Tenth Symposium on Neutron Dosimetry Uppsala, Sweden, 12 – 16 June 2006 PRELIMINARY ANALYSIS RESULTS S S S S OF N-DOSYS DOSIMETERS MEASUREMENTS OF N DOSYS DOSIMETERS MEASUREMENTS F. Groppi, M. L. Bonardi, L. Gini 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 transfer through (n, γ ) and (n,p) reactions with H and heavier t f th h ( ) d ( ) ti ith H d h i 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. g 12 -16 June 2006 N-DOSYS measurements results 2
Neutron Detection by PADC Neutron Detection by PADC •Poly allyl diglycol carbonate (PADC) is an organic material th t h that has an intrinsic sensitivity to fast neutrons: i t i i iti it t f t t neutrons interact with H producing recoil protons that are i ionizing particles which cause latent tracks in PADC; i i ti l hi h l t t t k i PADC •By chemical etching the latent tracks become visible and can B h i l t hi th l t t t k b i ibl d be counted by a track reader system. Usually a pre-etching step is commonly applied to remove U ll t hi t i l li d t the alpha tracks of the environmental radon, to achieve the low detection limit required. l d t ti li it i d 12 -16 June 2006 N-DOSYS measurements results 3
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. This system uses a pre-treatment in CO 2 , an unique approach Thi t t t t i CO i h to solve at the same time two different problems: 1 th 1. the separation of the alpha particles tracks of the ti f th l h ti l t k f th environmental radon; 2. to enlarge the small and pale tracks of the recoil 2 t l th ll d l t k f th il protons generated by fast neutrons, improving remarkably the image contrast. k bl th i t t E. Hulber, D. Selmeczi, Counting proton tracks on PADC without a pre-etching step. A novel approach for neutron dosimeter application, Rad. Meas., 40 (2005) 616-619 . 12 -16 June 2006 N-DOSYS measurements results 4
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 252 Cf source; tested with a 241 Am(Be) source b) 0 1 mSv Hp(10) b) 0.1 mSv, Hp(10) – tested with a Am(Be) source. 4. Typical background – transit track density: 0 1 tracks mm -2 0.1 tracks mm 12 -16 June 2006 N-DOSYS measurements results 5
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 of Pavia University at a constant thermal neutron flux; of 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 of dosimeters of dosimeters. 12 -16 June 2006 N-DOSYS measurements results 6
LASA exposure set LASA exposure set- -up up No comparison with a rem counter or with a spectrometer is made for the measures presented. 12 -16 June 2006 N-DOSYS measurements results 7
LASA results LASA results Am(Be) neutron calibration source: 1 Ci = 2.7 10 6 n s -1 a) at 1/1/1992 Conversion factor: 0.740 n s -1 cm -2 = 1 μ Sv h -1 H*(10) conversion factor b),c) : 1.05 ( ) Exposure Distance neutron N-DOSYS N-DOSYS N-DOSYS ε % ε % time time dose H*(10) dose H (10) density density dose H*(10) dose H (10) dose H*(10) dose H (10) tracks mm -2 h cm mSv mSv mSv 1.52 0.6 49 49 200 200 0 37 0.37 0 67±0 11 0.67±0.11 84 84 1.83 0.8 84.68 41.3 36.8 43.8±3.5 19 604 70 94 85 94.85 46 3 46.3 0.3 tracks mm -2 N-DOSYS: background: 0.49 mSv·(tracks mm -2 ) -1 conversion factor: 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) c) A. Klett, B. Burgkhardt, The new remcounter LB6411: measurement of neutron Ambient Dose Equivalente H*(10) 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 . 12 -16 June 2006 N-DOSYS measurements results 8
LENA results LENA results The dosimeters are exposed to thermal neutron flux into piercing channel. Exposure neutron dose N-DOSYS N-DOSYS dose N-DOSYS dose time H*(10) density tracks H*(10) H*(10) mm -2 h h mSv mSv mm mSv mSv mSv mSv 0.60 0.146 1 0.05 0.1 0.43 0.062 0.43 0.062 5 0.22 0.1 0.45 0.066 45 μ Sv h -1 Ludlum Mod. 12-4: 45 μ Sv h -1 1 200 n cm -2 s -1 S h 1 2 1 F From ICRP 60: ICRP 60 45 1 200 0.3 tracks mm -2 N-DOSYS: background: 0 49 mSv (tracks mm -2 ) -1 0.49 mSv (tracks mm 2 ) 1 conversion factor: conversion factor: 12 -16 June 2006 N-DOSYS measurements results 9
S. Anna results S. Anna results Instrumentations used 2 Linear Accelarators – photon beam: 18 MV VARIAN Clinac 1800 VARIAN Clinac 2100 Current 7.5 μ A 2.4 Gy min -1 5 10 9 n s -1 1 9 1 Rem counter (Anderson & Braun) – BF 3 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. Use c o o V p o o be s equ o . . 12 -16 June 2006 N-DOSYS measurements results 10
S. Anna results S. Anna results Neutron Neutron N-DOSYS N-DOSYS Dose Dose N-DOSYS d dose d dose Hp(10) Hp(10) density Hp(10) Hp(10) μ Sv/mount μ Sv/mount tracks mm -2 μ Sv μ Sv bibl bibl. meas meas. VARIAN TSRM 0.45 73 3 ÷ 6 1.65 ÷ 3.3 100 ÷ 200 Clinac 1 1 0 62 0.62 157 157 1800 VARIAN TSRM 0.49 95 4.7 ÷ 7 4.7 ÷ 7 2.2 ÷ 3.5 2.2 ÷ 3.5 Clinac Clinac 100 100 2 0.41 52 2100 0.3 tracks mm -2 N-DOSYS: background: 0.49 mSv (tracks mm -2 ) -1 conversion factor: 12 -16 June 2006 N-DOSYS measurements results 11
Conclusions Conclusions 1 1. For dose equivalent values greater than the LLD of dosimeters the agreement 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 3. The LENA results are related to very low fluxes: in this case it may be useful to 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 p g dosimeter (background tracks mm -2 ). 12 -16 June 2006 N-DOSYS measurements results 12
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