SIR #: 403
Section: V1M6, Section 188.8.131.52
Section 184.108.40.206(c) in TNI Standard V1M6 is not clear in regards to counting two Radiation Measurement Batches (RMBs) by sharing the same detector between the batches (“interspersing” samples).
For example, the lab utilizes an internal procedure and log to define the Radiation Measurement Batch (RMB) and relevant “grouping” of samples as required in section 220.127.116.11(c). The two separate RMB batches, which are started on separate dates, last for 14 days from their respective starting dates. One RMB batch consists of NPW (accredited by TNI) with a 1.5-L counting geometry, whereas another RMB batch consists of charcoal (non-accredited by TNI) in a 50-mL counting geometry. The batches have their own, independent Quality Control (QC) systems of 4 QC samples each. The detectors are independently calibrated for these geometries. The detectors are performance tested according to Section 18.104.22.168. Therefore, each RMB has full QC ensuring that the data of accredited samples are not compromised by the non-accredited samples and vice-versa.
The gamma spectrometry counting of these RMBs shares the detectors, for the following reason. Since the samples for each RMB arrive in the lab with time gaps within 14 days, these gaps are filled by counting samples from another batch. Allocating a specific detector to an RMB would result in the detector idling during the time gaps. This lab cannot process all its customers’ samples in a timely fashion with essential equipment idled. TNI V1M6 Section 22.214.171.124(c) does not stipulate that detectors cannot be shared. TNI V1M6 does not require allocation of the detectors to batches, although it does not prohibit it.
The lab questions are as follows: 1) Are samples within an RMB required to be counted on the detector consecutively? 2) Is it acceptable for 2 different RMBs to be counted on the same detector if the samples between 2 different RMB are interspersed, resulting from time gaps in each RMB?
TNI FINAL RESPONSE:
Section 126.96.36.199.c) is part of the overall 1.7.2 section for "Quality Control for Radiochemistry". Specifically 188.8.131.52.c) defines how samples shall be grouped for the purpose of assigning batch QC, allowing for use of Preparation Batch or RMB as outlined in the section. This section does not discuss sample counting/measurement. Note: the Preparation Batch and Radiation Measurements Batch (RMB) are defined in section 1.3 "Terms and Definitions".
There is not a requirement set out in Module 6 for all samples in a Preparation Batch or RMB to be counted in a consecutive order without other samples being interspersed. In fact, unless specifically stated in a promulgated method, samples can be counted across multiple detectors on multiple days, with samples from other batches (Preparation Batches or RMB) counted in-between on the same detector(s). All that is required for any individual sample measurement is that the requirements in section 1.7.1 are met for the detector on which the sample is counted. This would include documented Initial Calibration, Calibration Verification, Instrument Performance Checks, Subtraction Background Measurements, etc., as outlined in the subsections of 1.7.1.