Analysis of Radioactive Disequilibrium in Natural Decay Chains due to Processing Hans-Jürgen Lange 1, Rainer Dargel 2 1Canberra GmbH, Walter-Flex-Str. 66, 65428 Rüsselsheim Phone: +49 160 5822545, e-mail address: 12 jlange@canberra.com
Fundamental basics What do we need for accurate activity measurements of Natural Occuring Radioactive Material?
Fundamental basics Information about nuclear decays (nuclear data) nuclide library information Detector efficiency as a function of detector, geometry, matrix, Improvement of background by passive and active shielding, flushing with nitrogen Adjustment of peak fit algorithm. Interactive check! Information about processing of material prior to measurement True Coincidence effects on special energies for certain nuclides
0.72% 235 U (T 1/2 =7*10 8 a) 231 Th (T 1/2 =25,6 h) β - 231 Pa (T 1/2 =3,3*10 4 a) 227 Ac (T 1/2 =22 a) (1,2%) β - (98,8%) 223 Fr (T 1/2 =22 m) 227 Th (T 1/2 =18,7 d) Based on: U. Schkade, priv.com. Measurement of 235 U and daughters β - 223 Ra (T 1/2 =11,4 d) 219 Rn (T 1/2 =3,9 s) Gas! γ : 143,76 kev ; 10,96 % γ : 163,33 kev ; 5,08 % γ : 185,72 kev ; 57,20 % γ : 205,31 kev ; 5,01 % 223 Ra 226 Ra (144,23 kev; 3,22 %) (186,10 kev; 3,51 %) γ : 235,97 kev ; 12,3 % γ : 269,46 kev ; 13,7 % γ : 271,23 kev ; 10,8 % 228 Ac (270,25 kev; 3,46 %)
Measurement of 235 U and daughters 219 Rn (T 1/2 =3,9 s) Gas! 215 Po (T 1/2 =1,8 ms) 211 Pb (T 1/2 =36,1 m) β - 211 Bi (T 1/2 =2,15 m) (99,68%) β - (0,32%) 207 Tl (T 1/2 =4,8 m) 211 Po (T 1/2 =0,52 s) β - 207 Pb (stabil) Additionally 219 At, 215 Bi und 215 At are produced!
Measurement of 238 U and daughters 99.27% Recoil loss possible 238 U (T 1/2 =4.5*10 9 a) 234 Th (T 1/2 =24.1 d) β - 234m Pa (T 1/2 =1.2 m) β - 234 U (T 1/2 =2.5*10 5 a) 230 Th (T 1/2 =8*10 4 a) γ : 92,37 kev ; 2,42 % γ : 92,79 kev ; 2,39 % γ : 92,6 kev ; 4,81 % Th-Kα1 (93,35 kev; 5,6 %) γ : 1001,03 kev ; 0,839 % γ : 766,37 kev ; 0,316 % γ : 63,28 kev ; 4,1 % 232 Th(63,81 kev; 0,263 %)
Measurement of 238 U, 226 Ra and daughters Gas!! 226 Ra (T 1/2 =1600 a) 222 Rn (T 1/2 =3.8 d) 218 Po (T 1/2 =3.05 m) (99,98%) β - (0.02%) 214 Pb (T 1/2 =26.8 m) 218 At (T 1/2 =2 s) β - 214 Bi (T 1/2 =19.8 m) γ : 186,10 kev ; 3,51 % 235 U : (185,72 kev; 57,2 %) γ : 295,22 kev ; 18,15 % γ : 351,93 kev ; 35,10 % 211 Bi (351,06 kev; 12,91 %) γ : 609,31 kev ; 44,6 % γ : 1120,29 kev ; 14,7 % γ : 1764,49 kev ; 15,1 %
Measurement of 238 U, 226 Ra and daughters - Measurement of the 186,10 kev-linie ; 3,51 % - But interfering with 185,72 kev; 57,2 % of 235 U 1- Use of 235 U-activity from other energy lines and correct the 226 Ra-activity 2- Calculate 238 U-activity from daughter nuclides. Use of natural ration for 238 U/ 235 U=21,7 for 235 U-activity => For 2 equillibrium is essential!
Measurement of 238 U, 226 Ra and daughters - Measurement of daughters 214 Pb and 214 Bi - But 222 Rn gaseous => losses 214 Pb γ : 295,22 kev ; 18,15 % γ : 351,93 kev ; 35,10 % Interferenz 211 Bi (351,06 kev; 12,91 %) 214 Bi γ : 609,31 kev ; 44,6 % γ : 1120,29 kev ; 14,7 % γ : 1764,49 kev ; 15,1 % Gastight container for measurement and storage needed!
