Alpha energy adsorption in filters and its potential to degrade air monitoring accuracy. David Ryden November 2008

Transcription

1 Alpha energy adsorption in filters and its potential to degrade air monitoring accuracy. David Ryden November 2008

2 Alpha energy absorption in filters 1. Some basic principals 2. Investigation of spectra obtained from calibrated 239 Pu aerosols collection by filters 3. Performance with heavily degraded spectra 4. Information available in published papers and reports

3 Alpha Energy Degradation can occur 1. In the active aerosol particle (diameters > 1 µm) 2. In the filter material 3. In other particulates collected by the filter 4. In the air gap between filter and detector 5. In the window of the detector Only the last two are taken into account when calibrating with a reference source

4 Alpha Particle Stopping Power and Range

5 Stopping Power of Alpha Particles (MeV/cm) in Air versus Energy Alpha Partices: Stopping Power (Mev per cm air) versus Energy (MeV) Stopping Power (MeV per cm air ) Energy (MeV)

6 Range of Alpha Particles (mg/cm 2 ) versus Energy Alpha Partices: Projected Range (g /m2) versus Energy (MeV) Range (g/m2) Energy (MeV)

7 Range of Alpha Particles (cm) in Air versus Energy 10 Alpha Partices: Projected Range in Air (cm) versus Energy (MeV) y = x x R 2 = Range (cm) Energy (MeV)

8 Approximate ranges of alpha particles Alpha Energy (MeV) Material (mg/cm 2 ) Air (mm) Water (µm)

9 Mass concentrations of aerosols (PM10) found in air Typical Urban sites: Median concentration = 0.05 mg/m 3 (typical range 0.01 to 1mg/m 3 ) Waste Isolation Pilot Plant (WIPP): Median concentration = 5mg/m 3 (range 0.3 to 30mg/m 3 )

10 Time to accumulate significant dust loadings If air containing 0.05 mg/m 3 of particulates is drawn at a rate of 40 LPM through a 25 mm filter then in 24 hours the filter will accumulate a layer equal to 12% of the range of a 5.5 MeV alpha

11 The effects of accumulated particulates The impedance to flow increases as particulates accumulate The efficiency of collecting aerosols tends to increase as the particulates accumulate. For this reason the alphas emitted by freshly collected activity may sometimes suffer less energy degradation with a dirty than with a clean filter. However the energy of alphas emitted by activity already collected on the filter will obviously tend to be degraded by the further collection of additional particulates

12 Some differences in Alpha Spectrum Shapes

13 Difference in spectrum shape with location i-cam COMPARE SPECTRA RECORDED IN DIFFERENT LOCATIONS ITOTAL Location: Pit 3 Location: G11 Snaphot _icam Snaphot _icam3801 ITotal in Pit 3 Channel Counts Channel Number ITotal in G11 x7.84 Extrap ThC' Tail Extrap RaC'Tail Extrap ThC' Tail Extrap RaC'Tail Pit 3 RaA/ThC peak: CN 147 RaC' peak: CN 192 ThC' peak: CN 224 G11 RaA/ThC peak: CN 147 RaC' peak: CN 195 ThC' peak: CN 225

14 The next slide shows an example of improving alpha spectrum resolution with increasing accumulation of aerosol

15 An example of improved energy resolution with accumulated aerosol NRPB Radon Chamber. Changes in spectrum shape with accumulation of test aerosol Filter: Millipore SS After 20 hours After 0.5 hours 1000 Channel Counts 100 T1$7 T1$ Channel Number

16 However note that this is radon progeny spectrum. The short half life of RaA and RaC means that most of their alphas are emitted by relatively freshly collected aerosols This large change in resolution should not be taken as typical

17 Filtration Mechanisms

18 Filtration Efficiency Contributing collection mechanisms versus aerosol particle size Face Velocity = 20 cm/s (6 LPM with 25mm diameter filter, 24 LPM with 50 mm diameter filter) Filter Collection Efficiency 100% 90% 80% Filter fibre dia = 2 micron Filter porosity = 0.92 Filter density = gm/cm3 Face Velocity =20 cm/sec 70% 6 LPM (Filter dia =25 mm) Collection efficiency 60% 50% 40% 30% 20% 10% 0% Particle Diameter (microns) 24 LPM (Filter dia =50 mm) Interception: Impaction: Diffusion: Interaction: Gravitation: Electrostatic: Overall Filter Efficiency:

