Radiation Detection

December 1, 2006
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Radiation detection has become increasingly applicable in industrial settings as technologies using radioactive materials have migrated into many new territories. Those who work with radioactive materials need special equipment to ensure their safety and the safety of those around them.

Equipment types

There are four main types of radiation detection instruments found in industrial and response applications: personal radiation detectors, dosimeters, identifiers and survey meters. All have inherent strengths and weaknesses, depending on how and where they are applied.

Personal radiation detectors — A personal radiation detector (PRD) is a small pager-like device that measures radiation dose rate. Its main purpose is to alert the wearer to the presence of radiation as quickly as possible. In addition to fast response times, PRDs have intrinsic safety certifications and are designed for reliable use in unknown environments.

Most detectors use scintillation crystals to detect gamma or neutron radiation. Gamma radiation is the most abundant and easiest to detect. Neutron radiation is much rarer, but can be deadly in smaller doses than other types of radiation, and is an indicator of potential weapons-grade materials, such as plutonium. Typical scintillator crystals are made of cesium iodide (CsI), sodium iodide (NaI), or lithium iodide (LiI) because of their fast response time. Other detectors use semiconductor sensors composed of cadmium-zinc-telluride (CZT) or silicon.

Dosimeters — A dosimeter accurately measures the accumulated radiation dose that the wearer receives while wearing the dosimeter. The radiation sensor in a dosimeter is energy compensated, which translates to a more accurate total dose measurement.

Dosimeters come in many forms, from film badges to self-reading electronic pagers, and use Geiger-Mueller tubes or silicon sensors to measure gamma, alpha, beta and neutron radiation doses. Most electronic personal dosimeters (EPDs) measure only gamma radiation because it is the most likely type of radiation exposure.

Identifiers — Identifiers are instruments that use the differences in radiation emission energies to determine which radioisotope is present. Every radioisotope has a unique “signature” of radiation emission types and energies that allows an instrument to identify it. Identifiers are mainly used to determine an unknown radioactive source or contamination. They are larger than both detectors and dosimeters, and come in many form factors.

Identifiers typically employ scintillation crystals (CsI or NaI) or semiconductors (CZT or germanium). Units utilizing scintillators tend to be able to identify radioisotopes faster than those using either CZT or germanium. CZT and germanium sensors are more accurate if multiple sources are present, but require longer sampling times.

Survey meters — Survey meters measure radiation levels using the same radiation sensors employed in detectors and dosimeters. They are the oldest type of device discussed here, and have a probe that’s held in one hand and a meter box held in the other. Each probe is specifically tailored to a particular type of radiation, and can measure gamma, neutron, alpha or beta radiation levels.

Make the appropriate choice

Most users only need one or two device types. The following are suggestions for the types and minimum amounts of equipment needed to successfully detect radioisotopes.

First responders – fire and hazmat
  • One personal radiation detector per person
  • One identifier per team (optional, hazmat only)
  • One survey meter per team (optional)

First responders in firefighting and hazmat (hazardous materials) need the most rugged and fastest-responding equipment possible to work in unknown hazardous environments. Since hazmat responders may be exposed to significant amounts of radiation, a detector-dosimeter combination instrument is ideal. Responders near high risk areas for a terrorist attack or close to facilities that house fissionable materials should have at least some team members equipped with detectors for gamma and neutron radiation.

Emergency medical services teams
  • One electronic personal dosimeter or detector-dosimeter combination per person
  • One identifier per vehicle/team (optional)
  • One survey meter per department (optional)

Emergency medical services personnel may be exposed to radiation if they are responding to an incident where an area and people in that area have been contaminated with radioactive material. Because life-threatening conditions must be tended to before decontaminating a victim, EMS personnel may be exposed to radiation or contaminated, and their accumulated radiation exposure needs to be measured to ensure they do not receive too high a dose. One dosimeter or detector-dosimeter combination, worn on the torso, is recommended for each EMS responder.

Law enforcement/security
  • One personal radiation detector per person

Law enforcement and security officers (at nuclear, medical, industrial facilities or high-risk buildings) need fast-responding equipment and, therefore, each officer should be equipped with a radiation detector. Because a first response team should be called in an alarm situation, it is not typically necessary that a security team have additional equipment. However, security personnel at a nuclear facility or other place where radioactive material is regularly transported or stored may be called upon to act as first responders and, as such, should be outfitted with the same equipment as a first response team and should consider detectors that measure both gamma and neutron radiation.

Radiation workers
  • One dosimeter per person
  • Identifiers for health physics (optional)
  • Survey meters for health physics

Radiation workers are specially trained people who work in facilities where large amounts of radioactive material are stored or used, and who regularly enter radiation fields as a result. Each radiation worker should wear a dosimeter when entering a radiation area. Identifiers can be used to identify contamination around the facility. Radiation field strengths are mapped by a health physicist using a survey meter, and are updated frequently.

Workers in industrial facilities
  • Survey meters as needed
  • Personal radiation detectors for workers entering into areas where radioactive material is stored/used

Many industrial facilities, such as refineries and chemical and manufacturing plants, house radioactive materials in the forms of liquid level gauges and imaging and sterilization equipment. This equipment should not require personnel to be trained as radiation workers. Personnel entering areas where the radioactive material is stored should wear a personal radiation detector to alert them to any leaking sources and high dose rate areas, and at least one survey meter should be on the premises to ensure that no sources are leaking and that a safe dose rate is maintained around the sources. Workers at refineries and chemical plants have the additional need for intrinsically safe equipment.

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