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7/23/2019 Particle Accelerators and Detectors
1/37
Particle acceleratorsJ.2.1 Explain the need for high energies in
order to produce particles of large mass.
J.2.2 Explain the need for high energies in
order to resolve particles of small size.
J.2.3 Outline the structure and operation of alinear accelerator and of a cyclotron.
J.2.4 Outline the structure and explain the
operation of the synchrotron.
J.2.5 tate !hat is meant "y "remsstrahlung
#"ra$ing% radiation.
J.2.& 'ompare the advantages and disadvantages
of linear accelerators( cyclotrons and
synchrotrons.
J.2.) olve pro"lems related to the production
of particles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
7/23/2019 Particle Accelerators and Detectors
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Particle acceleratorsExplain the need for high energies in order to
produce particles of large mass.
+,ecalling the mass-energy relationship !e see
that from E mc2!e o"tain
+/ote that the "igger the mass of the particle !e
desire to produce( the larger Emust "e.
Option J: Particle physics
J2 *article accelerators and detectors
mass-energy equivalencem E/c2
E0*E uppose you !ant to create a proton from
energy. o! much energy must you provide6
O789O/ *article creation must adhere to
conservation la!s.
+ince the "aryon num"er of a proton is :1( and
the "aryon num"er of a photon is zero( an anti-
proton must also "e created.
+8hus !e need at least E 2#;3< e=% 1
7/23/2019 Particle Accelerators and Detectors
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Particle acceleratorsExplain the need for high energies in order to
produce particles of large mass.
*,'89'E
>ind the energy needed to create an electron.
8hen sho! that conservation of charge andconservation of lepton num"er are "oth satisfied.
O789O/
+8he rest energy of an electron is ?.511 e=.
+8hus !e need E 2#?.511 e=% 1.?22 e= to
create an electron( anti-electron pair.
FYI
8he minimum energy of any accelerator must "e
t!ice the rest energy of the heaviest particle itis desi ned to detect@create.
Option J: Particle physics
J2 *article accelerators and detectors
2e-: e:
CHARGE
LEPTON NUMBER
? -1 :1
? :1 -1
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Particle acceleratorsExplain the need for high energies in order to
produce particles of large mass.
+Aou may "e as$ing yourself BHow do you get high
energy photons6C
+Aou can BharvestC high energy photons from t!osources
1% 8he energy that is released "y the
annihilation of matter@anti-matter particles
#that !ere created else!here%.
2% 8he D9/E89' E/E,A of the particles Fust"efore they collide.
Option J: Particle physics
J2 *article accelerators and detectors
FYI
8o maximize the amount of EKconverted to the
photonsG energy the particle and anti-particleare made to travel in opposite directions.
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Particle acceleratorsExplain the need for high energies in order to
produce particles of large mass.
Option J: Particle physics
J2 *article accelerators and detectors
*,'89'E ccelerators use E-fields and H-fields
to control the speeds and paths of the charged
particle "eams they accelerate. Explain ho! thisis advantageous !hen using matter( anti-matter
"eams traveling in opposite directions.
O789O/
+atter and antimatter have opposite charges.
+,ecall FB qvBsin( and FE qE.+8hus the directions of the magnetic force #given
"y the right hand rule% and the electric force
depend on the signs of the charges the forces are
acting on.
+ince matter and antimatter have opposite signs(
the samefields !ill control "oth "eams at onceI
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Particle acceleratorsExplain the need for high energies in order to
resolve particles of small size.
+,ecall that the !avelength of a photon ofenergy Eis given "y E hf hc/.
+'learly( the "igger the energy Ethe smaller the
!avelength .
+,ecall also that the smaller the !avelength( the
"etter the resolution.
+8hus( the "igger the energy( the smaller the
particle that can "e resolved.
Option J: Particle physics
J2 *article accelerators and detectors
wavelength energy relationship hc/E
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Particle acceleratorsOutline the structure and operation of a linear
acceleratorand of a cyclotron.
