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Authorization and Inspection of Cyclotron Facilities
Cyclotron Accelerators: Operation and
Components
Authorization and Inspection of Cyclotron Facilities
Objectives
Become familiar with the basic principles of
operation of cyclotrons and auxiliary systems.
Identify the different types of accelerators,
particle energies and currents.
Targets: Types, preparation and recovery
Authorization and Inspection of Cyclotron Facilities
1) History;
2) Operating basics;
3) Ion sources;
4) Magnetic field;
5) Radiofrequency;
6) Beam extraction systems;
Authorization and Inspection of Cyclotron Facilities
7) Beam delivery systems;
8) Target holders;
9) Vacuum systems;
10) Cooling Systems;
11) Uses of cyclotrons.
Authorization and Inspection of Cyclotron Facilities
• In the 30s, Ernest Lawrence
built the first circular accelerator
named cyclotron.
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
350 (in the world)
262 (39 IAEA Members)
246 (2002)
Authorization and Inspection of Cyclotron Facilities
• Some modern accelerators
IBA cyclotron
Authorization and Inspection of Cyclotron Facilities
ACSI cyclotron
Authorization and Inspection of Cyclotron Facilities
GE cyclotron
Authorization and Inspection of Cyclotron Facilities
Siemens cyclotron
Authorization and Inspection of Cyclotron Facilities
A cyclotron is a compact device for accelerating charged
particles to high energies.
Motion of charged particles in an electromagnetic field:


 
F  qE  q v  B
Authorization and Inspection of Cyclotron Facilities
The correct choice of electric and magnetic fields
results in a semicircular movement of charged
particles. The electric field accelerates the particles at
every turn.
Electromagnet producing the constant magnetic field.
Authorization and Inspection of Cyclotron Facilities
2 Dees connected to an RF generator producing the
electric field.
The charged particles rotate in the plane perpendicular
to the magnetic field.
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
Alternative to provide an
acceleration on every moment.
Charged
particle
Magnetic
field
Electric
field
Acceleration in a circular trajectory
Authorization and Inspection of Cyclotron Facilities
The ion beam is injected into the center of the cyclotron,
accelerated by an electric field, when it crosses the space
between the Dee's. Under the action of a magnetic field, the
beam is deflected until it reaches the other side of the Dee's and
it is accelerated again. The process is repeated until the particle
reaches the expected energy value, where it is directed to the
target to be bombarded, through a device called stripper.
Authorization and Inspection of Cyclotron Facilities
Central region
DEE’s
Authorization and Inspection of Cyclotron Facilities
DEE’s
Authorization and Inspection of Cyclotron Facilities
Beam delivery system-extractor (negative ion)
Carbon (stripper) foils
H-
18F
2
6
11C
H-
5
18F-
4
15O
3
Ion Source
H-
2
18F-
1
e-
H+
D-
Authorization and Inspection of Cyclotron Facilities
The magnitude of the force exerted by a magnetic field is :
F  Q.v.B
where
Q : particle charge (C).
m
v : particle velocity ( )
s
B : Magnetic field (T)
F : Force (N)
Dee
Authorization and Inspection of Cyclotron Facilities
In a circular movement, the centripeta l force can be described as :
v2
FC  m
r
where
m : mass of the particle (kg).
m
v : particle velocity ( )
s
r : radius (m)
FC : Force (N)
Authorization and Inspection of Cyclotron Facilities
where
The radius of the orbit is :
FC  F
2
v
m  QvB
r
Then
mv
r
QB
m : particle mass (kg).
v : velocity of the particle (
Q : particle charge (C).
B : magnetic field (T)
r : radius (m)
m
)
s
Authorization and Inspection of Cyclotron Facilities
1 2
The particle kinetic energy (E  mv ) is :
2
r 2Q 2 B 2
E
2m
Authorization and Inspection of Cyclotron Facilities
r
• Time- t
v
t
 r
v
 r
t
Authorization and Inspection of Cyclotron Facilities
v
 r
t
qBr

