methods and instruments for dosimetric measurements in mixed neutron-gamma radiation fields

CENTRAL LABORATORY FOR

RADIOLOGICAL PROTECTION

IAEA PROJECT RER/9/117 Regional Workshop on Regulatory Control of Radioactive Discharges to the Environment

17-21 June 2013, Warsaw, Poland

DEVELOPMENT OF NUCLEAR SAFETY AND RADIOLOGICAL PROTECTION METHODS FOR THE NUCLEAR POWER ENGINEERING’S CURRENT AND FUTURE NEEDS

Polish National Centre for Research and Development (NCBiR)

1

METHODS AND INSTRUMENTS FOR DOSIMETRIC MEASUREMENTS IN

MIXED NEUTRON-GAMMA RADIATION FIELDSNATALIA GOLNIK

NATIONAL CENTRE FOR NUCLEAR RESEARCH







MARIA REACTOR

LABORATORY FOR MIXED RADIATION DOSIMETRY

NCBJ IN OTWOCK-ŚWIERK







Neutron dosimetryTHE BASIC PROTECTION QUANTITY FOR IONISING RADIATION IS THE ABSORBED DOSE IN AN ORGAN OR TISSUE.

BECAUSE DIFFERENT TYPES OF RADIATIONS HAVE DIFFERENT DEGREES OF BIOLOGICAL EFFECTIVENESS ACCOUNT MUST BE TAKEN FOR RADIATION TYPE.

THE CONCEPT OF WEIGHTED DOSE SEEMS AT PRESENT THE BEST AVAILABLE.

THE PRESENT SYSTEM, RECOMMENDED BY ICRP INVOLVES A COMPLEX COMBINATION OF EFFECTIVE DOSE, THE SO CALLED „PROTECTION QUANTITY” WHICH IS USED IN LEGISLATION AND THE OPERATIONAL QUANTITIES WHICH INSTRUMENTS AND DOSEMETERS SHOULD REALISE.







Neutron dosimetry

AONGSIDE THE PROBLEMS OF THE COMPATIBILITY OF THE PROTECTION AND OPERATIONAL QUANTITIES THERE REMAINS THE PROBLEM OF PROVIDING DEVICES WHICH MEASURE THE OPERATIONAL QUANTITIES ACCURATELY, IN A ROUTINE AND SIMPLE WAY.

THERE REMAINS MUCH TO DO IF SUCH DEVICES ARE TO BECOME WIDELY AVAILABLE.







NUNC

CU

UDLT







1. Calibration laboratoryP. Tulik, Sz. Domański

NEUTRON SOURCES 241AM BE, 252CF, TRACEABLE TO NATIONAL PHYSICAL LABORATORY, UK, 239PU BESOURCES CAN BE EXPOSED FREE IN AIR OR IN MODIFYING FILTERS. DOSE EQUIVALENT RATE: 2 ÷1400 μSv/h.137CS GAMMA SOURCES GIVE FIELDS TRACEABLE TO POLISH COMMITTEE FOR NORMALISATION AND MEASUREMENTS; DOSE EQUIVALENT RATE OF 2 μSv/h ÷ 20 mSv/h







1. Calibration laboratory







2. Instrument for low-level gamma and neutron monitoring

S. Pszona, A. Bantsar, K. Wincel. B. Zaremba

PHOTONS IN COMMON/AVAILABLE NEUTRON MONITORS ARE USUALLY DISCRIMINATED

NEW DESIGNED DEVICE GIVES POSSIBILITY OF REGISTRATION GAMMA AND NEUTRON COMPONENTS IN SEPARATE „WINDOWS”

0

500

1000

0 25 50 75 100 125 150

coun

ts p

er c

hann

el, a

u

channels

gammawindow

neutronwindow








FOR THERMAL AND EPITHERMAL NEUTRONS THERE IS A SIGNIFICANT CONTRIBUTION FROM SECONDARY GAMMA GENERATED BY NEUTRONS IN (N,P) REACTIONS (MONTE CARLO CALCULATIONS)

VALUE NORMALIZED TO H*(10)

