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Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 1QUADOSQUADOS
Problem 6Environmental Scatter
Miloslav Králík
Intercomparison on the Usageof Computational Codes in Radiation Dosimetry
Workshop in Bologna-Italy July 14 -17 2003
Inspectorate for Ionizing RadiationCzech Metrology Institute
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 2QUADOSQUADOS
Problem 6: Environmental Scatter
Shadow coneShadow conewith two layerswith two layers
Position 1Position 1
Position 2Position 2
252Cf- isotropic252Cf- isotropicpoint source inpoint source incentrecentre
y
xx
A bare 252Cf neutron source is located at the centreof a concrete walled calibration room.
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 3QUADOSQUADOS
∫ ⋅Φ=Φ E dE)E(max
min
E
E
∫ ⋅Φ⋅=max
min
E
EE
* dE)E()E,10(h)10(H*
∫ ⋅Φ⋅=max
min
E
EEE dE)E()E(RR
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 4QUADOSQUADOS
.constd)d(R 2 =⋅
For the point source and the point detectorin vacuum.
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 5QUADOSQUADOS
Moderated 252Cf source
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 6QUADOSQUADOS
Berthold LB 6411 survey meter
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 7QUADOSQUADOS
Properties of the neutron survey meter
Response:
should be isotropic because instrument indicatesarea dose
should follow the conversion function of neutronfluence to ambient dose equivalent
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 8QUADOSQUADOS
E / MeV
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103
h*(1
0,E
) /
pSv•
cm2
0.1
1
10
100
1000
Fluence -> H*(10) LB 6411: Resp*355
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 9QUADOSQUADOS
F3(d) - corrects for the deviation of the count ratefrom the simple inverse square law
d / cm
0 50 100 150 200 250 300
F 3
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0LB 6411
252Cf source
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 10QUADOSQUADOS
Bonner Spheres Spectrometer
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 11QUADOSQUADOS
E / MeV10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102
R /
cm
2
10-3
10-2
10-1
100
18
15
12
10
87
6
0
22..5
3
3.5
44.5567
Responses of CMI Bonner spheres
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 12QUADOSQUADOS
d / cm
0 50 100 150 200 250 300
F 3
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2 2.5 3 3.5 4 4.5 5 6 7 8101215
2
2.5
3
4
15
8
6
3.5
12
10
75
4.5
BSSModerated 252Cf
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 13QUADOSQUADOS
Neutron spectrum behind the shadow cone
E / MeV
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101
E • Φ
E(E
) /
cm-2
0
2e-7
4e-7
6e-7
8e-7
1e-6
170 cm 300 cm
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 14QUADOSQUADOS
Ambient dose equivalent spectrum behind the shadow cone
E / MeV
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101
E • Φ
E(E)
• h*(
10,E
) /
pSv
0.0
5.0e-5
1.0e-4
1.5e-4
2.0e-4
2.5e-4
170 cm 300 cm
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 15QUADOSQUADOS
Concluding remarks:
• Metrologists are obliged to specify neutron fluence and its energy distribution at the calibration point.
• For dosimetric instruments indicating operational dosimetric quantities neutron fluence must be converted to some operational quantity. Neutrons with higher energies are more important; the influence of scattered neutrons is substantially lower.
• My suggestion for the next comparison/exercise devoted to study of the environmental effects: to include a real instrument and its response function.
Environmental ScatterWorkshop in Bologna July 14-17 2003
P6 16QUADOSQUADOS
Reference:
1. ICRP 74 / ICRU 572. ISO 8529 -1, -2, -33. IEC 61005 Neutron ambient dose equivalent (rate) meters4. IAEA, Vienna, 2001, Tech. Rep. Series No. 403