PRELIMINARY ANALYSIS RESULTS S S S S OF N-DOSYS DOSIMETERS - - PowerPoint PPT Presentation

Tenth Symposium on Neutron Dosimetry

S S S S

Uppsala, Sweden, 12 – 16 June 2006

PRELIMINARY ANALYSIS RESULTS OF N-DOSYS DOSIMETERS MEASUREMENTS

• F. Groppi, M. L. Bonardi, L. Gini

OF N DOSYS DOSIMETERS MEASUREMENTS

F. pp , . L. , L. LASA, Radiochemistry Laboratory, Segrate ENEA Universita’ degli Studi and INFN ENEA, Universita degli Studi and INFN, Milano, Italy

• Z. B. Alfassi
• Z. B. Alfassi
• Dept. Nuclear Engineering, Ben-Gurion

University University Beer-Sheva, Israel

Neutron Personal Dosimeters Neutron Personal Dosimeters Deep penetrating neutron radiation is detected by the energy t f th h ( ) d ( ) ti ith H d h i transfer through (n,γ) and (n,p) reactions with H and heavier elements. In personal neutron dosimetry the more common dosimeters commercially available are: commercially available are:

• Poly allyl diglycol carbonate (PADC);

y y g y ( );

• Thermoluminescent Albedo Dosimeter – TLAD;
• Nuclear Track Emulsion;
• Bubble detectors;
• Ion Storage devices.

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g

Neutron Detection by PADC Neutron Detection by PADC

• Poly allyl diglycol carbonate (PADC) is an organic material

th t h i t i i iti it t f t t that has an intrinsic sensitivity to fast neutrons: neutrons interact with H producing recoil protons that are i i i ti l hi h l t t t k i PADC ionizing particles which cause latent tracks in PADC; B h i l t hi th l t t t k b i ibl d

• By chemical etching the latent tracks become visible and can

be counted by a track reader system. U ll t hi t i l li d t Usually a pre-etching step is commonly applied to remove the alpha tracks of the environmental radon, to achieve the l d t ti li it i d low detection limit required.

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Neutron dosimeter system N Neutron dosimeter system N-

• DOSYS

DOSYS N-DOSYS is an integrated personal neutron dosimeter system based upon the well-known PADC/CR-39 track-etch y p technology, manufactured by Radosys Ltd. Thi t t t t i CO i h This system uses a pre-treatment in CO2, an unique approach to solve at the same time two different problems: 1 th ti f th l h ti l t k f th

• 1. the separation of the alpha particles tracks of the

environmental radon; 2 t l th ll d l t k f th il

• 2. to enlarge the small and pale tracks of the recoil

protons generated by fast neutrons, improving k bl th i t t remarkably the image contrast.

• E. Hulber, D. Selmeczi, Counting proton tracks on PADC without a pre-etching step. A novel approach for

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neutron dosimeter application, Rad. Meas., 40 (2005) 616-619.

N-

• DOSYS dosimeter specifications

DOSYS dosimeter specifications

• 1. 2 Chips
• Chamber n.1 – PADC chip with PE converter, to monitor fast

p , neutron region;

• Chamber n. 2 – PADC chip with PA converter, to monitor

thermal neutron region.

• 2. Detectable neutron Energy Range:

a) from 0.5 to 10 MeV, without converter; b) from 20 meV to 20 MeV, with converter.

• 3. Lowest Level of Detection (LLD):

a) 0.3 mSv, Hp(10) – tested with a 252Cf source; b) 0 1 mSv Hp(10) tested with a 241Am(Be) source b) 0.1 mSv, Hp(10) – tested with a Am(Be) source.

• 4. Typical background – transit track density:

0 1 tracks mm-2

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0.1 tracks mm

N-

• DOSYS dosimeters

DOSYS dosimeters

The Radosys N-DOSYS dosimeters are exposed:

• 2 at LASA exposed to an Am(Be) calibrated source;
• 2 at LASA exposed to an Am(Be) calibrated source;
• 2 at LENA exposed at research Nuclear Reactor TRIGA MARK II
• f Pavia University at a constant thermal neutron flux;
• f Pavia University at a constant thermal neutron flux;
• 2 are used as personal dosimeters by two TSRM at S.Anna Hospital

(Como); (Como);

• 2 at Joint Research Centre (JRC) of the European Commission -

Ispra (VA) Ispra (VA). No dosimeters can be used as blank. This is revealed as a difficult to background evaluation especially for very low expositions, in particular for doses near to low detection limit

• f dosimeters

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• f dosimeters.

LASA exposure set LASA exposure set-

• up

up

No comparison with a rem counter or with a spectrometer is made for

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the measures presented.

LASA results LASA results

Am(Be) neutron calibration source: 1 Ci = 2.7 106 n s-1 a) at 1/1/1992 Conversion factor: 0.740 n s-1cm-2 = 1μSv h-1 H*(10) conversion factor b),c) : 1.05 ( ) Exposure time Distance neutron dose H*(10) N-DOSYS density N-DOSYS dose H*(10) N-DOSYS dose H*(10) ε% time h cm dose H (10) mSv density tracks mm-2 dose H (10) mSv dose H (10) mSv ε% 49 200 0 37 1.52 0.6 0 67±0 11 84 49 200 0.37 1.83 0.8 0.67±0.11 84 604 70 36.8 84.68 94 85 41.3 46 3 43.8±3.5 19 94.85 46.3

N-DOSYS: background: 0.3 tracks mm-2 conversion factor: 0.49 mSv·(tracks mm-2)-1

a) F.H. Attix, Radiation Dosimetry, Accademic Press, Inc., USA, 1969. b) B.R.L. Siebert, H. Schumacher, Quality Factors, Ambient and Personal Dose Equivalent for neutrons, based on the new ICRU Stopping Power data for protons and alpha particles, Rad. Prot. Dos., 58(3), (1995) 177-183. c)

• A. Klett, B. Burgkhardt, The new remcounter LB6411: measurement of neutron Ambient Dose Equivalente H*(10)

12 -16 June 2006 N-DOSYS measurements results 8 c)

• A. Klett, B. Burgkhardt, The new remcounter LB6411: measurement of neutron Ambient Dose Equivalente H (10)

according to ICRP60 with high sensitivity, IEEE Trans.Nucl. Science, 44(3) (1997) 757-759.

