Marco Silari, CERN RP at High Energy Proton Accelerators 1
RADIATION PROTECTION AT HIGHENERGY PROTON ACCELERATORS
Marco Silari and Graham R. StevensonCERN
1211 Geneva 23, Switzerland
International School of Radiation Damage and Protection10th Course: Accelerator Radiation Protection
Marco Silari, CERN RP at High Energy Proton Accelerators 2
Summary of the presentation
• Characteristics of hadron cascades• Particularity of high-energy hadron accelerators
– accelerators, targets areas, experimental areas,superconducting RF cavities
• Prompt radiation• Muons• Potential exposure to secondary beams• Hazard of heavy ion beams• Radiation protection at future accelerators
Marco Silari, CERN RP at High Energy Proton Accelerators 3
Hadron cascade
• The way in which the radiological problems associated with a proton accelerator vary with energy depends on two parameters:– the multiplicity of the
production of secondary particles which increases as the proton energy increases, and
– the increase in average energy of these secondarieswhich makes them capable of producing further inelastic interactions.
Marco Silari, CERN RP at High Energy Proton Accelerators 4
Secondary particle production (1)
The fluence ofhadrons with energy greater than 40 MeV at 1 metre per proton interacting an a 5 cm long copper target at proton energies of 7 (*), 23 (+), 225 ( ) and 400 GeV (∇)
Marco Silari, CERN RP at High Energy Proton Accelerators 5
Secondary particle production (2)
This increase in the fluence of secondaryhadrons will have as a direct consequence an increase in the induced radioactivity in an object installed close to a loss point such as an extraction septum, target or vacuum chamber for a given number of lost protons.
The length of the activated regions downstream of such an interaction point also increases dramatically with the energy of the proton beam.
Marco Silari, CERN RP at High Energy Proton Accelerators 6
Secondary particle production (3)
FLUKA simulation of the star density distribution per interacting proton in a 10 cm radius iron cylinder, 0.5 cm thick, placed around a thin copper target struck by protons of different energies
Marco Silari, CERN RP at High Energy Proton Accelerators 7
Secondary particle production (4)
FLUKA simulations of cascades in ironshowing contours of star density(10-3 stars cm-3) per interacting proton in a dump struck by protons of different energies⇒ This behaviour governs the thickness of lateral shielding required for proton beam-dumps
Marco Silari, CERN RP at High Energy Proton Accelerators 8
Lateral shielding requirementsLateral shield thickness in metres required to achieve 10 μSv h-1
alongside a beam dump for a proton beam intensity of 1012 s-1. N.B. 0.5 m of concrete must be added to all iron thicknesses.
Proton Energy Concrete (ρ = 2.4 g cm-3) Iron (ρ = 7.2 g cm-3)
3 GeV 6.56 2.78
10 GeV 7.02 2.97
30 GeV 7.44 3.15
100 GeV 7.91 3.35
300 GeV 8.34 3.53
1 TeV 8.81 3.72
(Data from Fassò et al., Shielding against high-energy radiation, Landolt-Börnstein,1990).
Marco Silari, CERN RP at High Energy Proton Accelerators 9
Energy dependence of hadronic activity (1)
Hadronic activity is e.g. the total number of stars produced in a cascade or the number of neutrons produced having energies between 1 and 10 MeV.
Let N(E) be one such measure of activity and consider the activity N(nE) produced by a hadron of energy nE, where n is a multiplier roughly identified with the average multiplicity of high-energysecondaries (charged and neutral) produced in the first collision. Unless it is a π0, a secondary with energy Ei produces a hadronicactivity N(Ei) , and
∑=i iENnEN )()(
)()1()( 0 EnNfnENπ
−≈
fraction of the energy lost to the hadronic sector through π0 in a single interaction
Marco Silari, CERN RP at High Energy Proton Accelerators 10
Energy dependence of hadronic activity (2)
mKEEN =)(
( )n
fm
ln)1/(1ln
1 0π−
=−
If n and fπ0 can be regarded as constants independent of energy, a solution to the iterative equation above is a power law:
with
In the energy range from several GeV to 1 TeV, fπ0 = 0.25 - 0.33 and n = 5 - 10.
