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Induced radioactivity in the target station and in the decay tunnel

from a 4 MW proton beam

S.Agosteo(1), M.Magistris(1,2), Th.Otto(2), M.Silari(2)

(1) Politecnico di Milano;

(2) CERN

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Introduction

• In a Neutrino Factory, neutrinos result from the decay of high-energy muons

• These muons are themselves decay product of a pion beam generated by the interaction of a high-intensity proton beam with a suitable target

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Introduction

There are two different ideas for producing a neutrino beam:

• Muon storage ring

• Neutrino super beam

These results give some guide-lines, which are intended for both facilities

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Introduction

• An important aspect of a future Neutrino Factory is the material activation in the target system and its surroundings.

• A first estimation of the production of residual nuclei has been performed by the Monte Carlo cascade code FLUKA

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FLUKA simulations

• A compromise between CPU time and precision:

A simplified geometryDEFAULTS SHIELDIN, conceived for

calculations for proton accelerators

The new evaporation module is activated (EVAPORAT)

The pure EM cascade has been disabled

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An overview of the facility

The facility consists of a target, two horns, a decay tunnel and a dump.

It is shielded by 50 cm thick walls of concrete and is embedded in the rock.

Top view Top view

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Target and horns

• A 4 MW, 2.2 GeV proton beam is sent onto the target with a flux of 1.1E16 protons/s.

• A liquid mercury target is presently being considered, inserted in two concentric magnetic horns for pion collection and focusing.

Proton beam

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Decay tunnel

The decay tunnel consists of a steel pipe filled with He (1 atm), embedded in a 50 cm thick layer of concrete

60 m long

Inner diameter of 2 m

Thickness of 16 mm

Cooling system (6 water pipes)

Front view

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Rooms for maintenance

• Two small rooms of 6 m2, filled with air, have been placed upstream of the magnetic horns for dose scoring

• Two concentric magnetic horns

• (300 kA, 600 kA) surround the target

Top view

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• Two small rooms of 6 m2, filled with air, have been placed upstream of the magnetic horns for dose scoring

• Two concentric magnetic horns

• (300 kA, 600 kA) surround the target

Side view

Rooms for maintenance

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Beam dump

Downstream of the decay tunnel, a dump consisting of:

• An inner cylinder of graphitic carbon

• An outer cylinder of polycristalline graphite

• An iron shielding

Side view

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Surroundings

• The whole structure (target, horn and decay tunnel) is embedded in the rock, which has been divided into 100 regions for scoring the inelastic interaction distribution

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Surroundings

• The whole structure (target, horn and decay tunnel) is embedded in the rock, which has been divided into 100 regions for scoring the inelastic interaction distribution

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Horn

• Material: ANTICORODAL 110 alloy (Al 96.1%)

• Irradiation time: six weeks

• Specific activity (Bq/g) at different cooling times

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Horn, after 6 weeks of irradiation

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Steel pipe

• Material: steel P355NH (Fe 96.78%)

• Average values for the whole pipe (60 m long)

• 10 years of operation• Operational year of 6

months (1.57*107 s/y)• Specific activity (Bq/g)

Steel pipe

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Steel pipe, after 10 years of operation

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Steel pipe: 24 regions for scoring

• In order to obtain the spatial distribution of stars and induced radioactivity, the steel pipe has been divided into 24 regions

5 m long

1.6 cm thick

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Steel pipe, star density per proton

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Steel pipe, after 10 years of operation1 year of cooling

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Steel pipe, power density crossing the inner surface

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Steel pipe, central part

• Induced activity (Bq/g) in the central part of the pipe and multiples of EL (Exemption Limits) calculated with the addition rule

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Steel pipe, after 10 years of operation

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Steel pipe, after 10 years of operation

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Concrete

• The target system is shielded by 50 cm thick walls of concrete

• Specific activity (Bq/g) after 10 years of operation, operational year of 6 months

Concrete around the tunnel

Concrete around the horn

HeAir

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Concrete, after 10 years of operation

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Earth around the decay tunnel

• Dividing the earth into six concentric layers (1 m thick)

The distribution of the induced radioactivity in the earth has been obtained:

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Earth around the decay tunnelThe distribution of the induced radioactivity in the earth has been obtained:

•Dividing each layer into twelve regions

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Earth, after 10 years of operation

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Earth, after 10 years of operation

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Earth, after 10 years of operation

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Earth, after 10 years of operation

Exponential fit at 10 m, 35 m, 55 m

from the target.

Lambda=0.86 (+/-2.2%)

1 year of cooling

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Earth, after 10 years of operation

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Earth, after 10 years of operation

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Conclusions

• Every year of operation, 4 horns become highly radioactive and require a long term deposit, e.g. underground close to the facility

• After 10 years of operation, the steel pipe in the decay tunnel, the concrete and a 2 m thick layer of earth have to be treated as radioactive waste

• Outside this “hot region”, after 10 years of operation and 20 years of cooling the induced radioactivity in the earth goes below the Swiss exemption limit

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Future work

Based on these simulations, estimation of the dose-equivalent rate due to

• The horn• The steel pipe • The concrete

for maintenance, dismantling and radiation-protection issues