APPLICATION OF A FREE PARAMETER MODEL TO PLASTIC SCINTILLATION SAMPLES

Transcription

1 APPLICATION OF A FR PARAMTR MODL TO PLASTIC SCINTILLATION SAMPLS Alex Tarancón Sanz 1, Hector Bagan 1, Karsten Kossert 2, Ole Nähle 2 1 Departmento de Química Analitica de la Universidad de Barcelona. Spain 2 Physikalisch-Technische Bundesanstalt (PTB). Braunschweig. Germany LSC conference. Paris. France. 6-1 September 21

2 Plastic Scintillation microspheres Solid solution of a fluorescence solute in a polymeric solvent. Applications. Continuous detector. Scintillation support for selective extractative compounds. Scintillation reagent for measure of salty samples.. In general alternative to LSC as does not produces mixed wastes. Behavior. Similar to LSC for high energetic beta emitters. Different to LSC for low energetic beta emitters and alpha emitters.

3 Main differences between PS and LS are based on the different path of the particle in the aqueous media before it reaches the scintillator Plastic scintillation Liquid scintillation Objective: Application of a free parameter model to PS samples Determine a theoretical model valid to PS samples valuate the effect of micelles in Liquid Scintillation

4 xperimental Measure of different beta radionuclides solution with PS microspheres in a TDCR PS microspheres: UPS-89. From Detec-Rad (Canada) with a diameter between 12 and 2 µm Sample preparation: - 2g of PSm in 6 ml P-vials - active solution plus inactive carrier: 1 g - 1 minutes in ultra sonic bath - centrifugation: about 1 min at 5 min -1 Radionuclides: H-, Ni-6, S-5, Ca-45, P-, Tc-99, Cl-6, Sr-9/Y-9, P-2 and Y-9. The activities of all reference solutions can be traced back to primary standardizations at PTB.

5 TDCR (triple to double coincidence ratio) xperimental determination of the number of double and triple coincidences (R D and R T ) d e S = ε M Q T max ) ( 1 ) ( d e e S = ε M Q M Q D max ) ( 2 ) ( ) ( ( ) ( ) D T D T R R M M = ε ε M (free parameter) of a determined scintillation system d e S = ε M Q T ) ( max 1 ) (

6 Measure of PSm samples with TDCR detector Radionuclide Maximum nergy (kev) TDCR Reference Activity (kbq/g) Calculated activity (kbq/g) Deviation (%) 6 Ni 66.98(15) (26) 44.7(6) S (8) (56) 76.6(5) -6. P 248.5(11) (59) 14.(5) Ca 256.4(9) (46) 14.2(2) Tc 29.8(14) (46) 11.(1) Sr/ 9 Y 545.9(14).99.28(91) 27.8(1) Cl 78.6() (29) 89.(4) P (21) (46) 197.2(2) Y (17) (55) 442.(9) Counting efficiency depends on the energy of the radionuclide. Deviation depends on the energy of the radionuclide. Lower energy higher errors

7 Mechanism overview in LS The energy ( ) of the particle when reaching the scintillator is similar to that of the initial particle () S( ) S ' ( ) All the particles reach the scintillator P(, x, y, z) = 1 i ε T = max S( ) 1 exp Q( ) M d

8 Mechanism overview in PS Reduction of the energy ( ) of the particle when reaching the scintillation microspheres S ( ) > S ' ( ) Reduction of the probability that a particle reaches the scintillator P(, x, y, z) 1 i ε ' T = max S'( ) 1 exp Q( ) M d ε T = P ' ( i, x, y, z) εt

9 Monte Carlo simulation of the electron track in the aqueous phase (Penelope package) S() Penelope Monte Carlo S ' ( ) simulation software Geometry of the detection system (unit cell of 1mm filled with polyethylene spheres with Simulation conditions P reach = P(, x, y, z) 1 i radius of 87.8 µm and water) Absorption energies (5 ev), lastic scattering parameters (.5), Collisional and radiative energy cutoffs (5 ev), Number of simulations (2 1-5 ). Particle random location in water material. Particle is relocated into the cell when escapes. Particle is only detected once.

10 Geometry description 18 Probability in % Mean radius: 87.8 ± 28. µm. Degree of space filled: 6-66% Diameter in µm Ideal Geometries (cell of 1mm filled with polystyrene spheres with radius of 87.8 µm and water) SP (52.6%) BCCP (68.2%) HCP (74.5%) CP (74.5%)

11 Random geometries (cell of 1mm filled with polyethylene spheres and water) AL1 (59.4 ±.9 %) Sphere radius was selected following the probability size distribution The spheres are located in a random free position into the cell The spheres are move in the Z, X and Y axis Probability in % Diameter in µm AL2 Sphere radius was selected following the probability size distribution The spheres are located in the position with lowest Z axis value (62. ±.9 %) The spheres are move in the Z, X and Y axis. AL (6.8 ±.5 %) Sphere radius was 87.8 µm The spheres are located in the position with lowest Z axis value The spheres are move in the Z, X and Y axis.