n = 5, fπ0 = 0.25 ⇒ m = 0.82
fπ0 = 0.33 ⇒ m = 0.75. A suitable average value of m ≈ 0.83
n = 10, fπ0 = 0.25 ⇒ m = 0.87
Marco Silari, CERN RP at High Energy Proton Accelerators 11
Radiation areas in the SPS
H > 2 mSv/h
100 μSv/h < H < 2 mSv/h
7.5 μSv/h < H < 100 μSv/h
Peculiarities:• Spatial separation of problems• Induced activity includes a lot of spallation products ⇒ relevant for the production of radioactive waste• With increasing energy the extent of regions with an induced activity hazard increases
Marco Silari, CERN RP at High Energy Proton Accelerators 12
Classification of radiation areas AREA Dose rate limit (μSv/h) Consigne
Average Maximum
Nondesignated ≤ 0.15 ≤ 0.5 • No film badge required
• Public exposure < 1 mSv/year Supervised
≤ 2.5 ≤ 7.5 • No film badge required• Employees exposure < 1 mSv/year
Simplecontrolled ≤ 25 ≤ 100
• Film badge required• Employees exposure cannot exceed 15 mSv/year
Limited stay ≤ 2 mSv/h • Film badge and personal dosimeter required
• Work needs authorisation of RP or RSO High
radiation> 2mSv/h
but≤ 100 mSv/h
• Film badge and personal dosimeter required• Strict access control enforced• Access needs authorisation of RP or RSO
Prohibited
≥ 100 mSv/h• Access protected by machine interlocks• Access needs authorisation of division
leader, Medical Service and RP group• Access monitored by RP group
Marco Silari, CERN RP at High Energy Proton Accelerators 13
CERN area monitors
Several types of ionisation chambers(air-, hydrogen or argon-filled) and rem counters are used to monitor the radiation fields in the accelerator tunnels, in the experimental areas and in the environment.
Marco Silari, CERN RP at High Energy Proton Accelerators 14
CERN RP central data acquisition system
All installed radiation monitors can be read remotely. Data are stored in a database for future retrieval.
Monitor parameters such as alarm threshold can only be modified by authorised personnel.
Marco Silari, CERN RP at High Energy Proton Accelerators 15
Controlled access to accelerator areas (1)
Access to primary beam areas is supervised by the Accelerator Control Room
Access is granted via a film badge reader. Upon check that the person is authorised to access the area, the operator frees a key and gives access
Marco Silari, CERN RP at High Energy Proton Accelerators 16
Controlled access to accelerator areas (2)
Areas in the SPS can either be under closed, supervisedor free access
Marco Silari, CERN RP at High Energy Proton Accelerators 17
Ring survey in the SPS
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
200 204 208 212 216 220 224 228 232
Position
Dos
e eq
uiva
lent
rat
e (µ
Sv/
h)
ProtonsIons
LSS2
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
400 404 408 412 416 420 424 428 432
Position
Dose
equ
ival
ent r
ate
(µSv
/h)
ProtonsIons
LSS4
Horizontal dispersion in meters
-1
0
1
2
3
4
5
Position
Marco Silari, CERN RP at High Energy Proton Accelerators 18
Electron emission in superconducting cavities
HIGH INTENSITY, LOW ENERGY(~ 0.5 MeV) ELECTRONS
LOCATION OF MAXIMUM ELECTRIC FIELD (IRIS)
LOW INTENSITY, HIGH ENERGY ELECTRONS
50 cm
Marco Silari, CERN RP at High Energy Proton Accelerators 19
Stray radiation from SC RF cavities
0 5 10 15 200
20
40
60
80
100
120
140
Conditioning time (h)
Gam
ma
dose
rate
(mG
y/h)
B
0
2
4
6
8
10
Elec
tric
field
(MV
/m)
0 2 4 6 8-20
0
20
40
60
80
100
120
140
160 helium processing without helium processing
Gam
ma
dose
rate
(mG
y/h)
Electric field (MV/m)
Each cavity has its own “history” and the conditioning process can vary significantly from unit to unit, as does the intensity of thebremsstrahlung radiation
Sharp increase in the radiation emission when the electric field ⇒is raised above a given threshold
Marco Silari, CERN RP at High Energy Proton Accelerators 20
Induced radioactivity in LEP cavities
• The dose rate decreases by about a factor of 10 in 40 minutes, due to the decay of short-lived radionuclides, followed by a much slower decrease (another factor of 10 in about 48 hours).• Stainless steel
• Short-lived:50Cr(γ,n)49Cr (half-life 42.1 min), 54Fe(γ,n)53Fe (8.51 min), 54Fe(γ,n)53mFe (2.6 min), 92Mo(γ,n)91mMo (1.09 min) and 92Mo(γ,n)91Mo (15.49 min)• Long-lived: 48V, 51Cr, 52Mn, 54Mn, 56Ni, 57Ni, 56Co, 57Co, 58Co, 60Co, 88Y, 92mNb, 95Nb, 99Mo
• Copper:• Short-lived:63Cu(γ,n)62Cu (half-life 9.74 min) and 63Cu(γ,3n)60Cu (23.2 min)• Long-lived: 51Cr, 54Mn, 56Co, 57Co, 58Co, 60Co, 65Zn, 72Se, 75Se, 74As, 120Sb
Marco Silari, CERN RP at High Energy Proton Accelerators 21
Radiation fields around proton accelerators: neutrons
Neutron spectral fluence outside a 80 cm thick concrete shield and a 40 cm thick iron shield
NeutronsProtonsCharged particles
– muons (leptons, m=105 MeV, τ=2.2 10-6 s)
– protons
– ...
