A Brief Study of Ionising Radiation and the Private Mineral Collector (Part 1)
Written by John Cooke, Mineral Enthusiast and Part-Time Volunteer Curator
There is only so much decorating and gardening that a sane person can do before there is a need for a more cerebral challenge. To this end and because of the years I have been collecting Victorian boxed mineral collections the answer came to me in a flash. I know, I will clear out the garage and locate that old Geiger counter then I can check all my specimens for ionising radiations. That was the easy part. The Geiger counter was eventually discovered and cleaned to perfection – well what else can you do in forced isolation? Batteries recharged and fitted and the unit fired up with a voltage… but alas no response from the GM tube. Well, it is Civil Defence issue from 1954. Even though extremely well built, it is a Dad’s Army relic and most probably handled by Pike. The unit has since been presented to a relative (under suitable social distancing rules) who knows something about electronics and will investigate immediately (because there is nothing else to do). So, what to do now? Investigating a suitable on-line auction site for a possible replacement was greeted by that famous Yorkshire expression – “HOW MUCH?” More about this later.
Ionising radiation is a serious issue. I purchased a Cornish collection of minerals in a mahogany box three years ago but it came without a catalogue or any identifying labels. A friendly source at the local university allowed me to take the collection in and use both their XRF machine for identification and their Geiger counter to locate any specimens of a radioactive nature. It flagged three specimens that were ores of uranium and these specimens became entombed in a box of lead-flashing left over from a job on the chimney. This made me wonder how many other specimens were radioactive within the collection and are there any regulations that are relevant to the average collector. Where museum geological specimens come into contact with the public or curatorial staff there is an obligation to determine which specimens are radioactive and minimise exposure to acceptable levels. For the personal collector however, no such regulations appear to exist apart from guidance on best practice.
So, what are the problems? Well, radioactive geological specimens emit three types of radiation:
- Alpha radiation: Positively charged particle that has a range of very few centimetres at most in air.
- Beta radiation: Negatively charged particle that has a range of tens of centimetres. These are particularly hazardous to the eyes and skin.
- Gamma radiation: Electromagnetic radiation, which is the most penetrating kind of all. This is a hazard to all organs of the body. Beware!
To reduce and manage the exposure it is advised to address the following issues; Time, Distance, Shielding and Labelling.
The dose received is time-dependant, so keep inspection down to an absolute minimum. It is also advised not to investigate the mineral through a lens.
The rule to adopt is; double the distance and quarter the dose rate. This is referred to as the inverse square law. Store specimens as far away as possible from view, such as back of the draw or display cabinet.
Use the appropriate screening material which may be glass, plastic or lead.
The use of the “ionising radiation symbol” may be used on the specimen tray which gives an immediate visible caution.
For the preceding section I have drawn heavily on two sources which for the interested collector I can thoroughly recommend; Price et al, 2013* and Rowan, 2017**.
So, what happened to the Cold War Civil Defence device, I hear you say? It died! Well, not quite, the transformer was only generating 60 volts and I am reliably informed that the GM tube requires at least 350 volts to operate, so no detection system. So here I am facing the computer screen looking at a small portable radiation detector and there is a “Buy Now” box flashing away. I pressed the button now comes the hard part, explaining to my wife who believes I’ve just purchased another toy…
I shall follow up this discourse in Part 2 in which I will give the results of my investigations.
* Price, M., Horak, J. and Faithfull, J. 2013. Identifying and managing radioactive geological specimens. Journal of Natural Science Collections. 1, 27-33
** Rowan, A. 2017. Here be Dragons: The Care and Feeding of Radioactive Mineral Species. Web document. pp 1-78