Answer to Question #8689 Submitted to "Ask the Experts"

Is there any training a physicist can take to learn how to remove radioactive sources that are used as external standards in liquid scintillation counters?

The radioactive sources that are used as external standards in liquid scintillation counters (LSC) generally contain relatively small amounts of activity, often around 3.7 × 10⁴ Bq and generally not more than a few tens of microcuries. Commonly used radionuclides are ¹³⁷Cs, ¹³³Ba and, more recently, ¹⁵²Eu; some older LSCs used ²²⁶Ra as the source. In all cases, even though activities are relatively low, the sources must be disposed of in accordance with federal and state regulatory requirements. The radioactive material is encapsulated in an appropriate capsule to prevent leakage of the radionuclide, and this can be easily manipulated, by a knowledgeable person, with no significant dose impact so that the source can be retrieved and prepared for proper disposal. Such preparation should include leak testing of the source to confirm the encapsulation integrity.

If you work in a facility that has a radiation safety office, I would recommend that you first contact the individual in charge and discuss your plans to remove the source. Representatives of some radiation safety offices will carry out the source removal, handling, and packaging for disposal, although, depending on how the safety program functions, you may incur a charge for the service. Alternatively, you might contact the manufacturer of the LSC system. Many manufacturers also offer a source removal service, but the charges for this will usually exceed what you might be charged by your own radiation safety office. If you have plans to purchase another LSC system from the same manufacturer, you may well be able to work out an exchange deal that would result in little or no extra cost for getting rid of the source.

If you are concerned with only a single LSC unit, I would recommend that you consider one of the above approaches. If you have several LSCs that you are disposing of, then it could be worthwhile for you to obtain training that would suffice for you to handle the operations.

Different LSC manufacturers use different mechanisms for holding and moving the source within the LSC during regular operation. The technical manuals for the LSC may show details of how the source is held within the unit. If not, the manufacturer should be able to provide information necessary for the removal of the source. The major elements of the process involve the physical handling of the source, making appropriate radiation measurements to determine dose rates at fixed distances from the source; leak testing of the source; if the source is to be disposed of, proper packaging of the source; and proper transportation of the source. If you are also planning to get rid of the LSC unit, it should be checked (usually through appropriate wipe testing) to make sure that it is not contaminated with radioactive material (most often from poorly prepared or damaged liquid samples that have been in the machine in the past).

I do not know what your specific background is, but your statement implies that you are a physicist. A health physicist is trained in various aspects of radiation protection and is the usual person who would know how to handle the radioactive sources in question. If your facility has a radiation safety office, you should contact the individual in charge to inquire whether he/she would be willing to provide you with some fundamental training to do the work and/or whether the office could provide assistance or oversight to guide you in the work. Beyond that, there are companies that offer various short-term instructional programs that train individuals in the fundamentals of radiation safety, sometimes with emphases varying with intended specialty areas. Most of these programs probably deal with more than you are concerned with, and the costs may exceed the cost to have an outside firm handle the source removal. I am not aware of any formal training specific to the limited goal you describe, and I suspect your best bet would be to try to take advantage of local expertise.

You may be able to get some additional insight and recommendations by contacting your state radiation control program. You can access any of the state offices through the Conference of Radiation Control Program Directors website. Your state may also maintain a list of health physicists who act as consultants, and you may be able to work with one of these consultants to assist you in meeting your goals. If you wish to pursue the intensive training option you can find a list of some companies that offer various types of intensive health physics training on the Health Physics Society website (look under Training Programs).

George Chabot, PhD, CHP