Marco Silari, CERN RP at High Energy Proton Accelerators 22
Neutrons outside shielding of high-energy proton accelerators
Fraction of ambient dose equivalent below a given energy, as a function of energy, for the neutron spectral fluences outside a 80 cm thick concrete shield (0) and a 40 cm thick iron shield (*)
Marco Silari, CERN RP at High Energy Proton Accelerators 23
Radiation fields around proton accelerators: muons (1)
Muons arise from the decay of pions and kaons, either in particle beams or in cascade induced by high energy hadrons. They can also be produced in high-energy hadron-nucleus interactions
Decay lengths from pions and kaons are 55.9 m and 7.51 m times the momentum (in GeV/c) of the parent, respectively
Muons are weakly interacting particles → they can only be stopped by “ranging them out”. Muons mainly lose energy by ionisation, as their cross-section for nuclear interaction is very low.
Usually muon shielding is only important at accelerators above 10 GeV. At lower energy the shielding necessary to reduce radiation levels arising from nuclear cascade processes is in excess of the ionisation range of muons that could contribute to the radiation problem.
Marco Silari, CERN RP at High Energy Proton Accelerators 24
Radiation fields around proton accelerators: muons (2)
Muons from pion decay have a momentum spectrum that extends from 57% of the momentum of the parent pion to the pion momentum itself. Secondary pion beams generally have dumps of longitudinal depth of 1-2 m Fe → decay muons will penetrate the dumps for pion beams with momentum > 2-3 GeV/c
Muon shielding is therefore limited to the forward direction. Typical thickness of hadron dumps at high energy proton accelerators is a few metres of iron
A beam of 107 pions per pulse with momentum of 20 GeV/c travelling over a distance of 50 m ⇒ ~ 5 x105 muons per pulse (5% of the parent beam) ⇒ for a pulse repetition period of 2 s, taking an approximate fluence to dose equivalent conversion factor equal to 40 fSv m2 and assuming that the muon beam is averaged over a typical area for the human torso of 700 cm2 ⇒ 500 µSv/h
Marco Silari, CERN RP at High Energy Proton Accelerators 25
Effect of straggling on the range of muons
Shield
Material
Momentum
(GeV/c)
Most
muons
stop at:
(m)
10% go
beyond:
(m)
1% go
beyond:
(m)
0.1% go
beyond:
(m)
Range
determined
from
(dE/dx)total
(m)
Range
determined
from
(dE/dx)ionisation
(m)
Iron 200 110 120 132 140 105 132
ρ = 7.2
g cm-3
400 190 205 220 228 175 260
Earth 50 110 120 130 135 105 110
ρ = 2.0
g cm-3
100 210 220 235 245 205 210
200 390 410 430 445 380 410
400 710 740 780 800 670 815
500 870 890 930 950 800 1010
Marco Silari, CERN RP at High Energy Proton Accelerators 26
Muon shielding
Comparison of the longitudinal thickness in metres of iron shielding required to achieve 10 μSv h-1 due to the hadron and muon components of the cascade for a proton beam intensity of 1012 s-1.
