Electronic personal dosimeters (EPDs) provide one of the newest forms of dosimetry. In real time, EPDs provide users feedback on their exposure to radiation.
For example, the MBD-2 Tactical/Occupational Personal Dosimeter from Mirion Technologies is a real-time, self-indicating device that operates without user intervention. Intended for field use in military and homeland security applications, the EPD is based upon the company’s patented Direct Ion Storage (DIS) technology. DIS technology detects ionizing radiation by using an ion chamber detector combined with a simplified method for computing dose from a voltage value obtained from the detector.
The EPD measures and records dose for gamma and neutron with the capability of measuring pulsed X-ray measurements to 65 nsec pulses. Worn on the wrist with a watch-type design or clipped to a garment with a badge-type format, the device provides easy self-reading through a programmable display for effective decision making.
Another EPD employs a different sensing technique using three silicon diode detectors. Each detector provides a signal to dedicated amplifiers and counter circuits to measure soft gamma, hard gamma and beta radiation. The outputs from each detector chain are processed to calculate exposure rates. Radiation detected by the EPD is processed to give a real-time readout to the user via a liquid crystal display (LCD) for deep dose and skin dose rates.
Time-Weighted Average Exposure and Noise Dosimeters
In addition to radiation, workers in many industries can be exposed to other harmful factors, such as noise and hazardous substances such as dust, fumes, chemicals, gases or vapors that can accumulate over extended exposures to cause serious health problems. The time-weighted average (TWA) is a method of calculating a worker’s daily exposure to specific substances. Averaged to an 8-hour workday (or 40-hour week), along with the average levels of exposure to the hazardous substance and the time spent in that area, the TWA reflects the maximum average exposure a worker can be subjected to without experiencing significant adverse health effects over the standardized eight-hour work period. It is expressed in units of parts per million (ppm) or mg/m3.
In factories and other industrial environments exposure to noise is one of the hazardous factors commonly regulated by many governments including the U.S. Occupational Safety and Health Administration (OSHA). For example, the doseBadge noise dosimeter mounts on the shoulder, where it continuously monitors the sound levels that the worker is being exposed to.
Unlike a hand-held sound level meter that can measure the typical sound levels at various work locations and then put them all together to calculate the overall exposure or TWA, a noise dosimeter that stays with the worker can measure/calculate the noise exposure automatically.
Four independent channels allow simultaneous monitoring to address compliance to different regulations, such as OSHA and ISO. The main measurement parameters include Lavg – average sound level with slow time weighting and thresholds, TWA, dose (in %) and peak. The self-contained noise dosimeter has no cables and mounts on the worker’s shoulder.