1 induced radioactivity in the target station and in the decay tunnel from a 4 mw proton beam...
TRANSCRIPT
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 geometryDEFAULTS 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 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 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
10
• 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
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
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*107 s/y)• Specific activity (Bq/g)
Steel pipe
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
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
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
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 tunnelThe distribution of the induced radioactivity in the earth has been obtained:
•Dividing each layer into twelve regions
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
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