Synthesis of Plastic Scintillation microspheres: composition evaluation and alpha/beta discrimination capabilities

Transcription

1 Synthesis of Plastic Scintillation microspheres: composition evaluation and alpha/beta discrimination capabilities Luz M. Santiago, Alex Tarancón, Héctor Bagán, Jose Francisco García Department of Analytical Chemistry of the University of Barcelona 1

2 OUTLINE General aspects about Plastic Scintillation microspheres Synthesis of polymeric microspheres PSm Synthesis variable composition. PSm Synthesis Evaluation of α/β discrimination PSm Synthesis Modification of synthesis parameters. 2

3 PLASTIC SCINTILLATION MICROSPHERES (PSM) Solid solution of fluorescence solutes (PPO, POPOP, pt, Bis-MSB, ) in a polymeric solvent (polyvinyltoluene or polystyrene) and other additives. Diameter: from tent to hundreds of micrometers MEASUREMENT WITH PSM Procedure similar to LS Low efficiency for low energy beta emitters Similar efficiency for high energy beta emitters 3

4 USES AND ADVANTAGES OF PSm No production of mixed waste. Sample recovery after measurement. Salty samples can be used avoiding phase separation. Immobilization of selective extractans compounds onto the PSm surface. Capability for real time and continuous monitoring. Reusability. SUPPLIERS OF PSm Bicron Detec-Rad NOT REGULAR SUPPLIERS FIXED COMPOSITIONS 4

5 DEVELOPMENT OF A METHOD TO SYNTHESIZE PSM SYNTHESIS METHODOLOGIES Use of supercritical fluids Extraction/Evaporation method Monomer polymerization Drop disruption with ultrasounds Successfully applied to the encapsulation of pharmaceutical products in polymeric microspheres 5

6 Mixing DCM Organic Phase Polystyrene Fluorescent solutes Aqueous phase (2 L) is formed by water and surfactant (PVA (1%)). Organic phase (100 ml) composed by PS and fluorescent solutes is added to the aqueous phase. An emulsion is obtained. DCM is extracted and evaporated. DCM DCM Aqueous Phase DCM DCM Stirring (16.7 Hz) Mixing (24 hours) Mixing 6

7 PSM SYNTHESIS OF VARIABLE COMPOSITION Polymeric solvent (10 g) Primary fluorescent solute (5%) Secondary fluorescent solute(2%) PSm1 polystyrene PSm2 polystyrene PPO --- PSm3 polystyrene p-tp PSm4 polystyrene PPO POPOP PSm5 polystyrene p-tp bis-msb In all cases around 10 g PSm were obtained 7

8 CHARACTERIZATION LS single wavelength laser diffraction particle analysis Scanning Electron Microscopy (Stereoscan S-300) 8

9 RADIOMETRIC CAPABILITIES Detection efficiency (in %) Name Bkg (cpm) Composition 3 H 14 C 90 Sr/ 90 Y 241 Am SQP(E) PSm polystyrene Polystyrene is a scintillating polymer, but a poor one (λ emission =270 nm) 9

10 RADIOMETRIC CAPABILITIES Detection efficiency (in %) Name Bkg (cpm) Composition 3 H 14 C 90 Sr/ 90 Y 241 Am SQP(E) PSm polystyrene PSm PSm1+ PPO PSm PSm1+ pt The addition of a primary solute leads to an increase of the detection efficiency (λ emission,ppo =354 nm and λ emission,pt =337 nm) and the SQP(E) 10

11 RADIOMETRIC CAPABILITIES Detection efficiency (in %) Name Bkg (cpm) Composition 3 H 14 C 90 Sr/ 90 Y 241 Am SQP(E) PSm polystyrene PSm PSm1+ PPO PSm PSm1+ pt PSm PSm2+ POPOP PSm PSm3+Bis-MSB The addition of a secondary solute leads to an increase of the detection efficiency for 3 H and 14 C and an improvement on the SQP(E) 11

12 SPECTRUM ( 3 H) Compound Emission wavelength (nm) Polystyrene 270 PPO 353 p-tp 337 POPOP 407 bis-msb 417 The addition of primary and secondary solute leads to an increase of the number of photons detected by the PMT 12

13 EVALUATION OF α/β DISCRIMINATION CAPABILITIES Discrimination based on the delay of alpha pulses Discrimination in PS is more difficult due to the fast decay time Addition of naphthalene may delay pulses 13

14 Quantity of Naphthalene (g) EVALUATION OF NAPHTHALENE IN THE α/β SEPARATION PSm6 PSm7 Composition PS+PPO+POPOP+Naphtalene PS+pT+bis-MSB+Naphtalene A 0 0 B C D E F G H Same synthesis parameters as PSm1-5 are used. 14

15 SIZE AND MORPHOLOGY PPO/POPOP + naphthalene pt/bis-msb + naphthalene 0 g 0.8 g 1.2g 0.05g 0.1g 1.2g 15

16 RADIOMETRIC CAPABILITIES PS+PPO+POPOP+Napht Detection efficiency (in %) Name Napht (g) Bkg (cpm) H-3 C-14 Sr-90/Y-90 Am-241 SQP(E) A 0 1,10 1,19 51,2 180,6 76,7 782 C 0.8 0,97 0,960 47,2 174,9 72,4 791 E 2.0 1,09 1,120 51,1 180,7 77,2 796 G 3.0 1,46 0,718 44,0 194,1 64,3 775 PS+pT+bis-MSB+Napht Detection efficiency (in %) Name Napht (g) Bkg (cpm) H-3 C-14 Sr-90/Y-90 Am-241 SQP(E) A 0 1,16 1,14 49,8 178,7 73,2 783 D 0.1 1,21 0,74 46,4 187,8 72,6 746 F 0.6 0,89 0,79 44,3 181,6 70,9 791 H

