Your smartphone is radioactive!

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 semi-truth and abysmal lies have fostered a generation in Germany that thinks nuclear emission-free energy is outdated, and that radioactivity, where it exists, must be avoided like hell (or forbidden by the government :-))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.

capacitive_touchscreen_ITO
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.

pancakedetector

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.

background_max

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.

ontop_max

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?

5 Responses to “Your smartphone is radioactive!”

  1. maxgacode Says:

    Considering that the content of Indium in LCD is 0.65-0.95 g/m^2 a cell phone has 2.4 mg of Indium in each ITO sheet for a 30 cm^2 LCD. The atomic weight of Indium is 114.8 g/mole , that means there are 2.0910^-5 mol of Indium or 1.26 10^19 atoms of Indium in each ITO sheet. The half life of Indium is 4.41 10^14 years and so the total activity of Indium is 1.26 10^19 ln(2) / HalfLife (in seconds) or 0.0006 decay per seconds (Becquerel). The background, measured with an Inspector Alert, you are measuring is equivalent to (roughly) 0.5 decay per seconds. So the activity (total) in a single ITO sheets is 1000 times lower. The Geiger you used has a geometry factor of 30% (roughly) and a beta efficiency of 20% that means the radioactivity of a single layer is 1/15000 of the background. Your measurement is absolutely WRONG! The observed increasing of radioactivity (if any) is NOT related to Indium!

    References (freely available over internet):

    [1] Recovery of Indium from End-of-Life Liquid Crystal Displays – Industrial Materials Recycling Department of Chemical and Biological Engineering

    [2] http://www.chemicalelements.com/elements/in.html

  2. fmassen Says:

    maxgacode, I disagree, even if your calculations seem reasonable. I remade the same measurements today, but adding a new iphone 5s that replaces my old iphone 4. I noted down only the minimum activity (in uSV/h) over a period of ca. 10 minutes. Here the results:
    background: minimum = 0.077
    iphone 5s: minimum = 0.071
    iphone 4 : minimum = 0.173

    So indeed, the iphone 5s does not seem to create any increase, but clearly the iphone 4 does.. The maximum values for background and iphone 5s were about the same (~0.221) but went up to 0.323 for the iphone 4.
    I do not agree that my measurements are wrong; the increased radioactivity of my iphone 4 seems real; is it due to the indium ITC or is there another cause? That is the question…

  3. maxgacode Says:

    Your measurement are incorrect (may be “wrong” is a rude term) in different way:

    1) You are telling us that the increase of “background” is related to Indium. As I shown that is false. My calculations are very simple and any physicist should be able to check the correctness in few seconds (if you think I made a mistake please let me know)

    2) If your data are correct you should look for a different mechanism. Geiger counter are prone to electrical noise, please can you repeat the measurement with phone turned off? Far from electrical devices, neon lamps….

    In any case your measurement may show that ONE Iphone 4 is generating counts more than ONE Iphone 5. For sure Indium is not the guilty! You are jumping to a pre-defined conclusion (your expectation) not using scientific criticism.

    Unfortunately for your thesis both Iphone4 and Iphone5 are using Indium Oxide touchscreen. So?

    My computation can be verified easily, is there any mistake? In case there are no mistake I’m expecting you to accept the Indium has nothing to do with the observed increase of counts. Your conclusion is “incorrect” by 4-5 order of magnitude!!!!

  4. Michael Mann Says:

    A weak beta my not be measured by some Geiger counters, if the “window” is too thick/robust it doesn’t take much to shield a weak beta.

    • maxgacode Says:

      Indium-115 is emitting beta with a maximum energy equal to 630 keV, so the average beta energy is about 200 keV. The LND sensor has roughly 20% efficiency (2 pi geometry) at 200 keV. So the geiger shuol be able to detect 20% of…..nothing (as I shown the activity in one cell phone is to low) that is equal to zero!

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