ABSTRACT
Objective:To investigate the application of therapeutic grade ionization chamber to rapid measurement of short pulsed and high-dose-rate X-ray.Methods:The half-value layer of pulsed X-ray caused by an electron accelerator was measured by interpolation method and its equivalent energy was estimated. The cumulative doses from a certain amount of pulsed radiation at different distances in the same direction around the equipment were compared using the therapeutic grade ionization chamber and thermoluminescence measurement method . The relationship between the measurement result by using ionization chamber dosimeter and the distances away from source was analyzed. The cumulative doses from a certain amount of pulsed radiation at the same location at different frequencies were compared.Results:In working condition, 100 pulses of radiation were received accumulatively at 1 to 12 meters away from the outer wall of the equipment. The range of air Kerma was 0.08-9.65 mGy measured by using thermoluminescence dometers and 0.08 - 9.85 mGy using the ionization chamber dosimeters, respectively. The difference between both is within 10%. At different frequencies (1-10 Hz), there was no significant difference in X-ray air Kerma from 100 pulses measured by ionization chamber dosimeter at 2 m away from the front of the equipment ( P>0.05). Conclusions:The therapeutic grade ionization chamber dosimeter can be used for the rapid measurement of short pulsed X-ray radiation dose in the range of dose rates and pulse frequencies involved in the experimental accelerator device.
ABSTRACT
Objective To develop a promising type of radiation dosimeter based on doped hydroxyapatite,and to study the stability of dosimetric characteristics indepth.Methods The samples prepared by stereotyping techniques were stored under different temperatures,humidity and illumination conditions after 60Co γ-ray irradiation.Electron spin resonance (ESR) technique was used to quantitatively measure the radiation-induced free radical signal.Results The signal change was less than 3% when the dosimeter was preserved at 4℃ or room temperature within 3 months in the experiment.At 40℃,the signal changed by about 13%,but at room temperature with the humidity less than 36%,the signal changed less than 2%.The change rose to about 8% when humidity was 76%.However,no significant decay of signal strength occurred at relatively high temperatures and under high humidity conditions.When the samples were stored under average illumination of 1600 lux or in a light-resistant container,the signal changes were less than 3.8% or 3.4% respectively.Long-term stability inspection at room temperature suggested a signal change within 4.8%.Conclusion The dosimetric properties of the material don't change significantly below room temperature in a natural environment and exhibit good stability over long-term storage.The free radical signal is not influenced drastically by relatively strong light exposure.However,a high temperature or a highly humid environment may have some effect on the measurement process,which should be taken into consideration in further applications.
ABSTRACT
Objective To calculate the electric field intensity and transmembrane voltage of spherical cells and ellipsoi -dal red blood cells ( RBC) in an extremely low frequency electromagnetic field .Through this calculation , we can provide reference to the search for interaction targets and mechanics between the extremely low frequency electromagnetic field and organisms.Methods The Finite Element Method was used in the numerical computation for the spherical cell model and the ellipsoidal RBC model .Results The electric field intensity of the two types of cells on the cellular membrane was both significantly higher than the applied electric field strength , and the values of the induced field strength and transmembrane voltage varied with the direction of the electric field periodically .Conclusion The cell shape and direction of the applied electric field are not the main determinants of the cellular membrane electric field intensity and the transmembrane voltage compared with electromagnetic parameters .The distribution of the electric field intensity and transmembrane voltage are re-lated to the direction of the applied electric field.