m
Independent of the radius
t
 m
qB
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
• A real cyclotron requires more than:
– RF (electric field)
– Magnetic Field
• It is necessary:
– Vacuum
– Ion Source
• For radionuclides production is necessary:
– Extraction
– Targets
Authorization and Inspection of Cyclotron Facilities
•
The ion source that generates the particles;
•
The vacuum system to avoid collisions;
•
The magnet field (B) to provide the circular path;
•
The RF system that accelerates the particles;
•
The extraction system that extracts the particles;
•
Targets, where radioisotopes are produced.
Authorization and Inspection of Cyclotron Facilities
There are several types of ion
sources with different performance
characteristics. The sources most
commonly used today are:
•
•
•
•
Hot cathode;
Cold cathode;
External source, and
Internal source.
External Ion Source
Authorization and Inspection of Cyclotron Facilities
Positive Ions
• Based on the ionization of a gas;
•A hot filament produces free electrons in the magnetic
field;
•An electric field accelerates the electrons through the
gas - there is production of plasma therein;
•Positive ions from the plasma are extracted through a
slit.
Authorization and Inspection of Cyclotron Facilities
Ion Sources – Positive Ions
Cooling (water)
Electrical connections
Gas Inlet
Vacuum shutter
Authorization and Inspection of Cyclotron Facilities
Commercial compact cyclotrons
eB
H2
Negative Ions
H
Extraction
Aperture
•
•
•
Discharge
Power
Supply
Plasma is created between two cathodes.
The magnetic field maintains the arc confined.
The entire system is maintained in a closed volume
to avoid the gases to influence the cyclotron
vacuum.
eCathode
Anode
Authorization and Inspection of Cyclotron Facilities
Chimney: copper-tungsten alloy
Cathodes: tantalum
Authorization and Inspection of Cyclotron Facilities
Internal Ion Source – PIG type
Authorization and Inspection of Cyclotron Facilities
 To produce the circular path;
 To contain the plasma in the ion source;
 Is generated by two coils (top and bottom);
 Big electromagnet (20 tons).
Authorization and Inspection of Cyclotron Facilities
Yoke
Coils
Poles
Authorization and Inspection of Cyclotron Facilities
The generated magnetic field allows the acceleration
of protons and negative ions.
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
 The function of the RF
system is to direct the ions
from the ion source, in order
to produce their acceleration,
giving the conditions for
achieving the required
energy for the nuclear
reaction.
Creation of the field E
Authorization and Inspection of Cyclotron Facilities
Trajectory in a field with azimuthally variation
Dee Gap: acceleration
Valley: almost-straight
trajectory
Hill: curved trajectory- 90º
Authorization and Inspection of Cyclotron Facilities
yoke
Ion source
Dees
Poles
Authorization and Inspection of Cyclotron Facilities
 The method of extraction of the beam into the cyclotron
depends on the sign of the charge particles.
Positive particles: deflector.
Negative particles: extraction foils (strippers).
Authorization and Inspection of Cyclotron Facilities
Inside view of a cyclotron - 2 deflectors
• Electrostatic device
used to remove
particles from the
magnetic field.
Authorization and Inspection of Cyclotron Facilities
 Beam losses in the deflector (50 - 90%);
 Difficulties with cooling the deflector;

Increased activation of components;

Need for high electrostatic fields (100 kV / cm).
Authorization and Inspection of Cyclotron Facilities
Beam delivery system– stripper
stripper
2 e-
H+ => to the target
Authorization and Inspection of Cyclotron Facilities
• Thin carbon foil
placed in the
extraction radius.
Authorization and Inspection of Cyclotron Facilities
 Ions have their electrons removed and become positive;
 The direction of rotation is inverted suddenly and ions are
extracted from the magnetic field;
 Almost no losses in the stripper foil, therefore there is
little activation and possibility of higher currents;
 Each stripper position corresponds to a single beam
position  limited energy possibilities (frequently one
for each type of particle).
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
 Increased autonomy to
develop target holders and
transfer systems.
Authorization and Inspection of Cyclotron Facilities
Authorization and Inspection of Cyclotron Facilities
Bipolar Coils;
Quadrupole coils;
Pressure Sensors;
Collimators.
Authorization and Inspection of Cyclotron Facilities
Targets can be:
solid
liquid or
gas
Authorization and Inspection of Cyclotron Facilities

18O(p,n) 18F
Authorization and Inspection of Cyclotron Facilities
Beam
• Beam power ~ 1800 Watts
– Volume: 3 ml
– Pressure: 40 bars
Authorization and Inspection of Cyclotron Facilities

