and Compton scattering were relatively equal at low photon energies, thus the shielding design was optimized using three Monte Carlo codes for the conformity of calculation results. Consequently, 8% Gd-doped polymer with thickness less than 2 cm and density of 6 g cm-3 was adequate for X-ray room shielding to attenuate more than 95% of the 150-keV incident photons. An average dose rate reduction of 88% can be achieved to ensure safety of the radiation area.
PHOTON FIELD OF ~100-200 KEV FOR ENVIRONMENTAL DOSEMETER CALIBRATION

Tajudin SM, Namito Y, Sanami T, Hirayama H

Radiat Prot Dosimetry, 2020 Jul 02;188(4):486-492.
PMID: 31950186 DOI: 10.1093/rpd/ncz308

As a reference photon field, several radionuclides have been used frequently, such as 241Am,137Cs and60 Co for calibration. These nuclides provide mono-energy photons for dosemeters covering few tens of keV-MeV. The main energy around 200 keV is important for both environmental and medical fields since the former should consider scattering photons and the later should measure photons from X-ray generator. In our previous work, a backscattered layout can provide a uniform photon field spectra and dose rate with an energy of 190 keV by using an affordable intensity 137 Cs gamma source. Several other quasi-monoenergetic photon fields in the range of 100-200 keV could be obtained by using several available gamma sources. Two calibrated environmental CsI(Tl) survey meters, Horiba PA-1000 and Mr. Gamma A2700, had been measured with the developed backscattered photon field to understand energy-dependent features in order to confirm dosemeter readings. Consequently, both scintillator instruments are sensitive for measurements of the relatively low dose rates at 190 keV.
Response of plastic scintillator to gamma sources

Tajudin SM, Namito Y, Sanami T, Hirayama H

Appl Radiat Isot, 2020 May;159:109086.
PMID: 32250760 DOI: 10.1016/j.apradiso.2020.109086

In this study, we developed a method for directly determining the energy deposited over the entire energy range by monitoring the light output from a plastic scintillator under gamma irradiation. The relative light output was analyzed based on Birks' semi-empirical formula for ionization to obtain the quenching parameter as kB = 0.016 ± 0.0004 g cm-2 MeV-1. Comparisons of experimental and calculated results for the light output spectra showed that considering the quenching effect, background subtraction, source casing, and energy sampling were essential for achieving good agreement.
CORRIGENDUM TO: PHOTON FIELD OF ~100-200 KEV FOR ENVIRONMENTAL DOSEMETER CALIBRATION

Tajudin SM, Namito Y, Sanami T, Hirayama H

Radiat Prot Dosimetry, 2020 Sep 16;190(3):353.
PMID: 32844231 DOI: 10.1093/rpd/ncaa122
Assessment of natural radioactivity levels and hazard indicators in Tarakeshwor Municipality, Nepal through in-situ technique and multivariate analysis

Upadhyay DR, Phuyal A, Tajudin SM, Khanal R

Heliyon, 2024 May 30;10(10):e30822.
PMID: 38803985 DOI: 10.1016/j.heliyon.2024.e30822

