Dosimeters for all3 December 2012
Two hand-held radiation detectors for the consumer market are now in the final stages of development. Both connect into smartphones and tablet computers such as the iPad through the audio jack; both operate from software downloaded on to the device. The prime market for both is Japan, whose citizens have had to learn to live with the fear of radiation since the Fukushima Daiichi disaster in March 2011. By Will Dalrymple
The $100 ‘DO-RA.classic’ device plugs straight in to the top of a smartphone; it is designed in a crescent shape designed to fit tight to the curves of the top of a phone.
It works with iOS, Android, Windows Phone 7, BlackBerry, Symbian and JavaME-based phones. Its internal Russian-made Geiger-Mueller tube detects gamma radiation in the 60 keV to 3 MeV energy spectrum, with an intensity of 1.5 uSv/hr to 14.4 mSv/hr to a maximum error of +/- 15%. The measurements occur every four seconds over the period of a minute, during which time the device checks for accuracy. After a minute, an indication of ambient equivalent of dose, and/or power of ambient equivalent of dose is displayed, along with coloured display backgrounds and audible alarms corresponding to safety threshholds: green for normal, yellow for warning, red for dangerous. DO-RA can measure the accumulation of dose, and also transfer this information to the phone and on to the internet; radiation readings can be linked to photographs taken with the device. It can also measure hard beta radiation in the energy range of 155 keV to 3.5 MeV. A second version, the DO-RA uno, has a different shape—it hangs over the back side of the phone—and carries a silicon-based detector.
The Russia-based vendor, a start-up company founded by Vladimir Elin and supported by grants from the Skolkovo Innovation Centre, has received 400 pre-orders via its website, www.do-ra.ru. Application software is available on mobile device networks such as the Apple app store and Android marketplace. Batches of devices ranging from 500-1000 units will be produced for testing in Russia and Japan over the next few months. It hopes to be able to gain distribution via local networks of mobile operators and smartphone manufacturers worldwide.
The DO-RA vendor points out that its product is only intended to be a detection device, not a measuring tool. Not so the $2000 RadAngel, a small grey box about the size and weight of a deck of cards (130 g) which promises to not only detect radiation but to positively identify instances of caesium contamination, and separate man-made from background radiation.
“Most geiger counters are programmed for a specific isotope energy level and dose around that,” says CEO of vendor Kromek Arnab Basu. “When the dose is at a different energy, you need to look up the reading in calibration tables, or adjust the device with built in ones. The trouble comes in a mixed environment. For a single-point calibration device, it is difficult to give an accurate rate unless we know where the dose is coming from; then we use a calibration table. Because we use spectral dose technology, we are not dependent on knowing where the dose is coming from. The device automatically gives an accurate dose rate from a mixed-source environment, from a wide dynamic range of isotopes.”
The RadAngel has a 4000-channel multi-channel analyser (MCA) that interprets gamma radiation received from a CdZnTe detector, in the range 30 keV-3 MeV. Unlike DO-RA, it is powered not by the phone, but by an internal rechargeable battery (nominal eight-hour life).
There are two parts to the smartphone/tablet device display, which connects to RadAngel by a male-to-male headphone cord (smartphone/iPad) or USB (PC). At the top is a speedometer-type view, whose needle displays the gamma radiation count per second (cps) in real time. The colour of the dished background behind the speedometer needle grades into hotter colours (from green to yellow to orange then red) with increasing numbers to indicate the radiation’s relative risk to health. A blue circle in the middle displays the cps value in figures; at the left-hand side is a dose rate reading. Below is a display of the radiation by energy level computed from the spectra of the radiation. High levels of radiation at a particular energy are coloured red. It is this graphical display, which Kromek calls the RadBar, that enables users to differentiate manmade sources, which have a telltale energy signature, from natural background radiation, which is spread out over many energy levels. One particular signature flagged up is that of caesium 137 (660 keV), which is the most significant long-term radioisotope released by a nuclear accident, such as at Fukushima. RadBar graphs are not displayed in real-time; the calculations involved take perhaps 10-30 seconds, depending on the strength of the source. The weaker the source, the greater the uncertainty, and the longer time required. Calculations are performed on the attached device to 99.95%.
Measurements—dose, spectrogram, time, date, and location and type (soil, environment or a [radioactive] source)—are automatically stored in a calendar on the smartphone or tablet. Users can then upload the measurement to a shared map on www.radangel.net. Users can share their data with a community of selected RadAngel users, or to everyone. The map, which is compatible with Google Maps, shows the dose and spectrogram at the location the reading was taken.
The RadAngel is based on other devices (particularly the GR1 spectrometer and RayMon 10 radiation monitor) sold by Kromek, a spin-off of Durham University specialising in detectors. Basu said it has been developed over the past 10 months. As of early October the RadAngel can be bought through its distributors in Japan (Niki Glass Co Ltd) and the USA (NOVA Inc in California and JGW Associates in Virginia); the company is hoping to organise other sales channels by November.
This article first appeared in the November 2012 issue of Nuclear Engineering International magazine.