Transcript Accelerator Radiation Protection

FLUKA for accelerator radiation
protection –Indian perspective
Sunil C
Accelerator Radiation Safety Section
Radiation Safety Systems Division,
Bhabha Atomic Research Centre
Accelerator Radiation Safety Section
• Operational radiation protection
• Associated R&D
• Heavy Ion Accelerators (TIFR Bombay and VECC,
Calcutta
– ~5-7 MeV/amu Pelletron
– ~10 MeV/amu with a superconducting linac booster
– ~100 MeV/amu superconducting cyclotron
• Electron accelerators (RRCAT Indore)
– 20 MeV Microtron to 2.5 GeV electron synchrotron
– High current industrial accelerators
Future plans
• ADSS
– Proton accelerators
• 20 MeV to 1 GeV
• Swimming poll critical reactor that can also be
operated in sub critical mode with 600 MeV protons
incident on LBE
– 14 MeV neutron generators
• Bare
• Injectors for sub critical assemblies
Uses of FLUKA
• Routine accelerator radiation protection
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Source term calculations
Shielding
Induced activity
Synchrotron hutch shielding
Photoneutron estimation
ADSS
Proton accelerators
Secondary particle dose from heavy Ion reactions
Muon Transport and dose estimation
Spallation yields comparison with JQMD
Heavy Ion accelerators
• Neutron source term calculations
– EMPIRE, PACE (heavy ions) ALICE, PRECO (protons)
– Transport using the source.f
• BME!
– 10 MeV/amu to 100 MeV/amu
– Hauser-Feshbach for compound nucleus?
• Induced activity calculations
• Neutron spectrometry using passive techniques
• ECR ion sources
– Simulate electric fields?
20 MeV proton on Be
Electron Accelerators
• Photon (Bremsstrahlung) spectrometry
– High energy
• Detector response studies
– neutrons and photons
• Photoneutron spectrometry and dosimetry
• Synchrotron dosimetry
– Low energy (< 10 keV)
Photoneutrons
• Contribution to the exposure in electron
accelerators
• A new technique to predict the neutron
spectra using empirical relations
– Spectra from FLUKA fitted to a Maxwellian
• Temperature
• Yield
– Form a couple equation to predict the GDR
part of the photoneutron spectrum
Check
The procedure
Y (GeV
d 2Y
)  
dEd 
dEd 
1
YGDR  Y  m
Y ( En) 
Z
c
ASn
M En
 En 
exp   
3
2   2
  
 (MeV )  a  be  fA
Sunil C, Sarkar P K, “Empirical estimation of photoneutron energy distribution in high energy electron
accelerators”, Nuclear Instruments and Methods A 581, (2007), 844-849.
Independent FLUKA
Calculation
Experiment
Our Calculation
Neutrons > 50 MeV
• Experimental verification using Bi fission foils,
track etch membranes shows higher values
when compared to FLUKA calculations.
• How much is photon induced fission?
• The cross section is 1% of neutron fission
(>200 MeV)
• But at the experimental area, the photon fluence
is expected to be several times higher than
neutrons!
• Calculate photon induced fission using FLUKA?
Photon Transmission
• 30 cm diameter and 30 cm long cylindrical
detector (approximating the upper trunk of
a human body) is used to count the
photons.
• USRTRACK estimator tallies the photon
fluence.
• Deq99 (FLUSUW) subroutine used to fold
the fluence with the dose conversion
coefficients to obtain ambient dose
equivalent
Transmitted dose
H  H 0 exp(t ).
Unshielded Dose rate
H 0  aEb
Variation with detector size
Effect of detector size
Measured angular distribution of bremsstrahlung
photons at BM-3 (Storage ring, Indus-1)
50
40
30
20
10
0
-10
-20
-30
-40
-50
angle(deg.)
4%
8%
14%
100%
13%
5%
4%
0%
relative dose(% )
20%
40%
60%
80%
100%
Variation with detector size
Residual activity
• 2.5 GeV electron incident on 10 X0 -1Xm
targets.
• DPMJET activated using PHYSICS
• LAM-BIAS at 100
• Photon transport cut off to 10 MeV
Residual Activity (Bq/g)
SS
2.5 GeV e-, 1mA, 24 hours
Target
Ni
Ta
Radionuclide
Half life
Mode of production
Estimated Activity
(MBqW-1)
57Co
271 d
58Ni(,n)
400
182Ta
114 d
181Ta(n,
)
282
180Ta
8.1 h
181Ta(,n)
510
179Ta
1.8 a
181Ta(,2n)
430
55Fe
2.7 a
51Cr
27.7 d
54Fe(n,
) 56Fe(,n)
400
)
130
SS316L
50Cr(n,
Residual Nuclei
• In SS, 51Cr was reported by Fasso with a higher neutron
cutoff energy.
• Swanson’s technique and present calculation agree
within a factor of 2; for example 57Co in Ni target, 63, 65Cu
from Cu target.
• 59Fe in SS (58Fe(n,)) target in this calculation was found
to be four orders less compared to that obtained by Sato
and Fasso
• Most of the important nuclides formed are in the range of
200 -500 MBqW-1.
Synchrotron Hutch Shielding
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Hutch design in INDUS (2.5 GeV, 1 mA)
Bremsstrahlung mixed with SR
Experiments claim existence of SR
Transportation tough - low energy at the
edge of FLUKA capabilities.
• Can it be simulated using FLUKA?
Heavy Ion reactions
• Work done at PTB Germany
• 200 MeV 12C ions on water phantom
• Score neutron fluence and dose inside 5.7
cm spheres at different angles.
• Compare with measurements done at GSI
– Spectra from TOF (GSI measurements)
– Dose using a TEPC (PTB measurements)
– Dose using WENDI (GSI measurements)
Neutron Spectra
200 MeV/amu 12C incident on 15 cm diameter cylindrical water phantom
Neutron and charged particles
Charged particles
Apply coincidence measurements
Response Matrices
• Neutron attenuation through a target of
finite thickness.
• Response of Bonner sphere type passive
techniques.
• Response of liquid scintillators
• Bismuth fission detectors
– Neutron induced fission
– Photon induced fission
ADSS
• A sub critical assembly driven by 14 MeV
neutrons
• 256 nat.U rods inside water column, beam tube at
center.
• Analog mode
• 36 hours for 106 histories !
• And still large errors (10%-30%)
Proton accelerators for ADSS
• Plans to couple a sub critical reactor to a
proton accelerator
• Source term for lateral shielding of the
accelerator tunnel, reactor pool top
• Residual activity in LBE loop
• Activation of magnets concrete wall
• LBE window rupture due to heat load
ADSS problems
• High beam current ;1-5 mA!
• Proton energies varying from 100 MeV to 1GeV
• Shielding calculations
– Reduce dose by 9 orders:- ~7 meters!
• Induced activity after several meters of water
– Explicit Transport !? Or calculate neutrons at
intermediate thicknesses?
• Induced activity in magnets, concrete walls.
• Induced activity in LBE after several
combinations of irradiations.
Shielding

d 

H (d , E )  r  2 H 0( E ) exp 
  (E) 
H (d )   H (d , E )
E
• Attenuation length from IAEA
283
• n/p ratio from FLUKA
• Multiply end result by the n/p
ratio to get the transmitted
dose after shield
• Biasing!
Simplified view
concrete
7m
water
Window
Further work
• Establish attenuation curves for different
shield configurations.
– Different types of concrete
• Transport neutrons through several meters
of water and calculate induced activity.
• Irradiation profile, raddecay, dcytimes,
usrbin
Thank you