Isotope Identification: How Does it Work?

Although we can’t feel, see, or hear it, we live in a sea of radiation. Cosmic rays from outer space continually bombard our planet, natural radioactive materials produce a steady stream of radiation, and many man-made materials constantly emit radiation in our homes and vehicles. Although much of this radiation is weak and harmless, there are some sources, as well as elevated radiation levels, that are best avoided. This is the reason that isotope identification is so important.

The term isotope is often misunderstood: not all isotopes emit radiation. Rather,  the term isotope has to do with the number of neutrons in the nucleus of an atom. Each element is defined by a set number of protons (or atomic number), by which it is listed on the Periodic Table. Iodine, for example, has 53 protons. But there are different versions or isotopes of iodine with varying numbers of neutrons, which are denoted in the isotope name. I-127 is the most common isotope of Iodine and is stable, meaning that its atoms don’t give off radiation or change to other isotopes.  But I-129 and I-131, which are produced in nuclear processes, are unstable and give off radiation that can be dangerous.

Isotope identification consists of finding out which radioactive isotopes are responsible for radiation. It is possible to figure this out by closely measuring the energy levels of radiation. Each radioactive particle or photon has a certain energy level, and each radioactive isotope emits a different set of energy levels. For example, here is a radiation measurement taken by a Rad-ID device:

Isotope Identification from the Rad-ID

As you can see, there are two energy peaks (at 25 keV and 88 keV) shown on the graph.  These two peaks appear because the isotope gives off a higher percentage of 25 keV and 88 keV radiation than radiation at other levels. By matching these measured energy peaks to pre-programmed energy peaks for known radioactive isotopes, isotope identifiers can narrow down and found out which isotopes are emitting the radiation.

There are a few difficulties that occur in the isotope identification process. First, no matter how well a radiation reading matches the pre-programmed energy levels, there is always at least a slight chance of an incorrect identification. This probability grows dramatically if the measured radiation levels can’t be matched very well. This is why it’s important to understand how good the match is and if there are lots of isotopes involved. Confidence bars can help out with this. Another problem is shielding. These two pictures show measurements an unshielded source on the left and a shielded source on the right:  

If you look closely at the two pictures you'll notice that a large energy peak on the left side of the first  (unshielded) reading is missing in the second. This  happens because shielding tends to block high-energy photons much better than the low-energy ones, which penetrate better. This can drastically change the shape of radiation measurements, and with enough shielding, completely block the radiation.

Measuring energy levels precisely enough to make an identification takes a very specialized instrument, different than a normal radiation detector. Identifiers usually have a LaBr3 or CZT detector, as does the Rad-ID.  These detectors are much more accurate than other types of radiation detectors. The Rad-ID also uses a large scintillation detector (NaI(Tl)), a Geiger-Mueller detector and an optional He3 tube to find a wide range of gamma and neutron radiation. In fact, the Rad-ID can identify 107 different radioactive isotopes, even if a measure sample is reading radiation from several isotopes.

With a good isotope identifier, you can be sure that you know what isotopes are in the environment and if you need to worry about them.

D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.

D-tect Systems Video

To give a better idea of what we do here at D-tect Systems, we shot this short film on site here at our Draper, Utah facility. It gives a short introduction to the radiation and chemical detection field and then gives a short description of each of our products. We hope it can give you a sense of what D-tect is all about!

D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.

My Trip to Japan

While in Japan, I was paired with a group that was sent to check on the structural integrity of several church buildings in several cities. My role was to show them how to use the equipment and gauge the levels of radiation at each site. To check on these levels I went armed with two different radiation detectors: the MiniRad-D (a small, pager-sized detector) and the Rad-ID (a portable radiation identifier).

In my visits to cities from Tokyo to Iwaki I checked radiation levels and talked with the local church officials about what those levels meant. Radiation levels in downtown Tokyo were near natural background levels but the closer I got to Fukushima, the higher the radiation levels rose. The cities I visited showed readings of anywhere from 0.35 µSv/hr to 2 µSv/hr above background radiation, which are elevated levels, but definitely not dangerous. Using the Rad-ID, I found out that most of the radiation came from the radioactive isotopes Co-60, I-131, I-132, and Cs-137, which are commonly given off in nuclear processes.


An interesting observation that I made was that storm drains in the areas I visited showed higher levels of radiation than the surrounding areas. I surmised that rainfall had carried down and collected some of the radioactive dust in the air and deposited the contamination as it flowed down these drains.


Although the Japanese have shown amazing resilience and are working as hard as they can to solve these enormous problems, there is still much uncertainty about health risks and what the future will bring. We’ll be back soon to check on the radiation levels again. If you’d like to brush up on your radiation basics, you can check out this sheet we’ve complied. It has basic conversions, safety levels, and doses to put radiation exposure in perspective. An interesting chart on radiation dose rates can be found here.