Exposure Rate Calculations曝光率的计算.pptVIP

ACADs (08-006) Covered Keywords Line source, disk source, 6CEN Description Supporting Material 3.3.1.10 4.12.2 Exposure Rate Calculations In order to get an idea of what the exposure rate is from a gamma emitting radionuclide one needs certain information Activity Energy Efficiency Do all gammas that are emitted from the source come in your direction? Dose In order to determine the dose given to a space at a certain distance one needs to determine two things Total number of gamma rays coming off of the source Total surface area of a sphere of radius of that distance Does one need the area of the object that is irradiated? Activity to dose Gamma flux D= 3.7 x 1010 C E 4π r2 Top is total number of photons Bottom is total surface area of sphere with radius r Units are G/sec/cm 2 Convert to dose using chart that relates gamma energy to conversion factor Activity to Dose Main parameters that determine dose from source is g/d and energy of gamma If one were to use nuclide specific information for each radionuclide and perform the calculations The only unknown would then be the activity of the source Can simplify equation Short formula Pre calculated conversion factors for activity to exposure rate conversion. (mR/hr calculated at 1 foot) Cs-137 Multiply # of mCi X 3.4 Ir-192 Multiply # of mCi X 6 Ra-226 Multiply # of mCi X 8.8 Co-60 Multiply # of mCi X 14.5 Am-241 Multiply # of mCi X 0.15 Dose Rate Can calculate dose rate from any gamma emitting radionuclide if you have Activity Gamma ray emission rate Energy of gamma ray Dose Rate D = 6CEN D= exposure rate at 1 foot in R/hr C= number of Ci E= energy of emitted gamma ray in MeV N= number of gammas per disintegration Good for any gamma emitting radionuclide Dose Rate Co-60 Cs-137 Am-241 Distance For unshielded point sources exposure is inversely proportional to the square of the distance I = Io (r0/r1) 2 or I1 r21= I0 r20 I = intensity at point 2, Io = intensity at po