19 Filtration Efficiency Contributing collection mechanisms versus aerosol particle size Face Velocity = 50 cm/s (15 LPM with 25mm diameter filter, 60 LPM with 50 mm diameter filter) Filter Collection Efficiency 100% 90% 80% Filter fibre dia = 2 micron Filter porosity = 0.92 Filter density = gm/cm3 Face Velocity =50 cm/sec 70% 15 LPM (Filter dia =25 mm) Collection efficiency 60% 50% 40% 30% 20% 10% 0% Particle Diameter (microns) 59 LPM (Filter dia =50 mm) Interception: Impaction: Diffusion: Interaction: Gravitation: Electrostatic: Overall Filter Efficiency:

20 Filtration Efficiency Contributing collection mechanisms versus aerosol particle size Face Velocity = 125 cm/s (37 LPM with 25mm diameter filter, 147 LPM with 50 mm diameter filter) Filter Collection Efficiency 100% 90% 80% Filter fibre dia = 2 micron Filter porosity = 0.92 Filter density = gm/cm3 Face Velocity =125 cm/sec 70% 37 LPM (Filter dia =25 mm) Collection efficiency 60% 50% 40% 30% 20% 10% 0% Particle Diameter (microns) 147 LPM (Filter dia =50 mm) Interception: Impaction: Diffusion: Interaction: Gravitation: Electrostatic: Overall Filter Efficiency:

21 Filtration Efficiency at two face velocities Filter Collection Efficiency Face Velocity =20 cm/s Face Velocity =50 cm/s 100% 95% 90% 85% Collection efficiency 80% 75% 70% 65% 60% 55% 50% Particle Diameter (microns)

22 Spectra from calibrated radioactive aerosols collected on two types of filter

23 239 Pu and 137 Cs aerosols Activity Median Aerodynamic Diameters AMAD =0.4µm AMAD = 4 µm

24 Radon ( 222 Rn) progeny AMAD =0.2µm Equilibrium Factor F=0.4 Concentration= 40Bq/m3

25 Filter materials Whatman GF/A (Glass microfibre) Fluoropore FSLW (3µm PTFE filter)

26 Radon progeny (RaA+RaC ) aerosols (AMAD= 0.4 µm) collected by Whatman GF/A and Fluoropore FSLW flters icam IRSN Spectra: radon-222 progeny collected on GF/A (glass -fibre) and FSLW (PTFE) Filters F12 GFA Radon (F=0.4) F13 FSLW Radon (F=0.4) Fractiobn of Counts in Channel

27 Radon progeny (RaA+RaC ) aerosols (AMAD= 0.4 µm) collected by Whatman GF/A and Fluoropore FSLW flters icam IRSN Spectra: radon-222 progeny collected on GF/A (glass fibre) and FSLW (PTFE) Filters F12 GFA Radon (F=0.4) F13 FSLW Radon (F=0.4) Fraction of counts in channel

28 Pu-239 aerosols (AMAD= 0.4 µm) collected by Whatman GF/A and Fluoropore FSLW flters icam: Spectra from Pu-239 Aerosols of AMAD 0.4 collected on GF/A & FSWL filters F1 Sens Pu-239 (0.4um) GFA (ST= 4.7 hrs) F2 Sens Pu-239 (0.4um) FSWL (ST= 2.1 hrs) Fraction of Spectrum in Channel

29 Pu-239 aerosols (AMAD= 0.4 µm) collected by Whatman GF/A and Fluoropore FSLW flters icam: Spectra from Pu-239 Aerosols of AMAD 0.4 collected on GF/A & FSWL filters 0.1 F1 Sens Pu-239 (0.4um) GFA (ST= 4.7 hrs) F2 Sens Pu-239 (0.4um) FSWL (ST= 2.1 hrs) Fraction of Spectrum in Channel