Proton Energy Hadron shield Muon shield
5 GeV 3.4
10 GeV 4.6 6.0
30 GeV 14.0
100 GeV 8.4 36.0
300 GeV 77.0
1 TeV 10.2 170.0
Marco Silari, CERN RP at High Energy Proton Accelerators 27
Experimental areas
Vertical longitudinal cut through the beam lines of the CERN SPS North Experimental Areas
Marco Silari, CERN RP at High Energy Proton Accelerators 28
Narrow beam dosimetry
Since in the case of partial irradiation effective dose is not an adequate risk indicator as it is unable to take into account the incidence of deterministic effects, both effective dose and organ dose in the exposed tissue or organ have to be considered. The absorbed dose in an organ is an estimator for deterministic effects should the threshold for such effects be reached. Where this threshold is not reached, the effective dose can be used to estimate the probability of stochastic effects.
Marco Silari, CERN RP at High Energy Proton Accelerators 29
Effects of partial-body irradiation
50 Gy for most organs will cause an effect in 1-5% of persons irradiated
70 Gy for most organs will cause an effect in 25-50% of persons irradiated
Tissue and Effect Threshold(Gy)
Annual Limit (Sv)Alone Whole-body
TestesTemporary sterility 0.15 0.2 0.05Permanent sterility 3.5 0.2 0.05
OvariesSterility 2.5-6.0 0.2 0.05
Lens of the eyeDetectable opacities 0.5-2.0 0.15 0.05Cataract 5.0 0.15 0.05
Bone MarrowDepression of hematopoeises 0.5 0.4 0.05Fatal aplasia 1.5 0.4 0.05
Marco Silari, CERN RP at High Energy Proton Accelerators 30
Beam loss
Beam Beam intensity to cause Death Temporary Sterility (5 Gy) (0.15 Gy)
20 GeV protons 5 X 1013 1.5 X 1011
450 GeV protons 2 X 1012 1 X 1010
7 TeV protons 1 X 1011 3 X 108
50 GeV electrons 1 X 1012 1.5 X 1010
An SPS beam of several hundred GeV (250 machine pulses per hour) and 108 particles per pulse can give rise to a dose rate
at 1 metre of approximately 50 mGy/h or 250 mSv/h
Marco Silari, CERN RP at High Energy Proton Accelerators 31
In-beam exposure (1)
FLUKA calculations of dose in a 1 mm radius cylinder around proton beams of different energies in tissue-equivalent material: * 20 GeV,
100 GeV, + 500 GeV, 2 TeV and × 7 TeV
Dose at the surface ≈ 10-8
Gy per incident particle
Marco Silari, CERN RP at High Energy Proton Accelerators 32
In-beam exposure (2)
FLUKA calculations of dose in a 1 mm radius cylinder around electron beams of different energies in tissue-equivalent material: * 20 GeV, 50 GeV, + 100 GeV, 200 GeV and × 500 GeV
Dose at the surface ≈ 10-8
Gy per incident particle
Secondary electron beams can be created at proton accelerators
Marco Silari, CERN RP at High Energy Proton Accelerators 33
Minimum-ionizing particles• A minimum-ionizing particle loses energy at a rate of about
2 MeV/(g cm-2)
• For a uniform flux and without any cascading, and assuming that the beam corresponds to an area of 2 X 2 mm2,
this corresponds to:
2 X 1.6 X 10-13 (J/MeV) X 1000 (g/kg)/4 X 10-2 cm2 = 8 X 10-9 Gy
• This corresponds well to the FLUKA calculations at the surface
• This means that we shall cause a detectable opacity in the lens of the eye with a single pulse of 108 particles
Marco Silari, CERN RP at High Energy Proton Accelerators 34
Organ doses - Summary
We can now determine the number of pulses which will cause damage for a beam intensity of 108
particles per machine pulse.
