1. DETERMINATION OF AN ENVIRONMENTAL BACKGROUND SPECTRUM AND DATA TO BE USED FOR ROUTINE ANALYSES OF WHOLE BODY COUNTS
F BEESLAAR

2. CONTENT Introduction and Background Method Results
Discussion and Conclusion

3. INTRODUCTION AND BACKGROUND
Occupational Monitoring of Necsa workers for incorporated nuclides
In-Vivo technique:
Whole Body Counting and Lung Counting
Whole Body Counting: Monitor internal exposures to
long/short lived fission and activation products
medical isotope production
industrial source production
Lung Counting: Low energy gamma emitters (235U)
Routine counting regimes:
Whole Body: 10 min, 30 min, 60 min (special counts)

4. Introduction and Background
Canberra Whole Body and Lung Counter system
4 x BEGE Lung detectors and 1 x Scanning NaI Whole Body detector
Shielded container

5. Introduction and Background

6. Introduction and Background
Peak Centroid (Channel Number/Energy)

7. Introduction and Background
Energy spectrum contains
spectral photo peaks from artificial nuclides incorporated during occupational exposure and
photo peaks due to radioactivity in counting environment
Natural radiation
Cosmic -, Terrestrial – and Internal Radiation (40K)
Problem Statement:
Artificial and environmental peaks close together:
131I keV and 214Pb – 352 keV due to poor energy resolution
Differentiate between Environmental and Artificial peaks
Technical justification to exclude certain peaks from occupational exposure assessment

8. Method
Over several months acquired spectrums for different counting times
10 min, 30 min and 60 min, 120 min (improved detection)
Blank spectrum: i.e. no human or phantom
Peak Centroid determined and Net Peak Area calculation done by software (GENIE 2000)
Allocate peaks to expected Environmental Peaks
Basic Statistical Analyses:
Peak Energy (centroid) and Net Peak Area (counts) – Variations?
Avg, SD, CV and determined Upper and Lower Limit

9. Mehod

10. Results Peak Centroid [keV] Possible Nuclides Source 188
Ra-226 (186 keV)
U-238 Decay Series
(U-235!)
243
Pb-212 (238 keV); Pb-214 (242 keV)
U-238/Th-232 Decay Series
299
Pb-214 (295 keV)
356
Pb-214 (351 keV)
(I-131!)
507
Annihilation (511 keV)
Pair production in shielding material from high energy gamma/cosmic rays
609
Bi-214 (609 keV)
938
Bi-214 (934 keV); Ac-228 (911 keV & 969 keV)
1136
Bi-214 (1120 keV & 1155 keV)
1454
K-40 (1460)
Primordial

11. Results Count Time : 7200 s CV high for Net Peal Area - ???
Lookup Table with Upper and Lower limit (2 x STDev)
Centroid
Avg (STDev) [keV] CV
Net Peak Area
Avg (STDev) [Counts]
188
2.2%
1737
56.1%
243
1.0%
5839
21.5%
299
1730
44.6%
356 (3.1)
0.9%
4905 (817)
16.7%
507
0.7%
2006
20.0%
609
2919
13.7%
938
1306
23.5%
1136
1.5%
429
26.2%
1454
0.9
1208
17.1%

12. Results: Lookup Table E.g. Spectrum from Rad Worker:
Peak at 360 keV with NPA = 6800 counts

13. Discussion Environmental spectrum taken once a week for 2 hours
Terrestrial radiation from 238U and 232Th decay chains
However there are changes from day to day and seasonal. Even from morning to afternoon. Variability in Net Peak Area due to
Net Peak Area: 222Rn daughters - seasonal, time of day, weather,
Energy Centroid: room temperature
Daily QC check – energy correcting (adjusting gain)
Software report a peak if above Environmental Peak

14. Discussion Lookup Table used for routine evaluation of staff counts
Judgement by technical expert (Spectroscopy and RP)
Knowledge of exposure environment
Deliberation captured in report
Missed dose in case of wrong allocation to environmental peak as false negative
(e.g. 131I few μSv)

15. THANK YOU Question? Dosimetry is not an exact science!
Internal Dosimetry is more and art than science!
We are not chasing uSv!

16. Questions?