1 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

2 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

3 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

4 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

5 FLUKA simulations A compromise between CPU time and precision: A simplified geometry DEFAULTS SHIELDIN, conceived for calculations for proton accelerators The new evaporation module is activated (EVAPORAT) The pure EM cascade has been disabled

6 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

7 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

8 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

9 Rooms for maintenance Two small rooms of 6 m 2, 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

10 Two small rooms of 6 m 2, 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

11 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

12 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

13 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

14 Horn Material: ANTICORODAL 110 alloy (Al 96.1%) Irradiation time: six weeks Specific activity (Bq/g) at different cooling times

15 Horn, after 6 weeks of irradiation

16 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*10 7 s/y) Specific activity (Bq/g) Steel pipe

17 Steel pipe, after 10 years of operation

18 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

19 Steel pipe, star density per proton

20 Steel pipe, after 10 years of operation 1 year of cooling

21 Steel pipe, power density crossing the inner surface

22 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

23 Steel pipe, after 10 years of operation

24 Steel pipe, after 10 years of operation

25 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

26 Concrete, after 10 years of operation

27 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:

28 Earth around the decay tunnel The distribution of the induced radioactivity in the earth has been obtained: Dividing each layer into twelve regions

29 Earth, after 10 years of operation

30 Earth, after 10 years of operation

31 Earth, after 10 years of operation

32 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

33 Earth, after 10 years of operation

34 Earth, after 10 years of operation

35 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

36 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