Calibration of the Geiger Counter and Technical Advice For First Responders

Certain Geiger counters especially previous designs need calibration for making sure that the readings are accurate. The instruments from International Medcom include innovative design techniques and high-quality components. In over 26 years of manufacturing of the Radalert, Radalert 50, Radalert 100, the Inspector, Inspector Alert and similar instruments, the company ascertains that these instruments maintain their original calibrations remarkably well.

Frequency of Calibration

Certain facilities require calibration certificates or annual calibration with an NIST-traceable source. After manufacture, these instruments are electronically calibrated and except for the CRM-100, an electronic calibration certificate is shipped along with each order. In case, NIST-traceable calibration is needed, it can be offered at an additional fee when the order is placed.

If the instrument is for educational purposes or as a hobby, calibration is not need on a regular basis, however periodic checking against a known radioactivity source makes sure it is working perfectly. If the instrument is used professionally in an environment with radioactive materials, a calibrated check source can be periodically used for the same purpose.

Determining the Minimum Detectable Activity of Beta Radiation

In order to determine the minimum detectable activity of beta radiation the following factors need to be considered:

  • Firstly, it is essential to know the efficiency of the detector for the specific radionuclide, after which the sampling time needs to be determined to obtain the needed statistical level of confidence.
  • It is also important to consider the detector geometry with respect to the source for instance, in case of conducting measurements on a flat surface, only the radiation that decays in the direction of the detector can be detected hence using a 1000 DPM point source with 100% detection efficiency, it is possible to detect approximately 500 DPM.
  • By using the Radalert 100 or the Inspector Alert in the total mode (accumulated counts) the sensitivity is considerably improved by enabling a longer sampling period.

Technical Advice for First Responders

Difference between a Combination Device with Base Unit with Different Probes and a Comprehensive Device

Combination survey meters having a base unit with an interchangeable GM probe and/or a scintillation probe are a bulky and costly solution. A comprehensive device is light-weight, easy to operate and less costly. This may be a suitable instrument if you are an advanced user and are conversant with differences between the probes and know how appropriate adjustments have to be made on the instrument to accommodate them.

Type of Instrument to be Purchased by First Responders

The customer must understand the limitation of instruments that detect gamma radiation above a certain energy level. A first responder can consider a rate meter that senses gamma between the energy ranges of 15 keV and 10 MeV and also detects alpha, beta and X-radiation. The first responder must be able to detect alpha, beta and low energy gamma radiation as well as high energy gamma radiation because since there are a number of radio nuclides that only emit alpha, beta or low energy gamma radiation.

In case a first responder has an instrument with capability of detecting only high energy gamma radiation, it is possible that many possible dangerous radionuclides that could be used for a dirty bomb are not detected. Some examples are:

  • Americium 241 normally emits alpha radiation as well as a small amount of low energy gamma radiation. It is found in household smoke detectors and many industrial devices, and this radionuclide could be very easily accumulated to a quantity that will make a dirty bomb.
  • Only beta radiation is emitted by Strontium 90. Strontium 90 is found in reactor waste and is a byproduct of nuclear reactors.
  • Plutonium 239 emits alpha radiation and very less amount of gamma radiation. Plutonium 239 is considered highly dangerous and is considered a nuclear weapons material. Furthermore, alpha and beta radiation are significant health risks in case they are ingested or inhaled. Any of these three radionuclides and several others will be impossible or very difficult to detect with a gamma only detector.

Need for Purchase of a Rate Meter or Dosimeter by First Responders

It is essential for first responders to be equipped with rate meters instead of dosimeters since a rate meter instantly alerts the user if radiation is present above the normal background level. The wearer is alerted by the dosimeter that he has absorbed a specific amount of radiation. However, it will take some time for the wearer to actually absorb the radiation hence the wearer would not be alerted immediately when she/he was in a radiation field. In case a first responder was trying to find out if a bomb or package contained radioactive materials, a rate meter will be the right device as it will immediately alert the user to the presence of radioactive materials.

A dosimeter is suitable 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 who is in a clean-up situation will require a dosimeter whereas a first responder responding to the scene of a bomb or a suspicious package would require a rate meter.

Need of Purchase of Neutron Detector by First responder

Neutron radiation comes only from Plutonium 239, which is a weapons-grade radionuclide, operating nuclear reactors and other uncommon isotopes. Neutron radiation may not be encountered, as this would occur in the case of a real nuclear bomb not a dirty bomb. When there is nuclear bomb, there will be all types of nuclear radiation, also neutron detectors are quite costly. Neutron detectors can be used to detect shielded sources of Plutonium 239.

Sensor Size Considerations

The sensor size is very important in a nuclear radiation detector. The larger the sensor size, the more sensitive the device is as well as the more likely that it comes into contact with nuclear radiation.

Device with an Alert System

Many of the devices have a factory pre-set alarm level with high settings in place that cannot be changed. Most first responders will 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?

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

About International Medcom

International Medcom was founded in 1986 to develop and produce high quality radiation detection instruments and systems. Medcom serves individuals, institutions and communities concerned with health and safety, environmental protection, and education. Medcom instruments are widely used throughout the world, and meet stringent European standards for safety, quality and accuracy.

International Medcom has been selected to provide community monitoring systems for the community surrounding Three Mile Island, and the community surrounding the Seabrook nuclear power station. The TMI monitoring system was developed in cooperation with a blue ribbon scientific panel chaired by Dr. Karl Morgan, known as the Father of Modern Health Physics. The system was mandated by a Federal Court order, and is operated by an independent nonprofit grass roots organization, Three Mile Island Citizens' Monitoring Network (TMI-CMN), in partnership with the City of Harrisburg. The Seabrook monitoring project is operated by C-10 Radiological Monitoring Network, also a grass roots nonprofit organization, and funded by the Commonwealth of Massachusetts Legislature.

Technical achievements of the Medcom team include a highly stable and sensitive portable gamma spectroscopy meter designed to detect smuggled Uranium 235 at borders in Khazakstan and Belarus. This project was developed under the Mutual Threat Reduction Treaty, mandated by Nunn-Lugar.

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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  1. Sharon Reidy Sharon Reidy United States says:

    This article says that "these instruments are electronically calibrated and, except for the CRM-100, an electronic calibration certificate is shipped along with each order." Is the CRM-100 not calibrated, too? If so, does it not need calibration?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of

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