APPLICATION OF A FREE PARAMETER MODEL TO … Tarancón Sanz1, Hector Bagan1, Karsten Kossert2, Ole...

Tarancon et al. Application of a free parameter model to plastic scintillation samples.

APPLICATION OF A FREE PARAMETER MODEL TO PLASTIC SCINTILLATION SAMPLES

Alex Tarancón Sanz1, Hector Bagan1, Karsten Kossert2, Ole Nähle2

1 Departmento de Química Analitica de la Universidad de Barcelona. Spain2 Physikalisch-Technische Bundesanstalt (PTB). Braunschweig. Germany

LSC conference. Paris. France. 6-10 September 2010


Plastic Scintillation microspheresSolid 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.


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• Evaluate the effect of micelles in Liquid Scintillation


PS microspheres: UPS-89. From Detec-Rad (Canada) with a diameter between 120 and 230 µm

Sample preparation:- 2g of PSm in 6 mL PE-vials- active solution plus inactive carrier: 1 g- 10 minutes in ultra sonic bath- centrifugation: about 10 min at 3500 min-1

Experimental

Measure of different beta radionuclides solution with PS microspheres in a TDCR

Radionuclides:

H-3, Ni-63, S-35, Ca-45, P-33, Tc-99, Cl-36, Sr-90/Y-90, P-32 and Y-90 . The activities of

all reference solutions can be traced back to primary standardizations at PTB.


TDCR (triple to double coincidence ratio)

Experimental determination of the number of double and triple coincidences (RD and RT)

dEeES=εE

MEQE

T ∫ ⎟⎠⎞

⎜⎝⎛ −

−max

0

33

)(·1)(

dEeeES=εE

MEQE

MEQE

D ∫ ⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛ −−⎟

⎠⎞

⎜⎝⎛ −

−−max

0

33

)(·23

)(·121·3)(

( )( ) D

T

D

T

RR

MM

=εε

M (free parameter) of a determined scintillation system

dEeES=εE M

EQE

T

3

0

3)(·

max 1)(∫ ⎟⎟⎠

⎞⎜⎜⎝

⎛−

⎟⎠⎞⎜

⎝⎛ −


RadionuclideMaximum

Energy (keV)

TDCRReference Activity(kBq/g)

Calculated activity(kBq/g)

Deviation (%)

63Ni 66.980(15) 0.871 436.2(26) 44.7(6) -89.835S 167.14(8) 0.961 191.4(56) 76.6(5) -60.033P 248.5(11) 0.976 243.4(59) 143.3(5) -41.1

45Ca 256.4(9) 0.978 182.7(46) 104.2(2) -43.099Tc 293.8(14) 0.978 169.2(46) 110.3(1) -34.8

90Sr/90Y 545.9(14) 0.993 30.28(91) 27.8(1) -8.336Cl 708.6(3) 0.991 98.13(29) 89.0(4) -9.332P 1710.66(21) 0.999 198.8(46) 197.2(2) -0.890Y 2279.8(17) 0.998 4525.4(55) 4432.3(9) -2.1

. Counting efficiency depends on the energy of the radionuclide

. Deviation depends on the energy of the radionuclide. Lower energy higher errors

Measure of PSm samples with TDCR detector


)()( ' ESES ≈

1),,,( =zyxEP i

The energy (E’) of the particle when

reaching the scintillator is similar to

that of the initial particle (E)

All the particles reach the scintillator

dEM

EQEES=εE

T

3

0

max

3)(·exp1)(∫ ⎥⎦

⎤⎢⎣

⎡

⎭⎬⎫

⎩⎨⎧−−

Mechanism overview in LS


'),,,( TiT εzyxEP=ε ⋅

)()( ' ESES >

1),,,( ≤zyxEP i

Reduction of the energy (E’) of the particle when reaching

the scintillation microspheres

Reduction of the probability that a particle reaches the

scintillator

Mechanism overview in PS

dEM

EQEESεE

T

3

0

' max

3)(·exp1)('∫ ⎥⎦

⎤⎢⎣

⎡

⎭⎬⎫

⎩⎨⎧−−=


)(ES

Geometry

of the detection system(unit cell of 1mm3 filled with

polyethylene spheres with

radius of 87.8 µm and water)

Penelope Monte Carlo

simulation software

Simulation conditions

Absorption energies (50 eV), Elastic scattering parameters (0.05), Collisional and radiative energy cutoffs (50 eV), Number of simulations (2·10-5). Particle random location in water material. Particle is relocated into the cell when escapes. Particle is only detected once.