30 Three test runs with 239 Pu aerosols The instrument sampled air containing 239 Pu aerosols at calibrated concentration levels for between 5 and 6 hours. Air sampling then continued for at least a further 16 hours with activity-free air

31 Three test runs with 239 Pu aerosols Run 1 Filter: Whatman GF/A Aerosol: 239 Pu (AMAD=0.4µm) Mean concentration: 10 Bq/m 3 Duration with 239 Pu: 5 hours 20 minutes Total sampling duration: 22 hours Run 2 Filter: Whatman GF/A Aerosol: 239 Pu (AMAD=4µm) Mean concentration: 13 Bq/m 3 Duration with 239 Pu: 6 hours Total sampling duration: 22 hours Run 3 Filter: Fluoropore FSLW Aerosol: 239 Pu (AMAD=0.4µm) Mean concentration: 9 Bq/m 3 Duration with 239 Pu: 5 hours 20 minutes Total sampling duration: 22 hours

32 239 Pu Concentration and Air Sampling Rate vs Time Filter = GF/A Aerosol AMAD = 0.4µm Pu-239 Conncentration (Bq/m3) and Air Sampling Rate (LPM) vs Time ICARE Alpha Conc (Bq/m3) Resp Pu-239 (0.4um) Filter: GFA Sampling rate M2 (LPM) Pu-239 Concentration (Bq/m3) :00 12:00 14:00 16:00 18:00 20:00 22:00 00:00 02:00 04:00 06:00 08:00 10:00 Air Sampling Rate (LPM)

33 239 Pu Concentration and Air Sampling Rate vs Time Filter = GF/A Aerosol AMAD = 4 µm Pu-237 Concentration (Bq/m3) and Air Sampling Rate (LPM) vs Time Pu-239 Concentration (Bq/m3) Resp Pu-239 (4um) Filter: GFA ICARE Alpha Conc (Bq/m3) Sampling rate M2 (LPM) Air Sampling Rate (LPM) :00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00

34 Pu-239 Concentration (Bq/m3) Pu-239 Concentration (Bq/m3) and Air Sampling Rate (LPM) vs Time Resp Pu-239 (0.4um) Filter: FSWL ICARE Alpha Conc (Bq/m3) Sampling rate M2 (LPM) :00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Air Samping Rate (LPM)

35 Fall in Air Sampling Rate as 239 Pu aerosol is collected GF/A filter: The impedance to flow increased moderately with time when sampling 0.4 µm AMAD aerosols. Fluoropore filter: The impedance to flow increased significantly with time when sampling 0.4 µm AMAD aerosols. GF/A filter: The change in impedance to flow was insignificant when sampling 4 µm AMAD aerosols.

36 Fall in Air Sampling Rate as 239 Pu aerosol is collected by filter Filter Pu-239 Aerosol AMAD Initial Air Flow Rate Final Air Flow Rate Fall in Air Flow Rate Fall in Air Flow Rate GF/A 0.4 µm 43 LPM 39 LPM 4 LPM 9 % GF/A 4 µm 42 LPM 41 LPM 1 LPM 2 % FSLW 0.4 µm 49 LPM 39 LPM 10 LPM 20 %

37 Alpha Spectra. Run 1 Filter: Aerosol: Whatman GF/A 239 Pu (AMAD=0.4µm) Mean concentration: 10 Bq/m 3 Duration with 239 Pu: 5 hour 20 minutes Total sampling duration: 22 hours

38 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts at hourly intervals Linear Scale icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (0.4um) GFA (ST= 2 hrs) Pu-239 (0.4um) GFA (ST= 3 hrs) Pu-239 (0.4um) GFA (ST= 4 hrs) Pu-239 (0.4um) GFA (ST= 5.4 hrs) Pu-239 (0.4um) GFA (ST= 11.8 hrs) Pu-239 (0.4um) GFA (ST= 22.2 hrs) Fraction of counts in channels

39 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts at hourly intervals Log Scale icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes 0.1 Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (0.4um) GFA (ST= 2 hrs) Pu-239 (0.4um) GFA (ST= 3 hrs) Pu-239 (0.4um) GFA (ST= 4 hrs) Pu-239 (0.4um) GFA (ST= 5.4 hrs) Pu-239 (0.4um) GFA (ST= 11.8 hrs) Pu-239 (0.4um) GFA (ST= 22.2 hrs) Fraction of counts in channels