The evaluation of primordial radionuclide concentrations in rapidly urbanized and concrete-laden areas through the importation of construction materials from various regions of Nepal is both important and essential. This study utilized a portable gamma-ray spectrometer (PGIS 2) to analyze the distribution of three natural radionuclides: uranium (238U), thorium (232Th), and potassium (40K) in Tarakeshwor Municipality, Kathmandu, Nepal. The measured dose rates ranged from 70.22 nSv hr-1 to 163.66 nSv hr-1, with an average of 124.65±20.29 nSv hr-1, surpassing the global average of 59 nSv hr-1. The activity concentrations of 40K, 238U, and 232Th exceeded global averages, indicating relatively higher natural radioactivity concentrations in the region. Specifically, the average values for 40K, 238U, and 232Th were 935.26±172.30 Bq kg-1, 80.47±15.53 Bq kg-1, and 80.44±18.58 Bq kg-1, respectively. The calculated radium equivalent (Raeq) ranged from 132.26 to 351.22 Bq kg-1, and the annual gonadal equivalent dose (AGED) varied from 372.61 to 1028.81 μSv yr-1. The annual effective dose rates for indoor and outdoor environments were 0.54±0.09 mSv yr-1 and 0.15±0.03 mSv yr-1, respectively, both exceeding the global average. The representative level index (RLI) within the study area averaged 1.96±0.32, indicating an elevated radiation risk. The excess lifetime cancer risk (ELCR) values for outdoor and indoor environments were 0.52×10-3 ±0.09 ×10-3 and 1.87 ×10-3 ±0.31×10-3, respectively, surpassing the world average. Additionally, external hazard indices (Hex) ranged from 0.36 to 0.59, while internal hazard indices (Hin) ranged from 0.38 to 1.20, both indicating values higher than UNSCEAR recommendations. These findings underscore the necessity for further experimental analysis employing ex-situ equipment. The data generated in this study can provide a valuable baseline for future assessments and interventions in radiation risk management guidelines within the country.
Fulltext Dosimetry characteristics of polycarbonate/bismuth oxide nanocomposite for real-time application in the field of gamma-rays

Veiskarami A, Malekie S, Kashian S, Tajudin SM

Rep Pract Oncol Radiother, 2024;29(4):413-425.
PMID: 39895958 DOI: 10.5603/rpor.101397

BACKGROUND: Polymer-carbon nanostructures have previously been introduced for dosimetry of gamma rays with potential application in radiotherapy. In this research work, bismuth oxide (Bi2O3) nanoparticles were added into the amorphous polycarbonate (PC) matrix to enhance the probability of the photoelectric effect and dosimetry response in parallel.
MATERIALS AND METHODS: PC/Bi2O3 nanocomposites at concentrations of 0, 5, 20, 40, and 50 Bi2O3 wt% were fabricated via a solution method. Afterward, the samples were irradiated by gamma rays of cobalt-60 (60Co) related to Picker V-9, and Therarton-780 machines at 30-254 mGy/min. Dosimetric characteristics were carried out including linearity, angular dependency, energy, bias-polarity, field size, and repeatability.
RESULTS: Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses exhibited an appropriate dispersion state. The dosimeter response was linear at 30-254 mGy/min for the all samples. The 50 wt% sample exhibited the highest sensitivity at 4.61 nC/mGy. A maximum angular variation of approximately 15% was recorded in normal beam incidence. The energy dependence at two energies of 662 and 1250 keV was obtained as 0.7%. Bias-polarity for the 40, and 50 wt% samples at 400 V were measured as 15.9% and 9.0%, respectively. The dosimetry response was significantly dependent on the radiation field size. Also, the repeatability of the dosimeter response was measured as 0.4%.
CONCLUSIONS: Considering the dosimetry characteristics of PC-Bi2O3 nanocomposites, and appropriate correction factors, this material can be used as a real-time dosimeter for the photon fields at therapy level.
Investigation of natural radionuclide and associated radiological parameters of selected construction materials used in Nepal

Upadhyay DR, Shah BR, Tajudin SM, Khanal R

Environ Monit Assess, 2025 May 08;197(6):639.
PMID: 40338326 DOI: 10.1007/s10661-025-14099-y