)(' ES

1),,,( ≤= zyxEPP ireach

Monte Carlo simulation of the electron track in the aqueous phase (Penelope package)


SP (52.36%) BCCP (68.02%) CP (74.05%)HCP (74.05%)

Geometry description

Ideal Geometries (cell of 1mm3 filled with polystyrene spheres with radius of 87.8 µm and water)

0

2

4

6

8

10

12

14

16

18

80 100

120

140

160

180

200

220

240

260

280

300

320

340

360

Diameter in µm

Prob

abili

ty in

%

. Mean radius: 87.8 ± 28.0 µm

. Degree of space filled: 60-66%


• 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.

Random geometries (cell of 1mm3 filled with polyethylene spheres and water)

• AL1(59.4 ± 0.9 %)

• AL2(62.3 ± 0.9 %)

• Sphere radius was selected following the probability size distribution

• The spheres are located in the position with lowest Z axis value


• AL3(60.8 ± 0.5 %)

• Sphere radius was 87.8 µm

• The spheres are located in the position with lowest Z axis value


0

2

4

6

8

10

12

14

16

18

80 100

120

140

160

180

200

220

240

260

280

300

320

340

360

Diameter in µm

Prob

abili

ty in

%


Preach

AL1(n=3)

AL2(n=3)

AL3(n=3)

PS(n=1)

BCCP(n=1)

HCP(n=1)

CCP(n=1)

63Ni 8.0 ± 0.1 8.7± 0.6 9.2± 0.8 7.0 12.3 15.6 15.535S 33.8 ± 0.3 35.6 ± 1.7 36.9± 0.1 30.7 45.2 49.9 50.133P 51.4± 0.4 53.6± 1.8 54.6± 0.1 48.3 62.2 66.6 66.6

45Ca 51.3± 0.5 53.3 ± 1.8 54.5± 0.2 48.5 62.1 66.2 66.199Tc 59.0 ± 0.5 60.7± 1.6 62.5± 0.1 56.5 68.7 71.9 72.036Cl 89.6 ± 0.1 90.1 ± 0.1 90.5 ± 0.1 88.9 92.3 93.0 93.032P 97.4 ± 0.1 97.5 ± 0.2 97.7 ± 0.1 97.2 98.3 98.5 98.590Y 97.5 ± 0.1 97.6 ± 0.1 97.7 ± 0.1 97.2 98.3 98.5 98.4

ExperimentalPS

efficiency63Ni 835S 3733P 55

45Ca 5299Tc 6136Cl 8832P 97.390Y 97.6

Probability values for AL2 geometry are similar to experimental efficiency values

Simulation with Penelope (Preach)


• In reduce spectra the mean energy is moved to higher energies

• Weak particles are stopped in the aqueous phase and those that arrive are more energetic

• Normalized spectra, REDUCED SPECTRA, must be used on TDCR calculations

0 1 2 3 4 5 6 7

x 104

-1

0

1

2

3

4

5

6

7x 10-4 Ni-63 normalized probability

Energy (eV)

Pro

babi

lity

Nor

mal

ized

(1/p

artic

le)

AL2HCPSPNI63 SPECTRA

Simulation with Penelope (Spectra)

0 0.5 1 1.5 2 2.5 3

x 105

0

1

2

3

x 10-4 Tc-99 normalized probability

Energy (eV)Pro

babi

lity

norm

aliz

ed to

1 (1

/par

ticle

)

AL2HCPSPTC99 SPECTRA

0 0.5 1 1.5 2 2.5

x 106

0

0.5

1

1.5

2

2.5

3

3.5x 10-4 Y-90 normalized probability

Energy (eV)

Pro

babi

lity

Nor

mal

ized

(1/p

artic

le)

AL2HCPSPY90 SPECTRA


Radionuclide Reference Activity(kBq/g) TDCR Preach(AL2) Calculated Activity

(kBq/g)Deviation

(%)63Ni 436.1792 0.871 8.8 509.97 16.535S 191.426 0.961 36.0 211.45 11.033P 243.399 0.976 53.8 267.25 9.5

45Ca 182.65 0.978 53.7 194.28 6.299Tc 169.2 0.978 61.1 180.76 6.8

90Sr/90Y 30.28 0.993 180.0 27.78 1.936Cl 98.13 0.991 90.2 88.99 0.532P 198.79 0.999 97.6 201.93 1.790Y 4525.42 0.998 97.6 4539.26 0.3

dEM

EQEESP=εE

reachT

3

0

max

3)(·exp1)('∫ ⎥⎦

⎤⎢⎣

⎡

⎭⎬⎫

⎩⎨⎧−−⋅

Geometry is still not correctly defined !!!

