NMi, Van Swinden Laboratorium,

Eduard van Dijk

The primary air kerma standards for 60Co and 137Csin the Netherlands

10 May 2007 Eduard van Dijk

10 May 2007 Eduard van Dijk 2

Content

• Kwall determination by extrapolation measurements• Kwall determination by Monte Carlo calculation• Results NMi 60C0• Results NMi 137Cs (preliminary)

The primary air kerma standards for 60Co and 137Csin the Netherlands

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Kair(p) : Kerma to air = E / mair (J/kg) at point p

The primary air kerma standard

Photon beam

P

air

100 cm

60Co

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Kair(p) : Kerma to air = E / mair (J/kg) at point p

The primary air kerma standard

Carbon spherePhoton beam

P

air

R

100 cm

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The primary air kerma standard

Photon beam Carbon sphere

P

air

Kair(p) : Kerma to air = E / mair (J/kg) at point p

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air

Carbon sphere

The primary air kerma standard

Photon beam

Air volume (i)P

( ) kcarbonattsckSene

WV

iKa i

C

air

air

Cair

Π+⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛ −

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛ −

=

−

...... ρρ

μρ

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air

Photon beam Carbon sphere

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Ion.current

Correction for attenuation and scatter

Ion. current

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air

Photon beam Carbon sphere

1 2 3 4 5 6

mm carbon buildup

Kwall

Correction for attenuation and scatter

Ion. current

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air

1 2 3 4 5 6

mm carbon buildup

Kwall

Cep

Mean center of electron production

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air

1 2 3 4 5 6

mm carbon buildup

Kwall

Cep

Mean center of electron production

Kcep

Air volume (i)

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Central electrodeChamber wall 4mm

5cm3 air volume

( )EEE

kiii

ii

1,0,

0,sc +∑

∑=

Si

hvhv

hv’

hv’Ei,1

Stemholder

Graphite Air

Ei,0e-

e-Ei,0

MC PENELOPE simulation of attenuation and scatter

EeEkii

iis ii

0,

0,att ∑

∑ ⋅=

μ

Kwall = Katt . Ksc

5 cm3 spherical standard

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radiaal

Radial orientation calculated with: 3mm, 4mm, 5mm and 6mm wall thickness

MC calculation of attenuation and scatter

100 cm from source reference point

Photon beam

2.5 cm3 cylindrical standard

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axiaal

Axiaal orientation calculated with: 3mm, 4mm, 5mm and 6mm wall thickness

MC calculation of attenuation and scatter

100 cm from source reference point

Photon beam

2.5 cm3 cylindrical standard

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Oblique (45o)

Oblique orientation calculated with: 3mm, 4mm, 5mm and 6mm wall thickness

MC calculation of attenuation and scatter

100 cm from source reference point

Photon beam

2.5 cm3 cylindrical standard

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Gammatron3 60Co radiator head

60Co source holder

Set diaphragm

5 cm3 NMi standard

Beam sharpener

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Diaphragm and beamsharpener Gammatron3

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Rotating source drum

Beam sharpener

Diaphragm

60Co source

Light mirror

Uranium

Tungsten

Stainless steelLead

Beam limiter

MC simulation Gammatron3 radiation head

60Co beam

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Results 60Co measurements and calculations

2.5 cm3

3 mm4 mm5 mm6 mm

774.11772.64769.66767.07

Standard Orientation Wall thickness Kwall Imeasured (pA) K (Gy/h)

2.5 cm3

2.5 cm3

3 mm4 mm5 mm6 mm

5 cm3

Standard Orientation Wall thickness Kwall Imeasured (pA) K (Gy/h)

Standard Orientation Wall thickness Kwall Imeasured (pA) K (Gy/h)

Standard Orientation Wall thickness Kwall Imeasured (pA) K (Gy/h)

4 mm

1.04911.05101.05451.0563

3 mm4 mm5 mm6 mm

34.10934.10434.08834.030

802.06798.04794.38790.72

1.01111.01511.01931.0232

34.05834.02434.00633.979

-790.30784.11778.50

-1.02551.03451.0409

-34.03734.06534.033

1.0214 1581.12 34.019

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Results 60Co measurements and calculations

2.5 cm3

3 mm4 mm5 mm6 mm

Standard Orientation Wall thickness

2.5 cm3

2.5 cm3

3 mm4 mm5 mm6 mm

5 cm3

Standard Orientation Wall thickness

Standard Orientation Wall thickness

Standard Orientation Wall thickness

4 mm

3 mm4 mm5 mm6 mm

Average: 34.083 Gy/h st.dev. 0.1%

Average: 34.045 Gy/h st.dev. 0.1%

Average: 34.017 Gy/h st.dev. 0.1%

34.019 Gy/h st.dev. 0.1%

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2.5 cm3 4 mm

5 cm3 4 mm

Ratio 5 cm3 and 2.5 cm3 = 1.0002,

with an expanded uncertainty of 0.36 % (coverage factor k = 2).

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100 cm

137Cs source

Lead shieldingPhase space determination

Tungsten diaphragm

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Results 137Cs measurements and calculations

2.5 cm3

3 mm4 mm5 mm6 mm

Standard Orientation Wall thickness

2.5 cm3

2.5 cm3

3 mm4 mm5 mm6 mm

Standard Orientation Wall thickness

Standard Orientation Wall thickness

3 mm4 mm5 mm6 mm

Average: 21.441 Gy/h st.dev. 0.1%

Average: 21.396 Gy/h st.dev. 0.1%

Average: 21.462 Gy/h st.dev. 0.1%

Average 137Cs 2.5 cm3 = 21.433 Gy/h (1m STP)

with an expanded uncertainty of 0.60 % (coverage factor k = 2).