BAS-ION Istituto di Radioprotezione A new CR-39 nuclear track passive thoron measuring device Massimo Calamosca, Silvia Penzo 24 th International Conference

BAS-ION Istituto di Radioprotezione

A new CR-39 nuclear track passive thoron measuring device

Massimo Calamosca, Silvia Penzo

24th International Conference on

Nuclear Tracks in Solids Bologna

1-5 September 2008

224th International Conference on Nuclear Tracks in Solids

ThoronThoron scenarioscenario

Insufficient knowledge compared to radonInsufficient knowledge compared to radon

Not explicitly addressed from the national lawNot explicitly addressed from the national law

No standard measurement method availableNo standard measurement method available

Scarcity of available calibration facilities Scarcity of available calibration facilities

Absence of intercomparisons up to nowAbsence of intercomparisons up to now

Usually the thoron risk caused by TnDP is not evaluatedUsually the thoron risk caused by TnDP is not evaluated

Short TShort T1/21/2

Low exhalation probabilityLow exhalation probability

In-homogeneity of thoron concentration In-homogeneity of thoron concentration


Interest in risk assessment of thoron exposure is Interest in risk assessment of thoron exposure is world-wide increasingworld-wide increasing

ThoronThoron scenarioscenario

Specific thoron harm >specific radon harm for the same CSpecific thoron harm >specific radon harm for the same Ceqeq

CCpp thoron (75.66 nJ Bq thoron (75.66 nJ Bq-1-1) > C) > Cpp radon (5.56 nJ Bq radon (5.56 nJ Bq-1-1))

Some building materials (as for instance in the case of tuff) Some building materials (as for instance in the case of tuff) can cause can cause 220220Rn decay products exposure comparable or also Rn decay products exposure comparable or also greater to greater to 222222Rn decay products exposureRn decay products exposure


The standard procedure proposed by ENEA to The standard procedure proposed by ENEA to assess equivalent dose due to thoron exposure assess equivalent dose due to thoron exposure

Sampling selection.Sampling selection.

Mean thoron gas concentration measurement by ATD-PD.Mean thoron gas concentration measurement by ATD-PD.

Experimental determination of effective room diffusion Experimental determination of effective room diffusion coefficient.coefficient.

Thoron exhalation rate from room surfaces.Thoron exhalation rate from room surfaces.

Thoron decay products (TnDP) concentration computationThoron decay products (TnDP) concentration computation

Experimental validation of the computed TnPD mean Experimental validation of the computed TnPD mean concentrations.concentrations.

Definition of occupancy factor and exposure assessment.Definition of occupancy factor and exposure assessment.

DE assessment by applying the conversion dose factor DE assessment by applying the conversion dose factor

0,50 mSv (mJ h m0,50 mSv (mJ h m33))-1-1..


The new ENEA ATD-TnPD The new ENEA ATD-TnPD

Closed type, under patent, to be used coupled to our ATD-RnPDClosed type, under patent, to be used coupled to our ATD-RnPD

Start pointStart point: ATD-RnPD (patent : ATD-RnPD (patent MI2006A000703) with changes MI2006A000703) with changes aimed to aimed to

Increase of the diffusion Increase of the diffusion free surfacefree surface

Reduction of the Reduction of the diffusion timediffusion time

Increase of thoron Increase of thoron concentration concentration

Increase the thickness of Increase the thickness of the window between the the window between the volume of the device and volume of the device and the ATD surfacethe ATD surface

Improve the thoron sensitivity:Improve the thoron sensitivity:

Decrease the radon sensitivity:Decrease the radon sensitivity:


Diffusion kinetic test facilitiy: schematic diagramDiffusion kinetic test facilitiy: schematic diagram

Pump

Radon Chamber

Radonsource

8,8 MeV

8,8 MeV

6,8 MeV

6,8 MeV

ATD-TnPD

ATD-RnPD

Filter

MCA

Preamplifiers

Test Chamber

Amplifiers

Preamplifier

PC

Biassupply

Filter

N2 tank

Flowmeter

Exit tothe fumehood

The CR-39 detectors in the ATD-RnPD and ATD-TnPD have been The CR-39 detectors in the ATD-RnPD and ATD-TnPD have been substituted by PIPS detectors to record the time development of the substituted by PIPS detectors to record the time development of the spectra due to the radon exposure of the two ATD-PD spectra due to the radon exposure of the two ATD-PD

