Wipe tests measure for removable radioactive contamination—contamination that transferred by one surface coming into contact with another, e.g., from a bench top to a person’s hand.
When do I survey?
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Mandatory:
Recommended:
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How do I document my surveys?
Must be reported in dpm or μCi. If the LSC does not print in dpm, then a conversion between cpm and dpm must be shown on each test.
Must document decontamination of areas above 200 dpm/100 cm2 or 9.1×10-5 μCi/100 cm2
Tests must be dated
LSC printout must be attached
How do I set up my LSC?
LSC should be set up to evaluate entire spectrum. For Beckman counters, this covers from 0-1000 channels.
If your counter reports in dpm, RS recommends
using a dual dpm label with a third channel.
Gives dpm for H-3 and C-14 channels
Gives cpm for P-32 channel. As P-32 is nearly 100% efficient, this is as good as a dpm reading.
Covers from 0-1000 channels. Any contamination will show up somewhere inside those channels.
Help! My LSC does not report in dpm!
Use a wide or open window setting on your LSC to evaluate your samples
Use contamination wipe survey results sheet http://www.ehs.umaryland.edu/rad/pdf/contamination.pdf
List the efficiencies for all the nuclides on your authorization (exceptions would be sealed sources and I-125 used only in the Central Iodination Facility).
Using
the minimum efficiency, calculate the cpm equivalent of 200 dpm (action level
= efficiency x 200 dpm)
e.g., action level = 75% efficiency X 200dpm = 150 cpm
any
sample in any channel over the action level would need to be decontaminated.
The efficiency for H-3 and C-14 can be determined using your LSC standards
For all other nuclides, please contact your service technician.
What if I use gamma-emitters?
If you have access to a gamma counter, you should use that to evaluate the locations in which you work with gamma emitters, in addition to wipe tests for your beta emitters
If you do not have access to a gamma counter, then calculate an action level as specified above based on the efficiency of your gamma emitters in a wide or open window of your LSC
Final notes:
Remember wipe tests are to be analyzed only in your authorized counting room. If your liquid scintillation counter is not working correctly, you may bring your wipe tests to Radiation Safety for evaluation.
Your help in improving safety at the University
is appreciated!
Safety Alert #0416
Safety Alert Archive