+s the name implies( a
linear acceleratoror
linac is a straight tu"e.+8he longer it is( the more
energy the accelerated particle
!ill have !hen it reaches the
end of the linac( at !hich
point it smashes into a targetat the end of the tu"e.
FYI
8he accelerated particle is
charged. 8he alternating p.d. must "e timed so
that the charge is repelled from the B"ehindCtu"e and attracted to the Bin-frontC tu"e.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorsOutline the structure and operation of a linear
acceleratorand of a cyclotron.
*,'89'E Explain !hy the successive tu"es
increase in length in the linac.
O789O/+ince the particle is
accelerating( the distance
covered in a fixed time
interval increases.
+8he tu"es are designed so
that the freKuency of the
alternating p.d. can remain
fixed.
FYI
n alternate design might vary the freKuency and
$eep all of the tu"e lengths eKual.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorsOutline the structure and operation of a linear
accelerator and of a cyclotron.
+8he cyclotronaccelerates
particles !ithin t!o L-shaped
hollo! containers( li$e theones sho!n here.
+Each L is connected to opposite
terminals of an alternating p.d.(
!hich accelerates the charged
particle from the center.+ perpendicular magnetic field causes the
particles to follo!ed a curved spiral until
reaching the outside circumference of the LGs.
+s the follo!ing slide !ill sho!( the period T
of the alternating p.d. is independent of theradius of the particleGs traFectoryM
Option J: Particle physics
J2 *article accelerators and detectors
+
B
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Particle acceleratorsOutline the structure and operation of a linear
accelerator and of a cyclotron.
+9n order for the particle of
mass m and charge qto
experience a centripetal force(it must satisfy F mac.
+8he force Fis caused "y the
magnetic force F qvB.
+Hut the centripetal acceleration ac v2/r.
+8herefore F qvB macso thatqvB mv2/r( or
qB mv/r m#2r@T%/r 2m/T.
Option J: Particle physics
J2 *article accelerators and detectors
+
B
FYI
/ote that f# 1@T% does not depend on theradius of the path. 9t depends onlyon m,qand B.
period of a cyclotronT 2m/#qB%
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Particle acceleratorsOutline the structure and operation of a linear
accelerator and of a cyclotron.
+8o get an idea of the energy
capa"ilities of a cyclotron
consider the intermediate stepfrom the previous slide
+>rom qB mv/r !e get v qBr/m
so that
EK #1@2%mv2 #1@2%m#qBr/m%2.
Option J: Particle physics
J2 *article accelerators and detectors
+
B
FYI
8he energy capa"ilities of the cyclotron are
proportional to the sKuare of its radius.
ince creating large dis$s of vacuum !ithin the
LGs is very difficult( the largest cyclotrons areonly a"le to produce energies in the e= range.
energy of a cyclotronEK q2B2r2@#2m%
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Particle acceleratorsOutline the structure and explain the operation
of the synchrotron.
+8he synchrotronis similar to a linac in that
acceleration occurs "et!een tu"es.
+8he tu"es in a synchrotron(ho!ever( are all the same
length( and they are arranged
in a circle.
+8he charges are accelerated
"et!een the tu"es "y anelectric field applied across
t!o plates.
+8he tu"es are surrounded "y a
magnetic field that causes the
charged particles to follo! a curve.
Option J: Particle physics
J2 *article accelerators and detectors
!a"netic #iel$%en$s %ea!
electric #iel$
accelerates
%ea!
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Particle acceleratorsOutline the structure and explain the operation
of the synchrotron.
+8he alternating p.d. units are complex. 8hey
must "e synchroniedprecisely to the
accelerating particles #hencethe name synchrotron%.
+8he magnetic field strength
must also vary as the
particles pic$ up speed.
+8he advantage of asynchrotron over a linear
accelerator is that the
particle can ma$e as many
circuits as needed to
accelerate it to any energy.
Option J: Particle physics
J2 *article accelerators and detectors
!a"netic #iel$%en$s %ea!
electric #iel$
accelerates
%ea!
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Particle acceleratorsOutline the structure and explain the operation
of the synchrotron.