Flow rate=1300 l/h


Diffusion kinetic test Diffusion kinetic test

Requirements to perform the testRequirements to perform the test High radon concentration (High radon concentration (~~ 400 kBq/m400 kBq/m33) ) Concentration in the radon chamber ≥ 90% equilibrium valueConcentration in the radon chamber ≥ 90% equilibrium value

The equilibrium in the test chamber is reached very fast: tThe equilibrium in the test chamber is reached very fast: t90%90%=19 s =19 s

=> the delay time does not affect significantly the measurement => the delay time does not affect significantly the measurement uncertaintyuncertainty

Dwelling time = 600 sDwelling time = 600 s

The alpha energy spectra, sequentially saved with short dwelling The alpha energy spectra, sequentially saved with short dwelling times, were analysed and corrected for the times, were analysed and corrected for the 218218Po and Po and 214214Po spectra Po spectra spill overspill over the the 222222Rn ROIRn ROI

Asymptotic Asymptotic concentration concentration growth in the growth in the

radon chamberradon chamber


Diffusion kinetic test: resultsDiffusion kinetic test: results

Increase of Increase of radon radon

concentration concentration in the two in the two devicesdevices

3.08 min (2.323.08 min (2.32÷÷4.58) (k=2) ATD-TnPD4.58) (k=2) ATD-TnPD

20.8 min (15.320.8 min (15.3÷÷32.4) (k=2) ATD-RnPD32.4) (k=2) ATD-RnPDMean diffusion timeMean diffusion time

6.0 % (4.06.0 % (4.0÷÷8.0) (k=2) ATD-RnPD8.0) (k=2) ATD-RnPD

30.3 % (22.630.3 % (22.6÷÷36.6) (k=2) ATD-TnPD36.6) (k=2) ATD-TnPD

Equilibrium ratio between Equilibrium ratio between internal and external internal and external 220220Rn Rn concentrationconcentration

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

0 500 1000 1500 2000 2500 3000 3500

Co

un

ting

ra

te R

n-2

22

[cp

s]

Time [s]

ATD-RnDP

ATD-TnDPy=0.768*(1-Exp(-8.0E-4*x))

R2 = 0.87

y=0.669*(1-Exp(-5.42E-3*x))

R2 = 0.73


Thoron exposure: the calibration exposure chamberThoron exposure: the calibration exposure chamber

Thoron Chamber

MCA

Preamplifier

PC

Biassupply

Filter

Filter

Flowmeter

Pump

Thoronsource

2° Filter

1° Filter

Amplifier

Si Detector

Pressuremeter

By pass

Pressuremeter

Temperaturemeter

Cleaning air

Filter

Exit to fume hood Fan

Flow rate = 18.0 l/min


Thoron exposure: the Thoron exposure: the 220220Rn sourceRn source

Sample ofSample of Monazite Monazite mineralmineral was crushed, sieved and wet-grinded by was crushed, sieved and wet-grinded by a Turbula to reduce the grain size to a Turbula to reduce the grain size to ~~ 1µm, so to increase the thoron 1µm, so to increase the thoron emanation. emanation. The suspension obtained was filtered and piled up in set of 15 filters.The suspension obtained was filtered and piled up in set of 15 filters.The sourceThe source is constituted by 3 towers of 15 filters each, 3 mm is constituted by 3 towers of 15 filters each, 3 mm spaced, connected in series and installed within a stainless-steel spaced, connected in series and installed within a stainless-steel vessel.vessel.

232232Th and Th and 226226Ra activities measured by HPGeRa activities measured by HPGe232232Th=(8.82±0.19) kBq, Th=(8.82±0.19) kBq, 226226Ra (355±18) Bq, Ra (355±18) Bq, 226226Ra/Ra/232232Th = 4%Th = 4%


How to determine the thoron exposure:How to determine the thoron exposure: the thoron monitor (TM) the thoron monitor (TM)

A new monitor based on the two-filter method has been devised to A new monitor based on the two-filter method has been devised to absolutely measure the absolutely measure the 220220Rn concentration Rn concentration directlydirectly at the exit of the at the exit of the chamber. chamber.

