Nuclear energy and all thinks related to radioactivity have nowadays a bad press in Europe; few people remember their high-school physics with experiments on radioactive decay, and hopefully some information on the ubiquitous radioactive radiations that are a part of nature since the beginning of our planet. Decades of scare stories. semi-truth and abysmal lies have fostered a generation in Germany that thinks nuclear emission-free energy is outdated, and that radioactivity, where it exists, must be avoided like hell (or forbidden by the government :-))
It may come as a surprise that your humble smartphone that you use so frequently is a radioactive gadget. I learned this after reading an excellent article by David Jones at the website Brave New Climate.
1. The ITO touchscreen
All smartphones and tablets use touchscreens, which are one of the principal causes for easy use.
This picture (adapted from www.ti.com/lit/ah/slyt513/slyt513.pdf) shows that the principal element are the two ITO (indium tin oxide) sheets: these are transparent foils covered with a very thin layer of indium and tin oxide. Indium is element number 49, and the isotope used here is the most abundant I115. This isotope is a beta- emitter (it emits electrons from its nucleus, and converts to Sn115, which is tin.)
The energy of these electrons is rather small (495 keV), and the half-live of the indium is huge: 4.14*10^14 years! Indium is the 65th most frequent metal in the Earth crust, where it is found at a very small concentration of about 160 ppb (parts per billion). The minable world reserve is estimated at 6000 to. With steady increasing use in electronic devices and wind-mills, it may become a bottleneck for further development.
2. Measuring the radioactivity of an Iphone 4
Can the radioactivity of the Iphone touchscreen be detected? To answer this question, I put up a quick experiment, using a semi-professional Geiger counter, the INSPECTOR from S.E. International. This instrument has a very large pan-cake Geiger tube of about 48mm diameter; this means it is very sensitive even to small radioactivity levels. The picture shows the back-side of the INSPECTOR, with the wire mesh protecting the counter tube.
The experiment was done in two steps, each taking 10 minutes: first I ran the counter positioned left to the Iphone (which was switched on during the full experiment), and noted the minimum and maximum of the readings (there is about one reading every 2 seconds). Here is a picture, the counter showing a reading of 0.161 uSv/h, close to the maximum.
Secondly, I put the counter on top of the Iphone, so that the pancake Geiger tube covered the screen. The next picture also shows a reading, also close to the maximum of that part.
Here the results (all in uSv/h):
Background: minimum = 0.065 Maximum = 0.167
On top of screen: minimum = 0.161 Maximum = 0.275
We note that the second range begins practically where the first one stops: the minimum radiation on the screen is equal to the maximum of the background, and the maximum of the screen exceeds the background maximum by 65%. If we use the mid-points between minima and maxima (116 and 218) as relevant indicators, we see that the touchscreen increases ambient radioactivity levels by 88% !
This means that the tip of your finger is exposed to about two times of what is the normal background radiation in Luxembourg.
Should you be afraid? Yes if you have been brainwashed to believe that all radioactivity is dangerous! No if you remember your physics teacher and have kept a modicum of common sense!
PS1: When the Geiger counter is put on the backside of the Iphone, readings are similar to the background: the beta radiation does not cross the phone’s case. You may want to put your phone in the shirt pocket with the screen facing out :-))
PS2: There are alternatives to the use of indium in the laboratories: graphene, carbon nano-tubes etc. are some potential candidates. They will most certainly be used in the future, when demand makes Indium (now at ~800 US$/kg) too expensive. So, when will Apple launch with great fanfare the non-radioactive Iphone model?