+nother advantage of the synchrotron over either
of the previous accelerators is that you can have
a matter "eam( andan antimatter "eam(
circulating at the
same time in
opposite
directions.
+s !e have
already discussed(
head-on collisions
maximize the energy
output of the
collisions.
Option J: Particle physics
J2 *article accelerators and detectors
&er!ila%
Bata'ia()llinois.
protonantiproton
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Particle acceleratorsOutline the structure and explain the operation
of the synchrotron.
+8he synchrotronGs maximum energy capa"ility is
limited "y its curvature. 8he faster a particle
travels( the larger the centripetal forces themagnetic field needs to provide. *7 due to
relativistic effects( the faster a particle goes(
the more massive it
"ecomes-thus adding to
the difficulty of ma$ing
it turn in a circle.
+8he largest synchrotron
in the !orld is at 'E,/(
in eneva( and has a
circumference of 2) $m.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorstate !hat is meant "y "remsstrahlung #"ra$ing%
radiation.
+Nhen a charge is accelerated( it produces
electromagnetic radiation called%re!sstrahl*n"
ra$iation.+iven that an
acceleration is a
change in velocity
and that velocity
can change in itsmagnitude #across the plates% or its
direction #the magnetic field tu"es% !e get
radiation at "oth locations in the synchrotron.
+ince the radius of curvature is so large( the
radiation from the tu"es is relatively smallcompared to that of the plates.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorstate !hat is meant "y "remsstrahlung #"ra$ing%
radiation.
+8he radiation at the plates is in the 0-ray
region of the spectrum( and is highly polarized.
+Hecause the 0-rayradiation is very
intense( very
parallel( and very
polarized( it is
!ell-suited for0-ray diffraction and other experiments
investigating the properties of materials.
Option J: Particle physics
J2 *article accelerators and detectors
FYI
9n fact( there are some synchrotrons that have
"een "uilt solely for 0-ray diffraction andmaterials physics.
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Particle accelerators'ompare the advantages and disadvantages of
linear accelerators( cyclotrons and synchrotrons.
+ince there are no curves in the linear
accelerator( there is no radiation loss due to
direction change as there is in the synchrotron.+9n the linac and the cyclotron( if you miss the
collision at the end of the run( the proFectiles
are lost( !hereas in the synchrotron the
particles can continue to go around as many times
as is needed to effect a collision.+8he difficulty in constructing large enough
evacuated LGs and large-area magnetic fields
prevents the cyclotron from "eing a serious
contender in very high energy physics research.
+8he cyclotron is the simplest to construct forlo!-energy applications.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorsolve pro"lems related to the production of
particles in accelerators.
+9f a particle and an antiparticle collide head-
on then !e not only get the energy of
annihilation #the rest mass energy of the t!oparticles% "ut !e harvest all of the original
$inetic energy of the particles "efore their
collision.
+9f a particle collides !ith a stationary target
not all of the energy can "e converted to ne!particles. 8his is "ecause to conserve momentum
the ne! particles must move in the same direction
as the original "eam.
+8hus the energy needed to produce particles
stri$ing a stationary target must exceed theactual rest mass energy of the particles created.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle acceleratorsolve pro"lems related to the production of
particles in accelerators.
+8he minimum availa"le energy Eafor particle
creation o"tained "y the collision of a particle-
proFectile of rest mass m and total energyE!itha stationary target of mass !is sho!n here
Option J: Particle physics
J2 *article accelerators and detectors
energy available in
collision of a
moving mass mwith
stationary mass M
Ea2 2!c2E :#!c2%2:#mc2%2
M+ tar"et rest !ass.m+ pro,ectile rest !ass.
E+ pro,ectile total ener"y.
FYI
/otice that each factor has the units of
energyP2. LonGt miss a sKuareI ny!here.
