Radiation Alert® Support / SEI Inspector, M4, M4EC, SentryEC, URSA-II, & GammaPAL


Support Links

Thank you for choosing a Radiation Alert® detector from S.E. International, Inc. Below you will find a number of helpful links, discussions, and videos to assist you in the use of your instrument.

Operation Manuals | Instrument Comparison | Radiation Basics | Discussion | FAQs

Quick Start Videos

  • SEI Inspector USB Chapter 1: Introduction
  • Digilert200 Introduction
  • Radiation Frisker Introduction
  • Observer USB Basics
  • GammaPAL Introduction
  • YouTube Channel
  • Monitor 4, Monitor 4EC, and MC1K

Ionizing Radiation Basics

Radiation Symbol Since our instruments are sometimes purchased by individuals with no background in radiation protection, we thought it would be helpful to include this information. The following information is based on features that are available with most of our Radiation Alert® meters.

Ionizing Radiation Basics

Will The Observer USB work with older models of Radiation Alert® Detectors?

No. However, the Serial Observer Software will work and includes the cable to connect your detector to a computer via the 3.5mm headphone jack.

How do I turn on the data logging on my SEI Inspector USB, SEI Inspector Xtreme USB, SEI Inspector EXP or Digilert 200?

You can do this one of two ways. You can turn on the data logging via the Utility Menu on the unit itself. You can access the Utility Menu by holding down the plus button while powering on your detector. Set the date and time first, then turn on the recording feature. You can also turn on the data logging with the Observer USB Software by synching the time and date of your computer and turning on the data logging via the Cal Panel.

How often should I calibrate my detector?

We recommend your instrument be calibrated annually from the date it was placed in service, but certain industries or applications may require them more frequently. For more information on how to calibrate your device, please click here.

What levels of radiation are considered safe?

For the best information on what levels of radiation are considered safe, it is best to consult a Radiation Safety Professional. For your convenience, we have included a list of useful links below to assist you in finding the information you need. You can also check out our growing list of General Radiation Info FAQs

Radiation Info Links

| RadiationAnswers.org
| HPS.org
| CRCPD.org is a great source for information on regulations and radiation safety officers in your area.
| ENENEWS.net
| Our Radiation FAQs
| Radiation Basics
| What Are Safe Levels of Radiation?

Can I use Radiation Alert Detectors on microwaves, radar, and cell phones?

NO! CAUTION! DO NOT PLACE OUR INSTRUMENTS IN A MICROWAVE AS IT MAY DAMAGE THE INSTRUMENT OR THE MICROWAVE OVEN.

Our instruments detect ionizing radiation. Microwaves are non-ionizing radiation. For more information on the differences between ionizing (sometimes called nuclear, alpha, beta, gamma, neutron, or x-ray radiation) and non-ionizing (cell phones, microwaves, wireless, and radar), please refer to the electromagnetic spectrum.

Are there any websites available that show information about radiation levels in my area?

For your convenience, we have included a list of useful links below showing the various radiation levels in your area. For information on radiation levels displayed on the various maps available, please contact the host of the site where the data is displayed.

Radiation Map Websites

| RadCast.org

| Safecast.org

| EPA RadNet

| RadViews.com

| National Radiation Tracking Center

Can I use a gieger counter, like The SEI Inspector Family of detectors, to detect radiation in food?

A Geiger counter is a "Yes or no and how much" type of detector. They cannot determine the distribution of the incident radiation energy, so they cannot identify which potential isotopes are present. To identify specific isotopes, a radiation spectrum analyzer with a sensitive enough scintillation detector for the application would be necessary. Geiger counters are ideal for basic screening, especially if you do long timed counts and, in most instances, will give you an indication regarding foods that are significantly contaminated.


When using a Geiger counter to test food, you should take into consideration that the meter is likely missing a bit of the radiation. This is due to the shielding of the radiation by the density of food, and the limitations posed by the detection range of the meter. Alpha radiation can be detected on the food's surface, but can be blocked if there is internal contamination. You can better test food by grinding it into a paste and taking a timed count. This may give an indication that you have contamination in your food, though it will not qualify what type of radiation may be present in the sample.


