bad approximation of composition materials
Chloé Largeron
Dear Pyne-developers,
I have encountered an issue with using the Material object of pyne.
I have constructed a dictionary with composition of 12 elements where one is really high = 0.99970 and the others are really low = 0.00001 or 0.00005
The sum of these elements is not exactly one (the sum is equal to 1.0000800000000003)
I don’t provide to you the exactitude of my composition since I might be not allowed to.
Then when I construct it with the Material object with pyne (which is normalized) I obtain an high approximation of the really high elements (= 0.999620030397568) and the lowest elements = 9.99920006399488e-06
My dictionary has the following values (please change XX by an element) :
{'XXhigh': 0.9997, 'XX': 2e-05, 'XX': 2e-05, 'XX': 2e-05, 'XX': 0.0002, 'XX': 2e-05, 'XX': 1e-05, 'XX': 5e-05, 'XX': 1e-05, 'XX': 1e-05, 'XX': 1e-05, 'XX': 1e-05}
The composition I obtain with the Material object is :
{XX: 9.99920006399488e-06, XX: 9.99920006399488e-06, XX: 9.99920006399488e-06, XX: 9.99920006399488e-06, XX: 1.999840012798976e-05, XX: 1.999840012798976e-05, XX: 1.999840012798976e-05, XX: 1.999840012798976e-05, XX: 9.99920006399488e-06, XX: 4.99960003199744e-05, XXhigh: 0.9996200303975682, XX: 0.0001999840012798976}
The atomic fraction of each element has changed with using the material object, the difference between 0.9997 and 0.99962 is not acceptable to my study.
How could I fix this problem ? How can you explain such differences ?
Thank you,
Best regards,
Chloé Largeron
Research engineer
Paul Wilson
Hello Chloé,
I think what you are seeing is the correct behavior. You have defined your material with atom fractions that sum to a number greater than 1, namely 1.0000800000000003. PyNE normalizes these material fractions to 1 by dividing all these values by this total: 0.9997/1.0000800000000003 = 0.99962
Can you clarify what you expect? Perhaps there is another way to use PyNE to meet your expecations.
Paul
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