Background radioactivity level estimation and passive shield optimization using adjoint Monte Carlo method.

The current study proposes a procedure to estimate the activity concentration of natural radionuclides and to optimize passive shielding solutions for HPGe detectors using adjoint Monte Carlo (MC) simulation technique of Geant4 for the first time. The background spectrum is acquired for 1.56 × 106 s using an HPGe detector model (GC3020), set inside a shielding solution, during 2021-2022 to estimate the activity concentration of natural radionuclides inside the shielding. While, a background spectrum for 65,000 s is acquired with shielding removed to estimate the concentration of natural radionuclides in the building materials of the laboratory. The detector design used in the simulations is validated by comparing computed and measured Full Energy Peak Efficiency (FEPE) for point sources 241Am, 152Eu, 137Cs, 133Ba, and 60Co. Adjoint MC simulations are used to compute the activity concentration of natural radionuclides assuming an isotropic distribution. The activity concentration of 40K, 226Ra and 232Th in the building material is found to be 524 ± 140, 83 ± 20 and 65 ± 18 Bqkg-1, respectively. The computed values are found in good agreement with the published data. The natural radioactivity levels of 40K, 226Ra and 232Th measured in lead shielding are 155.7 ± 0.1 mBqkg-1, 24 ± 13 mBqkg-1 and 33 ± 17 mBqkg-1 respectively. The radiological risks arising due to natural radioactivity is assessed by calculating radium equivalent activity (Raeq), indoor radiation hazard index (Hin) and annual effective dose equivalent. All the radiological parameters are found below their permissible limits and building materials may be considered radiologically safe. The optimal lead shield thickness for the detector is determined to be 12 cm, resulting in reduction of background signal by two orders of magnitude compared to an unshielded detector. The adjoint MC simulations in Geant4 are 103-104 times more rapid as compared to normal simulations for shield optimization of HPGe detectors and therefore, are identified as viable computing solution to calculate the activity of the background radiation.

Clinical manifestations and outcome of patients with primary amoebic meningoencephalitis in Pakistan. A single-center experience.

Primary amoebic meningoencephalitis (PAM) is a rapidly progressing central nervous system (CNS) infection caused by Naegleria fowleri, a free-living amoeba found in warm freshwater. The disease progression is very rapid, and the outcome is nearly always fatal. We aim to describe the disease course in patients admitted with PAM in a tertiary care center in Karachi, Pakistan between the periods of 2010 to 2021. A total of 39 patients were included in the study, 33 males (84.6%). The median age of the patients was 34 years. The most frequent presenting complaint was fever, which was found in 37 patients (94.9%) followed by headache in 28 patients (71.8%), nausea and vomiting in 27 patients (69.2%), and seizures in 10 patients (25.6%). Overall, 39 patients underwent lumbar puncture, 27 patients (69.2%) had a positive motile trophozoites on CSF wet preparation microscopy, 18 patients (46.2%) had a positive culture, and 10 patients had a positive PCR. CSF analysis resembled bacterial meningitis with elevated white blood cell counts with predominantly neutrophils (median, 3000 [range, 1350-7500] cells/µL), low glucose levels median, 14 [range, 1-92] mg/dL), and elevated protein levels (median, 344 [range, 289-405] mg/dL). Imaging results were abnormal in approximately three-fourths of the patients which included cerebral edema (66.7%), hydrocephalus (25.6%), and cerebral infarctions (12.8%). Only one patient survived. PAM is a fatal illness with limited treatment success. Early diagnosis and prompt initiation of treatment can improve the survival of the patients and reduce mortality.

A novel method to estimate the dead layer of HPGe detector for Monte Carlo FEPE computation.

In this study, a novel method to determine the surface and lateral dead layers of p-type HPGe detector is proposed to compute the full energy peak efficiency (FEPE). The method employed standard radioactive point sources 241Am, 133Ba and FEPE measurement at low energies to estimate the thickness of frontal and lateral dead layers. The method is simple to apply, requires only two standard radioactive sources to estimate the optimum thickness of frontal and lateral dead layers. The proposed method is validated by measuring the efficiency of various point sources and a volume source in the energy range from 59 to 1408 keV. The measured efficiencies agree to simulation with relative deviation less than 4.0% at each energy. The proposed detector model enables to calibrate the detector for environmental radioactivity measurement without standard volume sources.

Reorganising for COVID-19 Pandemic: A Review of Structural Modifications by the Department of Internal Medicine in Low to Middle-income Countries.

Scientists classified the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a novel coronavirus on January 7, 2020. The World Health Organization (WHO) acknowledged the SARS-CoV-2 outburst a public health emergency of international concern on January 30, 2020. Since its origin, this virus has disrupted the best healthcare systems, economies, and strained financial resources; and for underdeveloped countries' healthcare systems, the virus has become a crisis. To tackle the potential hazards from this virus, our Department restructured the services that not only helped us to cope with the pandemic, but also provided an example to copy for other contemporary institutes. This article aims to describe the measures and structural changes undertaken by the Internal Medicine Department, Aga Khan University Hospital (AKUH), Karachi, Pakistan. Key Words: COVID-19, Internal medicine, Structural modifications, Pandemic.

