Answer to Question #8191 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Personnel Monitoring (PM)

The following question was answered by an expert in the appropriate field:

Q
I am interested in checking my public-level exposure to radiation with a dosimeter. I want to buy a passive dosimeter to measure my exposure dose to x-ray and neutron emission. I was wondering if you can recommend any brand/type of dosimeter that is resilient to electromagnetic interference and is relatively inexpensive.

A

I do not know whether you are presently employed as a radiation worker or have any other experience that familiarizes you with dosimetry devices; I shall assume you do not and go from there.

There are various companies that manufacture and/or distribute personnel dosimeter devices for measurement of dose from x rays and/or gamma rays. Some also provide neutron measurement capability. A passive device accumulates a signal in response to energy deposition by ionizing radiation; the cumulative signal then has to be read out in an appropriate fashion and, through a calibration process, the signal is related to dose to the individual who was wearing the device.

The commonly used passive devices are film, thermoluminescent dosimeters (TLDs), and optically stimulated luminescence (OSL) devices, with the latter two being currently more common than film. Film and TLDs can be specially fabricated/adapted to make them sensitive to neutron exposure as well as x and gamma rays (and some charged particles). The larger vendors of these devices commonly use a different system, using a plastic material (commercially referred to as CR-39) in what is called a track etch detector to assess dose from energetic neutrons. The types of devices referred to above are free of any sensitivity to extraneous electromagnetic interference.

Vendors of these personnel dosimetry devices commonly offer services to facilities that employ radiation workers. The devices are supplied on a regular basis, commonly monthly, worn by employees likely to be exposed to radiation, and returned to the vendor for processing. The vendor then supplies the dose results to the facility receiving the service. Costs vary, depending on what dosimetry is being supplied and how many people are being monitored.

It is possible for the user, him(her)self, to process the dosimeters, but this typically requires a rather large investment (often tens of thousands of dollars) in the equipment necessary to do the processing and necessary radiation sources to carry out appropriate calibrations to determine the dose responses of the devices being used.

If a facility has a large number of employees being monitored, the cost per individual for a vendor to supply the necessary dosimetry devices and to carry out the dosimeter processing may be quite small (possibly a couple of dollars per individual per month for monthly processing).

Costs per participant tend to get higher as the number of monitored individuals decreases. I suspect that a single individual, such as you, might have difficulty getting a vendor to provide you with passive dosimetry of the sort mentioned here at a reasonable cost. However, if you want to try, you can find some links to providers of personnel dosimetry on the HPS website where there is a Buyer's Guide available that is comprised of affiliates of the Society. You can also find vendors on the internet by searching under personnel dosimetry or related topics. One consideration that is important to keep in mind is that some of these devices (TLDs and OSL dosimeters, but not film) can be used for an extended period, from several months possibly up to year, before they need to be processed. For someone who wants just a record of dose over an extended period, the cost might be quite small compared to some of the other options.

There are various active devices that are also used to assess doses to personnel. These are in use among radiation workers and some have also garnered favor with personnel involved in emergency response and homeland security. They have the advantage that they provide a real-time indication of the dose or dose rate. Many of these are electronic devices, often small enough to fit into a shirt pocket or be clipped on a belt, that provide a visible display of the accumulated dose and/or dose rate when exposed to ionizing radiation. Most of the devices have been intended for gamma or x-ray dose assessment, but there have been some made that are also sensitive to neutrons. These devices frequently cost from about $200 to more than $1,000 each, depending on specific characteristics and the number being purchased. Some companies that offer various versions of these electronic dosimeter devices are available through the link to the HPS Buyer's Guide cited above. You can also find vendors by searching for "electronic dosimeters" on the internet. Neutron-sensitive electronic dosimeters are more rare than x and gamma sensitive devices, and you may have to consult the manufacturers to evaluate their capability.

In addition, there are some less expensive personnel monitoring devices that are not as sophisticated as some of the above electronic dosimeters that might be of some interest. One example is the self-reading pencil (or pocket) dosimeter that is basically a small electroscope that discharges in response to ionizing radiation (primarily x or gamma rays); the movement of the "leaf," usually a lightweight quartz fiber, is viewed through self-contained optics. Such devices usually cost about $150; unfortunately, you will also need a charger to charge the device, and this will cost around $200.

You can see examples of the pencil dosimeter (and charger) at various vendor sites. There is also at least one relatively low-cost electronic device that responds to x and gamma radiation by producing flashing lights for which the frequency of the flashing depends on the dose rate. The color of the flashes changes from green to red, and an audible alarm sounds when the dose rate exceeds a preset level (this is the K-8 device shown on the Ludlum site). This last device is not heavily RF-shielded and may give a false reading when exposed to some electromagnetic fields.

Beyond the dosimeter-type devices, there are a variety of handheld instruments that are available for measuring radiation, and you can see some of these at some of the same sites that deal with personnel dosimeters and at other sites such as those available at the cited HPS Buyer's Guide under Health Physics Instrumentation. Some of these are not any more expensive than some of the electronic dosimeters, although they do not offer the convenience of being able to be held in a pocket or on the belt. I am sorry that there is a not a simple and satisfactory answer to your question. Good luck in your pursuits.

George Chabot, PhD, CHP

Answer posted on 2 April 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.