Selection of Filter Media in Alpha Air Monitors for Emergency ...

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P-4a-262 Table 1 Summary of characteristics of the test filters Filter Type and Designation Surface collection efficiency (%) Relative pressure drop (sharpness of alpha-ray energy peaks) GLASS-CELLULOSE FIBER TOYO HE-40T ( Glass 20%, Cellulose 80%) 45 0.17 TOYO HE-40TA ( Glass 30%, Cellulose 70%) 56 0.20 GLASS FIBER TOYO GB-100R 65 0.26 PALL-GELMAN T60A20 56 0.11 WHATMAN GF/F 94 1.41 SILICA FIBER TOYO QR100 76 0.48 MEMBRANE (CELLULOSE ACETATE TYPE) MILLIPORE AA (0.8 µm pore size) 94 1 TOYO A080A (0.8 µm pore size) 95 1.15 TOYO A100A (1.0 µm pore size) 90 0.76 MILLIPORE SMWP (5.0 µm pore size) 79 0.42 MEMBRANE (PTFE TYPE) TOYO T080A (0.8 µm pore size) 97 2.11 TOYO T100A (1.0 µm pore size) 98 1.45 TOYO T300A (3.0 µm pore size) 87 0.50 MEMBRANE (PTFE with backing TYPE) TOYO J100A (1.0 µm pore size) 99 0.63 MILLIPORE FSLW (3.0 µm pore size) 99 0.31 SUMITOMO LWP-300-75 (3.0 µm pore size) 95 0.28 PREFILTER FOR MEMBRANE FILTER TOYO Y008A 98 1.80 TOYO Y020A 82 0.83 TOYO Y100A 69 0.27 MILLIPORE AW19 91 0.54 Room air dust Prefilter Flow meter Test filter Air Thoron decay products generator Air pump Chamber Air pump Figure 1. Experimental apparatus for the examination of the surface collection efficiency. 2
P-4a-262 Count (nomalized) 1.0 0.8 0.6 0.4 0.2 0.0 GB-100R Count (nomalized) 1.0 0.8 0.6 0.4 0.2 0.0 FSLW 2000 4000 6000 8000 10000 Energy (keV) 2000 4000 6000 8000 10000 Energy (keV) Figure 2. Alpha spectrum of thoron decay products collected on GB-100R and FSLW. T080A GF/F AA Pressure drop ( mmHg ) 10 2 10 1 AW19 FSLW GB-100R HE-40T 10 0 10 1 10 2 Face velocity (cm s -1 ) Figure 3. Relationship of pressure drop to face velocity for various test filters. RESULTS and DISCUSSION Figure 2 shows the examples of alpha spectrum of thoron decay products collected on GB-100R (Toyo Roshi Co. Ltd.) and FSLW ( Millipore Corporation ), respectively. The sharpness of alpha-ray energy peaks obtained for test filters is shown in Table 1. Figure 3 shows the relationship of pressure drop to face velocity for some test filters. The relative pressure drop defined by a ratio of the pressure drop for the filter of interest to that for AA ( Millipore Corporation ) at the face velocity 50 cm s –1 is also shown in the right column of Table 1. All types of fiber filters, except GF/F (Whatman LabSales ) , show poor surface collection efficiencies. GF/F has a high surface collection efficiency, but this filter is not suitable for alpha monitoring because of high pressure drop. All types of membrane filter show high surface collection efficiencies. Small pore membrane filters have a tendency toward high pressure drop. Of membrane filters which have the same 1.0 µm pore size, J100A is superior to the other filters, A100A and T100A, because J100A has a lower pressure drop and a similar surface collection efficiency to that of A100A and T100A. FSLW is a PTFE (polytetrafluoroethylene) membrane filter with polypropylene backing and LWP-300-75 ( Sumitomo Electric industries Ltd. ) is a PTFE membrane filter with polyethylene baking. Both of these filters show a similar performance to that of J100A. In addition, of prefilters, AW19 has relatively high surface collection efficiency in spite of low pressure drop. 3
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