Mineralogical Consequences of Lockdown – Part III

A Brief Study of Ionising Radiation and the Mineral Collector – Part III

Written by John Cooke, Mineral Enthusiast and Part-Time Curator

For those following this saga featured in previous blogs (Part I and Part II), you will be relieved to know this is the final contribution on this subject. The reader might recall that a “hotter” than normal pitchblende was banished to the shed within a lead coffin and then a further glass box, then into a non-ventilated museum display cabinet (it came from a museum of knitting in Nottingham – purchased many years ago from a prominent auction website).

The label associated with the pitchblende specimen (now safely stored in the shed!). © John Cooke.

It was suggested by a relative, who just happened to have a radon detector, that it might be useful to know if the pitchblende was emitting a radioactive gas and if so, at what concentration.

The actual device used was a Safety Siren Pro Series 3 Radon Gas Detector (see below). This detector is primarily for the American market and so the results are expressed in their preferred units, pico Curies/Litre (pC/L). The instrument has an accuracy level of +/- 20 %. Using the American standard set by their Environmental Protection Agency it is shown that domestic average readings are approximately 1.3 pC/L but levels above 4 pC/L would indicate the need for intervention. British authorities measure radon in Becquerels per metre cubed (Bq/m³), a normal domestic level being 20 Bq/m³, and for levels at or above 200 Bq/m³, there is a recommendation that intervention should be required. So, to compare the British standard to the American standard, the conversion factor for the British standard would be:

200 Bq/m³ = 5.4 pC/L          (i.e. 1 Bq/m³ = 27 pC)

The detector was placed at 10 cms from the specimen which was already entombed in lead (roof flashing). It is advised to leave the instrument for up to 2 weeks for a more accurate representation and stabilisation of the instrument which is constantly taking an average value. After this period, the instrument was removed and placed under the cabinet on the floor of the shed which is subject to far more ventilation. Again, readings were taken for 2 weeks. Subsequently, as a control, the instrument was placed on the floor in the house away from the mineral collection to determine a base level.

The results are as follows:

Location Readings in picocuries/Litre
Within cabinet in shed (non-ventilated) 4.7
Shed floor 1.8
House control 1.5

This experiment is not intended to be a university standard investigation but a general indication of the radioactive processes within nature. From the readings it can be demonstrated that radon is accumulating in an unventilated environment. This is an example that radon is not just a bother when building houses in prone areas of the country where ventilation is mandatory, but it can be a domestic issue for the mineral collecting fraternity. This study is a reminder, if one were needed, that ventilation is as important as minimising the exposure to ionising radiations.

The radon detector used for the experiment. Image courtesy of F. Cooke.

The experiment could have been extended over a much longer period of time to determine if higher concentrations of radon might be encountered in an unventilated cabinet but this course of action was regarded as introducing a level of danger which might prove to be unacceptable.

So, what happened to the pitchblende? It has been moved to a protected but draughty area within the shed awaiting discussions on its fate and final resting place.

A worrying statistic from America is that next to smoking, radon poses the biggest risk of induced lung cancer deaths (calculated as 21,000 radon-related lung cancers a year). Now, that is cause for concern!

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