AARST_Radon_Reporter_July_2023

THE RADON REPORTER | 13 RESEARCH environment. For these final exposures, a fourth AlphaGUARD loaned by the US EPA Las Vegas laboratory joined the lineup. The four instruments were exposed to outdoor concentrations as low as a tenth of a pCi/L and indoor concentrations as high as 150 pCi/L as part of their final assessment. The results are impressive and reassuring to all who use radonmeasurements to make decisions. Imagine if calibration chambers differed greatly–not only would it require immediate corrective action, but thousands of measurement results, with no fault of the field technicians, would be called into question. FIGURE 1. MEAN RELATIVE PERCENT ERROR FOR EACH CALIBRATION CHAMBER The benchmark was the average of the three traveling AlphaGUARDs–in other words, each chamber’s response was compared to the average of the three traveling instruments. As shown in the Figure 1, no chamber differed by more than 8% from the average of the three AlphaGUARDs, and 11 were within 2%. Considering that each chamber calculates and measures its own concentrations, this is very impressive. This finding is very important as it dovetails with the requirements in ANSI/AARST MS-QA Standard (https://aarst. org/product/ms-qa-2019/ ) that calibration facilities stated one-sigma uncertainty (see MS-QA for explanation and your calibration certificates) for a 48+ hour measurement must be 8% or less. This is the starting uncertainty, upon which every step of the measurement process adds some uncertainty, with the goal that the overall error of field measurements is less than 25%. The final exposure in Flagstaff is shown as FF4 in the charts, where the fourth AlphaGUARD from the US EPA Las Vegas was used as the “chamber” reported concentration. This final Flagstaff comparison showed a Relative Percent Error (RPE) of 1.9% between the average of the three traveling AlphaGUARDs and the fourth instrument. Again, this is impressive, considering the thousands of miles traveled by the instruments, the range of conditions and concentrations in the chambers, and the final environment at 7500-foot elevation and 50-degree F range of temperature. continued on page 14