Analysis of materials containing radioactive sources
AssigneeBritish Nuclear Fuels plc
InventorsJohn Thomas Caldwell, Stephanie Ann Jones, Matthew Robert Newell
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Abstract
The invention provides a technique for correcting gamma ray intensities detected to account for variation in attenuation effects with energy. The corrected intensity values enable more accurate isotopic analysis to be conducted and render such techniques applicable to low level emission cases. The technique is particularly useful in investigate waste materials with a gamma emitting content which needs to be determined. The attenuation is corrected for using a bi-modal function to account for the attenuation effects arising from low and high atomic mass components of the material in which the emitters are present.
Claims27
A method for investigating the level of one or more gamma emitting materials in a sample, the method comprising:
- obtaining an intensity signal at a plurality of gamma ray energies, the plurality of energies including a plurality of energies characteristic of an isotope, the intensity at the plurality of energies for the isotope being corrected for variation in attenuation with energy;
- and
- calculating levels for the isotope and/or one or more other isotopes from the corrected intensities for the plurality of energies for the isotope.
A method for investigating the level of one or more gamma emitting materials in a sample, the method comprising:
- obtaining an intensity signal at a first gamma ray energy, the intensity at the first energy being corrected for variation in attenuation with energy;
- obtaining an intensity signal at a second gamma ray energy, the intensity at the second energy being corrected for variation in attenuation with energy;
- the first and second energies being energies characteristic of a first isotope;
- and
- calculating levels for the first isotope and/or one or more other isotopes from the corrected intensities for the first energy and second energy.
A method for investigating the level of one or more gamma emitting materials in a sample, the method comprising:
- obtaining an intensity signal at a first gamma ray energy, the intensity of the first energy being corrected for variation in attenuation with energy, calculating an apparent isotope mass for the first energy;
- obtaining an intensity signal at a second gamma ray energy, the intensity of the second energy being corrected for variation in attenuation with energy, calculating an apparent isotope mass for the second energy;
- combining the first energy apparent isotopic mass and second energy apparent isotopic mass in a weighted manner to give a first and second energy apparent isotopic mass combination;
- obtaining an intensity signal at a further gamma ray energy, the intensity at the further energy being corrected for variation in attenuation with energy, calculating an apparent isotopic mass for the further energy;
- obtaining an intensity signal at a still further gamma ray energy, the intensity at the still further energy being corrected for variation in attenuation with energy, calculating an apparent isotopic mass for the still further energy;
- combining the further energy apparent isotopic mass and still further energy apparent isotopic mass in a weighted manner to give a further and still further energy apparent isotopic mass combination;
- the correction for variation in attenuation with energy involving a factor, the factor having a different value for the first and second energies to the value used for the further and still further energies;
- and
- comparing the standard deviation for the first and second energy apparent isotopic mass combination with the standard deviation of the further and still further energy apparent isotopic mass combination;
- the combination giving the lowest standard deviation giving the values for the factor used to correct for variation in attenuation with energy to be used in correcting intensities at other gamma ray energies;
- the ratio between pairs of corrected energies of an isotope being used to calculate the level of that isotope in the sample.
Dependencies are inferred from the claim text.