40 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts after 1 and 5 hours sampling activity Linear Scale 0.07 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) 0.06 Pu-239 (0.4um) GFA (ST= 5.4 hrs) Fraction of counts in channels

41 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts after 1 and 5 hours sampling activity Log Scale 0.1 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (0.4um) GFA (ST= 5.4 hrs) Fraction of counts in channels

42 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts At end of activity-sampling period (5h 20m) and at 12 and 22 hours Linear Scale 0.05 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 5.4 hrs) Pu-239 (0.4um) GFA (ST= 11.8 hrs) Pu-239 (0.4um) GFA (ST= 22.2 hrs) Fraction of counts in channels

43 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts At end of activity-sampling period (5h 20m) and at 12 and 22 hours Log Scale 0.1 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 5.4 hrs) Pu-239 (0.4um) GFA (ST= 11.8 hrs) Pu-239 (0.4um) GFA (ST= 22.2 hrs) Fraction of counts in channels

44 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts at hourly intervals Integrated Spectrum icam: Integrated spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (0.4um) GFA (ST= 2 hrs) Pu-239 (0.4um) GFA (ST= 3 hrs) Pu-239 (0.4um) GFA (ST= 4 hrs) Pu-239 (0.4um) GFA (ST= 5.4 hrs) Pu-239 (0.4um) GFA (ST= 11.8 hrs) Pu-239 (0.4um) GFA (ST= 22.2 hrs) Fraction of counts in channels

45 GF/A Filter collecting Pu-239 aerosol (AMAD 0.4) 20 minute counts after 1 and 5 hours sampling activity Integrated Spectrum icam: Integrated spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (0.4um) GFA (ST= 5.4 hrs) Fraction of counts in channels

46 Alpha Spectra. Run 2 Filter: Aerosol: Whatman GF/A 239 Pu (AMAD=4µm) Mean concentration: 13 Bq/m 3 Duration with 239 Pu: 5 hour 20 minutes Total sampling duration: 22 hours

47 GF/A Filter Spectra from 4µm Pu-239 aerosols 20 minute counts after 1 hour and 6 hours sampling activity LINEAR SCALE 0.07 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (4um) GFA (ST= 1 hrs) 0.06 Pu-239 (4um) GFA (ST= 5.9 hrs) Fraction of counts in channels

48 GF/A Filter Spectra from 4µm Pu-239 aerosols 20 minute counts after 1 hour and 6 hours sampling activity LOG SCALE 0.1 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (4um) GFA (ST= 1 hrs) Pu-239 (4um) GFA (ST= 5.9 hrs) Fraction of counts in channels

49 Comparison of Alpha Spectra from 0.4 µm and 4 µm 239 Pu aerosols

50 GF/A Filters Spectra from 0.4 µm and 4µm Pu-239 aerosols 20 minute counts after 1 hour sampling activity LINEAR SCALE 0.07 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) 0.06 Pu-239 (4um) GFA (ST= 1 hrs) Fraction of counts in channels

51 GF/A Filters Spectra from 0.4 µm and 4µm Pu-239 aerosols 20 minute counts after 1 hour sampling activity LOG SCALE icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) GFA (ST= 1 hrs) Pu-239 (4um) GFA (ST= 1 hrs) Fraction of counts in channels

52 Run 3 Filter: Aerosol: Fluoropore FSLW 239 Pu (AMAD=0.4µm) Mean concentration: 9 Bq/m 3 Duration with 239 Pu: 5 hour 20 minutes Total sampling duration: 22 hours

53 Fluoropore FSLW Filter Spectra from 0.4µm Pu-239 aerosols 20 minute counts after 1 hour and 5h 20m sampling activity LINEAR SCALE 0.09 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes 0.08 Pu-239 (0.4um) FSLW (ST= 1 hrs) 0.07 Pu-239 (0.4um) FSLW (ST= 5.5 hrs) Fraction of counts in channels