9n general( the num"ers are more managea"le if!e $eep the energies in e= #or even e=%M
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Particle acceleratorsolve pro"lems related to the production of
particles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
energy available in
collision of a
moving mass mwithstationary mass M
Ea2 2!c2E :#!c2%2:#mc2%2
M+ tar"et rest !ass.
m+ pro,ectile rest !ass.E+ pro,ectile total ener"y.
E0*E o! much energy !ould "e availa"le if a
15 e= proton collided !ith a stationary proton6
O789O/
+m ! ;3< e= c-2 ?.;3< e=c-2. E 15 e=.
Ea2 2!c2E :#!c2%2:#mc2%2
Ea2 2#?.;3
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olve pro"lems related to the production ofparticles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
+The E#iel$ accelerates the char"e$
particles.
+The B#iel$ !a/es the char"e$
particles t*rn an$ #ollo0 a circ*lar
tra,ectory.
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olve pro"lems related to the production ofparticles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
+As vincreases so $oesm( an$ thecentripetal #orce Fc+mac +mv
1/r!*st also
increase to /eep the particles !o'in" in the
synchrotron2s circ*lar path.
+3ince FB+ qvB + Fc(mv1
/r+ qvBqB+mv/r.+Th*s r+mv/qB.
+3ince r+ CON3T #or a synchrotron( B!*st
increase 0ithmvas the particle ener"y
increases.
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olve pro"lems related to the production ofparticles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
+Each %ea! sho*l$ s*pply E = 4415 Me-
6hal# o# 1175 Me-8 in /inetic ener"y.
+EK+ Em5c1+ 4415 9 ;< + 4 EK%eca*se the
annihilation pro'i$es so!e ener"y.
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olve pro"lems related to the production ofparticles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
+&or a stationary tar"et*seEa
1+ 1Mc1E> 6Mc181> 6mc181( 0hereEa+ 1175(M+ ;
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olve pro"lems related to the production ofparticles in accelerators.
Option J: Particle physics
J2 *article accelerators and detectors
@EK+ 4
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Particle accelerators
Option J: Particle physics
J2 *article accelerators and detectors
linac
cyclotron
synchrotron
detail
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Particle detectorsJ.2.< Outline the structure and operation of a
"u""le cham"er( the photomultiplier and the
!ire cham"er.
J.2.; Outline international aspects of research
into high-energy particle physics.J.2.1? Liscuss the economic and ethical
implications of high-energy particle physics
research.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle detectorsOutline the structure and operation of a%*%%le
cha!%er( a photomultiplier and a !ire cham"er.
+8he particles created in collisions must
someho! "e detected. 8he%*%%le cha!%er!as
one of the first detectors for such particles.+Nhen you pop the top of a soda( pressure is
suddenly released !ith a fizzing sound.
+9f pressure is released the liKuid reaches
its "oiling point( and "u""les form. 9n the
case of soda( the "u""les are 'O2.
+Each "u""le forms at the site of an
impurity - if there !ere no impurities( "u""les
!ould not form automatically.
+9nstead of !ater and 'O2( a "u""le cham"er uses
hydrogenthat has "een cooled to the liKuid stateFust "elo! its "oiling point.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle detectorsOutline the structure and operation of a%*%%le
cha!%er( a photomultiplier and a !ire cham"er.
+8he "u""le cham"er consists
of a liKuid-hydrogen-filled
cylinder having one of itsfaces made of glass.
+9ncoming particles stri$e the
target and produce ne! particles.
+8he piston moves out!ard(
lo!ering the liKuid pressure.
+Hu""les form in the depres-
surized liKuid hydrogen along
the path of the particles.
+ magnetic field passing through the "u""le
cham"er ensures that the particles !ill have
curved traFectories if they are charged.
Option J: Particle physics
J2 *article accelerators and detectors
Stationary Target
Piston
Camera
Light
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Particle detectorsOutline the structure and operation of a "u""le
cham"er( aphoto!*ltiplierand a !ire cham"er.
+ome of the products of collision experiments
are gamma particles( !hich are of course high-
energy photons.+amma particles are very adept at ionizing
matter( "ut the act of ionization a"sor"s
the photon( removing it from the picture.
