Answer to Question #162 Submitted to "Ask the Experts"

Category: Policy, Guidelines, and Regulations — Policy and Cost-Benefit Issues

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

Using the new ANSI/HPS N13.12-1999, would it be permissable to have removable contamination of up to 6000 dpm/100 sq cm for Ir-192 as a screening level for clearance? Removable contamination levels per 4.6 does not seem very clear. Does anyone have clarification?

Iridium-192 is one of the Group 2 radionuclides, with a derived screening level of 6,000 dpm/100 cm². This level would be the total contamination allowed as either fixed or removable, or a combination of both, unless other radionuclides are present. If a mixture of radionuclides is present, the contribution of each to the total screening level is found using the sum of fractions rule. While the screening levels in ANSI N13.12 do not differentiate between fixed and removable contamination, it is recognized that radiation protection programs have typically imposed an additional limit on removable contamination, depending on the situation, to foster contamination control and in keeping with ALARA. Section 4.6 of the standard simply recognized that, under some conditions, measurements of removable contamination may be appropriate and may be included in the survey protocol. Examples are for characterizing hard-to-detect surfaces (inside pipes) or for estimating the levels associated with hydrogen-3.

William E. Kennedy, Jr.,

Chairperson ANSI/HPS N13.12-1999 Working Group

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