It consists of a small aluminium cylindrical tube with two filters in It consists of a small aluminium cylindrical tube with two filters in series separated by a delay volume to permit series separated by a delay volume to permit 220220Rn decay, Rn decay, 216216Po Po growth and a negligible presence of growth and a negligible presence of 218218Po.Po.


The thoron monitor: sectorsThe thoron monitor: sectors

1° sector 1° sector (sampling head & (sampling head &

1° filter)1° filter)

2° sector 2° sector (Body)(Body)

3&4° sectors 3&4° sectors (PIPS)(PIPS)

5° sector 5° sector (Volume & 2° (Volume & 2°

filter)filter)


Thoron exposure: the thoron monitorThoron exposure: the thoron monitor

The thoron concentration is determinated by The thoron concentration is determinated by 220220Rn and Rn and 216216Po Po counts counts counted during the sampling (1000 s). counted during the sampling (1000 s).

0

0,2

0,4

0,6

0,8

1

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Act

ivity

to in

let R

n-2

20

co

nce

ntr

atio

ns

ratio

Transit time [s]

Rn-220

Po-216 -1° stage

Po-216 -2° stage

Po-216 - PIPS

Po-216 -4° stage

Po-216 -5° stage1° filter

2° filter


Thoron monitor: uncertainty budgetThoron monitor: uncertainty budget

Uncertainty sources on instrument response ∂f/∂x u(x) (∂f/∂x)2*u2(x) Weight Loss constant sector 2 1,4E+01 1,2E-01 2,9E+00 41,1% Filter efficiency (216Po) 9,7E+02 1,4E-03 1,9E+00 26,7%

216Po 1,1E+01 6,6E-02 5,3E-01 7,50% Loss constant sector 4 2,0E+00 3,6E-01 5,1E-01 7,14% Loss constant sector 5 5,3E-01 1,3E+00 4,4E-01 6,13%

Flow 1,9E-01 3,0E+00 3,2E-01 4,56% Loss constant sector 3 6,1E-01 7,7E-01 2,2E-01 3,11%

Diameter sector 4 2,9E+00 1,1E-01 9,8E-02 1,37% Height sector 4 7,6E+00 4,0E-02 9,2E-02 1,30% Height sector 5 1,1E+00 1,7E-01 3,8E-02 0,53%

counting volume efficiency sector 4 2,5E+02 4,3E-04 1,2E-02 0,17% Diameter sector 2 7,8E-01 1,1E-01 6,8E-03 0,10% Diameter sector 5 8,6E-01 8,8E-02 5,7E-03 0,08%

counting volume efficiency sector 5 7,5E+01 9,7E-04 5,3E-03 0,074% Diameter & height sector 4 (Covariance) 9,0E-01 - 3,8E-03 0,054% counting surface efficiency sector 5 1,8E+01 2,2E-03 1,6E-03 0,022%

Diameter sector 3 3,3E-01 1,1E-01 1,2E-03 0,017% Height sector 2 7,5E-02 4,6E-01 1,2E-03 0,017%

Sum - - 7,1 -


Thoron exposure: calibration resultsThoron exposure: calibration results

Low Exposure Medium Exposure High Exposure

Exposure time [s] 83886 60360 233487

Post exposure time [s] 252000 252000 252000

Mean circuit flow [cm3 s-1] 315.5 306.5 302.8

N. Sampling 5 4 3

Mean counts±SD 85.6±4.1 252±19 249.3±6.3

Mean u(counts)±SD 9.25±0.22 15.85±0.61 15.78±0.20

Mean TnMR ±SD [Bq m-3] 129.62±0.83 132.7±1.2 131.64±0.37

Mean u(TnMR)±SD [Bq m-3] 2.592±0.017 2.654±0.024 2.6328±0.0073

Mean TnM concentration±SD [kBq m-3] 11.10±0.58 33.4±2.8 32.82±0.92

Mean u( TnM concentration)±SD [kBq m-3] 1.219±0.036 2.21±0.11 2.179±0.036

Mean TnM flow±SD [cm3 s-1] 311.1±4.4 295.0±6.0 300.4±1.9

Mean volume post chamber correction ±SD 1.001243±0.000018 1.001311±0.000027 1.0012872±0.0000080

