1. The National Standard of the Radionuclides Activity Unit in Poland R. Broda, A. Chyliński, T. Radoszewski, K. Małetka, T. Terlikowska-Droździel Radioisotope Centre POLATOM, Świerk, Poland

2. The standard is applied and kept in the Radioisotope Centre POLATOM in Świerk  The President of the Central Office of Measures established the National Standard of the Radionuclides Activity Unit in Poland in 1999

3. The National Standard consists of:  Measurements systems:  triple - double coincidences (TDCR)  4  (LS)-  coincidences and anticoincidences  X-  coincidences  Absolute measurements methods:  triple to double coincidences ratio (TDCR)  4  (LS)  (X,e A )-  coincidences and anticoincidences, tracer, multi-parameter  X-  coincidences  Measured sources:  sources in liquid scintillator  point sources

4. PMT S A BC 1. Triple - double coincidences TDCR system  The triple to double coincidences ratio (TDCR) method  For standardisation of the  -emitters (e.g. 3 H, 14 C, 63 Ni) and EC-emitters (e.g. 55 Fe, 54 Mn)  Pulses are registered in channels: AB, BC, AC, ABC (denoted T), AB+BC+AC (denoted D)  The detection efficiency is changed by the PMT defocalisation and a set of counting points is obtained - the liquid scintillator source S

5. DD K AoAo 55 Fe  Activity (A o ) is determined by solving the system of equations at each counting point: N AB = A o  AB (  A,  B ) N BC = A o  BC (  B,  C ) N AC = A o  AC (  A,  C ) N T = A o  T (  A,  B,  C )  Parameter is calculated: K = N T /N D =  T /  D  The counting efficiency (  ) is calculated using the theoretical model of the LS-detector  The fitting of the theoretical function  D (K) to the set of counting points is checked

6.  1 PMT NaI S  2  1  2 2. coincidences and anticoincidences system 2. 4  (LS)-  coincidences and anticoincidences system  For standardisation of the  - ,  - , (X,e A )-  emitters and radionuclides with a complex decay  Counting rates registered: LS-channel (  1 -  2 coincidence) N LS  -channel (  1 +  2 sum) N   -  coincidence N C  -  anticoincidence N AC  Window in the  -channel is selected, detection efficiency  LS is changed by the HT in the LS-channel S - the liquid scintillator source

7. Eu 152 A o = 561,8  1,2 kBq/g (1-  LS )/  LS  The activity (A o ) is determined by linear extrapolation in coincidence (C): N LS N  N C AoAo 1-  LS  LS 0 NCNNCN  LS = if where in anticoincidence (AC): N LS N  N  - N AC AoAo N  - N AC N   LS = 1-  LS  LS 0if where Various linear extrapolation with three different windows (I, II and III) in the  -channel

8. P  1 PMT NaI  2 3. coincidences system 3. X-  coincidences system - the point source (P) on the Mylard foil  For standardisation of the EC-emitters (where X are followed by  of a very similar energy) e.g. 125 I  Counting rates registered:  1 -channel N 1  2 -channel N 2  1 -  2 coincidence N C  Activity of the 125 I source is calculated: N C 2 N 2 + () N C 2 N 1 + () A o = 0,997 2 N C

9. Uncertainty of measurements  The overall uncertainty can be reduced by simultaneous measurements in the TDCR and 4  (LS)-  system % Counting statistic0,1 - 0,2 Detector draft0,1 - 0,4 Detector system parameters0,1 Weighing of the solution 0,1 - 0,2 Nuclear data0,01 - 0,3 Theoretical model of the method 0,2 - 0,8 Overall expanded uncertainty (k=2)   2,0 %

10. Application of the National Standard An example of transfer of the radionuclides activity unit: calibration of the HPGe detector N  A o i   (E) = E [keV] (E)(E) Cd 109 Co 57 Hg 203 Sn 113 Zn 65 Am 241 Sr 85 Cs 137 Mn 54 Co 60 Co 60

11.  Many types the secondary standards (e.g. solutions, solid sources, multi-gamma) of nearly 50 radionuclides are produced in the RC POLATOM: 3 H, 14 C, 22 Na, 24 Na, 32 P, 35 S, 42 K, 45 Ca, 46 Sc, 51 Cr, 54 Mn, 55 Fe, 57 Co, 58 Co, 59 Fe, 60 Co, 63 Ni, 64 Cu, 65 Zn, 75 Se, 76 As, 82 Br, 85 Sr, 86 Rb, 90 Sr+ 90 Y, 99 Mo, 109 Cd, 110m Ag, 113 Sn, 124 Sb, 125 I, 131 I, 133 Ba, 134 Cs, 137 Cs, 144 Ce+ 144 Pr, 152 Eu, 169 Yb, 170 Tm, 192 Ir, 198 Au, 203 Hg, 204 Tl, 241 Am  International measurements traceability of the National Standard is based on participation in 27 intercomparisons (organised by BIPM, ICRM, EUROMET, other)