17 SPECTRUM PS+PPO+POPOP+Napht PS+pT+Bis-MSB+Napht 17

18 Misclassification % Misclassification % α/β SEPARATION IN QUANTULUS DETECTOR (PPO/POPOP) Error of beta (in%) Error of alpha (in %) PSA 0 g 0.6 g 0.8 g 1.2 g 2.0 g g PSA The addition of naphthalene improves discrimination of alpha but get worse for the beta Misclassification errors at crossing point are high (26%, PSA140, 2g) 18

19 Misclassification % Misclassification % α/β SEPARATION IN QUANTULUS DETECTOR (pt/bis-msb) Error of beta (in%) Error of alpha (in %) PSA 0 0,3 0,6 0,8 1, g 0.05 g 0.10 g PSA The addition of naphthalene has higher impact than in PPO/POPOP The addition of naphthalene improves discrimination of alpha but get worse for the beta Misclassification errors at crossing point are high (30%, PSA200, 0.8g) 19

20 Time Time α/β SEPARATION IN TRIATHLER DETECTOR (PPO/POPOP) Portable one PMT 3D alfa/beta discrmination 10 BETA, PPO+POPOP ALPHA, PPO+POPOP Energy Energy Alpha are more delayed than beta 20

21 Time Time α/β SEPARATION IN TRIATHLER DETECTOR (pt/bis-msb) 10 5 BETA, pt + Bis-MSB Energy 10 5 ALPHA, pt + Bis-MSB Energy Alpha are beta highly delayed with the addition of naphthalene

22 Time Time α/β SEPARATION IN TRIATHLER DETECTOR PS + PPO + POPOP +1.2 g of naphthalene PPO + POPOP gr NAFTALENO 30 Beta Alfa PS + pt + Bis-MSB +0.6 g of naphthalene tp + bis-msb gr NAFTALENO 30 Beta Alfa Bkg (in cpm) Energy Efficiency (in %) Error (in %) Beta Alpha Bkg (in cpm) Energy Efficiency (in %) Error (in %) Beta Alpha

23 PSM SYNTHESIS MODIFICATION OF SYNTHESIS PARAMETERS Parameter Polystyrene (g) st Fluorescent solute (%) 5 2on Fluorescent solute (%) 2 DCM volume (ml) 100 PS:DCM proportion (g:ml) 1:10 Surfactant (%) Aqueous phase (ml) 2000 Stirring speed (Hz) 16.5 Temperature (ºC)

24 Standard 200 ml DCM 400 ml DCM 20 g polymer 40 g polymer 2% PVA 5% PVA 13.2 Hz 8.25 Hz 35 ºC 30 g; 300 ml :6% 30 g; 600 ml 6% SIZE

25 MORPHOLOGY 500 µm standard 100 µm 400 ml DCM 500 µm 35ºC PSm in general resulted spherical and smooth. PSm using 400 ml DCM: smaller and flattened PSm carried out at 50ºC were porous and didn t show uniformity. 25

26 EFFECT OF THE ORGANIC SOLVENT AND THE PS QUANTITY PSm6 Detection efficiency % Name Bkg (CPM) H-3 C-14 Sr-90/Y-90 Am-241 SQP(E) Standard Eff% Eff% 200 ml DCM ml DCM g polystyrene g polystyrene Increase of Decrease of Decrease of Increase Decrease volume the micelle the PS of the on the of organic phase size diameter efficiency SQP(E) 26

27 EFFECT OF THE STIRRING SPEED AND PVA PROPORTION PSm6 Detection efficiency % Name Bkg (cpm) H-3 C-14 Sr-90/Y-90 Am-241 SQP(E) Standard Hz Hz Eff% 2% PVA % PVA Increase of Decrease of Decrease of Increase Decrease surfactant the micelle the PS of the on the proportion size diameter efficiency SQP(E) 27

28 EFFECT OF THE TEMPERATURE PSm6 Detection efficiency % Name Bkg (CPM) H-3 C-14 Sr-90/Y-90 Am-241 SQP(E) Standard Eff% 35 C C Increase of T leads to an too fast evaporation of DCM and the formation of big and irregular PSm 28

29 Conclusions The method of evaporation/extraction has been applied with success to the synthesis of PSm of different composition PSm synthesized present values of detection efficiency similar or better than the commercial ones The addition of naphthalene improves the discrimination capabilities of alpha and beta particles. In recent studies naphthalene has been substituted by diisopropylnaphthalene The optimization of the synthesis conditions allow us to obtain PSm of different diameters with improved detection efficiencies

30 THANK YOU FOR YOUR ATTENTION 30

31 SPECTRUM

32 SYNTHESIS REPLICATES HOMOGENEOUS PSm PSm6 1,033 ± (3.2%) 1,027 ± (1.5 %) PSm7 0,752 ± (9.7%) 0,819 ± (1.1%)

33 FINAL CONDITIONS Parameter Polystyrene (g) 30 1st Fluorescent solute (%) 5 2on Fluorescent solute (%) 2 DCM volume (ml) 600 PS:DCM proportion (g:ml) 1:10 Surfactant (%) 6 Aqueous phase (ml) 2000 Background (cpm) 1.21 H-3 (%) 4.51 C-14 (%) 74.3 Sr-90/Y-90 (%) Am-241 (%) Stirring speed (Hz) 16.5 Temperature (ºC) 20