X hits on this document

PDF document

Date: August 10, 2009 - page 7 / 16

33 views

0 shares

0 downloads

0 comments

7 / 16

A9.06057E-1 & 2

45Z09

09-810-7932-04

A9.06058F-1 & 2

46Z09

09-840-9175-01

A9.06059G-1 & 2

47Z09

09-810-8213-05

A9.06060Z-1 & 2

48Z09

09-810-8037-04

A9.06061A-1 & 2

49Z09

09-840-9961-02

A9.06062B-1 & 2

50Z09

09-840-9139-07

A9.06063C-1 & 2

51Z09

09-840-9858-07

A9.06064D-1 & 2

52Z09

09-840-9962-09

A9.06065E-1 & 2

53Z09

09-840-9707-02

A9.06066F-1 & 2

54Z09

09-810-8036-04

A9.06067G-1 & 2

55Z09

09-810-8235-04

A9.06068H-1 & 2

56Z09

09-810-8236-01

A9.06069YJ-1 & 2

57Z09

09-810-7339-01

A9.06070YB1 & 2

58Z09

09-810-8357-09

Analysis at NAREL

The 21 samples were counted without re-packaging, however, NAREL re-weighed each sample. Twelve high-purity germanium (HPGe) gamma-ray detectors of various types and sizes were used. NAREL uses peak background correction based on 3000-minute background measurements. The most recent back-ground measurement, started on July 2, 2009, was used. Count time was preset to 170,000 seconds (47.2 hours) for all samples. The samples were divided into two quality control batches, the first with 11 samples, the second with 10. Instrument quality control checks consisting of peak center channel, peak resolution at Full Width at Half Maximum, and efficiency, at three different energies, were performed before and after each measurement and all were within their limits. For each batch of samples, one replicate count, one laboratory control sample (LCS), and one method blank were counted. These quality control samples met acceptance criteria for the first batch. As of 4:30 pm CDT on July 27th, counting of the quality control samples for the second sample batch is not complete.

NAREL analyzes gamma spectra using Quantum Technology's GDR Version 6.1. This software performs a Mariscotti peak search (versus a library-directed peak search).

Selection of the appropriate efficiency calibration to use is a matter of professional judgment when a sample does not closely match an existing calibration. Because all of the sample containers as received at NAREL were nearly full (maximum capacity is about 450 mL), NAREL used a 400 mL liquid density efficiency calibration for all 21 samples. Some samples had densities significantly below 1.0 g/mL, which would be expected to overestimate activity, particularly at lower energies. During review of the FDOH spectra files, NAREL noticed that some appear to have been analyzed using efficiency calibrations and background corrections for a 300 mL geometry. Using a smaller volume geometry that more closely matches the actual density is just as valid a professional judgment call as using a geometry (as NAREL did) that matches the volume but not the density. However, using the smaller volume geometry would be expected to underestimate activity, particularly at higher gamma-ray energies.

Comparison of Lab Results from FDOH and NAREL

Two types of statistical tests were performed on the paired results from FDOH and NAREL to test for a systematic difference between the two labs. Each test was performed once for each of

the four radionuclides originally measured by FDOH: 226Ra, produce results for 232Th and 238U but it produced results for

40 228 K, 232Th, and 238U. NAREL did not Ra and 234Th, which are based on

7

8/10/2009

Document info
Document views33
Page views33
Page last viewedMon Dec 05 17:20:11 UTC 2016
Pages16
Paragraphs433
Words3975

Comments