12 Simulation with Penelope (P reach ) P reach AL1 (n=) AL2 (n=) AL (n=) PS (n=1) BCCP (n=1) HCP (n=1) CCP (n=1) 6 Ni 8. ±.1 8.7±.6 9.2± S.8 ±. 5.6 ± ± P 51.4±.4 5.6± ± Ca 51.±.5 5. ± ± Tc 59. ±.5 6.7± ± Cl 89.6 ± ± ± P 97.4 ± ± ± Y 97.5 ± ± ± xperimental PS efficiency 6 Ni 8 5 S 7 P Ca Tc 61 6 Cl 88 2 P Y 97.6 Probability values for AL2 geometry are similar to experimental efficiency values

13 Simulation with Penelope (Spectra) Probability Normalized (1/particle) 7 x 1-4 Ni-6 normalized probability x 1 4 nergy (ev) AL2 HCP SP NI6 SPCTRA In reduce spectra the mean energy is moved to higher energies x 1 5 Weak particles are stopped in the aqueous phase and those that arrive are more energetic Normalized spectra, RDUCD SPCTRA, must be used on TDCR calculations Probability normalized to 1 (1/particle) Probability Normalized (1/particle) 2 1 x 1-4 Tc-99 normalized probability nergy (ev).5 x 1-4 Y-9 normalized probability AL2 HCP SP TC99 SPCTRA x 1 6 nergy (ev) AL2 HCP SP Y9 SPCTRA

14 Results of TDCR measure with reduced spectra and reach probability ε T = P reach max S'( ) 1 exp Q( ) M d Radionuclide Reference Activity (kbq/g) TDCR P reach (AL2) Calculated Activity (kbq/g) Deviation (%) 6 Ni S P Ca Tc Sr/ 9 Y Cl P Y Geometry is still not correctly defined!!!

15 Interaction probability is correlated with the degree of space filled 9 Y 99, y = 6,67-2x + 9,5+1 BCCP 9 Y probability in % 98,5 98, 97,5 R 2 = 9,9-1 AL SP AL2 HCP and CP AL1 97, Degree of volume filled with spheres in % Poor correlation: Degree of space filled do not depend on the microspheres diameter Distance from a random position in a random direction to the microspheres

16 New geometry parameter (P <5µm ) P <5µm : Probability to travel less than 5 µm in a lineal path from a random position in the aqueous phase in a random direction. 6 Ni Geometry PL5m OUT_1 (AL1) 4.2 Geometry PL5m OUT_26 (HCP) y =,8x 2 -,1566x + 7,72 OUT_ (AL1) 44.2 OUT_27 (BCP) R 2 =,9942 OUT_4 (AL1) 4.42 OUT_1 (AL2) 47.4 OUT_5 (AL2) 4.62 OUT_6 (AL2) OUT_28 (SP) 8.22 OUT_29 (CCBP) Ni probability in % OUT_11 (AL) OUT_12 (AL) OUT_1 (AL) P <5µm

17 PSm-TDCR-Penelope tracing method 6 Ni solution measure with PSm in a TDCR detector TDCR computation of the activity using the 6 Ni reduced spectra (AL2) Calculation of the 6 Ni P reach value needed to match the measured activity with the reference activity Calculation of the P <5µm value. Reference Activity Measured Activity (kbq/g) (kbq/g) P reach (%) Ni probability in % y =,8x 2 -,1566x + 7,72 R 2 =,9942 P <5µm = 54. % Property of our geometry P <5µm

18 PSm-TDCR-Penelope tracing method Radionuclide solution measure with PSm in a TDCR detector Calculation of the P reach at 5.4 % P <5µm value TDCR activity computation using the reduced spectra (AL2) Calculation of the corrected activity. 5 S probability in % 55 y =,12x 2 +,4564x + 11,61 5 R 2 =, P <5µm Radionuclide TDCR Reference Activity (kbq/g) Calculated activity (kbq/g) P reach (%) ( at P <5µm =54.) Corrected activity (kbq/g) Deviation (%) 5 S P Ca Tc Cl Sr/ 9 Y P Y

19 Conclusions We have established a method based on TDCR-PSm-PNLOP using 6 Ni as tracing radionuclide for the measure of beta radionuclides with quantification deviation lower that %. We have established a theoretical model based on Monte Carlo simulation that allows to predict with high accuracy the lost of energy in the aqueous phase in microscopic geometries. We have evidenced the relevance to take into account the aqueous phase in the simulation of microscopic system (PS) but also in case of nanoscopic systems (LSC or Gel scintillation) in case of low energy beta emitters ( H) or electron capture emitters ( 125 I).

20 Acknowledgments DAAD (Deutsche Akademische Austauschdienst) for financial support All the people from the Unit of activity of the Radioactivity department of the PTB for their help and warm reception during my stage in Braunschweig on the 29 summer.

21 THANK YOU FOR YOUR ATTNTION