Biomedical subjects

M Voytchev

Publications and source records attributed to M Voytchev.

5 recordsLinked to original sources

PubMed2002

Thermoluminescence measurements of neutron dose around a medical linac.

The photoncutron ambient dose around a 18 MV medical electron lineal accelerator has been measured with LiF:Mg,Ti chips of 3 x 3 x 1 mm inside moderating spheres. During the measurements a water phantom was irradiated in a field of 40 x 40 cm2. Two methods have been considered for comparison. In the first, a TLD-600/TLD-700 pair at the centre of a 25 cm diameter paraffine sphere was used, with the system behaving as a rem meter. In the second method, TLD-600/TLD-700 pairs, bare and at the centre of 7.6, 12.7, 20.3, 25.4, and 30.5 cm diameter polyethylene Bonner spheres were used to obtain the neutron spectrum. This was unfolded using the BUNKIUT code with the SPUNIT algorithm and the UTA4 and ARKI response functions. The neutron dose was followed by multiplying the unfolded neutron spectrum by the ambient dose equivalent to neutron fluence conversion factors. Both methods result in 0.5 mSv x Gy(-1) m away from the isocentre.

Electrons↗

PubMed2002

Response components of LiF:Mg,Ti around a moderated Am-Be neutron source.

The responses of TLD-1010, TLD-700 and TLD-600 thermoluminescence dosemeters to the radiation field inside a water tank enclosing an isotopic 241Am-Be neutron source are analysed. Separate contributions coming from thermal neutrons, neutrons with energies above thermal and gamma rays to the total response of the three types of TLD are obtained. This is accomplished by assuming that the gamma responses for materials with different 6Li enrichments are identical and that the neutron response of TLD-700 is negligible compared to TLD-100 and TLD-600. The last assumption is tested by Monte Carlo simulations of the neutron energy spectrum at the points where the TLDs are irradiated.

Americium↗

PubMed2001

The use of silicon photodiodes for radon and progeny measurements.

Reduced cost, high quantum efficiency and very good detection characteristics of PIN silicon photodiodes made possible their utilization for alpha particles detection. This paper presents different studies and applications of this type of detector for qualification and quantification of radon and its progeny in laboratory and in the field. Since photodiodes are sensitive to environmental electromagnetic fields, protecting cells were adapted for use around the detector. A small three-channel (2-5.5 MeV; 5.5-6.5 MeV; 6.5-8.2 MeV) portable alpha counter was developed that allows the determination of the radon concentration and the radon exhalation rate. Numerous field applications were conducted in different conditions (uranium waste storage, dwellings, etc.) where this simple and inexpensive instrumentation demonstrated very good performance, reliability, and easiness of operation while measuring radon concentrations from 50-100 Bq m(-3) to several MBq m(-3).

Equipment Design↗

PubMed2001

Simulation of the radon and radon progeny detection by silicon photodiodes.

The use of silicon photodiodes for field radon measurements requires the utilization of measuring cells for protection against environmental electromagnetic fields. It is very important to study and optimize the impact of geometry conditions (dimensions of the measuring cell) on the photodiode detection efficiency that can be reduced more than 10-30 times. Two models (for volume-distributed nuclides around the detector and for radon progeny deposited on the diode surface radon progeny) were applied for simulation of the photodiode detection in measuring cells of different sizes. Their use allows an optimal choice of the most appropriate cell regarding the measurement conditions. Thus, for soil gas measurements cells we use a cell of 3.6 cm in diameter by 20 cm in height; for determination of the radon exhalation rate we use a cell of 16 cm in diameter by 14 cm in height; and for measurements in dwellings and large spaces we use cells larger than 20 cm and lower than 4 cm.

Cell Size↗

PubMedDate not supplied

Radon emanation measurements using silicon photodiode detectors.

Driven by the global concern about radon hazards, a wide variety of methods to measure radon and its decay products have been developed. Pin silicon photodiodes are increasingly applied in this field, their main advantages being high detection efficiency for alpha particles and low cost. In this paper, we present a system to determine the emanation factor for 222Rn from porous material based on a pin photodiode. This equipment is valid both for field and laboratory measurements, allowing to monitor the external emanation conditions by means of temperature, humidity and pressure sensors. To illustrate the capabilities of the system, we present two case studies of samples with high and low 226Ra content. The activity of this radionuclide in the samples had been previously determined by gamma-ray spectrometry.

Electrochemistry↗