Temporal Variation In Ionising Radiation At A Single Location (part 1)
My twin-tube Geiger-Müller counter reveals some interesting patterns within what is supposed to be a random phenomenon
Back in April of 2023, and after a prolonged spell of being a particularly useful husband, Mrs Dee decided to treat me to a new gadget. The gadget I chose was a GQ Electronics GMC-500 dual tube Geiger counter, made by some nice people in Seattle, WA. I appreciate this is not to sort of everyday gadget that gets gifted these days but I’ve already got a vintage Texas Instruments TI-30 electronic calculator, five EDC penknives, an olive stoner, a mushroom combi knife/brush and a LW radio for listening to a channel that no longer transmits (BBC R4/World Service), so a Geiger counter it was.
My first encounter with radioactive stuff was quite physical. The physics teacher brought a heavy wooden box from the store cupboard and opened it to reveal an ancient Geiger counter and several radioactive samples that were kept in little lead containers. The class gathered round the front bench, all delighted and amused at the clicking sounds of the natural background radiation; then out came the first sample (the teacher using tongs and wearing goggles and a lead apron) and wham did that counter fire-up! We all withdraw in an instant but only by two feet or so – such is the logic of the Britlander.
Way back when another set of dangers were upon us (Birmingham pub bombings in 1974, London Tube bombings in 2005) I recall instances where somebody would point to an unattended bag and shout, “is this anyone’s briefcase?” If nobody claimed ownership within seconds we’d all step back about two feet or so. Those at the bar might move their stool 6 inches just to be on the safe side. I must conclude that Britlanders are invincible at distances of two feet and more unless they are drinking in which case the threshold drops to a short ruler.
But I digress. After a demonstration of the Geiger counter with different samples the class was divided into groups and a group leader chosen to facilitate responsible exploration of radioactivity for ourselves. This didn’t last long. The teacher made the mistake of mentioning the risk of sterility upon which certain boys were dropping samples into the back pockets of the unwary. Then came the hurling of samples around the room before everything was confiscated and detentions given out. Oddly enough we all survived that and more in those days.
Dee’s Detector
So there I was with my own Geiger counter back in April 2023 trying to figure experiments without frying myself. There are luminous antique watch dials to explore, smoke detectors containing Americium-241 to study, and Radon gas to monitor which, being heavy, accumulates in the cellars of old stone buildings in these parts. In the event I plonked the device in the corner of my office window sill and left it logging counts whilst I brewed an exciting experiment. Here it is quietly doing its thing 24/7/365:
Logging was activated at 09:39BST on 28 April 2023 and it has been collecting data ever since. Fortunately I had set the resolution from one second counts to one minute totals and this had given me 576,418 data records to handle come 16:37BST on 1 June 2024 when I downloaded data to see what I’d got.
One thing worth mentioning right up front is that the device detects beta (β), gamma (γ) and x-ray ionizing radiation and not alpha (α), but that’s good enough for me at present. The unit offers readings as counts per minute (CPM) that are also converted into equivalent ionizing radiation dose values of microsieverts per hour (μSv/h). In case folk are not familiar with the sievert, here’s what Wiki has to say:
The sievert is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing radiation, which is defined as the probability of causing radiation-induced cancer and genetic damage. The sievert is important in dosimetry and radiation protection. It is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation.
The sievert is used for radiation dose quantities such as equivalent dose and effective dose, which represent the risk of external radiation from sources outside the body, and committed dose, which represents the risk of internal irradiation due to inhaled or ingested radioactive substances. According to the International Commission on Radiological Protection (ICRP), one sievert results in a 5.5% probability of eventually developing fatal cancer based on the disputed linear no-threshold model of ionizing radiation exposure.
To calculate the value of stochastic health risk in sieverts, the physical quantity absorbed dose is converted into equivalent dose and effective dose by applying factors for radiation type and biological context, published by the ICRP and the International Commission on Radiation Units and Measurements (ICRU). One sievert equals 100 rem, which is an older, CGS radiation unit.
So there you go, with sieverts on offer down in the data log I decided to stick with those so we all know where we’re at with the numbers I am about to crunch, though do please pay attention to that little word stochastic, which is a fancy way of saying conjecture. Conjecturing over radiation doesn’t sit easy for me.
Anybody reading the Wiki entry on the sievert will realise just how complicated things get when it comes to measuring and assessing the effect of ionizing radiation on the human body so I’m not going to even think about going down that route. Instead, we’ll look at some statistical properties of those three types of ionizing radiation as expressed by my locality. What I will do, however, is furnish a pair of summary tables of dosing and dose rate examples that I’ve extracted from what is a rather messy Wiki entry. Herewith the best bits converted to microsieverts:
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