54 Fluoropore FSLW Filter Spectra from 0.4µm Pu-239 aerosols 20 minute counts after 1 hour and 5h 20m sampling activity LOG SCALE 0.1 icam: Spectra from calibrated Pu-239 aerosols_lt=20 minutes Pu-239 (0.4um) FSLW (ST= 1 hrs) Pu-239 (0.4um) FSLW (ST= 5.5 hrs) Fraction of counts in channels

55 The following slides show the increase in the proportion of the 239 Pu alpha counts that fall below the Alpha Region into the Beta Region as aerosol accumulates. Threshold of Alpha Region : Channel Number 60 (Alpha Energy = 2.5 MeV)

56 The increase in the proportion of the 239 Pu alpha counts that fall into the Beta Region during aerosol accumulation Proportion of Pu-239 Alpha signal counts falling below the Alpha Threshold (CN =60, Alpha Energy = 2.5 Mev) 9% Pu-239 (0.4um) GFA Pu-239 (0.4um) FSLW Pu-239 (4um) GFA 8% 7% 6% 5% 4% 3% 2% 1% 0% Elapsed Air Sampling Time (hours)

57 In the three test runs the proportion of 239 Pu alpha signal counts falling below the Alpha Region threshold was: greatest for 0.4µm aerosols collected by a Whatman GF/A filter significantly lower for 0.4µm aerosols collected by a Fluoropore FSLW filter the least for 4µm aerosols collected by a Whatman GF/A filter Presumably the proportion would have been lower with 4µm aerosols collected by a Fluoropore filter The collection of 4µm aerosols by GF/A showed no significant increase in impedance during accumulation

58 The results obtained with calibrated 239 Pu aerosols have shown small but significant losses in alpha signal due to alpha energy absorption by the filter material and by aerosols as they accumulate

59 Alpha Spectra heavily degraded by sampling active water droplets Note: In this example the alpha background is mainly due to thoron progeny ThC and ThC. The RaC contribution is very small

60 Alpha Spectrum acquired over 24 hours since last filter change Before arrival of active water drop LINEAR SCALE SR Snapshot Gross i-cam Spectrum Last Reset: 08:23 23/03/04 Snapshot : 08:16 24/03/04 Elapsed Time:23 hours:54 mins RaA/ThC peak: CN 139 RaC' peak: CN 160 ThC' peak: CN 213 K1= 60 K2= 125 K3= 146 K4= 164 Gross Cnts in A1: Channel Counts Cnts in A2: Cnts in A3: Cnts in A4: Cnts Alpha: Gross K K2 K3 K Channel Number

61 Alpha Spectrum acquired in 60minutes 24 hours since last filter change Before arrival of active water drop LINEAR SCALE SR Snapshot i-cam Spectrum Last Reset: 08:23 23/03/04 Snapshot : 08:16 24/03/04 RaA/ThC peak: CN 139 RaC' peak: CN 159 Gross LT Count Time:60 mins Elapsed Time:23 hours:54 mins ThC' peak: CN K1= 60 K2= 125 K3= 146 K4= 164 Channel Counts Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: Gross LT K1 K2 K3 K Channel Number

62 Alpha Spectrum acquired in 60minutes Before arrival of active water drop LOG SCALE 1000 SR Snapshot Gross LT Count Time:60 mins i-cam Spectrum Snapshot : 08:16 24/03/04 Elapsed Time:23 hours:54 mins RaA/ThC peak: CN 139 RaC' peak: CN 159 ThC' peak: CN 213 K1= 60 K2= 125 K3= 146 K4= Channel Counts Channel Number Gross LT K1 K2 K3 K4 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: 26099

63 Before arrival of active water drop Predicted ThC + ThC spectrum LOG SCALE SR Snapshot i-cam Spectrum Snapshot : 08:16 24/03/04 SpecSSp Tn2CtbSS+Tn1CtbSS Count Time:60 mins Elapsed Time:23 hours:54 mins Channel Counts Gross LT Tn2CtbSS+Tn1CtbSS K1 K2 K3 K4 K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 4003 Cnts in A2: Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: -1 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

