RAYSID – gamma spectroscopy on the go!

Today I want t show you a device that allows you to do gamma spectroscopy on the go! Let’s take a closer look at the RAYSID Gamma spectrometer.

RAYSID is a gamma compensated dosimeter, gamma spectrometer and radiation mapping/logging device all in one small package. There are 4 models with the cheapest being 300 euros and the most expensive being 600 euros. All of them have exactly the same features with the only difference being the value of the FWHM which is important only when doing gamma spectroscopy. So if you are not interested in doing gamma spectroscopy then you will be perfectly satisfied with the cheapest model but if you would like to do gamma spectroscopy then I would suggest you invest in the slightly more expensive model.

In terms of size, RAYSID is comparable to a Zippo lighter and weighs only 65 grams. Inside there is a rechargeable battery that lasts for over 10 days on a single charge. The heart of this device is a 5 cm3 Thallium activated Caesium Iodide (CsI(Tl)) scintillation crystal.

Inside the box, there is a manual, USB charging cable, caring case, selfie stick with a holder for RAYSID and RAYSID itself.

In order to use the RAYSID

to its fullest potential, it is best to connect it with RAYSID app. Unfortunately, the RAYSID app does NOT work with iOS and is only compatible with android 5.0 (or higher) devices.

In order to turn the unit on, we simply need to press the power button. Next, we can open the RAYSID app and connect RAYSID with our phone. In order to turn on/off the speaker simply press the power button once. To turn the unit off press and hold the power button.

Search mode

Search mode is useful when searching for radioactive hot spots. The upper side of the screen displays a graph showing current CPS and the dose while the lower side shows the rough gamma spectrum which is updated in real-time.

On the right side, there is a set of icons. The first one locks the display in the current position (vertical or horizontal). The camera icon allows you to take a photo with the current measurements.

Gamma Spectroscopy

One of the best features of RAYSID must be its ability to do gamma spectroscopy. Depending on the model, FWHM varies from >15% to <8.5%*. The smaller the FWHM the more accurate and narrow peaks. For the best result, it is best to have FWHM below 10%.

As of right now, the spectrum range is from 25 keV to 1000 keV which means you should be able to identify the most common radioactive isotopes such as U-238, Th-232, I-131 or Cs-137. In a future update, the range will be extended to 3000 keV allowing for the identification of radioactive isotopes such as K-40 or Co-60.

Another great feature is that RAYSID has a temperature compensation which results in the spectrum not being affected by the weather (in extreme cold or heat, spectrum mode is unavailable). Manual calibration can be done in the “settings” tab.

What I really like is that when doing a gamma spectrum, the app automatically identifies different isotopes based on their energy peaks which means you don’t need to analyse the spectrum to identify the isotope you are measuring. The average dose and CPS are also displayed.

It is also possible to save the background spectrum which helps visually to see any minor differences when measuring samples for a trace amount of radioactive contamination. In order to do that simply click on the “BG” icon with a “download” arrow. This will save the current spectrum as background. You can toggle on and off the background spectrum by pressing the “BG” icon.

Triple pressing the power button will restart the spectrum

*FWHM measured at 662 keV


Since RAYSID is so small, it is very portable and you can take it anywhere you want. What is even better is that it automatically makes a map of background radiation anywhere you go! You can set the map to show background dose (uSv/h, uR/h) or background activity (CPS, CPM and Bq/m2 (only for Cs137)).

To enable global map press the “web” icon. If you wish to share your map with RAYSID global map than press “share” icon. If you want to delete point on the map click the “bin” icon and hover the red square over the points you want to delete

You can have a look at the current state of the map by clicking HERE

Alarm & Log

A CPS or dose alarm can be set in the “setting” tab. When an alarm is trigger, it will be logged in the “Log” tab. Double pressing the power button will turn the alarm on or off.


I personally think that RAYSID is the best device of its kind. Relatively low price and very good performance make it one of my favourite radiation detectors in my collection and since it is so portable, I take it everywhere with me! So if you are in the market for a portable gamma spectrometer I highly recommend the RAYSID.

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