f. cerutti 1 , n. charitonidis 1,2 and m. silari 1 1 cern, 1211 geneva 23, switzerland

Neutron double differential distributions, dose rates and specific activities from accelerator

components irradiated by 50 – 400 MeV protons

F. Cerutti1, N. Charitonidis1,2 and M. Silari1

1CERN, 1211 Geneva 23, Switzerland2 Department of Physics, National Technical University of Athens,

Zografou Campus, 157 80 Athens, Greece

SATIF-10, 2-4 June 2010, CERN, Geneva, SwitzerlandSATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

Scope

• Activation data concerning the materials involved in CERN experimental facilities are rather specific

• Systematic Monte-Carlo simulations with the FLUKA code using a simplified geometry were performed

• The ambient dose equivalent rate, the residual nuclei inventory as well as the neutron spectra were scored for 5 common accelerator materials for proton energies in the 50 - 400 MeV range

• The results of the present study aim to provide a simple database for a first estimate of the radiological risk


Simulation set-up

• 2 sets of simulations with the same, simplified geometry

• 1st: Residual nuclei inventory in the target and ambient dose equivalent around the target, up to 1 meter distance, after 7 different cooling times

• 2nd: Prompt neutron spectra escaping from the target

The effect of a concrete tunnel around the target was studied with a special set of simulations


Geometry

Carbon Copper Iron

H=1.34cm

50MeV

250MeV

400MeV

H=23.04cm

H=50.04cm

H=0.46cm

H=7.50cm

H=16cm

H=0.50cm

H=8.18cm

H=17.6cm

Irradiation Profile: 9 months constant irradiation, 6E12 p/s or 1 µA beam current


Right, solid cylinders

Ambient dose equivalent as a function of the distance

Stainless Steel – Cooling time 1 day

50MeV 100MeV

200MeV 400MeV

~ 500 – 800 mSv/h

~ 10-20 mSv/h

~ 1000-1500 mSv/h

~ 50 – 100 mSv/h

~ 40-50 mSv/h

~ 800 – 1000 mSv/h

>1300 mSv/h

~ 100-200 mSv/h

Ambient dose equivalent as a function of the distance

Stainless Steel – Cooling time 3 months

50MeV 100MeV

200MeV 400MeV

~ 100-300 mSv/h

~ 500 – 700 mSv/h

~ 9 – 12 mSv/h

~ 5-10 mSv/h

~500-800 mSv/h

> 80 mSv/h

~ 6-7 mSv/h

~ 2-10 mSv/h

Ambient dose equivalent rate as a function of cooling time

BN

Cu

SS

Self absorption

The slope does not change accordingly to the width of the target

Radionuclide Inventory

Carbon (graphite) [400MeV]

EOB After 1 week11C, 7Be, 8Be, 10C, 12B, 8Li, 8B, 6He, 3H

7Be, 3H

Copper [400MeV]62Cu, 64Cu, 61Cu, 58Co, 57Co, 58mCo, 56 Co, 51Cr, 60Cu, 66Cu, 54Mn, 60mCo, 63Zn, 55Fe, 61Co, 48V, 52Mn, 62Zn, 52mMn, 49V, 56 Mn, 53Fe

58Co, 57Co, 56Co, 51Cr54Mn, 55Fe, 49V, 48V


Prompt neutron yield(escaping from the target)

• The neutron double differential yield was scored in 6 angular bins on the target boundary (0o - 15o, 15o - 45o, 45o - 75o, 75o - 105o, 105o – 135o and 135o - 180o) with respect to the beam axis

• Same geometry, same energy range, same materials

• Importance biasing to compensate for the attenuation of low energy neutrons


Neutron Spectra

100MeV 400MeV

Total Yield: 0.16 n/p


100MeV

400MeV



Copper

Carbon

Effect of concrete tunnel

• The effect of a concrete tunnel around the target was examined

• The tunnel was modeled as a concrete sphere enclosing the target

• The material chosen was Iron, and the beam energy chosen was 400MeV

• The escaping neutron spectra, as well as the ambient dose equivalent was scored


Tunnel’s width=1m

Tunnel’s height: 2m

Effect of concrete tunnel


Ambient dose equivalent

Increase of H*(10) due to concrete activation and thermal neutrons production increase (target activation)

Neutron population

5 orders of magnitude !

Conclusions

• An evaluation of the radiological risk through a simple database

• Critical role of the neutron thermalisation on the tunnel’s concrete and its effect on ambient equivalent dose


• Ongoing study for calculations of the same quantities with the presence of the wall

Thank you !

f. cerutti 1 , n. charitonidis 1,2 and m. silari 1 1 cern, 1211 geneva 23, switzerland

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