LENA results LENA results

The dosimeters are exposed to thermal neutron flux into piercing channel. Exposure time h neutron dose H*(10) mSv N-DOSYS density tracks mm-2 N-DOSYS dose H*(10) mSv N-DOSYS dose H*(10) mSv h mSv mm mSv mSv 1 0.05 0.60 0.43 0.146 0.062 0.1 5 0.22 0.43 0.45 0.062 0.066 0.1 Ludlum Mod. 12-4: 45 μSv h-1 F ICRP 60 45 S h 1 1 200

2 1

From ICRP 60: 45 μSv h-1 1 200 n cm-2 s-1

N-DOSYS: background: 0.3 tracks mm-2 conversion factor: 0 49 mSv (tracks mm-2)-1

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conversion factor: 0.49 mSv (tracks mm 2) 1

• S. Anna results
• S. Anna results

Instrumentations used

2 Linear Accelarators – photon beam: 18 MV VARIAN Clinac 1800 VARIAN Clinac 2100

1 9 1

Current 7.5 μA 2.4 Gy min-1 5 109 n s-1 Rem counter (Anderson & Braun) – BF3 range: 0.25 eV – 20 MeV N-DOSYS dosimeters to two TSRM from 17/1/05 to 28/2/05

Working conditions assumed

the operators stayed at the console with turn over on 5 days per week: the operators stayed at the console with turn over on 5 days per week: 1 turn/week on Varian 1800; 2 turn/week on Varian 2100; Use factor for 18 MV photon beams equal to 0.5.

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Use c o

• V p o o be

s equ

• . .

• S. Anna results
• S. Anna results

Neutron Dose Neutron Dose N-DOSYS N-DOSYS d N-DOSYS d Hp(10) μSv/mount bibl Hp(10) μSv/mount meas density tracks mm-2 dose Hp(10) μSv dose Hp(10) μSv bibl. meas. VARIAN Clinac 3 ÷ 6 1.65 ÷ 3.3 TSRM 1 0.45 0 62 73 157 100 ÷ 200 1800 1 0.62 157 VARIAN Clinac 4.7 ÷ 7 2.2 ÷ 3.5 TSRM 0.49 95 100 Clinac 2100 4.7 ÷ 7 2.2 ÷ 3.5 2 0.41 52 100

N-DOSYS: background: 0.3 tracks mm-2 conversion factor: 0.49 mSv (tracks mm-2)-1

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1 For dose equivalent values greater than the LLD of dosimeters the agreement

Conclusions Conclusions

1. For dose equivalent values greater than the LLD of dosimeters the agreement between the measured N-DOSYS values and the waited ones is quite good; 2. For very low neutron dose, near to N-DOSYS LLD, the discrepancy needs more y p y investigations. In this case the dosimeters can be used for more than 1 month (see S Anna results) or In this case the dosimeters can be used for more than 1 month (see S. Anna results) or in particular working conditions like for new installations.

Next steps Next steps

1. More measurements with Am(Be) source to control different exposure conditions are needed; are needed; 2. Rem counter measurements for comparison are needed; 3 The LENA results are related to very low fluxes: in this case it may be useful to 3. The LENA results are related to very low fluxes: in this case it may be useful to test the dosimeters inside other irradiation channels; 4. Particular attention must be pointed out on background measurements as for blank

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p g dosimeter (background tracks mm-2).

Conclusions Conclusions

In any case the advantage in using CR-39 plastic detectors are: 1. the background depends mainly on the manufacturing of the plastic detectors; 2. the fading begins to appear within 25 days after the irradiation date; 3. as all neutron sources and nuclear reactors are associated with attendant γ rays, but the sample irradiated by neutrons and γ rays has an un clear surface covered with white bubbles and background, whereas the other sample irradiated by neutrons only has a clear surface with lower background. y g

The investigated properties of solid-state nuclear track detector CR-39 type indicate a possible wide application as a fast neutron dosimeter type indicate a possible wide application as a fast neutron dosimeter.

A.P. Kobzev, M.R. El-Asser, A.A. El-Halem, U.S. Abdul-Ghaphar, T.A. Salama, Effects of g rays on fast neutron registration in CR 39 Rad Meas 37 (2003) 201 204 neutron registration in CR-39, Rad. Meas., 37 (2003) 201-204. S.L. Sharma, T. Pal, V.V. Rao, W. Enge, Effect of gamma irradiation on bulk etch rate of CR-39. Nucl. Tracks Radiat. Meas., 18 (1991) 385–389.

• E. Vilela, E. Fantuzzi, G. Giacomelli, et al., Optimization of CR-39 for fast neutron dosimetry applications,

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• Radiat. Meas., 31(1–6) (1991) 437–442.