64 Before arrival of active water drop Predicted ThC + ThC spectrum LINEAR SCALE Channel Counts SR Snapshot Gross LT Tn2CtbSS+Tn1CtbSS K1 K2 K3 K4 i-cam Spectrum Count Time:60 mins Snapshot : 08:16 24/03/04 Elapsed Time:23 hours:54 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 4003 Cnts in A2: Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: -1 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

65 Before arrival of active water drop LINEAR SCALE Spectrum after thoron progeny spectra stripped SR Snapshot i-cam Spectrum Elapsed Time:23 hours:54 mins Channel Counts SpecSSp Tn2CtbSS+Tn1CtbSS SpecSSp K1 K2 K3 K4 Count Time:60 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 4003 Cnts in A2: Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: -1 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

66 Before arrival of active water drop LINEAR SCALE Residual spectrum after radon and thoron progeny spectra stripped Channel Counts SR Snapshot Comp. LT i-cam Spectrum Count Time:60 mins Last Reset: 08:23 23/03/04 Snapshot : 08:16 24/03/04 Elapsed Time:23 hours:54 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: -1 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: SpecSS2p Cnts in A1: -77 Cnts in A2: Cnts in A3: 0 Cnts in A4: 0 Cnts Alpha: SpecSS3p 0 Cnts in A1: Cnts in A2: 0 Cnts in A3: -0.1 Cnts in A4: Cnts Alpha: Channel Number

67 Before arrival of active water drop LINEAR SCALE Residual spectrum after radon and thoron progeny spectra stripped Channel Counts SR Snapshot Comp. LT i-cam Spectrum Count Time:60 mins Last Reset: 08:23 23/03/04 Snapshot : 08:16 24/03/04 Elapsed Time:23 hours:54 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: -1 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: SpecSS2p Cnts in A1: -77 Cnts in A2: Cnts in A3: 0 Cnts in A4: 0 Cnts Alpha: SpecSS3p -20 Cnts in A1: Cnts in A2: 0 Cnts in A3: -0.1 Cnts in A4: 0-40 Cnts Alpha: Channel Number

68 Before arrival of active water drop LINEAR SCALE SR Snapshot i-cam Spectrum Last Reset: 08:23 23/03/04 Snapshot : 08:16 24/03/04 RaA/ThC peak: CN 139 RaC' peak: CN 159 Gross LT Count Time:60 mins Elapsed Time:23 hours:54 mins ThC' peak: CN K1= 60 K2= 125 K3= 146 K4= 164 Channel Counts Gross LT Cnts in A1: 4002 Cnts in A2: 5285 Cnts in A3: 731 Cnts in A4: Cnts Alpha: Gross LT K1 K2 K3 K Channel Number

69 After arrival of active water drop LINEAR SCALE SR Snapshot i-cam Spectrum Last Reset: 08:23 23/03/04 Snapshot : 13:11 24/03/04 RaA/ThC peak: CN 128 RaC' peak: CN 160 Gross LT Count Time:60 mins Elapsed Time:28 hours:48 mins ThC' peak: CN K1= 60 K2= 125 K3= 146 K4= 164 Channel Counts Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Gross LT K1 K2 K3 K Channel Number

70 After arrival of active water drop Predicted ThC + ThC spectrum LINEAR SCALE SR Snapshot SpecSSp Tn2CtbSS+Tn1CtbSS i-cam Spectrum Count Time:60 mins Last Reset: 08:23 23/03/04 Snapshot : 13:11 24/03/04 Elapsed Time:28 hours:48 mins RaA/ThC peak: CN 145 RaC' peak: CN 160 Channel Counts Gross LT Tn2CtbSS+Tn1CtbSS K1 K2 K3 K4 Gross LT RaA/ThC peak: CN 128 RaC' peak: CN 160 ThC' peak: CN 202 K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 6608 Cnts in A2: 3365 Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: 1636 Cnts in A2: -165 Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

71 After arrival of active water drop LINEAR SCALE Spectra before and after thoron progeny spectra stripped Channel Counts SR Snapshot SpecSSp Gross LT SpecSSp K1 K2 K3 K4 Tn2CtbSS+Tn1CtbSS i-cam Spectrum Count Time:60 mins Elapsed Time:28 hours:48 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 6608 Cnts in A2: 3365 Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: 1636 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