1,E-02

1,E-01

1,E+00

1,E+01

1,E-08 1,E-06 1,E-04 1,E-02 1,E+00R

espo

nse t

o se

cond

ary

gam

ma,

1/n

SvNeutron energy, MeV







Detector

Response to gammasnSv-1

Response to neutronsnSv-1

RemarksAm Cs Cf Am-Be

NEK 240G 160* 10.5 11.6 10.3 * without

Pb filter

6.0 8.5 11.6 10.3 with Pb filter

ALMOST EQUAL RESPONSE TO GAMMA AND NEUTRONS PB FILTER GIVES POSSIBILITY TO CORRECT GAMMA ENERGY DEPENDENCECHANNELS 125-160 GIVES POSSIBILITY TO CORRECT RESPONSE >10MEV








Recombination Chamber

REM-2 recombination chamber *LARGE CHAMBER (6 KG, 1800 CM3), 25 TE ELECTRODES WITH THE DIAMETER OF 12CM;*DISTANCE BETWEEN ELECTRODES - 7 MM.*USUALLY FILLED WITH A MIXTURE OF METHANE AND NITROGEN UP TO ABOUT 1 MPA.

High-pressure, tissue-equivalent ionization chamber,

operated under conditions of initial recombination of ions







00

voltage

ioni

s. c

urre

nt

00

saturation current

voltage

fi

i=

0

10 100 10000.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

September 1993 March 1995 August 1995

Ion

colle

ctio

n ef

ficie

ncy

Collecting voltage, V

Ion collection effciency







10 100 10000.0

0.2

0.4

0.6

0.8

1.0

137Cs neutrons:

14.8 MeV 2.5 MeV 0.9 MeVIo

n co

llect

ion

effic

ienc

y


Dependence on radiation quality







10 100 10000.0

0.2

0.4

0.6

0.8

1.0

URIon

colle

ctio

n ef

ficie

ncy


137Cs (reference)investigated radiation

Recombination index of radiation quality

=

RnR

4 Uf1Uf1

Q







AMBIENT DOSE EQUIVALENT*(10)

H*(10) = D*(10) X Q

APPROXIMATION WITHIN RECOMBINATION METHODS:

H*(10) ≈ D*(10) X Q4







3. MONITORING SYSTEM FOR WORKPLACES

REM-2

Keithley 6517B

Interface KUSB 448B

Software







RESULTSRad. source D*(10) [mSv/h] Q4 H*(10) [mSv/h]

Cs-137 6,10E-02 1,00E+00 6,10E-02

Cf-252 + LiF 1,10E-02 8,29E+00 9,10E-01

Cf-252 3,2E-02 8,04E+00 2,59E-01

Cf-252 + LiF 1,11E-02 8,29E+00 9,14E-01

AmBe-241 1,54E-02 7,44E+00 1,14E-01

Cs-137 6,10E-02 1,02E+00 6,22E-02

Cs-137 6,12E-02 1,00E+00 6,12E-02

PuBe-239 1,53E-02 7,59E+00 1,16E-01

Cf-252 1,60E-02 8,23E+00 1,31E-01







OVERNIGHT MEASUREMENTS







3. Monitoring system for workplaces

T

U

Chamber

Polarization electrodes Measure

electrodes

Ground

Electrometer

E U S

-U R

i S

i R i S - i R

SRii

= ~04.0i/i1iQi~Q)10(*D)10(*H SR

S4S4







22

3. Monitoring system for workplaces

THE IDEA OF THE TRIPLE-MODE DETECTOR (SUMMATION MODE RAISES SENSITIVITY, DIFFERENTIAL MODE GIVES POSSIBILITY OF DIRECT MEASUREMENTS OF THE AMBIENT DOSE EQUIVALENT RATE, IN CASE OF FLUCTUATIONS OF DOSE RATE. TWO SWITCHES ARE NEEDED FOR PROPER CONFIGURATION OF POLARIZING ELECTRODES AND FOR MEASUREMENTS OF IONIZATION CURRENT.

Chamber

Polarization electrodes

UR or UM

E1

H D

or Monitor Signal

E2 US

Measure electrodes

Switch 2

Switch 1







4. Ionization chamber containing 10BM.A. Gryziński, K. Tymińska, M. Zielczyński

DEVELOPMENT OF A METHOD FOR DETERMINATION OF AMBIENT DOSE EQUIVALENT, H*(10), USING AN IONIZATION CHAMBER FILLED WITH BF3 TARGET

Considered solutions

• Classic recombination chamber with addition of BF3 to the filling gas;

• High-pressure chamber filled with BF3 and placed in external moderator;

• Relatively small chamber (BOR-2) in spherical moderator

• Air filled ionization chamber with 10B in material of electrodes







ADDITION OF BF3 (ABOUT 0,1% ) IMPROVES THE CHAMBER SENSITIVITY FOR LOW ENERGY NEUTRONS (<10 KEV) AND ONLY SLIGHTLY INFLUENCES THE ENERGY DEPENDENCE FOR FAST NEUTRONS.