Mean chamber transit time ±SD [s] 51.04±0.73 53.8±1.1 52.85±0.83

Mean transit time correction±SD 1.3980±0.0070 1.425±0.011 1.4155±0.0032

Mean chamber concentration±SD [kBq m-3] 15.82±0.88 47.7±4.2 46.4±1.4

Mean u(chamber concentration)±SD [kBq m-3] 1.707±0.058 3.16±0.18 3.096±0.059

Sampling vs. circuit flow correction 0.9970 0.9827 0.9983

Exposure [kBq h m-3] 360 1090 3008

u(Exposure) [kBq h m-3] 44 110 220


Thoron exposure: calibration test designThoron exposure: calibration test design

3 thoron exposures3 thoron exposures

(360 ± 44) kBq h m(360 ± 44) kBq h m-3-3

(109 ± 11) (109 ± 11) 10 kBq h m10 kBq h m-3-3

(301 ± 22) (301 ± 22) 10 kBq h m10 kBq h m-3-3

3 radon exposures3 radon exposures

(273 ± 11) kBq h m(273 ± 11) kBq h m-3-3

(1365 ± 53) kBq h m(1365 ± 53) kBq h m-3-3

(395 ± 15) (395 ± 15) 10 kBq h m10 kBq h m-3-3

12 ATD-TnPDs12 ATD-TnPDs

6 ATD-RnPDs6 ATD-RnPDs

6 ATD-RnPDs (off position)6 ATD-RnPDs (off position)

6 ATD-TnPDs6 ATD-TnPDs

6 ATD-RnPDs6 ATD-RnPDs

Reference radon exposureReference radon exposure

(260 ± 10) (260 ± 10) 10 kBq h m10 kBq h m-3-36 ATD-RnPDs6 ATD-RnPDs

114 ATD-PDs114 ATD-PDs7 different etching times7 different etching times

Removed Layer range :Removed Layer range :

(7.84 ± 0.04) ÷ (12.54 ± 0.05 ) µm (7.84 ± 0.04) ÷ (12.54 ± 0.05 ) µm


The thoron chamber exposure: procedure requirementsThe thoron chamber exposure: procedure requirements

A high (18 lpm) circulating flow must be hold for all the course of A high (18 lpm) circulating flow must be hold for all the course of exposure exposure

To minimize To minimize 220220Rn decay the volume of the tubing Rn decay the volume of the tubing has to be kept as the minimumhas to be kept as the minimum

To minimize in-homogeneity exposure within the chamber, To minimize in-homogeneity exposure within the chamber, the use of a fan to mix air has been adoptedthe use of a fan to mix air has been adopted

To prevent the growing of radon in the circuitTo prevent the growing of radon in the circuitNitrogen has to be fluxed through the chamber at least every 24 hNitrogen has to be fluxed through the chamber at least every 24 h

The ATD-PD were stored for at least 70 h in a radon proof container The ATD-PD were stored for at least 70 h in a radon proof container to get the irradiation equilibrium for to get the irradiation equilibrium for 212212Bi (Bi (212212Pb)Pb)


Thoron exposure: net track density evaluationThoron exposure: net track density evaluation

D(TnPD,Tn Rn) ETn SENS(Tn,TnPD) ERn SENS(Rn,TnPD)

D(RnPD,Tn Rn) ETn SENS(Tn,RnPD) ERn SENS(Rn ,RnPD)

SENS(TnPD,Rn)

SENS(RnPD,Rn)

SENS(RnPD,Tn)

SENS(TnPD,Tn)

D(TnPD,Tn) D(TnPD,Tn Rn) D(RnPD,Tn Rn)

1

SENS(TnPD,Tn) D(TnPD,Tn)