Damage RequiredDose (Gy)
Machinepulses
Testes – Temporary sterility 0.15 2Bone marrow 1 15Testes or Ovaries – Permanentsterility 4 60
General organ damage 50 700
Marco Silari, CERN RP at High Energy Proton Accelerators 35
Organ dose and effective dose for protons
0 100 200 300 4001E-12
1E-11
1E-10
1E-9
Org
an d
ose
(Gy
per p
roto
n)
Proton Energy (GeV)
Eye Thymus Thyroid Breast Lung
DT = AD + BD log kE = AE + BE log k
(Gy or per primary particle)
k = particle energy in GeV
0 100 200 300 400
1E-12
1E-11
Effe
ctiv
e D
ose
(Sv
per p
roto
n)
Proton Energy (GeV)
Thyroid Breast Eye Thymus Lung
ORGAN AD BD AE BE
Right eye 3.24 10-10 2.38 10-11 4.63 10-13 8.77 10-13
Thyroid 5.82 10-11 1.20 10-11 1.47 10-11 3.76 10-12
Thymus 3.80 10-11 8.19 10-12 4.88 10-12 2.40 10-12
Breast 7.89 10-12 1.22 10-12 2.52 10-12 2.00 10-12
Lung 1.45 10-12 1.82 10-12 1.01 10-12 1.15 10-12
fitt
ing
para
met
ers
Marco Silari, CERN RP at High Energy Proton Accelerators 36
Organ dose and effective dose for electrons
0 100 200 300 4001E-12
1E-11
1E-10
1E-9
Org
an d
ose
(Gy
per p
rimar
y el
ectro
n)
Electron Energy (GeV)
Eye Thymus Lung Thyroid Breast
0 100 200 300 400
1E-13
1E-12
Effe
ctiv
e D
ose
(Sv
per e
lect
ron)
Electron Energy (GeV)
Thyroid Breast Eye Thymus Lung
Marco Silari, CERN RP at High Energy Proton Accelerators 37
Organs contributing to effective dose
0 100 200 300 400
0.1
1
Frac
tion
of th
e ef
fect
ive
dose
due
to n
on-ta
rget
org
ans
Proton Energy (GeV)
Breast Lung Thymus Thyroid
0 100 200 300 4001E-3
0.01
0.1
1
Frac
tion
of th
e ef
fect
ive
dose
due
to n
on-ta
rget
org
ans
Electron Energy (GeV)
Breast Thyroid Thymus Lung
Fraction of effective dose due to non-target organs for protons, for four of the five target organs investigated (the eye has no associated wT-value)
Same for electrons
Marco Silari, CERN RP at High Energy Proton Accelerators 38
Lead-ion beams (1): thick target
As for proton beams, the transverse shielding of high-energy heavy ion beams mainly involves the attenuation of the secondary neutrons generated in the hadronic cascade. Most of the available Monte-Carlo codes cannot be employeddirectly because they do not transport ions with masses larger than one atomic mass unit.
There is also a general lack of knowledge about the source terms for neutron production from high-energy heavy ions.
Recent measurements at CERN have shown that the spectralfluence of the secondary neutrons outside a thick shield is similar for light (protons) and heavy (lead) ions stopped in a thick target.
Marco Silari, CERN RP at High Energy Proton Accelerators 39
Lead-ion beams (2): thick target
The approach of considering a high energy lead ion as an independent grouping of free protons is sufficiently accurate for the purpose of evaluating the ambient dose equivalent of secondary neutrons outside thick shielding.
The neutron yield from lead beams dumped in a thick target appears to depend on energy as
8.0PbEY ∝
where EPb is the energy per nucleon of the lead ion beams.
The yield also appears to scale linearly with the mass number of the projectile.
Marco Silari, CERN RP at High Energy Proton Accelerators 40
Lead-ion beams (3): thin target
Beam FLUKA
(sr-1)
Experimental(FLUKA guess)
(sr-1)
Scaling factor(A=208)
40 GeV/c protons + π+ (3.199 ± 0.003) x 10-1 3.499 x 10-1
40 GeV/c lead ions (3.666 ± 0.003) x 10-1 (a) 26.6 A0.80
158 GeV/c lead ions (4.566 ± 0.003) x 10-1 (a) 41.1 A0.84
90° neutron yield from high energy protons and lead ions on a thin lead target (neutron per primary particle per steradian)
(a) The simulation results refer to a proton beam of the same energy per nucleon.
Marco Silari, CERN RP at High Energy Proton Accelerators 41
Lead-ion beams (4)• As far as we know, the stray radiation caused by realistic heavy ions rises no faster than with the number of nucleons in the projectile nucleus.Therefore the dose rates caused by a secondary SPS lead beam are about 200 times higher than a secondary proton beam of the same particle intensity.
