Geiger Counter Calibration and Technical Advice for First Responders

Some Geiger counters, especially older designs, require regular calibration to ensure that their readings are accurate. The instruments from Medcom incorporate novel design techniques and high-quality components. In more than 26 years of manufacturing the Radalert, Radalert 50, Radalert 100, the Inspector, Inspector Alert and similar instruments, the company confirms that these instruments maintain their original calibrations remarkably well.

Frequency of Calibration

Some facilities need calibration certificates or annual calibration with an NIST-traceable source. These instruments are calibrated electronically after manufacturing, and an electronic calibration certificate, except for the CRM-100™, are shipped with each order. In case one requires NIST-traceable calibration, this can be provided for an additional fee at the time of order placement.

In case the instrument is for hobby or educational purpose, there is no need for calibration on a regular basis but it will be checked periodically against a known source of radioactivity to make sure it is working perfectly. In case the instrument is used professionally in an environment with radioactive materials, a calibrated check source can be used periodically for the same purpose.

Determining the Minimum Detectable Activity of Beta Radiation

Firstly, one need to know the efficiency of the detector for the particular radionuclide, then one needs to determine the sampling time to obtain the (statistical) level of confidence that is required(for example, 2 sigma). The detector geometry also needs to be considered in relationship to the source; for example, in case of measuring on a flat surface, only the radiation that decays in the direction of the detector can be detected so, using a 1000 DPM point source with 100% detection efficiency, one will detect approximately 500 DPM.

With the use of the Radalert 100 or the Inspector Alert in the Total mode (accumulated counts) the sensitivity is greatly enhanced by providing a longer sampling period.

FAQs for First Responders

What is the difference between a combination device with base unit having different probes and an all-in-one device?

Combination survey meters that have a base unit with an interchangeable GM probe and/or a scintillation probe are a bulky and expensive solution. An all-in-one device is lighter, easier to operate and less expensive. If you are a sophisticated user and you understand the differences in the probes and you know how to make the appropriate adjustments on the instrument to accommodate them then this may be an appropriate instrument.

Should first responders purchase an instrument that has a sensor that only detects gamma radiation above a certain energy range (e.g. an energy compensated GM)?

It is important that the customer realizes the limitations of instruments that only detect gamma radiation above a certain energy level. We advise that you consider a rate meter that detects gamma between the energy ranges of 15 keV and 10 MeV and also detects alpha, beta and X-radiation.

It is important for a first responder to be able to detect alpha, beta and low energy gamma radiation in addition to high energy gamma radiation because there are many radionuclides that only emit alpha, beta or low energy gamma radiation. If a first responder has an instrument that only detects high energy gamma radiation, that person would not be aware of many possible dangerous radionuclides that could be used for a dirty bomb. For example, Americium 241 mostly emits alpha radiation as well as a little bit of low energy gamma radiation. Americium 241 is found in household smoke detectors and many industrial devices, and this radionuclide could easily be gathered in quantities large enough to make a dirty bomb. In fact, a few years ago, a boy scout gathered enough Americium 241 for a science experiment to endanger his entire neighborhood. Strontium 90 emits only beta radiation. Strontium 90 is a byproduct of nuclear reactors and is found in reactor waste. This radionuclide could also be obtained relatively easily for use in a dirty bomb. Plutonium 239 emits alpha radiation and very little gamma radiation. Plutonium 239 is regarded as highly dangerous and is considered a nuclear weapons material. Additionally, alpha and beta radiation are significant health risks if they are inhaled or ingested. Any of these three radionuclides and a host of others would be impossible or very difficult to detect with a gamma only detector.

Should first responders purchase a dosimeter or a rate meter?

It is important that first responders are equipped with rate meters instead of dosimeters because a rate meter immediately alerts the user to the presence of radiation above the normal background level. A dosimeter alerts the wearer to the fact that the wearer has absorbed a certain predetermined level of radiation. However, it could take the wearer a while to absorb this level of radiation, so the wearer would not be alerted immediately when he/she was in a radiation field. If a first responder was trying to determine if a package or bomb contained radioactive materials, a rate meter would be the appropriate device as it would immediately alert the user to the presence of radioactive materials. A dosimeter would not immediately alert the wearer to the presence of radioactive materials. Rate meters are perfect for users who do not know whether or not they are in the presence of excessive levels of nuclear radiation. A dosimeter is appropriate when the wearer knows that he/she is in a radiation field, but wants to get out before he/she has absorbed too much radiation. A person involved in a clean up situation after a dirty bomb would need a dosimeter, but a first responder responding to the scene of a bomb or a suspicious package would want a rate meter.

Should a first responder purchase a neutron detector?

Neutron radiation is very rare, and it basically only comes from Plutonium 239 which is a weapons-grade radionuclide, operating nuclear reactors and other uncommon isotopes. It would be highly unlikely to encounter neutron radiation, as this would most likely be in the event of a real nuclear bomb, not a dirty bomb. In the event of a nuclear bomb there would be all types of nuclear radiation present, not just neutron radiation. Neutron detectors are also quite expensive. Neutron detectors can be useful for detecting shielded sources of Plutonium 239.

Is the size of the sensor important?

The size of the sensor in a nuclear radiation detector is important. The larger the sensor, the more sensitive the device is in nuclear radiation detection. The larger the sensor, the more likely it is to come into contact with the nuclear radiation that is present.

Should a first responder buy a device that does not have a user adjustable alarm?

Many devices that have a factory pre-set alarm level have high settings in place that cannot be changed. Most first responders would want to be alerted to radiation levels at even low levels.

Should a first responder purchase a device that has 1 to 10 level read-outs?

Our devices have digital displays that tell the user exactly how much nuclear radiation is being detected at any given moment. A product that has a display of numbers 1 through 10 does not actually tell the user what the level of nuclear radiation is.

This information has been sourced, reviewed and adapted from materials provided by International Medcom.

For more information on this source, please visit International Medcom.

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