Ionization chamber containing 10Bclassic REM-2 with addition of BF3 to the filling gas

Dose response calculated with MCNPX code (per 1 neutron)

1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+021.00E-04

1.00E-03

1.00E-02

1.00E-01 methane + nitrogen (5%)methane + nitrogen (5%) + boron (1%)methane + nitrogen (5%) + boron (0.075%)ICRU

Energy [MeV]

Arbi

trar

y un

its







THICKNESS OF THE MODERATOR, GAS PRESSURE AND POLARISING VOLTAGE SHOULD BE OPTIMISED IN ORDER TO OBTAIN SIMILAR SENSITIVITY TO H*(10) FOR NEUTRONS AND GAMMA RADIATION IN CERTAIN ENERGY RANGE

10 100 1000

20

40

60

80

100

120

i / H

*(10)

[ p

A m

Sv-1 h

]

U [ V ]

Cs

Cf

PuBe

Ionization chamber containing 10B - high pressure chamber with moderator







MODERATORS MADE WITH POLYETHYLENE


90 60 45 30 0 0-dno25303540

Zależność kątowa komory

kąt [st.]

I [pA

]

Angular dependence of the chamber response







SATURATION CURVES OF THE REM-2 CHAMBER FILLED WITH BF3 HAVE BEEN DETERMINED IN NEUTRON AND GAMMA RADIATION FIELDS.


Relative ion collection efficiency for 137Cs and 252Cf







Optimum values

• Thickness of the external moderator – ca. 3 cm

• Gas pressure – 130 kPa

• Polarising voltage – 350 V for 4 cm moderator.

Ionization chamber containing 10B high pressure chamber with moderator

0 10 20 30 40 50 60 7030

40

50

60

70

80

Response of B-chamber (Cf-252)

[mm]

[pA]







5. Model of recombination chamber with spectrometric properties

M. Zielczyński, N. Golnik, M.A. Gryziński, M. Maciak, K. Tymińska

PATENT APPLICATIONModel. MCNPX Visual Editor

Considered solutions

• Number of electrodes - 21;

• Made with PP-EL

• Thickness of electrodes – 10 mm;

• Electrodes covered with B4C







5. Model of recombination chamber with spectrometric properties

NEUTRON FLUX ON THE CHAMBER LID (0) AND CHOSEN ELECTRODES (1 21) AT 25 ‐MG/CM3 B4C LAYER THICKNESS FOR BOTH MONTE CARLO CODES.







5. Model of recombination chamber with multilayer moderator

NEUTRON FLUX ON THE CHAMBER LID (0) AND CHOSEN ELECTRODES (1 21) AT 600 ‐MG/CM3 B4C

LAYER THICKNESS FOR BOTH MONTE CARLO CODES.







5. Model of recombination chamber with multilayer moderator

NEUTRON FLUX ON THE LOWEST ELECTRODE (21) FOR VARIOUS VALUES OF THE B4C LAYER THICKNESS FOR BOTH MONTE CARLO CODES.







6. Passive detector with multilayer moderatorN. Golnik, K. Dworecki, M.A. Gryziński, P.Tulik, K. Tymińska

Radiation







6. Passive detector with multilayer moderator







1.1 Górny MTS-6 91,896 Środek MTS-6 94,50 Dół MTS-7 3,01














5.3 Górny MTS-6 11,11 Środek - Dół MTS-7 0,61










7. Accident dosimetry







7. Accident dosimetry

NO. AMOUNT TITLE1 1 Power Output Coating2 1 Power Output3 1 Power Output Spacer4 1 Casing5 2 Capacitor 4.7nF M6 1 External Electrode7 1 Internal Electrode8 1 Measuring Output Spacer9 1 Grounding Output

10 1 Measuring Output11 1 Nut

PARTS LIST CAPACITORS AS A DETECTOR







THANK YOU FOR YOUR ATTENTION

WE WILL SHOW MUCH MORE IN NEXT YEAR

methods and instruments for dosimetric measurements in mixed neutron-gamma radiation fields

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