Is there a good reason why one should do alpha spectrometry when one considers its inherent problems?
- Less than 10% of all known nuclides decay by alpha particle emission
- The alpha particle is very big and heavy and therefore it looses energy very easily in interactions with atoms; its range in air is just a few centimeters. Therefore, in high-resolution alpha spectrometry one needs extremely thin samples (<1 µg/cm^2)
- The energy of most alpha particles from nuclear decay is between 3 MeV and 8 MeV. Considering a good resolution of 20 keV (FWHM) for an alpha peak the dynamic range in alpha spectrometry is small
YES, because alpha spectrometry is an extremely sensitive analytical tool
Taking a set-up with high efficiency of 40% (for example a Frisch Grid ionisation chamber) and assuming counting time of 1 hour one will measure:
|From 100 µg of Th-232 (T1/2 = 1.45E10 years)||590 counts|
|From 1 ng of Ra-226 (T1/2 = 1600 years)||53280 counts|
|From 1 pg of Po-210 (T1/2 = 22 years)||3875 counts|
In a clean set-up one has very few background counts, or the background countrate is well determined and can be considered, so alpha particle spectrometry provides
- extremely high sensitivity
- extremely low detection limits
- extremely specific and clear analyses
Alpha particle spectrometry is a very useful analytical technique
High resolution spectrometry
The following selection of fields using high resolution alpha particle spectrometry is by no means complete but rather shows the wide range of potential applications for this type of nuclear measurement.
Education and Training
A combination of theoretical lectures on alpha particle spectrometry and hands-on experience in various fields such as sample preparation, spectrum measurement and spectrum analysis is probably the best method to generate understanding in many fields of natural sciences such as physics, analog and digital electronics, spectrometric principles as well as the analytical chemistry of element separation.
Continuous supervision of drinking water, both from the surface and deep well sources, for its contents of radon and (more important) of radium or uranium is necessary to make sure that the water is suitable for daily consumption of man.
Federal and private institutions perform continuous measurement of foodstuff and raw materials in order to prevent distribution of radioactive contamination after radiological accidents or through improper production methods.
Measurement of alpha particle emission from natural sources such as top soil, surface water and stream sediments, or U/Th contents in quarry material serves to assure agreement with regulation limits. Quantification of U and Th and progeny in granite, clay, fertilizer or building materials is also important.
Radioactive species decaying by alpha emission are used in various fields of research in medicine, geology, material sciences and technology. There are also applications in forensic sciences.
Measurement of alpha activities associated with nuclear material for energy production (i.e. from mining, production, storage, reprocessing, disposal of material from military and civil origin) is an essential part of safety regulations. These measurements are less frequently made on the radioactive material itself but definitively in the surrounding environment.
Moreover, there is pollution control in areas of former open nuclear weapons tests as well as in warzones where U-enforced shells had been used.
Nuclear reaction studies
Products from a number of nuclear reactions decay by alpha emission and are therefore assayed by alpha spectrometry. Special detectors may be used in these surveys where one measures the energy of the alpha particle and at the same time the location where the alpha decay has taken place.
The presence and distribution of naturally occuring radioactive elements uranium and thorium and their progeny (NORM) is an essential tool in geochemical investigations and data systematics. The question of uranium/radium disequilibrium or the washout of Pb-210/Po-210 through rainfall and its concurrent sedimentation is also of high interest.
Process water in NPP
Measurement of alpha activities in process water from nuclear power plants is an effective method of monitoring the health status of the plant and its components.
Low resolution spectrometry
The following selection of fields where low resolution alpha particle spectrometry can play an important role is by no means complete but it rather shows the wide range of potential applications for this type of nuclear measurement.
The term “resolution” in alpha spectrometry, i.e. the FWHM of peaks, is primarily determined by the thickness of the source. “High resolution spectrometry” refers to measurement from samples that have been produced by element separation through chemistry, cleaning and subsequent generation of a very thin deposit. In contrast, low resolution samples rather stem from typical in-situ production where sample material has been ground, ashed, evaporated or not treated at all.
Measurement of alpha particle emission from natural sources such as top soil, surface water and stream sediments, or U/Th contents in quarry material serves to ensure agreement with regulation limits. Quantification of U and Th and progeny in granite, clay, fertilizer or building materials is also important.
There is pollution control in areas of former open nuclear weapons tests as well as in warzones where U-enforced shells had been used. Direct measurement of filters from air samplers serves for quantification of radon progeny concentration and aerosol density in air.
Direct measurement of rock powder or evaporated water from surface wells yields valid data on the U and Th concentration in rock material. Electrostatic collection of radon progeny and direct measurement of the samples yields high-resolution samples suitable for quantification of U and Th contents in soil; the method is listed here as it requires almost no sample preparation.
Process water and slug from drilling rigs is supervised for its contents of radioactive material in order to control occupational and public exposure. See also Scales and NORM below.
Scales and NORM
In some technical processes naturally occuring radioactive materials or other radioactive species may be accumulated in solid deposits which must be supervised and removed. For an example see the IAEA Safety Report Series No. 34 on Radioactive Waste in the Oil and Gas Industry.