The present study investigated the natural radioactivity levels of 226 Ra, 232 Th, and 40 K in various construction and building materials commonly used in Central Nepal, expressed in Bq kg - 1 , and analyzed the associated 13 radiological parameters for the evaluation of risks. Activity concentrations were determined using a thallium-activated sodium iodide crystal NaI(Tl) 3" × 3" scintillator detector. Multivariate statistical analysis was used to discern trends and depict the data. Among the material studied, granites, sand, and bricks exhibited concentrations and associated radiological parameters that exceeded world average. However, remaining aggregate, cement, concrete bricks, marble, and tiles showed activity concentrations and hazard indices comparable to or lower than the global average value reported by UNSCEAR, 1993 for building materials. The overall revealed mean ± S.D. concentration of 226 Ra, 232 Th and 40 K across 41 different materials as 43.2 ± 1.0 Bq kg - 1 , 56.8 ± 1.4 Bq kg - 1 , and 281.1 ± 5.3 Bq kg - 1 , respectively. The average values 226 Ra, 232 Th were above the world population average values of 50 and 50 Bq kg - 1 whereas the concentration of 40 K was well below the average value 500 Bq kg - 1 respectively. From this, it is concluded that the studied samples are safe to use. However, regulations are needed to evaluate the natural activity concentrations of radionuclides in geologically derived samples and the associated health implications related to materials utilized from the internal resources of the country and imported materials from a different country.
Fulltext Using 157Gd doped carbon and 157GdF4 nanoparticles in proton-targeted therapy for effectiveness enhancement and thermal neutron reduction: a simulation study

Tabbakh F, Hosmane NS, Tajudin SM, Ghorashi AH, Morshedian N

Sci Rep, 2022 Oct 18;12(1):17404.
PMID: 36258012 DOI: 10.1038/s41598-022-22429-0

There are two major problems in proton therapy. (1) In comparison with the gamma-ray therapy, proton therapy has only ~ 10% greater biological effectiveness, and (2) the risk of the secondary neutrons in proton therapy is another unsolved problem. In this report, the increase of biological effectiveness in proton therapy has been evaluated with better performance than 11B in the presence of two proposed nanomaterials of 157GdF4 and 157Gd doped carbon with the thermal neutron reduction due to the presence of 157Gd isotope. The present study is based on the microanalysis calculations using GEANT4 Monte Carlo tool and GEANT4-DNA package for the strand breaks measurement. It was found that the proposed method will increase the effectiveness corresponding to the alpha particles by more than 100% and also, potentially will decrease the thermal neutrons fluence, significantly. Also, in this work, a discussion is presented on a significant contribution of the secondary alpha particles in total effectiveness in proton therapy.
Assessing radioactive contaminants in Kathmandu soils: measurement and risk analysis

Upadhyay DR, Koirala G, Shah BR, Tajudin SM, Khanal R

Environ Monit Assess, 2024 Jan 23;196(2):190.
PMID: 38261087 DOI: 10.1007/s10661-023-12284-5

Soil samples from vegetable farmland in densely populated wards of Nepal were analyzed for natural radionuclide levels, employing a NaI(Tl) 3" [Formula: see text] 3" gamma detector. The study aimed to evaluate the causes of radiation risk, attributing it to soil contamination resulting from the rapid urbanization and concretization that followed the earthquake in 2015. The activity concentration of radium-226, thorium-232, and potassium-40 and the ranges observed are 2.080±0.084-33.675±1.356 Bq kg[Formula: see text], 17.222±0.198-119.949±1.379 Bq kg[Formula: see text], and 11.203 ± 0.325-748.828±21.716 Bq kg[Formula: see text], respectively. The average values obtained for hazard indices are as follows: radium equivalent activity (82.779 Bq kg[Formula: see text]), absorbed dose rate (36.394 nGy h[Formula: see text]), annual effective dose equivalent (0.045 mSv yearr[Formula: see text]), gamma index (0.291), external hazard index (0.224), internal hazard index (0.253), excess lifetime cancer risk (0.159), annual gonadal dose equivalent (243.278 mSv year[Formula: see text]), alpha index (0.054), and activity utilization index (0.716). However, in most places, thorium-232 concentration is greater than those of the world average and recommended values. In specific locations such as Ward 4 in Baluwatar, the soil was found to have concentrations of Ra[Formula: see text] and K[Formula: see text] exceeding recommended limits. Despite this localized concern, the overall analysis of hazard indices across the studied areas revealed that most values were within permissible limits. This suggests that, on a broader scale, radiation exposure may not be a significant concern in the investigated regions. Nonetheless, the study recommends regular monitoring in additional locations to ensure a comprehensive and ongoing assessment of radiation levels.