• Thus a lead beam containing 106 ions is equivalent to a “normal” beam of 2 X 108
particles.
BUT
• The Bethe-Bloch formulation for ionization energy loss tells us that the rate of energy loss varies as the square of the charge of the projectile nucleus.
• Thus the “minimum” energy loss rate of 2 MeV/g cm-2 becomes for a lead nucleus a loss rate of
13.4 GeV/g cm-2
• And this is not all distributed in “small” events as can be seen from emulsion photo-micrographs of cosmic-rays tracks.
Marco Silari, CERN RP at High Energy Proton Accelerators 42
Relativistic lead-ions in emulsions
Marco Silari, CERN RP at High Energy Proton Accelerators 43
Relativistic lead-ions in plastics
Marco Silari, CERN RP at High Energy Proton Accelerators 44
Damage caused by lead-ions
• The original line of dislocation damage in plastics has a diameter of about 100 Angstroms, or 0.01 microns. This can be etched to give a visible cone of about 35 microns depth/diameter.
• There is complete physical destruction of the structure of the plastic over an area of 10-12 cm2 or for a beam of 106 lead particles the surface area destroyed is 10-6 cm2.
• The lead tracks in emulsions have a core of about 20 microns in radius.Thus each lead track leaves a solid line of developed silver grains of 10-5 cm2 cross-sectional area.
• So a beam of 106 particles spread out uniformly can turn an emulsion of 10 cm2
cross-sectional area black.
• In a beam of 4 mm2 cross-section there is the power to physically destroy a fraction of 2.5 X 10-5 of its cross-sectional area or to put 250 times more energy into an emulsion than is necessary to make developable silver grains.
Marco Silari, CERN RP at High Energy Proton Accelerators 45
PB - Damage to tissue
• Multiplying the biological damage factors determined before simply by Z2
Pb = 6700 we might cause a detectable opacity in the lens of the eye with a single pulse of 1.5 X 104 lead of ions.
• The organ dose is at least 1.5 X 10-6 Gy per beam particle. Thus:
Damage RequiredDose (Gy)
Pb Intensity
Testes – Temporary sterility 0.15 3X104
Bone marrow 1 2X105
Testes or Ovaries – Permanent sterility 4 8X105
General organ damage 50 1.5X107
The conclusion is that it is more than prudent to keep out of a lead beam of 106 ions per burst!
Marco Silari, CERN RP at High Energy Proton Accelerators 46
CERN Neutrinos to Gran Sasso
Marco Silari, CERN RP at High Energy Proton Accelerators 47
CERN Neutrinos to Gran Sasso
Marco Silari, CERN RP at High Energy Proton Accelerators 48
Radiation hazard from neutrinos (1)
Annual dose equivalent (µSv)Solar neutrinos (Eν ~ 1 - 10 MeV) 10-7
Atmospheric neutrinos (Eν ~ 100 MeV - 2 GeV) 2 x 10-9
Neutrino experiments (Eν ~ 10 – 100 GeV): Fermilab (NuMI) SBL, 1 km distance 10
LBL, 730 km distance 8.5 x 10-6
CERN/Gran Sasso SBL 10Gran Sasso 5 x 10-5
Expected annual dose equivalent from natural and accelerator neutrino sources (Short and Long Baseline neutrino experiments)
Marco Silari, CERN RP at High Energy Proton Accelerators 49
CERN Neutrino Factory
Marco Silari, CERN RP at High Energy Proton Accelerators 50
Radiation hazard from neutrinos (2)
b
R
d
hs
z
θ∼1/γθ∼1/γ
φ
a
ν
s2 = 2 R d - d2 θ ∼ 1/γθ ∼ 1/γ
sin φ = s / R a ≅ 2 θ θ ss
h ≅ z tan φ b ≅ a / φ
E CoM d (m) s (km) φ z (km) h (m) θ a (m) b (m)0.5 TeV 100 35 5.6 10-3 10 56 424 10-6 30 53004.0 TeV 500 80 12.5 10-3 10 125 53 10-6 8.5 680
Marco Silari, CERN RP at High Energy Proton Accelerators 51
Radiation hazard from neutrinos (3)
Marco Silari, CERN RP at High Energy Proton Accelerators 52
Radiation hazard from neutrinos (4)
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