Document: NRC Regulatory Guide
Document ID: 688895c2-d1d9-44f3-9c79-3cf0daa88510
Document Type: regulatory_guide
Title: 
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML0037/ML003739541.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.5
CFR Part: 
CFR Title: 

Content:
Rinme the disc with H20, and dry it on a hotplate at medium heat for 5 min. The sample is ready for counting. F. Counting A properly electrodeposited sample should be free of residue. Normally, three plutonium peaks are distinguishable, the Pu-239/Pu-240 peak at 5.11.5.17 MeV. the Pu-238 peak at 5.46-5.50 MeV, and the Pu-236 peak at 5.72.5.77 MeV (or Pu-242 peak at 4.86-4.90 MeV). Since Pu-238 is readily resolved from the other plutonium isotopes, it is often advantqaous to use the Pu-238 to Pu-239/Pu-240 ratio as a possible tag for identifying the various sources from which the plutonium may have been released. In those cam where Pu-238 activity is very low, it is well to remember that Ani-241 has essentially the same alpha energy (5.44-5.49 MeV) as Pu-238 and will therefore add to the Pu-238 count if present. Although Am-241 is chemically removed from the plutonium fraction by this procedure, fresh Am-241 continues to grow in from the Pu.241 present. Depending on the amount of Pu-241 in the sample mad the ingrowth period, Am-241 activity could add sipdcantly to the Pu.238 peak. It is desirable, therefore, that the plutonium be counted as early as possible after its isolation. Traces of Pu-238 may be present in some Pu-236 sources; because of the relatively short half-life of Pu-236 (1,041 days), this problem worsens with age. Each Pu-236 source should be checked for potential contamination by other plutonium isotopes. Each plutonium isotope should be accurately determined as a fraction of the Pu-236 activity and should be corrected for in the analysis. Older Pu-236 sources also contain U-232 and Th.228 daughters with alpha energies in the 5.3 - 5.4 MeV range. Therefore, the plutonium fraction should be chemically isolated before a check is made for other plutonium isotopes in the Pu-236 source. Plutonium-236 should be corrected for decay if the decay period exceeds IS days. PFutonium-242 tracer, if available, could he used instead of Pu-236. There are several