Predatory functional response and fitness parameters of Orius strigicollis Poppius when fed Bemisia tabaci and Trialeurodes vaporariorum as determined by age-stage, two-sex life table.

BACKGROUND: The polyphagous predatory bug O. strigicollis is an active predator used to control thrips and aphids. The whitefly species Bemisia tabaci and Trialeurodes vaporariorum are voracious pests of different economic agricultural crops and vegetables. METHOD: In this study, the Holling disc equation and the age-stage, two-sex life table technique were used to investigate the functional response and biological traits of third instar nymphs and adult female O. strigicollis when presented third instar nymphs of both whitefly species as prey. RESULTS: The results showed a type II functional response for each life stage of O. strigicollis when fed each whitefly species. The calculated prey handling time for different O. strigicollis life stages were shorter when fed T. vaporariorum than when fed B. tabaci nymphs. In contrast, the nymphal development of O. strigicollis was significantly shorter when fed B. tabaci than T. vaporariorum nymphs. Additionally, the total pre-oviposition period of adult females was statistically shorter when fed B. tabaci nymphs than T. vaporariorum nymphs. Furthermore, the survival rates and total fecundity of O. strigicollis were higher when fed B. tabaci than T. vaporariorum. There were no significant differences in any population parameters of O. strigicollis when fed either whitefly species. These results show that O. strigicollis could survive and maintain its populations on both species of whitefly and could therefore serve as a biological control agent in integrated pest management (IPM).

Determination of fitness traits of Orius strigicollis Poppius (Hemiptera: Anthocoridae) on Pectinophora gossypiella (Lepidoptera: Gelechiidae) using two-sex life table analysis.

BACKGROUND: Pink bollworm (Pectinophora gossypiella) is a destructive insect pest of cotton crops in China and globally, which is actively predated on by Orius strigicollis. Studies on the fitness or survival of O. strigicollis fed on P. gossypiella at different temperatures have not been reported. The fitness of O. strigicollis may be well explained using two-sex life table parameters. Thus, the present study provides important insights for the effective biocontrol of P. gossypiella. METHODOLOGY: Considering the importance of fitness parameters and biocontrol, the present study explores the feeding potential and age-stage, two-sex life table traits of O. strigicollis on P. gossypiella eggs at different temperatures (24, 28 and 32 °C) in the laboratory. RESULTS: The intrinsic rate of increase (r) was higher at 28 °C (0.14 d-1) than at 24 °C (0.0052 d-1) and 32 °C (0.12 d-1). Similarly, the net reproductive rate (R 0) was higher at 28 °C (17.63 offspring) than at 24 °C (1.13 offspring) and 32 °C (10.23 offspring). This concluded that the maximum feeding potential and growth capacity of O. strigicollis could be attained at 28 °C when fed on P. gossypiella eggs. O. strigicollis adults preferred to feed on P. gossypiella eggs compared with first instar larvae. Based on these results, the present study suggests that O. strigicollis represents a promising biological control agent against P. gossypiella eggs in cotton fields.

Study of CdTe detection efficiency for medical applications using Geant4-based stochastic simulations.

The determination of detection efficiency and peak-to-total ratios has been performed for rectangular CdTe detectors for various x-ray and low-energy γ-ray source configurations including parallel beams, point, and cylindrical sources. The dependence of efficiency values on axial and off-axial distances, detector thickness and area, and source dimensions has been studied. The detector model developed in this work has been validated by comparing the Monte Carlo simulated values of detector efficiency for a parallel incident beam with the available published data and good agreement has been found with discrepancies remaining within 2% throughout the energy range. Geant4 simulations show nearly 100% photopeak and total efficiency with peak-to-total ratios approaching a maximum value of 1.0 for photons in the 4-70 keV energy range. Similar high values of detection efficiency have been obtained for brachytherapy I-125 seed sources having cylindrical geometries which indicates the suitability of CdTe detectors for the calibration of sources used in therapy. The logistic power curve was found excellent for empirically fitting the photopeak efficiency variations with axial displacement of the I-125 brachy source in the horizontal configuration. Geant4 simulations clearly show that small thicknesses, of the order of 0.5 mm, of CdTe material are sufficient for attaining almost 100% detection efficiency for low-energy photons having energies up to 100 keV.

Estimation of peripheral dose from Co60 beam in water phantom measured in Secondary Standard Dosimetry Laboratory, Pakistan.

BACKGROUND: Peripheral or scatter dose harms neighbouring normal tissues during administration of dose to cancerous tissues, therefore, knowledge of peripheral dose is an important consideration in radiotherapy. AIM: In present study, absorbed dose measurements in a water phantom were performed for three field sizes, 7 × 7 cm2, 10 × 10 cm2 and 15 × 15 cm2. MATERIALS AND METHODS: For each field size, dose was measured at six depths below the front surface of the water phantom; 2.5-15 cm with an interval of 2.5 cm. Measurements were made at equal transverse distances along the horizontal axis, from 1 cm to 6 cm, on both sides of the central beam axis and normalized with central axis dose of each field. All measurements were made at the source to surface distance of 100 cm. RESULTS: Variation of peripheral dose with lateral distance was analysed and an appropriate parametric equation for each field size and depth was constructed. CONCLUSIONS: The peripheral radiation dose showed a strong dependence on field size and distance from field boundary.