Answer to Question #1250 Submitted to "Ask the Experts"

While very important in preventing skin contamination/dose to the skin, the use of gloves is just one factor in the radiological protection equation for ³²P. Due to the relatively high energy of the ³²P beta (1.71 Mev Max [Kocher 1981]) I believe the first priority must be given to the use of shielding and remote handling of vials/containers which contain ³²P. The shielding of high-energy betas should be done with low-Z materials like Plexiglas/Perspex to prevent the production of secondary x rays and bremsstrahlung (Cember 1996).

For ³²P a recommended shielding thickness of approximately 1/4 to 3/8 of an inch is usually sufficient. Dose rates on contact with a 1 MBq source of ³²P in an unshielded 50 ml glass beaker or a 5 ml plastic syringe can range from 7.14×10^-4 to 2.4×10 mSv^-h, respectively (Delacroix et al.). The second priority, which addresses your question more directly, must be given to preventing skin contamination and proper monitoring of the work area, clothing, and skin. Prevention of contamination is optimally achieved by wearing two sets of gloves, either latex, butyl, or nitrile based which will be sufficient for most biomedical research handling of all radioactive materials.

The choice of glove material must be primarily based upon the chemical hazard of materials that are being used in the laboratory. Particularly one must consider the ability of the chemicals to either pass through the glove or degrade the glove so it develops rips or tears. A few good sources for glove information and selection are provided at the following Web sites:

• CDC/NIOSH Web page
   
• Dartmouth Web page  

As for monitoring, the outer set of gloves should be checked for contamination throughout the procedure using a pancake Geiger-Mueller-equipped survey meter. If contamination is detected, the outer gloves should be changed immediately, the inner glove surveyed for contamination, and, if clean, a new set of outer gloves put on. As far as what type of beta shielding gloves provide, this can be determined by using the computer code VARSKIN (NUREG 1992). However, in my opinion, wearing very thick gloves to attempt to achieve some beta shielding is not recommended. Wearing very thick gloves will reduce the tactile ability of the researcher and may increase the potential for spills and resulting contamination. In addition, it is important to discard contaminated gloves frequently throughout the procedure to reduce the spread of contamination to other equipment (such as pipettes, stirrers, etc.) and work surfaces.

If you look at the effect of adding glove thickness, "standard" vinyl, latex, and nitrile gloves add a density thickness of approximately 9.5, 11.9, and 11.7 mg cm^-2 respectively. These thicknesses were taken from the cuff, the thickness on the finger-tips can be about 50 percent greater. These gloves do reduce the beta dose. If we examine dose rates (Sv y^-1 per Bq cm^-2) as a function of depth we see that to reduce the dose rate by approximately factor of two from the dose at 7 mg cm^-2 (2.1×10^-2 to 1.1×10^-2 Sv y^-1 per Bq cm^-2) of ³²P on the skin (Kocher and Eckerman 1987), it takes a total added thickness of about 33 mg cm^-2, which represents approximately two to three pairs of standard gloves.

A typical pair of gloves (at 11 mg cm^-2) will reduce the dose rate by approximately 20 percent as calculated by VARSKIN. Finger-tip glove thickness (the thicker part of the gloves) ranges from 0.11 mm to upwards of 0.24 mm for SafeSkin Corp Nitrile (Purple Knight) and Latex (PFE-XTRA) gloves (Safeskin 2001). Our recommendation is to use Plexiglas-shielded vials/containers (shielding), do remote handling of vials using tongs (distance), double-glove, monitor, and change contaminated gloves frequently.

It is also important to optimize your efficiency and reduce the total amount of handling to a minimum (time). Thus, we use the three basic principles of radiation safety—TIME, DISTANCE, and SHIELDING—to reduce exposure. A fourth element, control of contamination by monitoring and glove changing, addresses the reduction of skin dose due to contamination. All individuals handling high-energy beta emitters should be evaluated for the use of extremity dosimeters and dosimeter placement to assure that representative exposure assessments are being performed. Typically researchers handling µCi to several mCi quantities of ³²P do not require dosimetry and exposure of the extremities is not a concern, particularly if the principles which we have outlined are followed.

Shawn W. Googins, MS, CHP
Karl W. Fischer, ME

References

• Kocher D. Radioactive decay data tables 1981. Oak Ridge National Laboratories: ISBN 0-87079-124-9.
   
• Cember H. Introduction to health physics. 3rd ed. (pp 129-131); McGraw-Hill: ISBN 0-07-105461-8; 1996.
   
• Delacroix D, Guerre JP, Leblanc P, Hickman C. Radionuclide and radiation protection data handbook 1998. Rad Prot Dos 1-2. Nuclear Technology Publishing. ISBN 1-870965-51-5; 1998 VARSKIN Mod 2 and SADDE Mod 2 - Computer Codes for Assessing Skin Dose from Skin Contamination NUREG/CR-5873,PNL-5610 (November 1992, Revised Oct/Dec 1994).
   
• Kocher DC, Eckerman KF. Electron dose rate conversion factors for external exposure of the skin for uniformly deposited activity on the body surface. Health Phys 53:135-141; 1987. Table taken from The Radiological and Health Physics Handbook. 3rd ed. (pp 13-23); Williams and Wilkins: ISBN 0-683-18334-6.
   
• SafeSkin and Shieldmaster Corporations Product Data Sheets; 2001.