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From: Ralph Stuart <membership**At_Symbol_Here**DCHAS.ORG>
Subject: [DCHAS-L] Dept of Energy EHS Lesson Learned: Detector Contamination Dispersal
Date: Tue, 17 May 2022 15:47:34 -0400
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID: 358767D0-220A-41D6-8814-5F39065A3350**At_Symbol_Here**dchas.org
https://doeopexshare.doe.gov/OPEXShareFiles/pdf/38393_LL-2022-6%20Detector%20Contamination%20Dispersal.pdf
Please post ‰?? approved for unlimited distribution at and outside LLNL
LL-2022-LLNL-6 LLNL-POST-835327 May 17, 2022
Detector Contamination Dispersal
A researcher was conducting experiments that required implanting the radioactive isotope beryllium-7 (Be-7) into a detector. Implantation was done at an external facility that can produce a beam of Be-7 ions. The Be-7 was implanted through a silicon collimator and into the detector at a voltage of 25 kV. This high voltage contributed to an expectation that the Be-7 would be non-dispersible (higher voltage = faster ions = deeper implantation into the detector).
When the detector assembly with the collimator was delivered to LLNL, the surfaces of the package were surveyed for gross radioactive and toxic metal contaminations and found to be free of contamination.
The researcher unpacked the assembly in their laboratory, placed it in their private vehicle, and transported it to a nuclear counting facility to confirm the implanted dose. The assembly was not placed inside a plastic bag or other secondary containment, and no Controlled Material ID (CMID) tag (normally used to ensure the appropriate transfer of controlled materials between buildings) was filled out. Once the initial count was complete, the researcher transported it back to their laboratory in their private vehicle. Soon after, it was discovered that the detector with the implanted isotopes had dispersed some of its radioactivity and contaminated parts of the counting facility. The dispersal was detected because the instrument used to quantify the implanted Be-7 dose detected a Be-7 signal after the detector was removed. The counting facility had to be closed to decontaminate the affected areas.
Fortunately, no radioactive contamination was detected in the researcher‰??s vehicle.
Contaminant dispersal. Radioactive materials implanted into solid-state detectors and collimators can still be dispersible, even when implanted at high voltages such as 25 kV. Also, it is possible that surface dust particles absorbed some of the radioactive ions from the Be-7 beam at the implantation facility.
The package contents were not surveyed upon receipt because the exterior was found to be free of contamination and standard procedure is not to open packages for surveying upon receipt.
The detector was not surveyed for Be-7 dispersal after opening the package in the researcher‰??s laboratory because these detectors are very fragile, the radioactivity was understood to be non-dispersible, and surveying package contents as part of unpackaging was not standard procedure for presumed non- dispersible materials.
If surface dust particles were contaminated as a result of absorbing some of the radioactive ions from the Be-7 beam at the implantation facility, they could be dispersed by flipping the detector over for measurements or other handling. The detector was flipped over for measurement at the counting facility to orient it to the counting instrument.
Contamination of the counting facility could have been avoided if the sample were in a sealed plastic bag or other secondary containment as required. It would have been possible to confirm the Be-7 source while the detector was wrapped in an appropriate secondary containment.
Personal vehicle use. Radioactive Be-7 decays over time. Decay decreases the signal, makes the experiment less meaningful, and imposes time constraints on the researcher. Government vehicles were available, but the (uncleared) researcher did not know about them because the keys and check-out documents were kept in a limited area and inaccessible to the researcher.
‰?˘ Assume that any radioactive source material is dispersible and implement procedures and practices that respond to this. Radioactive sources and detectors received in the future will be checked for contamination when their packaging is opened to detect any dispersed contamination as soon as possible.
‰?˘ Ensure that radioactive source materials are placed in appropriate secondary containment for transport and, when practical, storage, evaluation and/or use.
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