for example assume that i have three equal weighted quantities each one is 1 g of radioactive U-238 and then mix them with three different matrices i.e different elemental composition but finally all matrices after mix with the 1 g U-238 is having equal densities.then measure every sample with HPGe detector.
the question : is this correct method to measure the effect of different composition matrices on measured radioactivity.?
You may put each mixture into a sample vial with the same shape before measuring with HPGe detector.
sure to neglect geometry effect on measurements and hence i can say the differences in results obtained refer to the different matrix composition??
Different geometry of samples will effect the counting efficiency of detector
yes I understand that but here I am talking about how to study the effects of different matrix composition on the measured activity concentration when using HPGe detector provided that minimizing other factors effects on measurement like geometry........etc.
Omar,
Let me see if I understood your question.
Your are talking about shielding of a matrix used to immobilize a quantity of a radioactive material, correct?
If I am right about your question, you need to determine to each material the total mass absortion coefficient (in cm2/g) of the matrix material. Then you will discover how much radiation this matrix shield based on the density and "thickness"
I hope to help you.
Hi, Omar,
As it is already said, the matrix itself doesn't mattter. The measurement at a certain distance of the source depends only on the density and on the thickness of the source. Of course the source's geometry and also the source's distance must also be taken into account. For instance, if you have 3 sources of 1 liter each and you count them individually, one after the other, if you mix them, the final volume will be 3 liters, and the measurement of this mix 3 liters will be lower than the sum of each one individually, because the source's geometry changed and the distance too.
hi Jorge hi Gilberto thanks for interest
but let us assume that we have three different compositions solid samples with in each one the same amount of radioactive materials and finally the three samples measuring on HPGe detector with same geometry and same counting time what is the expected results due to differences in matrix compositions!?
If you measure with the HPGe samples with the same activity, same volume, same shape and same density, then indeed you should expect less counts when the average atomic number of the matrix is higher, because of more photoabsorption by the matrix. The amplitude of this effect will however strongly depend on the thickness and density of the matrix and on the energy of the gamma line used.
Omar,
Assuming all you said, only material density will impact in the results.
Look the absorber formulation:
I = I0*exp(-μ*X), where:
I0 is the counting before absorber insertion
I is the counting after absorber insertion
The half-value layer is when intensity with absorber insertion is half of without it.
So, you can determine μ in function of X. X is dependent only the thickness and density. Then, if you use same thickness, couting time and geometry, it will depend only the material density
I hope to help you.
Omar,
All analytical methods are extremely dependent on the sample's matrix. It is a normal lab's procedure to calibrate equipment according to the sample's matrix you have. As soon as another matrix must be analyzed you must re-calibrate your equipment with a standard consisting of the same matrix.
Some methods are more dependent on the matrix some are less dependent.
If you have 3 different samples each one having its own different matrix, you cannot mix them. You must analyze them each one separately. That's way background bases are probably different for each one. If they have different densities the response, the radiation that reaches the detector, will be attenuated differently as well.
But you can make a simple experiment. Analyze them separately. Then you mix them and see how different is the result.
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