72 After arrival of active water drop LINEAR SCALE Spectrum after thoron progeny spectra stripped Channel Counts SR Snapshot SpecSSp SpecSSp K1 K2 K3 K4 Tn2CtbSS+Tn1CtbSS i-cam Spectrum Count Time:60 mins Elapsed Time:28 hours:48 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Tn2CtbSS+Tn1CtbS Cnts in A1: 6608 Cnts in A2: 3365 Cnts in A3: Cnts in A4: Cnts Alpha: SpecSSp Cnts in A1: 1636 Cnts in A2: Cnts in A3: Cnts in A4: 0 Cnts Alpha: Channel Number

73 After arrival of active water drop LINEAR SCALE Residual spectrum after radon and thoron progeny spectra stripped SR Snapshot i-cam Spectrum Count Time:60 mins Snapshot : 13:11 24/03/04 Elapsed Time:28 hours:48 mins K1= 60 K2= 125 K3= 146 K4= Comp. LT Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Channel Counts SpecSSp Cnts in A1: 1636 Cnts in A2: -165 Cnts in A3: Cnts in A4: 0 Cnts Alpha: SpecSS2p Cnts in A1: Cnts in A2: Cnts in A3: 0 Cnts in A4: 0 Cnts Alpha: Comp. LT 80 Cnts in A1: Cnts in A2: 0 Cnts in A3: -0.1 Cnts in A4: 0-20 Cnts Alpha: Channel Number

74 After arrival of active water drop LINEAR SCALE Residual spectrum after radon and thoron progeny spectra stripped SR Snapshot Comp. LT i-cam Spectrum Count Time:60 mins Snapshot : 13:11 24/03/04 Elapsed Time:28 hours:48 mins K1= 60 K2= 125 K3= 146 K4= 164 Gross LT Cnts in A1: 8244 Cnts in A2: 3200 Cnts in A3: 1171 Cnts in A4: Cnts Alpha: Channel Counts SpecSSp Cnts in A1: 1636 Cnts in A2: -165 Cnts in A3: Cnts in A4: 0 Cnts Alpha: SpecSS2p Cnts in A1: Cnts in A2: Cnts in A3: 0 Cnts in A4: 0 Cnts Alpha: Comp. LT Cnts in A1: Cnts in A2: 0 Cnts in A3: -0.1 Cnts in A4: 0-20 Cnts Alpha: Channel Number

75 Counting the filter 7 days after removing it from the monitor confirmed the that the long lived alpha activity recorded by icam in real-time was due to 241 Am/ 239 Pu

76 Information from papers and reports The following is a list of some papers and reports that contain useful information

77 Pickering (1984) discusses self absorption as alpha energy in escaping from their individual aerosol particles Pickering and Fourcaudot (1987) describe how alpha-recoil affects the distribution of aerosols in filters Seiler, Newton and Guilmett (1988) give detailed theoretical models for continuous monitoring in a dusty environment

78 Moore, McFarland and Rodgers (1993) describe the factors that affect alpha particle detection by continuous air monitors Huang, Schery, Alcantara and Rodgers (2002) discuss the influence of dust loading on the alpha-particle energy resolution of continuous air monitors Huang, Schery, Alcantara, Dale and Rodgers (2002) provide useful information in a paper on test aerosols

79 Investigation of techniques to improve Continuous Air Monitors under conditions of high dust loading in environmental settings US DoE Report This is a particularly useful report by Huang et al Luetzelschwab, Storey, Zraly and Dussinger (200) describes measurements of self absorption of alpha energy in filters but only with sources rather than active aerosols Grivaud (1992) discusses alpha spectrum resolution obtained with different filters Grivaud and Pagliardini (2001) give a detailed assessment of Fluoropore FSLW (version 2)

80 Tony Geryes is two years into a doctoral thesis (Paris University) entitled Etude de la degradation de l energy des particules Alpha dans les filtres de surveillance de la radioactivity atmospheric He is supervised by Dr Celine Monsanglant Louvet at IRSN. When completed this promises to be a most useful study