احمد رمضانی مقدم

Having a portable and accessible radiation monitoring tool for members of the society, especially when faced with radiation caused by unwanted nuclear accidents, can provide a solution for radiation exposure monitoring. The monitoring is based on the sensitivity of CCD and CMOS semiconductor of smart mobiles to ionizing radiations. After receiving ionizing radiation such as gamma and X-rays, these sensors can receive the incident beam energy as a result of processes such as the photoelectric phenomenon and create charge carriers by creating ionization in the semiconductor medium of the sensor. The current resulting from the collection of charge carriers will result in the recording of bright (irradiated) and dark (unirradiated) spots on the camera sensor. Measuring the density of bright and dark points in the recorded images provides the possibility of estimating the amount of radiation exposure. In this research, four quality cameras and different brands were selected and dosimetry process for two sources of gamma radiation 60Co and 137Cs have been investigated.  The ratio of the total area of bright spots to the number of illuminated pixels per unit of time, which is proportional to the received dose, was measured and the calibration coefficient was determined for each camera. In the measurements made, the effect of time of death, resolution, stability and reproducibility have been checked and the necessary corrections have been applied. The obtained results show that for all the cameras used, there is a linear relationship between the recorded results and the received dose.

Melatonin as a compound made by photosynthetic organizers protects them against many environmental stresses. Modulating mechanisms of melatonin, as a protector are not well known in early eukaryotes, such as algae. In this research, the effect of melatonin pre-treatment on evaluating Chlorella vulgaris resistance to gamma ionizing radiation was investigated. The results showed that 100 µM concentrations of melatonin had a significant increase in the growth of algal cell and activity of the ascorbate peroxidase enzyme as one of the components of the enzymatic antioxidant system.

Melatonin has important roles in many growth and stress-related responsive processes in plants and algae. In this study, the mediating role of 100 and 500 µM melatonin on photosynthetic pigments and non-enzymatic antioxidant responses of microalga, Chlorella vulgaris to gamma irradiation stress has been studied. The result showed that the alga treated with 100 µM had a stable amount of chlorophyll and a more stability of cell membrane under gamma stress. It was concluded that although melatonin could increase resistance of alga to gamma by strengthen non-enzymatic antioxidant system like more production of proline, however this resistance probably further be related to enzymatic antioxidant system.

In this work investigated the determination of Selenium in wheat of Kashan's people's meal, via neutron activation analysis method (NNA) in “The Miniature Neutron Source Reactor” section. The γ transition produced in reaction of the neutron capture 77Se (n, γ) (T1/2= 17.4 s) was used to determine the concentration of Selenium, due to the rapid transfer of samples from the reactor. In this respect, we have first measured and compared with the available standards (B06Wheat Flour NBS–1567a, B12 and Hard Red Spring Wheat Flour RM – 8437, B18 Bovine Liver NIST – 1577b). Our obtained results show the selenium concentration in wheat samples varied from

Knowing patient exact dose during radiological activities is considered as one of the main principles to decrease radiation-induced dangers which are not really necessary and affect a great deal of people. In this respect, in recent years many extensive studies have been done on types of photodiodes and production of X-ray detectors using semiconductor elements. Since these elements are not very expensive and are too small in size and we can gain information of received dose immediately and without wasting time, they are mostly used. We aim to design a dosimeter using semiconductor elements for X-ray diagnostic radiation dosimetry. We used a typical silicon diode. Also, a stable circuit was applied to detect diagnostic X-ray radiations. To determine logical correlation between the electronic behavior of PIN sensor and specific parameters of X-ray (KV, mA.S), the designed circuit and calibrated ionization dosimeter were simultaneously irradiated by the diagnostic X-ray radiation with different energies and intensities. Finally, signal behavior was converted to digital amounts by the designed circuit. The amounts were then compared with received dose as recorded by ionization dosimetry. Results of the designed dosimetry behavior and ionization dosimetry simultaneously showed that the designed dosimetry responses are rather linear in different radiations whereas responses of the dosimetry under study is linear in low voltages while in high voltages no specific linear relation was found. It seems that used photodiode due to its availability, and low cost can be used as a dosimeter to measure diagnostic x-ray radiations in low energies.

Precise measurement of void coefficient in two phase flow is one of important parameters in thermal hydraulic parameters such as average density, two phase flow pressure drop and two phase flow pattern. In this study the void coefficient has been correlated experimentally based on attenuation coefficient gamma ray emitted form 137Cs source passing a rectangular channel. The average void fraction was reasonably measured for a two-phase flow in the rectangular channel

The ionizing radiations are able to make either a permanent or temporarily damage in the electronic circuits. The temporary effects during irradiation can be used to detect the ionizing radiation. In this study a diode in reverse bias has been used to investigate the effects of ionization radiation on semiconductors. The variation of reverse current of diode has been monitored due to interaction of gamma with semiconductor material. The commercially available diode N4001 was used in serial connection with resistant. Results show the major effect of irradiation on diodes is the increase in reverse current. The increase in reverse bias current is linked to the creation of mid-gap states. It is possible to detect the gamma radiation using a simple diode circuit in reverse bias. Thus, a silicon diode can be thought of as a solid-state equivalent to an ionization-chamber radiation detector.