Answer to Question #11103 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:

Q

I am considering working on determining concentrations of TENORM (technically enhanced naturally occurring radioactive materials) waste from samples of scales, sludges, sediments, soils, water, rock, brines, waxes, and oils from oil and natural gas production in the Niger Delta Region of Nigeria. What equipment and analytical methods can be employed for the studies?

A

The appropriate answer to your question depends on the particular identities and physical/chemical characteristics of the TENORM material to be analyzed, some of which you have specified, and on the specific analyses to be done.

TENORM may include a number of radionuclides. The major elements that are present in the earth's crust that include and/or produce radionuclides of possible concern are thorium, uranium, and potassium. Naturally occurring uranium includes 238U and 235U as precursor radionuclides. Each of these decays through a respective long chain of radioactive progeny, eventually terminating in stable lead isotopes; some commonly known radionuclides in the decay chain of 238U include 234U, 226Ra, 222Rn, 214Pb, 214Bi, 210Pb, 210Bi, and 210 Po. These progeny decay by either alpha or beta decay, often with the associated emission of characteristic gamma radiation. Thorium-232 represents the natural thorium precursor, which also results in the production of numerous radioactive progeny, including common radionuclides such as 228Ra, 224Ra, 220Rn, 212Pb, 212Bi, 212Po, and 208Tl. The naturally occurring isotope of potassium that is sometimes of concern is 40K, a radionuclide that decays by beta decay with the subsequent emission of a relatively high-energy gamma ray.

One of the most useful laboratory instruments for identification and quantification of many radionuclides of interest that emit distinctive gamma rays is a gamma-ray spectrometer, especially a spectrometer that employs a high-resolution germanium detector. One great advantage of gamma-ray spectrometry is that it often minimizes the amount of sample preparation required for analysis. There are a number of companies that manufacture/provide detectors and analyzing systems/software appropriate for spectrometry. Samples to be analyzed will require appropriate containers that can hold the samples in proximity to the detector. Simple plastic containers capable of holding the volume(s) of material(s) of interest are often suitable. Marinelli-style beakers are often desirable for holding large volumes of samples in a favorable geometry for counting.

You may require the usual laboratory equipment to handle and treat samples—e.g., beakers, flasks, graduated cylinders, hotplates for evaporation of excess liquids, a source of distilled water, balances for weighing samples, etc. Additionally, depending on what analyses you intend to perform, other common equipment may be necessary—e.g., pipettes, planchettes, filter paper and filtration assemblies, centrifuges, drying ovens, and/or ashing furnaces.

You may wish to do certain laboratory screening measurements for some samples—e.g., water samples that may be evaporated to a small solid residue that will be transferred to a planchette for gross alpha and beta counting. Small samples of solid samples may also be prepared for such counting. In such cases you will require an appropriate counting system; a gas flow proportional detection system is one of the most popular and useful choices for such applications. If you are expecting to count large numbers of samples, an automatic system capable of accommodating a large number of prepared samples is desirable. Alternatively, single-sample manual systems are available at considerably lower cost and are useful if relatively few samples are to be counted at any one time.

You should also have at least one portable instrument capable of making dose (rate) measurements. Such an instrument is useful if you will be making any assessments in the field but also for quickly assessing dose-rate significance of samples that are brought into the laboratory. Often, a thin window (pancake-type probe) is desirable since it has reasonable sensitivity to all the major radiation types (alpha, beta, and gamma) and can be used not only for dose-rate measurements but also for making measurements on surfaces to check for the presence of contamination, both in the laboratory and in the field. Portable instruments, such as pressurized ion chambers and plastic scintillator detector systems offer higher sensitivity for gamma measurements if such is required. Depending on your budget, another useful field instrument is a portable gamma-energy discriminating detector; common devices use a sodium iodide detector with microprocessors and appropriate digital output devices to exhibit gamma-ray energies and to show the accumulated pulse height distributions from selected measurements. These are especially useful for making quick measurements in the field to identify, for example, elevated levels of 226Ra/progeny and/or 40K in various media.

There are many other more specialized instruments that may be useful for some measurements—e.g., equipment to perform radium analysis by radon emanation or specialized liquid-scintillation counting systems that can perform simultaneous alpha and beta counting—but I do not think they require more elaboration unless you define a specific need for such.

I have not identified specific manufacturers of instruments and other materials that you might require, but there is a lot of such information available on the Internet by searching under the category of interest. One place you might look is the Buyer's Guide provided by the Health Physics Society. I wish you well in your work to identify and measure radioactive contaminants in the waste from the oil and gas production efforts that are ongoing in your country.

George Chabot, PhD

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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