+Letection of a single photon "eing
a"sor"ed is difficult( "ut it is made
possi"le "y a device called a
photo!*ltiplier.
+ single photon enters a photomultiplier
through a small !indo! and is a"sor"ed "y
a photosensitive plate( releasing an
electron according to the photoelectric effect.
Option J: Particle physics
J2 *article accelerators and detectors
50V
100V
150V
200V
250V
dynode
photo
!*ltiplier
photo
sensiti'e!aterial
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Particle detectorsOutline the structure and operation of a "u""le
cham"er( aphoto!*ltiplierand a !ire cham"er.
+9n the photomultiplier are a cascade of dynodes(
each at a higher potential than the previous.
+Hecause of the acceleration caused "ythe p.d.( more electrons are released
during each step in the cascade.
+8he end of the cascade has enough
electrons to create measura"le current.
FYI
8he eiger counter uses a photomultiplier.
>or very high-energy photons a photomul-
tiplier doesnGt !or$. 9nstead a scintillator
is used. scintillator has a screen of
phosphorescent material that glo!s !hen
struc$ "y a very high energy gamma photon.
Option J: Particle physics
J2 *article accelerators and detectors
50V
100V
150V
200V
250V
dynode
photo
!*ltiplier
photo
sensiti'e!aterial
7/23/2019 Particle Accelerators and Detectors
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Particle detectorsOutline the structure and operation of a "u""le
cham"er( a photomultiplier and a0ire cha!%er.
+9f high-energy particles pass through a
gas( the gas particles "ecome ionized.
8hin$ of the high-energy particle asB$noc$ingC electrons off of the gas
atoms as it passes "y.
+9f the gas is "et!een t!o !ires !hich
have a p.d. applied to them( these
freed electrons travel to the
positive !ire and a!ay from the
negative !ire( setting up a current.
+8he voltage across a resistor !hich
the current is made to pass through
can then "e digitally recorded.
+8his device is called a0ire cha!%er.
Option J: Particle physics
J2 *article accelerators and detectors
A
V R
0ire
cha!%er
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Particle detectorsOutline the structure and operation of a "u""le
cham"er( a photomultiplier and a0ire cha!%er.
+o ho! does one get a 3L picture
of particles6 imply set up an
array of !ire cham"ers( and recordnot only the place( "ut the time
the cham"ers detect a particle.
+8he%l*earray tellsus the left-
right coordinate of the particle.
+8he re$array tellsus the up-do!n
coordinate of the particle.
+8he ti!in" from one dou"le-grid to
the next tells us the for!ard-"ac$!ard
coordinate of the particle.
Option J: Particle physics
J2 *article accelerators and detectors
$o*%le"r
i$
$o*%le"ri$
12
3
4
1
2 3
4
12
3
4
1
2 3
4
FYI
3L images can then "e computer generatedI
64(4(t48 6;(1(t18
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Particle detectors
Option J: Particle physics
J2 *article accelerators and detectors
Lar"e Ha$ron Colli$er
%*%%le cha!%er
Gei"er
co*nter
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Particle detectorsOutline international aspects of research into
high-energy particle physics.
+Hecause of the extreme expense in "uilding and
operating high energy particle physics
installations( the larger ones have to "e aninternational colla"oration to help share the
costs.
+Hecause of the international aspect of particle
research( there is a tendency of the academic
edifices of the !orld to come together( even intimes of !ar.
+8he research is also transparent-no country can
"e the BclearinghouseC of the information
generated "y any international facility.
Option J: Particle physics
J2 *article accelerators and detectors
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Particle detectorsLiscuss the economic and ethical implications of
high-energy particle physics research.
+*eople as$ !hether the cost of E* is !orth it.
+8heoretical physics stagnates !ithout
experimental verification.+'uriosity is a fundamental part of the human
mind.
+haring large research costs among many
countries encourages cooperation "et!een
different cultures.+ynchrotron radiation has a large range of
applications( including "iology( medicine( and
technology.
Option J: Particle physics
J2 *article accelerators and detectors
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