Measurement of 238 U, 210 Pb and daughters 214 Bi (T 1/2 =19.8 m) (0,04%) β - (0.02%) 210 Tl (T 1/2 =1.3 m) 214 Po (T 1/2 =162 µs) β - 210 Pb (T 1/2 =22a) (7.5*10-7 %) β - (100%) 206 Hg (T 1/2 =8.1 m) 210 Bi (T 1/2 =5.0 d) β - (5*10-6 %) β - 206 Tl (T 1/2 =4.3 m) 210 Po (T 1/2 =138.4 d) β - 206 Pb (stabil) γ : 46,54 kev ; 4,25 %
Measurement of 232 Th and daughters Efficiencycheck 232 Th (T 1/2 =1,4*10 10 a) 228 Ra (T 1/2 =5,7 a) β - 228 Ac (T 1/2 =6,13 h) β - 228 Th (T 1/2 =1,9 a) 224 Ra (T 1/2 =3,64 d) 220 Rn (T 1/2 =55,6 s) 216 Po (T 1/2 =0,15 s) γ : 63,81 kev ; 0,263 % 234 223 Ra Th (63,28 kev; 4,1 %) γ : 209,25 kev ; 3,89 % γ : 338,32 kev ; 11,27 % γ : 911,20 kev ; 25,80 % γ : 968,97 kev ; 15,8 % (338,28 kev; 2,79 %) γ : 240,99 kev; 4,10 % 214 Pb Gas!! (242,00 kev; 7,12 %)
Measurement of 232 Th and daughters 216 Po (T 1/2 =0,15 s) 212 Pb (T 1/2 =10,6 h) β - 212 Bi (T 1/2 =60,6 m) (36,2%) β - (63,8%) 208 Tl (T 1/2 =3.1 m) 212 Po (T 1/2 =0.3 µs) β - 208 Pb (stabil) γ : 238,63 kev ; 43,30 % γ : 300,09 kev ; 3,28 % 227 Th 231 Pa (300,00 kev; 2,70 %) (300,07 kev; 2,47 %) γ : 727,33 kev ; 6,58 % γ : 583,19 kev ; 30,4 % γ : 860,56 kev ; 4,47 % γ : 2614,53 kev ; 35,64 % (Abundance * 0.362) 228 Ac (583,41 kev; 0,111 %)
Measurement of natural decay chains Step 1: Step 2: Is there a consistent analysis with all 3 decay chains in equilibrium? Is there a constant factor between the 238 U-chain and the 235 U-chain of 21.7 => easy interpretation Nuclide library with all lines correlated to the progenitor! 235 U, 238 U or 232 Th Abundances and halflives!
Measurement of natural decay chains Step 3: What are the nuclides that caused the disequilibrium? Does the disequilibrium comes from: 1- Geochemical processes 2- Effects from processing 3- Gas losses from measurement container Step 4: How do these disequilibria influence radiation protection Examples: 1-238 U/ 234 U-activity Recoil followed by solution in water 2-214 Pb- 214 Bi different to 226 Ra due to emanation 3-210 Pb activity increased by filtering of aerosols or electrostatic effects => Exact analysis of peak areas important
Steps to improve accuracy of net peak areas Background reduction (passive/active shielding) Improved efficiency functions and check of results Peak fit algorithm
Choice of detector (Calibration factor)
Ultra-Low-Level measurements Cellar Collaboration Source: Cellar booklett and priv. Communication M. Köhler
Efficiencies for different samples 3,00E-02 2,50E-02 5,00E-02 Ta-ore 3 cm Ta-ore vs Sand Ta-ore vs Sand Efficiency 2,00E-02 4,00E-02 Reihe1 5,00E-02 1,50E-02 Reihe2 Reihe1 3,00E-02 Reihe2 1,00E-02 4,00E-02 2,00E-02 5,00E-03 3,00E-02 0,00E+00 1,00E-02 2,00E-02 0 200 400 600 800 1000 1200 1400 1600 0,00E+00 1,00E-02 0 200 400 Energy 600 [kev] 800 1000 1200 1400 1600 Efficiency E fficiency 0,00E+00 Energy [kev} 0 50 100 150 200 250 300 Energy [kev}
Fundamental basics x-ray energies of elements Element O Fe Ge Zr Nb I Ta Hg Pb kα1 [ev] kα2 [ev] kβ1 [ev] 277 6.403 6.391 7.058 9.886 9.855 10.982 15.775 15.690 17.668 16.615 16.521 18.622 28.612 28.317 32.295 57.532 56.277 65.223 70.819 68.895 80.253 74.969 72.804 84.936
X-ray fluorescence analysis Output of x-ray fluorescence analysis can be used as input for Monte-Carlo modelling of efficiency function Ta-ore vs Sand 5,00E-02 4,00E-02 Reihe1 Reihe2 Efficiency 3,00E-02 2,00E-02 1,00E-02 0,00E+00 0 50 100 150 200 250 300 Energy [kev}
Validation of efficiency function
Validation of efficiency function
Validation of peak fit results E r e i g n i s s e 80000 70000 60000 50000 40000 30000 20000 10000 0 40 50 60 70 80 90 100 Energy [kev]
Validation of peak fit results
Validation of peak fit results Energy [kev] FWHM Events Energy [kev] FWHM Events 1 1 1 2 2,2 1,6 1,4 7 2,1 0,5 0,4 1,3 0,5 0,8 0,8
Time evolution of activity Example of Ra extraction from geothermal facilities D. Degering: Private communication from SAAGAS meeting september, 2010 Batemann, H. 1910, Solution of a System of Differential Equations Occuring in the Theory of Radioactive Transformations, Proc. Cambridge Philos. Soc. 15, 423-427. Decay Engine, http://www.nucleonica.ne t/application/fulldecay.a spx Degering, D., Köhler, M., SAAGAS meeting, Sept. 2010
True Coincidence γ- γ-coincidence X-ray- γ-coincidence γ-β-coincidence More:.. Inhomogenities Input: treatment of material and sample