The blind tube measurement of radiation to determine dose rate as a function of depth in contaminated land is performed currently with Geiger-Müller (GM) tubes on a push-rod cable. The former is installed in a water-proof housing and detects gamma radiation with which to infer the dose, whilst the latter is necessary to provide power and to recover signals, and also as the means by which the detector is deployed in a given measurement site (borehole/Blind Tube).
The sensitivity of the GM tube in this application is satisfactory and it is a robust, tried & tested technology. However, it is not sufficiently resilient to be left in-situ for long periods of time, either for the purposes of continuous monitoring or until such time that it might need to be used. Further, the relatively high cost of the system somewhat precludes a significant number of these devices being deployed at different sites at the same time. GM tubes, whilst sensitive, do not afford any spectroscopic functionality and hence, whilst the main constituent of the isotopic inventory is 137Cs, sensitivity to alternatives is not possible; neither is a relative measurement of the attenuation of the detected photons by the surrounding water when the instrument is submerged.
In this project the objective is to explore an alternative means by which blind tube measurements might be done that is more resilient, such that systems can be left in-situ for longer thus reducing the need for human intervention. Also we would like to consider a counter which yields a degree of spectroscopy to provide greater analytical insight of the measurement environment. We shall perform the following in this study: A thorough requirements specification for the instrument to be developed; an options study of the various candidate detectors that meet the needs of the requirements specification (for example, cerium bromide, silicon carbide, etc.); a campaign of laboratory-based tests in our dedicated soil tank with which to identify the best candidate; an extension of the former to explore its resilience for long-term use, in-situ. Finally, we shall construct a prototype with the intention of carrying out field tests of the system on site, comparing it to the existing system. The selection of exemplar detector materials cited above is not exhaustive: cerium bromide is suggested because it is radiation-tolerant and yields good energy resolution, particularly in the range needed for 137Cs. Silicon carbide is suggested because, whilst it might not yield spectroscopic information to match cerium bromide, it’s relatively cheap to produce, has a small form factor and is likely to be more resilient for high-dose applications for land quality assessment.
Academic Lead: Malcolm Joyce
Researcher: Soraia Elisio
Location: Lancaster University