Results of TDCR measure with “reduced spectra” and “reach probability”


90Yy = 6,67E-002x + 9,35E+001R2 = 9,39E-001

97,0

97,5

98,0

98,5

99,0

50 55 60 65 70 75

Degree of volume filled with spheres in %

90Y

pro

babi

lity

in %

HCP and CP

BCCP

AL3

SP

AL1

AL2

• 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

Interaction probability is correlated with the degree of space filled


P<50µm: Probability to travel less than 50 µm in a lineal

path from a random position in the aqueous phase in a

random direction.

Geometry PL50m

OUT_001 (AL1) 43.20

OUT_003 (AL1) 44.20

OUT_004 (AL1) 43.42

OUT_001 (AL2) 47.40

OUT_005 (AL2) 43.62

OUT_006 (AL2) 48.89

OUT_011 (AL3) 48.38

OUT_012 (AL3) 48.48

OUT_013 (AL3) 48.42

y = 0,0038x2 - 0,1566x + 7,732R2 = 0,9942

5

7

9

11

13

15

17

35 40 45 50 55 60 65 70 75

P<50µm

63Ni

pro

babi

lity

in %

Geometry PL50m

OUT_026 (HCP) 70.85

OUT_027 (BCP) 70.51

OUT_028 (SP) 38.22

OUT_029 (CCBP) 63.28

63Ni

New geometry parameter (P<50µm)


y = 0,0038x2 - 0,1566x + 7,732R2 = 0,9942

5

7

9

11

13

15

17

35 40 45 50 55 60 65 70 75

P<50µm

63Ni

pro

babi

lity

in %

• 63Ni solution measure with PSm in a TDCR detector• TDCR computation of the activity using the 63Ni reduced spectra (AL2)• Calculation of the 63Ni Preach value needed to match the measured activity with the reference activity• Calculation of the P<50µm value.

Reference Activity

(kBq/g)

Measured Activity

(kBq/g)

Preach

(%)

436.18 44.71 10.2

P<50µm = 54.3 %

PSm-TDCR-Penelope tracing method

Property of our geometry


Radionuclide TDCRReference Activity(kBq/g)

Calculatedactivity(kBq/g)

Preach (%)( at P<50µm=54.3)

Correctedactivity(kBq/g)

Deviation(%)

35S 0.961 191.426 76.6151 39.9 191.9 0.233P 0.976 243.399 143.3476 57.4 249.6 2.5

45Ca 0.978 182.65 104.1724 57.4 181.5 -0.699Tc 0.978 169.2 110.3408 64.6 170.9 1.036Cl 0.991 98.132 88.99979 91.2 97.6 -0.5

90Sr/90Y 0.993 30.282 27.7805 182.0 30.5 0.832P 0.999 198.79 197.209 97.9 201 1.390Y 0.998 4525.42 4432.28 97.9 4529 0.1

PSm-TDCR-Penelope tracing method

• Radionuclide solution measure with PSm in a TDCR detector• Calculation of the Preach at 53.4 % P<50µm value• TDCR activity computation using the reduced spectra (AL2)• Calculation of the corrected activity.

y = 0,0012x2 + 0,4564x + 11,61R2 = 0,9983

25

30

35

40

45

50

55

35 40 45 50 55 60 65 70 75

P<50µm

35S

prob

abili

ty in

%


Conclusions

• We have established a method based on TDCR-PSm-PENELOPE using 63Ni as tracing radionuclide for the measure of beta radionuclides with quantification deviation lower that 3 %.

• 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 (3H) or electron capture emitters (125I).


• 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 2009 summer.

Acknowledgments


THANK YOU FOR

YOUR

ATTENTION

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