ETn

Where D(XPD,Tn+Rn) is the track density measured in the X Where D(XPD,Tn+Rn) is the track density measured in the X passive device exposed to mixed irradiation (Tn+Rn, or Tn or Rn)passive device exposed to mixed irradiation (Tn+Rn, or Tn or Rn)

Where SENS(X,Y) is the response or sensitivity of the X passive Where SENS(X,Y) is the response or sensitivity of the X passive device to the Y (Tn or Rn) gasdevice to the Y (Tn or Rn) gas


Thoron exposure results: Thoron exposure results: dependence on etching time dependence on etching time

0,02

0,04

0,06

0,08

0,1

0,12

0,14

8 9 10 11 12 13 14 15 16 17

Diameter D95%

= 0. 056+0.00300D95%

R2 = 0.67, P<0.05, N=7

SENS(RnPD,Tn)

SENS(TnPD,Tn)


0,5

0,55

0,6

0,65

0,7

0,75

0,8

0,85

0,9

8 9 10 11 12 13 14 15 16 17

Diameter D95%

= 0.940 - 0.0218D95%

R2 = 0.912, P<0.01, N=7

Thoron exposure results: Thoron exposure results: dependence on etching time dependence on etching time

SENS(TnPD,Rn)

SENS(RnPD,Rn)


1

1,5

2

2,5

3

3,5

4

4,5

5

8 9 10 11 12 13 14 15 16 17 18

SE

NS

[(T

rack

s cm

^-2)

/(kB

q h

m^-

3)]

Diameter D95% [pixel]

SENS (ATD-TnPD,Rn)

SENS (ATD-RnPD,Rn)

Thoron exposure results: response of both Thoron exposure results: response of both devices to radon vs. etching timedevices to radon vs. etching time


0

0,05

0,1

0,15

0,2

0,25

0,3

8 9 10 11 12 13 14 15 16 17 18

SE

NS

[(T

rack

s cm

^-2

)/(k

Bq

h m

^-3

)]


SENS(ATD-RnPD,Tn)

y=0.214*(1-Exp(-0.1903*(x-4,91)))R2 = 0.78

Thoron exposure results: response of radon Thoron exposure results: response of radon passive device to toron vs. etching timepassive device to toron vs. etching time


1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9

8 9 10 11 12 13 14 15 16 17 18

SE

NS

[(Tr

acks

cm

^-2)

/(kB

q h

m^-

3)]


SENS = 1.840(1-Exp(-0.1826D95%))R2 = 0.941, P<0.01, N=7

Thoron exposure results: response of toron Thoron exposure results: response of toron passive device to toron vs. etching timepassive device to toron vs. etching time


ConclusionConclusion

The new ATD-TnPD has been completely characterised.The new ATD-TnPD has been completely characterised. The responses (SENS) to toron and radon result a little better than The responses (SENS) to toron and radon result a little better than

our previsions based on the preliminary testsour previsions based on the preliminary testsWe are always looking for an external calibration We are always looking for an external calibration

The new thoron source and monitor have resulted very effective, so The new thoron source and monitor have resulted very effective, so to be considered fit to be used in the calibration step.to be considered fit to be used in the calibration step.

And for the future…And for the future… A finer determination of the diffusion losses, that result the primary A finer determination of the diffusion losses, that result the primary

sources of uncertainty, is to be worked out, …sources of uncertainty, is to be worked out, …

Thank You for your attention… Thank You for your attention… and patienceand patience


0

5000

10000

15000

20000

25000

0 500 1000 1500 2000

Tra

ck d

en

sity

[tra

cks/

cm^2

]

220-Rn Exposure [kBq h/m^3]

ATD-RnPD

ATD-TnPD

SENS (ATD-RnPD) = 1.683±0.033

(tracks cm -2)/(kBq h m-3)

SENS (ATD-TnPD) = 9.98±0.14

(tracks cm -2)/(kBq h m-3)

Here is what did occur at PTB Here is what did occur at PTB !!

Documents

BAS-ION Istituto di Radioprotezione A new CR-39 nuclear track passive thoron measuring device Massimo Calamosca, Silvia Penzo 24 th International Conference