Later, reports of incidents of nuclear material occurred in Germany, the Czech Republic, Hungary and other central European countries.
Nuclear forensics relies on making these determinations through measurable parameters including, but not limited to chemical impurities, isotopic composition, microscopic appearance, and microstructure.
Identification of these parameters is an ongoing area of research, however, data interpretation also relies on the availability of reference information and on knowledge of the fuel cell operations.
In 1944, the US Air Force made the first attempts to detect fissiogenic 133Xe in the atmosphere in order to indicate the production of plutonium through the irradiation of uranium and chemical reprocessing in an effort to gather intelligence on the status of the German nuclear program.
When scientific laboratories outside the weapons and intelligence community took an interest in this methodology was when the term "Nuclear Forensics" was coined.
Essentially, if a nuclear material has been put through a refinement process to remove the daughter species, the time elapsed since purification can be "back-calculated" using radiochemical separation techniques in conjunction with analytical measurement of the existing parent-daughter ratios.
This strategy may not apply when the parent-daughter pair achieve secular equilibrium very rapidly or when the half-life of the daughter nuclide is significantly shorter than the time that has elapsed since purification of the nuclear material, e.g. 237Np/233Pa.
To avoid this, freshly prepared samples as well as complementary analysis methods are used for confident nuclear materials characterization.
[10] Chemical separation techniques are frequently utilized in nuclear forensics as a method of reducing the interferences and to facilitate the measurement of low level radionuclides.
Then the retained species can be eluted from the column by conversion to a neutral complex, typically by changing the mobile phase passed through the resin bed.
Speeding up the flow of the mobile phase tends to introduce problems such as impurities and jeopardize future investigations.
Actinide isolation by co-precipitation is frequently used for samples of relatively large volumes to concentrate analytes and remove interferences.
However, for longer half-lives, inorganic mass spec is a powerful means of carrying out elemental analysis and determining isotopic relationships.
Counting techniques of α,β,γ or neutron can be used as approaches for the analysis of nuclear forensic materials that emit decay species.
The advantages of alpha-particle spectroscopy include relatively inexpensive equipment costs, low backgrounds, high selectivity, and good throughput capabilities with the use of multi-chamber systems.
Also, spectral interferences or artifacts from extensive preparation prior to counting, to minimize this high purity acids are needed.
For nuclear forensic purposes it is essential that the mass spectrometry offers excellent resolution in order to distinguish between similar analytes, e.g. 235U and 236U.
In thermal ionization mass spectrometry, small quantities of highly purified analyte are deposited onto a clean metal filament.
A portion of the analyte will be ionized by the filament and then are directed down the flight tube and separated based on mass to charge ratios.
SIMS is a micro-analytical technique valuable for three-dimensional analysis of a materials elemental composition and isotopic ratios.
This method can be utilized in characterization of bulk materials with a detection limit in the low parts per billion (10−9 or ng/g) range.
In contrast to previously mentioned analysis techniques, these approaches have received relatively low attention in recent years in terms of novel advancement, and, typically, require greater quantities of sample.
The scanning electron microscope can provide images of an object's surface at high magnification with a resolution on the order of nanometers.
Neutron activation analysis is a powerful non-destructive method of analyzing elements of mid to high atomic number.
The advantages of this technique include multi-element analysis, excellent sensitivity, and high selectivity, and no time-consuming separation procedures.
X-Ray absorption spectroscopy (XAS) has been demonstrated as a technique for nuclear forensic investigations involving uranium speciation.
This spectroscopic method, when coupled with X-Ray diffraction (XRD), would be of most benefit to complex nuclear forensic investigations involving species of different oxidation states.
This method was developed to replace subjective colour reporting, such as by-eye observations, with quantitative RGB and HSV values.
The method has previously been demonstrated on the thermal treatment of uranyl peroxide powders, which yield distinctive yellow to brown hues.
[13] Hence, this method is noted as particularly useful in determining thermal processing history, especially where colour changes occur in uranium compounds of various oxidation states.