Water and food can also be a shield for radiation, so unless there is gamma radiation our instruments are not the most ideal without a little processing of the material in question (beta and alpha will not move very far in water and will be shielded by it). You can take a sample of the water and run it through a filter and test the filter or you can evaporate it down and test the swipe on an SEI Inspector USB with a Wipe Test Plate, however, the URSA-II with the appropriate detector would be much more efficient for this application, but scintillation based instruments are more expensive than the handheld GM based alternatives. Regardless, most of the higher energy betas and gamma radiation that falls within the sensitivity of the detector will be measured.


It is important to remember to establish a background count prior to surveying your samples. To do this, use your SEI Inspector in the Timed Count mode and take a background count of at least 10 minutes. Then, divide the total counts displayed on the unit by the number of minutes of your count. For instance, if you take a 10 minute timed count, divide the total counts by 10. If you're taking a 24 hour background count, then divide the total by 1440 (the number of minutes in a 24 hour period) to get your Counts Per Minute background level. The longer you take a timed count, the more statistically accurate your reading will be. You will then subtract that amount from the readings of your sample.

How do I determine a custom efficiency for my detector?

This procedure assumes that an alpha/beta source of known activity has been prepared and applied to a planchet. In addition, the average normal background (CPM) has already been determined with the Wipe Test Plate in position.

The first step is to take a ten minute count with the planchet (source) sitting on the Wipe Test Plate (shorter count times may be used). Using the Wipe Test Plate assures reproducible geometry and that results will be comparable. Next, convert the gross counts obtained for the ten minute interval into counts per minute (CPMnet) above normal background using the following equation:



Equation 1


After is obtained a value for the detector efficiency, E, can be determined.

The equation for E is as follows:



Equation2


It should be noted that both the count Rate and the activity must share the same units of time (i.e. CPM and DPM or CPS and Bq). The efficiency will always be less than 1 and have units of counts per disintegrations (c/d). The efficiency may also be expressed as a percent.

Finally, to convert a reading taken from a planchet using the Inspector + WTP into activity use Equation 4 or 5:


Equation 4


Or,


Equation 5


To determine activity when the efficiency is supplied in a percent, use either of the above equations and multiply the result by 100.

Finally, to convert DPM or DPS(Bq) into Curies(Ci) use Equation 6 or 7 :



Equation 6


Or,



Equation 7

Why is the alpha efficiency of a pancake detector considered low?

This has a lot to do with the alpha source itself. Starting with the source, not all particles are headed in the direction of the detector. The next challenge for the alphas is to make it off of the surface of the source. Alpha standards *must* be protected from the outside world to prevent the radioactive material from coming off. Typically, electroplated sources are used, but there are ones that exist generally using a thin sheet of mylar and adhesive. Also, many of the alpha particles are absorbed prior to escaping the source.

Efficiency measurements are specified at a fixed distance from the source. We recommend using a source to detector distance of 1 cm for all efficiency measurements. So the attenuation of 1 cm of air must also be figured in. This can be easily achieved using the Wipe Test Plate and the SEI Inspector USB.

In addition to this, the screen protects the detector face as well, so some of the incident alpha particles are stopped there.

Finally, the absorption of the mica window is considered. Once an alpha particle makes it into the active volume of the detector the intrinsic efficiency is essentially 100%.

It is possible to determine a different efficiency, using the alpha emission rate from the source (hence a 2-pi efficiency) instead of the total activity deposited. Since we have to use one number, we go with the activity-based, 4-pi efficiency, as that is most representative of how the majority of measurements are taken in the working environment. This is generally counting wipe samples and direct measurements on surfaces.

Can I customize each efficiency programmed into the SEI Inspector USB?

Note: Please be aware that the SEI Inspector USB does not identify isotopes. It quantifies, not qualifies. However, if you know the isotope that you are surveying, you can use the pre-programmed efficiencies to calculate the activity in Becquerels and Disintegrations Per Minute. You can program your own efficiencies into the unit for your own customized application. To do so, either enter the utility menu on your detector or use the Cal Panel in the free Observer USB Software for PC

2 Inch Detector Model Efficiencies (Counts Per Disintegration) :

Sulfur (35S): 0.0317
Strontium (90Sr/y): 0.2274
Cesium (137Cs): 0.2078
Phosphorus (32P): 0.2200
Carbon (14C): 0.0291
Iodine (131I): 0.0600
Cobalt (60Co): 0.1400
Alpha: 0.0420