Mehdi Sohrabi

Bio: Mehdi Sohrabi is an academic researcher from Amirkabir University of Technology. The author has contributed to research in topics: Dosimeter & Dosimetry. The author has an hindex of 19, co-authored 107 publications receiving 1493 citations. Previous affiliations of Mehdi Sohrabi include International Atomic Energy Agency & Atomic Energy Organization of Iran.

Human exposure to high natural background radiation: what can it teach us about radiation risks?

Abstract: Natural radiation is the major source of human exposure to ionising radiation, and its largest contributing component to effective dose arises from inhalation of 222Rn and its radioactive progeny. However, despite extensive knowledge of radiation risks gained through epidemiologic investigations and mechanistic considerations, the health effects of chronic low-level radiation exposure are still poorly understood. The present paper reviews the possible contribution of studies of populations living in high natural background radiation (HNBR) areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), including radon-prone areas, to low dose risk estimation. Much of the direct information about risk related to HNBR comes from case–control studies of radon and lung cancer, which provide convincing evidence of an association between long-term protracted radiation exposures in the general population and disease incidence. The success of these studies is mainly due to the careful organ dose reconstruction (with relatively high doses to the lung), and to the fact that large-scale collaborative studies have been conducted to maximise the statistical power and to ensure the systematic collection of information on potential confounding factors. In contrast, studies in other (non-radon) HNBR areas have provided little information, relying mainly on ecological designs and very rough effective dose categorisations. Recent steps taken in China and India to establish cohorts for follow-up and to conduct nested case–control studies may provide useful information about risks in the future, provided that careful organ dose reconstruction is possible and information is collected on potential confounding factors.

New public dose assessment of elevated natural radiation areas of Ramsar (Iran) for epidemiological studies

Abstract: The potential annual effective doses of the public in Ramsar and its elevated level natural radiation areas (ELNRA) from the external and internal exposures received indoors and outdoors were determined. This paper only reports the potential annual effective doses from the external exposure, the rate of which was measured in 1000 locations outdoors and in 800 locations indoors, 200 in ENLRA and 600 in low level natural radiation areas (LLNRA). An SPP2 Scintillometer, a Reuter-Stokes pressurized ionization chamber and a SAPOS system of an environmental early warning network were used for measuring the exposure rates. The distribution of the absorbed dose rates in air, indoors and outdoors, with their mean values were determined. The absorbed dose rates in the air outdoors range from 0.08 to 20 μGy h−1 with occasional higher values up to 100 μGy h−1 over some hot spots. The isodose and topological exposure rate maps of the region were drawn. The cosmic ray dose rate of 32 nGy h−1 was measured over the Caspian Sea using the pressurized ionization chamber. The absorbed dose rates in the air indoors range from 0.01 to 30 μGy h−1 with occasional higher values up to 105 μGy h−1 on the wall of one room in a house in Talesh Mahalleh. The topological map of the exposure rates over the wall is also reported. As expected, Talesh Mahalleh showed the highest potential effective public doses from terrestrial radiation. The potential annual effective doses of the public in ELNRA range from 0.6 to 131 mSv with a mean value of 6 mSv, and in LLNRA, these range from 0.6 to 1.5 mSv with a mean value of 0.7 mSv. The distributions of percent population in different annual effective dose intervals in Ramsar and its ELNRA were also obtained. The mean potential annual effective doses in ELNRA are about 10 times higher than those in ELNRA, but some individual effective doses are about 200 times higher than the mean of LLNRA. The results are reported and discussed.

Nuclear Tracks in Solids (Principles and Applications)

Abstract: (1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

Rare Earth Elements: Minerals, Mines, Magnets (and More)

Abstract: The rare earth elements (REEs) are all around us, not only in nature but in our everyday lives. They are in every car, computer, smartphone, energy-efficient fluorescent lamp, and color TV, as well as in lasers, lenses, ceramics, and more. Scientific applications of these elements range from tracing the provenance of magmas and sediments to studying body structures with magnetic resonance imaging. The realization that we need rare earths for so many applications, but that their supply is effectively restricted to several mining districts in China, has brought these elements to the headlines and created a critical-metals agenda. Here we introduce the REE family: their properties, minerals, practical uses, and deposits. Potential sources of these elements are diverse and abundant if we can overcome the technical challenges of rare earth mining and extraction in an environmentally and socially responsible way.