124Te(p,n)124I
Heat dissipation
Authorization and Inspection of Cyclotron Facilities
 Gases
14N(d,n) 15O
14N(p,α) 11C
Authorization and Inspection of Cyclotron Facilities
 Vacuum pumps:
 High vacuum is required to reduce
the interaction of the accelerated
particles with air molecules.
 Typical vacuum: 10-6 mbar for
positive ion cyclotrons, 10-8 mbar
for negative ions.
 All materials (connectors, flanges,
shutters, ...) must be compatible
with the vacuum level.
Authorization and Inspection of Cyclotron Facilities
 2 phases;
 40 or 80 m³/h;
 Atm -> to 10-3 mbar.
 3 phases;
 10-1 to 10-7 mbar.
Authorization and Inspection of Cyclotron Facilities
Cyclotron Vacuum
P [mbar]
1.E+03
P atmospheric
1.E+02
1.E+01
1.E+00
▲ 1 (P = 5,0E-1)
1.E-01
▼ 1 (P = 5,0E-2)
1.E-02
1.E-03
1.E-04
▼ 3 (P = 5,0E-5)
P =1,0E-5
P = 9,0E-6
1.E-05
1.E-06
0
20
40
60
80
100
120
140
T [min ]
Authorization and Inspection of Cyclotron Facilities
 Generally based on two subsystems:
 Primary, outside the cyclotron;
 Secondary, deionized water, supplying water
to all subsystems of the equipment.
Authorization and Inspection of Cyclotron Facilities
 Helium Refrigeration Units
 Cooling of the targets.
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons
• Radionuclide production
• For use in medicine, research and industry
• High energy charged particles introduce changes in the
nucleus of the atoms being irradiated
• Typically threshold reactions, hence minimal energy of particles
necessary
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Radionuclide production: g-emitters
Radio
nuclide
Use
Reaction
77Br
In vitro studies and optim. of chemistry
77As(a,2n)77Br
201Tl
Scintigraphy of the heart
203Tl(p,3n)201Pb201Tl
111In
Labelling of monoclonal anti-bodies
112Cd(p,2n)111In
56Co
Calibration source
56Fe(p,n)56Co
57Co
Haematological studies
58Ni(p,pn)57Ni57Co
58Co
Positron annihilation studies
59Co(p,pn)58Co
67Ga
Labelling of monoclonal anti-bodies
68Zn(p,2n)67Ga
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Radionuclide production: Positron emitters
Radio
nuclide
Use
Reaction
11C
14N(p,a)11C
13N
16O(p,a)13N
15O
14N(d,n)15O
18F
Labelling of molecules for PET studies
18O(p,n)18F
16O(a,pn)18F
75Br
75As(3He,3n)75Br
76Br
75As(a,3n)76Br
62Cu
63Zn(p,pn)62Zn 62Cu
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Radionuclide production
• Reactions with different particles  need to accelerate different
particles
• Different reaction thresholds  need to accelerate to different
energies
• Multi-particle, multi-energy cyclotrons: very flexible, but
complex machines, often positive ion cyclotrons
• Dedicated accelerators: usually 2 types of particles (p and d)
and 1 fixed energy for each particle, typical for negative ion
cyclotrons
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Simulation of radiation damage
• Often associated with fusion research: 2H + 3H  4He + n
• Materials exposed to intense beams of a-particles and
neutrons
• a-particles: implantation of He gas
• Neutrons: displacement of atoms in crystal lattice
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Fast neutron activation analysis (FNAA)
• Fast secondary neutrons used to activate samples
• Determination of activation products reveals information on
atomic composition of samples
• Need for a well-characterised multi-energy neutron source
• Proton induced X-ray Emission (PIXE)
• Excitation of K/L-electrons by protons followed by emission of
characteristic X-ray for determination of atomic composition
• Need for low energy proton beams of low intensity (1nA)
Authorization and Inspection of Cyclotron Facilities
Uses of cyclotrons (cont)
• Proton therapy
• Delivering high doses to malignant
tissue using proton beams in stead
of electron or photon beams
• Bragg peak: tissue sparing effect
is much larger and sharp dose
gradients are possible
• Patient and tumour positioning are
crucial