Primary Standardisation of I-125

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1 Primary Standardisation of S. Pommé, T. Altzitzoglou, R. Van Ammel, G. Sibbens Institute for Reference Materials and Measurements (IRMM) Geel, Belgium Stefaan Pommé, Key Comparison Workshop, BIPM

: Seven methods Photon sum-peak counting with ai well detector Photon sum-peak counting with CsI(Tl) spectrometer Total emission counting with CsI(Tl) spectrometer -,γ

2 : Seven methods Photon sum-peak counting with ai well detector Photon sum-peak counting with CsI(Tl) spectrometer Total emission counting with CsI(Tl) spectrometer -,γ coincidence counting with ai detectors (fixed or variable distance) electron,γ coincidence counting (PPC+aI well) electron,γ sum counting (PPC+aI well) Liquid scintillation counting

3 IM A544 (005) erratum IM A555 (005) 459 3

4 preparation sources quantitative drop deposition by pycnometer drop of 00 mg/l AgO 3 added to solution to precipitate volatile iodine source drying in laminar flow solid sources covered by 8-35 μg/cm VYS foil LSC: 5 ml Ultima Gold 5 ml Insta-Gel Plus 5 ml Ultima Gold + ml water 4

5 photon sum-peak counting in a ai well ai 6 x6 well 5

6 ratio doubles/singles peak => counting efficiency - and γ-rays in ai(tl) well + A x = + A singles peak doubles peak x =69.3% 6

7 pileup => increases doubles peak - and γ-rays in ai(tl) well singles peak doubles peak 7

8 pile-up correction formula A A ρτ = + e A A corr A, A area of singles and doubles peak ρ=the measured count rate τ is the characteristic (leading edge) pulse width 8

9 pile-up correction vs. count rate.00 photon sum-peak counting with ai well.080 correction factor count rate (cps) 9

10 photon sum-peak counting by ai well : results Act (kbq/g) mass (g) 0

11 CsI(Tl) sandwich spectrometer

12 photon sum-peak counting by CsI(Tl) sandwich spectrometer PM tube Source CsI

13 cover source by plastic caps to stop the electrons CsI(Tl) crystal with semi-spherical cavity source with semi-spherical caps 3

14 photon sum-peak counting,γ K rays and γ-rays (~30keV) are being measured electrons are stopped e - 4

15 photon sum-peak method by CsI(Tl) sandwich spectrometer - and γ-rays in CsI(Tl) x =99.3% singles peak doubles peak 5

16 photon sum-peak counting results Act (kbq/g) source mass (g) 6

17 total emission counting,γ K rays and γ-rays and electrons are being measured e - 7

18 Total emission counting by CsI(Tl) sandwich spectrometer photons only - and γ-rays and electrons in CsI(Tl) singles peak doubles peak 8

19 peak ratio vs. count loss 3% loss 0.339Y+0.045Y % Y=A /A loss % 0% A /A 9

20 results total emission counting Act (kbq/g) count rate (s - ) 0

21 -,γ coincidence by two moveable ai detectors vary distance symmetrically

22 -,γ coincidence by two fixed ai detectors vary efficiency by sandwiching the source between absorber foils

23 at first sight: non-linear? Act (kbq/g) cf. H. Schrader and K.F. Walz, Int. J. Appl. Radiat. Isot. 38 (987) 763

24 4 direct solution instead of extrapolation c c c + + = { } x x 0 / + =

25 direct solution vs. extrapolation Act (kbq/g)

26 residuals dev (kbq/g) bias at large distances 6

27 alternative type of extrapolation + + c as a function of efficiency ratio Act(kBq/g) f= A / B 7

28 escape peak of 35 kev γ-ray in ai number of counts % of spectrum 9% of γ-ray s below threshold error of 0.03% on activity channel number 8

29 Tereshchenko et al., Measurement Techniques 49 (006) 60 9

30 4π Κ,γ coincidence counting by PPC and well ai(tl) γ ai 6 x6 well PPC coinc. c β source 30

31 3 iterative solution { } { } { } + = + = + = β γ e x e x 0 c e e 0 x x 0 E E E E E E E E { } { } e x e c x E E E E E E E E + + = β { } { } e x x c e E E E E + + = γ { } x x 0 / + = γ discriminator energy>0 kev β c x 3. x x e

32 3 x0 5 x0 4 x0 3 choice of threshold PPC L LAuger threshold level K Auger L+ ce channel number number of counts relative activity

33 extrapolation to zero gas pressure => eliminate photon detection in PPC Act (kbq/g) PPC gas pressure (0 5 Pa) 33

34 4π,γ sum counting by PPC and well ai(tl) 34

35 summing method aims for 00% efficiency 0 = β + γ c discriminator thresholds as low as possible all sources were covered by thin VYS foil to avoid contamination beta efficiency variation by natural variation of self-absorption two discriminator threshold settings 35

36 classical extrapolation 460 Act (kbq/g) parabolic (- β )/ β 36

37 alternative extrapolation total count loss {[ A ( ) + B( ) + P ]( η ) + P } x e L KL { C ) + D( )} L ( x e M + count loss in PPC = ( β 0) {[ A + B( ) + P ]( η ) + P } e L KL { C + D( )} e L M + quite linear correlation if e x (nearly) constant 37

38 extrapolation (this work) 300 Act (kbq/g) 60 0 linear b / 0 38

39 Liquid Scintillation Spectrometry Wallac Quantulus 0 ultra low-level liquid scintillation counter picture PTB 39

Liquid Scintillation Spectrometry 900000 800000 700000 5 I spectrum 600000 500000

40 Liquid Scintillation Spectrometry I spectrum Energy (kev) Packard 300 TR/AB 40

41 Calculated uclide Efficiency 86 CIEMAT-IST C004 (PTB) 84 efficiency (%) Cocktail = 5mL Ultima Gold + ml H O tsie 4

42 Results 5 I by LSC activity concentration (kbq/g) should be independent of quenching tsie 4

43 Results 5 I KC ±0.6% Act (kbq/g) % 95 CsI(Tl) CsI(Tl) caps b-g sum g sum b-g coinc - coinc LSC 43

Activity measurement of 55 Fe within the scope of the BIPM comparison 2006

Activity measurement of 55 Fe within the scope of the BIPM comparison 2006 Karsten Kossert PTB, Department 6.1 Radioactivity BIPM Workshop 2 on CCRI(II) Activity Uncertainties and Comparisons, 17-18 September