M.I. Abbas - Alexandria University - EGYPT.

Professor of Radiation Physics Head of Radiation Physics laboratory ANS RPSD 2014 GAMMA-RAY DETECTORS EFFICIENCY CALCULATION INCLUDING SELF-ABSORPTION FOR VOLUMETRIC SOURCES Mahmoud I. Abbas Professor of Radiation Physics Head of Radiation Physics laboratory Physics department, Faculty of Science, Alexandria University, 21511 Alexandria, Egypt mabbas@physicist.net mahmoud.abbas@alexu.edu.eg M.I. Abbas - Alexandria University - EGYPT.

Detector with High EFFICIENCY An important reason to be proactive Detector with High EFFICIENCY You need M.I. Abbas - Alexandria University - EGYPT.

M.I. Abbas - Alexandria University - EGYPT. Why ? To determine the activity of an unknown radioactive source or radioactive waste. How ? By using Selim and Abbas Direct Analytical Method for calculating the absolute efficiency of NaI(Tl) and HPGe detectors. M.I. Abbas - Alexandria University - EGYPT.

  Outlines  Applications of Gamma Ray Spectroscopy.  Interaction of photons with matter.  Types of the detector efficiencies.  Method of the detector efficiencies determination.  The cylindrical detector efficiency.  The results and conclusions. 

Applications of Gamma ray Spectroscopy In radiation physics, measuring and studying the spectra of gamma ray photons emitted from radioisotopes are very important and have many applications: 1) Identification of the radioactive isotopes. 2) Study of the nuclear structure. 3) Measuring the absorbed doses. 4) Determination of the interaction cross section. ◘ To get a spectrum with high accuracy we must have ◘ 1) Detection and recording system “ method of measurements “. 2) Good values for the detector efficiencies, which needed to calculate the activity.

Interaction of photons with matter ■ The most important types of interaction ■ 1) Photoelectric absorption ()

Interaction of photons with matter ■ The most important types of interaction ■ 2) Compton scattering (σ)

µ=  + σ + k Interaction of photons with matter ■ The most important types of interaction ■ 3) Pair production (k) gamma 0.511 MeV Incident gamma E > 1.022 MeV gamma 0.511 MeV µ=  + σ + k The Total Attenuation Coefficients

Types of the detector efficiency 1) The geometrical efficiency (εg ). “The ratio between the number of photons that are entered the detector and the number of photons that are emitted from the source”. 2) The intrinsic efficiency (εi ) “The ratio between the number of photons that are recorded in the detector and the number of photons that are entered the detector”. 3) The total efficiency (εT ). “The ratio between the number of photons that are recorded in the detector with any possible energy during a certain time interval and the number of photons that are emitted by the source during the same time interval”.  

◙ There are different methods can be used such as ◙ Method of the detector efficiencies determination ◙ There are different methods can be used such as ◙  Experimental method. ♦ The easiest and most direct method. ♦ Depends on calibration curves (hυ- ε graphs) or tabulated in tables. ♦ The standard source activity must be know at every calibration. ♦ Source under investigation must have the same geometrical with standard source  The semi-empirical method. ♦ Achieved by fitting the basic data points (experimental) to various formulas.empirical ♦ The disadvantages. ◘ Depends on the interpolation method. ◘ Large number of parameter with hard values. ◘ Has a big error. ◘ Used in a small range of energy only.

The Direct mathematical method  Monte Carlo method. ♦ Simulation the history of great number of individual photons passing through the detector according to distribution function. ♦ The disadvantages. ◘ Depends on random number and probability theory. ◘ Follow large number of photon histories. ◘ A statistical error must calculate. ◘ To get a good probability the number of history must be large.  The present method.   The Direct mathematical method Selim and Abbas Method

Transmitted photons without interaction I0 e-μ d Transmitted photons without interaction Incident I0 photons The absorbed part = I0 - I = I0( 1 - e-µ d ). Absorption probability p = (I0-I)/I0 , is given by: By using this fact the efficiency can be calculated by:

Point source

M.I. Abbas - Alexandria University - EGYPT. The efficiency of a cylindrical detector, with radius R and height L, arising from a point source, (see the previous figure), is given by: i = 1 and 2 M.I. Abbas - Alexandria University - EGYPT.

Cylindrical source H ho L

M.I. Abbas - Alexandria University - EGYPT. The efficiency of a cylindrical detector, with radius R and height L, arising from a cylindrical source, with radius S (S<R) and height H (see the previous figure), is given by: M.I. Abbas - Alexandria University - EGYPT.

M.I. Abbas - Alexandria University - EGYPT. The total and full-energy peak efficiencies are calculated using the present expressions, and compared with those obtained by experimental measurement. M.I. Abbas - Alexandria University - EGYPT.

M.I. Abbas - Alexandria University - EGYPT. Conclusions The previous figure shows the calculated and measured photopeak efficiencies of a HPGe detector using radionuclides aqueous sources placed in a cylindrical beaker, it can be clearly seen that there is a good agreement between the measured and the calculated values. M.I. Abbas - Alexandria University - EGYPT.

M.I. Abbas - Alexandria University - EGYPT. Acknowledgement I would like to thank the Authorities of the Center for Ionizing Radiation Metrology, National Physical Laboratory (NPL), UK, for making it possible to carry out the measurements M.I. Abbas - Alexandria University - EGYPT.

M.I. Abbas - Alexandria University - EGYPT. Thanks for Listening M.I. Abbas - Alexandria University - EGYPT.