Radiant energy – Invisible radiant energy responsive electric signalling – With radiant energy source
Reexamination Certificate
2001-10-10
2004-05-25
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With radiant energy source
C250S394000
Reexamination Certificate
active
06740887
ABSTRACT:
This invention is concerned with improvements in and relating to apparatus and methods for materials investigations. The invention is particularly, but not exclusively, concerned with investigating gamma ray emissions from materials. The invention is still more particularly, but not exclusively, concerned with correction techniques including the provision of more suitable transmission sources and an improved correction technique.
In a variety of situations it is necessary to investigate emissions from radioactive sources in or on materials to form a basis for a variety of subsequent decisions, actions or further considerations. The investigations of the sample may relate directly to the emission, for instance the emission source, or indirectly, for instance the consideration of associated non-emitters or emitters which are not directly measurable. The emissions of interest are in particular gamma ray emissions, but other emission forms may be considered additionally or alternatively.
Emission investigation is particularly important in waste evaluation cases. For a given waste sample it is desirable to be able to determine a variety of unknowns. The unknowns may include, but are not limited to, one or more of the level, type, constituents, nature and distribution of the emissions, emission sources, associated materials or associated factors.
As well as simply using the results obtained from the detectors, emission count rates for the radioactive materials in the sample under consideration, it is known to investigate to an extent the effects of the all the material in a sample, through their effect on the transmission of external emissions from an applied source through the sample to the detectors.
The applicant has determined that such simple sources are not suitable for transmission based investigation and correction at the full variety of energies and with the full variety of materials. As a consequence the effectiveness of the correction technique based on these investigations is impaired.
The present invention seeks to provide a more widely accurate transmission based correction, which is also simple and easy to use across a full spread of situations which are encountered in practice.
In addition the existing transmission based correction techniques only go part way to account for the variables which affect the detected counts for the sources of the sample itself and as a result the correction technique is not fully effective.
The present invention has amongst its aims the provision of a more accurate and thorough correction technique based on transmission correction and the manner in which it is employed.
According to a first aspect of the invention we provide a method of investigating radioactive sources in a sample, the method comprising detecting a portion of the emissions arising from the sample, and further comprising the provision of a radioactive generator, passing at least a portion of the emissions of the generator into the sample, detecting at least a portion of the emissions from the generator leaving the sample, the radioactive generator emissions being of at least a plurality of emission energies and at least two of those energies being detected.
Preferably the method further provides that the detected portion of the source emissions relate to a detected level for the sources in a sample, the detected level being corrected according to a correction method to give a corrected level for the sources in a sample, the process being repeated for one or more other samples.
Preferably the correction method employs measured transmission coefficients in determining the correction. The measured transmission coefficients, for one or more of the energies, most preferably all, may be provided according to the equation:
Trans. Coeff.
=
R
R
o
where R is the rate of detected photons with the sample in place, R
o
is the rate of photons which would be detected without the sample in place.
Preferably the density determined is used as a factor in the correction method. The density used in the correction method may be an averaged density from the determinations or a weighted average density from the determinations.
For correction of source emission energies corresponding to a generator energy preferably the measurement based correction factor is used. For correction of source emission energies not corresponding to a generator energy preferably the correction factor is based on the extrapolation of the correction factors based on the measurements.
The generator is preferably a single isotope. Preferably the emission energies extend across a substantial portion of the range of energies emitted from the sample. A substantial portion may be 50%, preferably 75%, more preferably 90% and ideally 100% of the sample energies range. The generator most preferably of all emits energies encompassing the range of energies emitted by the sample.
152
Eu is a particularly preferred generator. Preferably at least 5 energies from the source are detected and used, more preferably at least 8 energies are detected and used.
Preferably the portion of generator emissions detected have passed through the sample. Preferably the generator is provided on the opposing side of the sample to the detectors, most preferably in direct opposition.
One or more of the detectors for the sources may be used for detecting the generator emissions and/or vice-versa.
According to a second aspect of the invention we provide apparatus for investigating radioactive sources in a sample, the apparatus comprising:
one or more detectors for emissions from the sources, the detectors generating signals indicative of the emissions detected;
an investigating location into which the sample is introduced;
signal processing means for relating the detector signals to one or more characteristics of the sources;
a radioactive emission generator separate from the sample; and
one or more detectors for emissions from the radioactive generator leaving the sample;
wherein the radioactive generator emissions are of at least a plurality of energies and a least two of the plurality of energies are detected.
The source detectors and the generator detectors may be one and the same in the case of one or more or all of the detectors.
The second aspect of the invention may include any of the features, options and possibilities set out on the first aspect of the invention, including apparatus suitable for the implementation of the method steps detailed therein.
According to a third aspect of the invention we provide a method of investigating radioactive sources in a sample, the method comprising detecting a portion of the emissions arising from the sample at an energy, the detected portion relating to a detected level, the detected level being corrected according to a correction method to give a corrected level, at that energy, the correction method including:
the provision of an emission generator, passing at least a portion of the emissions of the generator into the sample, detecting at least a portion of the emissions from the generator leaving the sample, and determining a value for a first relationship between the two portions;
calculating a value for a relationship of equivalent type to the first, the calculation being based on functions of an element's absorption of emissions and the amount of that element potentially encountered by emissions, for one or more elements;
adjusting one or more variables/functions in the calculated relationship to reduce the difference between the value of the determined relationship and the value of the calculated relationship for the sample at a plurality of the energies of emissions from the generator; and
obtaining the values of the calculated relationship functions from the reduction and calculating the calculated relationship from those factors at the sample source emission energy requiring correction and correcting the detected level using those values.
Preferably the generator emissions are of at least two emission energies, ideally multi-energy emissions are provided, and/or with at least two of tho
Parvin Daniel Francis
Ronaldson John Paul
Beyer Weaver & Thomas LLP
British Nuclear Fuels PLC
Gabor Otilia
Hannaher Constantine
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