Cell cycle control, checkpoint mechanisms, and genotoxic stress.

Abstract: The ability of cells to maintain genomic integrity is vital for cell survival and proliferation. Lack of fidelity in DNA replication and maintenance can result in deleterious mutations leading to cell death or, in multicellular organisms, cancer. The purpose of this review is to discuss the known signal transduction pathways that regulate cell cycle progression and the mechanisms cells employ to insure DNA stability in the face of genotoxic stress. In particular, we focus on mammalian cell cycle checkpoint functions, their role in maintaining DNA stability during the cell cycle following exposure to genotoxic agents, and the gene products that act in checkpoint function signal transduction cascades. Key transitions in the cell cycle are regulated by the activities of various protein kinase complexes composed of cyclin and cyclin-dependent kinase (Cdk) molecules. Surveillance control mechanisms that check to ensure proper completion of early events and cellular integrity before initiation of subsequent events in cell cycle progression are referred to as cell cycle checkpoints and can generate a transient delay that provides the cell more time to repair damage before progressing to the next phase of the cycle. A variety of cellular responses are elicited that function in checkpoint signaling to inhibit cyclin/Cdk activities. These responses include the p53-dependent and p53-independent induction of Cdk inhibitors and the p53-independent inhibitory phosphorylation of Cdk molecules themselves. Eliciting proper G1, S, and G2 checkpoint responses to double-strand DNA breaks requires the function of the Ataxia telangiectasia mutated gene product. Several human heritable cancer-prone syndromes known to alter DNA stability have been found to have defects in checkpoint surveillance pathways. Exposures to several common sources of genotoxic stress, including oxidative stress, ionizing radiation, UV radiation, and the genotoxic compound benzo[a]pyrene, elicit cell cycle checkpoint responses that show both similarities and differences in their molecular signaling.

Human exposure to high natural background radiation: what can it teach us about radiation risks?

Abstract: Natural radiation is the major source of human exposure to ionising radiation, and its largest contributing component to effective dose arises from inhalation of 222Rn and its radioactive progeny. However, despite extensive knowledge of radiation risks gained through epidemiologic investigations and mechanistic considerations, the health effects of chronic low-level radiation exposure are still poorly understood. The present paper reviews the possible contribution of studies of populations living in high natural background radiation (HNBR) areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), including radon-prone areas, to low dose risk estimation. Much of the direct information about risk related to HNBR comes from case–control studies of radon and lung cancer, which provide convincing evidence of an association between long-term protracted radiation exposures in the general population and disease incidence. The success of these studies is mainly due to the careful organ dose reconstruction (with relatively high doses to the lung), and to the fact that large-scale collaborative studies have been conducted to maximise the statistical power and to ensure the systematic collection of information on potential confounding factors. In contrast, studies in other (non-radon) HNBR areas have provided little information, relying mainly on ecological designs and very rough effective dose categorisations. Recent steps taken in China and India to establish cohorts for follow-up and to conduct nested case–control studies may provide useful information about risks in the future, provided that careful organ dose reconstruction is possible and information is collected on potential confounding factors.

A method for describing the doses delivered by transmission x-ray computed tomography

Abstract: A method for describing the absorbed dose delivered by x-ray transmission computed tomography (CT) is proposed which provides a means to characterize the doses resulting from CT procedures consisting of a series of adjacent scans. The dose descriptor chosen is the average dose at several locations in the imaged volume of the central scan of the series. It is shown that this average dose, as defined, for locations in the central scan of the series can be obtained from the integral of the dose profile perpendicular to the scan plane at these same locations for a single scan. This method for estimating the average dose from a CT procedure has been evaluated as a function of the number of scans in the multiple scan procedure and location in the dosimetry phantom using single scan dose profiles obtained from five different types of CT systems. For the higher dose regions in the phantoms, the multiple scan dose descriptor derived from the single scan dose profiles overestimates the multiple scan average dose by no more than 10%, provided the procedure consists of at least eight scans.