Dear Dr. Zoomie – I’m trying to figure out what goes into a radiation survey program and I have to admit I’m drawing a blank. Can you tell me how often I should be doing radiological surveys? Also, can you tell me how to do a survey? Thanks!
I should start by saying that I can often make a pretty good guess about the quality of a radiation safety program by looking at the quality of their surveys. In general, if I audit your facility and see that you’re doing your surveys properly then it’s pretty safe to say that the rest of your radiation safety program is likely to be squared away; at the same time, if you’re missing surveys or being slipshod in your survey technique I’m probably going to find other problems as well. Now, let’s talk about what goes into a survey program and how surveys are performed.
When to survey
We’ll start with when you should be surveying. First, there is no regulatory requirement on this – your survey requirements will be set by your internal procedures, your license application, and your license conditions. You’ll have to use your own judgement as to how often various areas need to be surveyed – if you don’t have the experience to make this decision on your own it’s not a bad idea to ask a consultant for suggestions, or even to ask your regulators what they recommend. Here are a few things to think about:
- Will people be using unsealed sources of radioactivity? For example, are they working with radiopharmaceuticals or radiolabeled compounds that can cause a spill? If so, you might want to ask people to survey workbenches or fume hoods for contamination daily when the area is in use and to survey the entire room (laboratory, hot lab, etc.) monthly.
- Are there activities taking place that can be expected to cause contamination? For example, in a rad waste storage room, are you compacting waste, crushing vials, or moving a lot of packages? If so then you should consider surveying for contamination at least weekly, as well as after any potentially contaminating activities.
- Are you storing radioactive materials in the area? If so then you should consider surveying for radiation at least every six months, as well as after any movement of radioactivity into or out of the area.
- Do you have radiation-generating machines (x-ray, electron microscopes, etc.)? If so, you might be required to survey annually for radiation leakage, scattered radiation, and/or the effectiveness of your shielding. If the device will be used for medical diagnosis or treatment there will be other requirements as well, including routine quality insurance checks on a daily, weekly, monthly, quarterly, or semi-annual basis.
- Have you had maintenance on anything that could affect your radiation shielding? Have you had an earthquake, flood, or anything else that could damage your shielding? If so, you should perform a radiation survey as soon as conditions stabilize to make sure the shielding is still intact and doing its job.
These are some of the most common circumstances and your facility might not fit into any of these categories. The important things are to think about how frequently people are using radiation and radioactivity, how potentially dangerous it can be, and what can happen that could cause radiation or contamination to be higher than what you’d normally expect (or want) them to be.
The next part of this discusses (briefly) how to perform radiation and contamination surveys. But please not – this is not the same as receiving formal training – this is a guide, but you should really receive appropriate training and develop a formal survey procedure before you do your own surveys. And remember – before you start ANY survey, make sure your instrument is in calibration, check to make sure the batteries are OK, ensure the meter, probe, and cable are all in good condition, and (for count-rate instruments) make sure to response check against a source of known strength.
Performing radiation surveys
Performing radiation surveys isn’t too difficult – mostly you’ll be walking around with your radiation dose-rate meter watching the dial; make a note of the dose rate on your survey map anyplace from time to time, especially in places where dose rates are higher than the rest of the area being surveyed. As a default, hold your meter about waist-high unless you’re measuring a specific location (say, in front of a source storage safe or a low-temperature freezer). Finally, you’re most interested in dose rates in “accessible areas” – that’s about one foot (30 cm) from any surface, and only in areas where a person could actually be expected to enter. So you don’t need to survey inside of refrigerators or fume hoods unless you expect people to spend a lot of time inside of them. Oh – and make sure that your meter has been calibrated within the last year so that your survey counts! All of your meters have to be calibrated annually (according to regulations) and you can’t meet a legal requirement with an illegal meter.
Performing contamination surveys
The key to any contamination survey is “low and slow.” You want to keep the detector as close as possible to whatever it is that you’re surveying without being so close that you contaminate the detector. And you want to move the detector no more than about 2-3 inches (about 5-8 cm) per second. If you hold the detector too far away you can miss some contaminated areas, and if you’re surveying too quickly then the probe might not be over a contaminated area long enough to pick up any counts. You should also try to survey as much of the surface as possible – 100% of the surface if you can – to avoid missing any contamination.
Alternately, you might want to perform a smear wipe survey to look for removable contamination (contamination that could come off on your hands or feet) – especially if you’re looking for radionuclides (such as tritium or carbon-14) that aren’t easily detected by hand-held radiation detectors. For a smear wipe survey you’ll need to use a piece of dry filter paper (a Watman or Milipore filter will do the trick) and you’ll need to wipe an area of 100 square centimeters (about 4”x4”). Apply enough pressure to the wipe to pick up any loose contamination, but not so much that you tear the wipe.
After you’re done with your survey you’ll have to records your results on a survey map; your survey map will have to be filed and maintained for three years (under normal circumstances) or longer if your survey is used to reconstruct the radiation dose to one of your workers. And – again – remember that there’s more to doing surveys than what’s provided here; this will give you a start, but there’s a lot more to the topic than what’s written here.