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