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Nepomuk OtteSchool of Physics &Center for Relativistic Astrophysics
Georgia Institute of Technology
Detectors in Particle Astrophysics
ermi Summer School !"#!
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Plan
● $hy a lecture on %etector physics
● A particle physics e'periment( re)uirements
●
Interaction of ioni*ing ra%iation +ith matter● ,etector Technologies
● Scintillators
●
Photon %etectors● Semicon%uctor %etectors
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$hy you shoul% kno+ a-out,etector Physics.
Because this is how you understand the instrument
/elps in several aspects(
0n%erstan%ing the physical limits of the e'periments
,evelopment of ne+ analysis metho%s
1aking non stan%ar% measurements
2222
You can design a new experiment
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This lecture can only serve as a starting point
If you want to learn more
Try the reviews published by the particle data group: http://pdg.lbl.gov/
Or any other good book about detectors in high energyphysics
Radiation Detection and easurement by !noll"article Detectors by #laus $rupen % &oris 'chwart(Detectors for "article Radiation by !onrad !leinknecht
http://pdg.lbl.gov/http://pdg.lbl.gov/
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Particle ,etectors( Re)uirements
● Particle %etection
●
1omentum 3 energymeasurement
● Particle i%entification
● Arrival %irection
● 1easurements of particle %ecay
length
● 222
You need to know
#2 /o+ particles 4interact5in matter
!2 /o+ materials4respon%5
62 $hat technologiese'ist to 4rea% out5%etector me%ium
To e'tract thisinformation
What you want to know:
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Things can -ecome pretty comple'
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1ost often a common Principle
Tracker
Calorimeter
+
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Neutrino Astrophysics
Antares
Ice Cu-e
Tracker an% Calorimeter in one
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Pierre Auger O-servatory
Surface array(#7"" stations
#28 km spacing
luorescence %etectors(
9 telescope enclosures7 telescopes per enclosure!9 telescopes in total
,etection of cosmic rays a-ove #"#7
e:
,etects sho+er particles coming to groun%
Tracker an%Calorimeter in
one
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Air Sho+ers
● Not like in a la-oratory● Remote places● $eather● Inhomogenous %etector me%ium● ;ackgroun% < light from the sky =
Rea%out(> luorescence light> Cherenkov light> Particles> Ra%io
?2 @oren*
Use measured air showercharacteristics for: calorimetry particle !D tracking
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Interaction of ionizing radiation with matter
)eavy charged particles *everything but electrons+
,lectrons/positrons
"hotons
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#harged particles - electrons
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?nergy @oss of heavy ;loch formula
● Ionisation through inelastic scattering & atomice'citation
● Glo-al minimum in %?3% B "#$%&' > 1inimum Ioni*ingParticle
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Small Angle ScatteringScattering(
multiple scattering: 3 4 (5
,ifficult to %escri-e multiple scattering 36(5
Statistical treatment( 1olière-theory
" F ra%iation length F material constant
Central H are normal %istri-ute%
0imit for resol1ing momentum7 1ertex7 and arri1al direction
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,lectrons
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?nergy @oss of ?lectrons
In a%%ition to ionisation ;remsstrahlung
1o%ifie% ;ethe>;loch(
Scattering of same type ofparticlemasses are the same
Critical energy( %?3%'Ion
F %?3%';rems
?CF87"1e:3E
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?nergy @oss %ue to ;remsstrahlung
Pro-a-ility
Ra%iation length
?nergy loss -y ;remsstrahlung(
Nuclear %ensity
?'ponential energy loss
Jg3cm!K
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"hotons
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Interaction of Gamma>Rays +ith 1atter
●
Photoelectric effect● Compton scattering
● Pair pro%uction
In general a-sorption(> Attenuation of photon intensity
μ = Attenuation coefficient
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Interaction of Photons in 1atter
● Attenuation of intensity
I
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nd...
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Cherenkov ?ffect
●
Not important for energy loss -ut very important mechanismin most astroparticle e'periments
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Ioni(ation free electrons0
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Ioni*ation yiel%
●?
IF Ioni*ation energy
●$ F Q?
e>ion pair
● $ ?I
● Np F primary generate% e>3Ion pairs N
p = total ionization yield (per cm)
$ant that large forenergy measurements
or 1IPs
A num-er to remem-er( Silicon $D627 e:
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$hy large NT >>?'ample( ?nergy measurements
N F Num-er of pairs generate% after energy loss ?
?D N an% ΔΕ ~ !rt(N)"ner#y lo i a tatitical proce
> energy resolution ΔΕ/" ~ !rt(N)/N ~ $/!rt(N)
Note that energy resolution also %epen%s on the energy of the primary
% ΔΕ/" ~ $/!rt(N) ~ $/!rt(")
0n%er the con%ition that all the energy is%eposite% in the %etector > energy resolution
improves +ith increasing particle energy
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Semicon%uctor ,etectors
How many electron/hole pairs areproduced by a MIP going through300 um thick silicon?
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Scintillators
● Organic scintillators● Inorganic scintillators
● Scintillating gasesSome of the ioni*e% electrons can pro%uce light in some materials
If material is transparent >> light can -e %etecte% +ith photon %etector
Photo%etectorparticle
Scintillationphoton
scintillatorelectronics
Scintillation mechanisms are complicate% an% not fully un%erstoo%> several contri-utions +ith %ifferent time constants2
h k % ll
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$hat makes a goo% Scintillator
● /igh conversion efficiency of %eposite% energy into photons
● @ight yiel% shoul% -e proportional to %eposite% energy over as +i%e arange as possi-le
● 1e%ium shoul% -e transparent to the +avelength of its o+n emission
● ast %ecay time of the in%uce% luminescence
● Goo% optical )uality an% availa-le in large )uantities● In%e' of refraction D#28 to allo+ goo% coupling to photo %etector
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Organic scintillators
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Transmission an% A-sorption
is use% as +avelength shifter
e2g2 matching to spectral response of photo %etector
T i l h t i ti
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Typical characteristics
,ensity #2"6 g3cm6
In%e' of refraction #28H
"
99 cm
@ight yiel% #"" e:38Attenuation length #>! m
%ecay time !>6 ns
9ma0
D9""nm
I i i till t
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Inorganic scintillators
●
)uch higher density than organic scintillators$%8 gcm%
/igh stopping po+er
/igh conversion efficiency for electrons3photons
9ood for energy measurements calorimetry;
●
;an%gap of 8>#" e:● Some crystals are intrinsic scintillators others
re)uire %opant
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Characteristics of typical inorganic scintillators
9"""" ph31e:
?mission spectra of a fe+
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pscintillators
Response of photon%etector an%emission spectrumshoul% match
Photomultipliers P1T
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Photomultipliers P1T
● A-sorption of photon an% emission of a photoelectron gains of several million possi-le
http(33sales2hamamatsu2com3assets3applications3?T,3
pmthan%-ook3pmthan%-ookcomplete2p%f
P1T han%-ook availa-le for %o+nloa%
The +orl% -iggest
http://sales.hamamatsu.com/assets/applications/ETD/http://sales.hamamatsu.com/assets/applications/ETD/
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The +orl% -iggest
amiokan%e
Photocatho%e
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Photocatho%e
● Photoeffect
● "lectron mi#ration throu#h cathode material
inimize ener#y loe: electron mut ha;e enou#h7inetic ener#y to o;ercome or7 function <
ecape depth depth from hich electron ma7e itto the urface
5n metal a fe nm
5n emiconductor up to ?@nm
*mall compared to aorption len#th of ;iile li#ht
Photocatho%e F Semicon%uctor U alkalimetals
Surface activation +ith Cs
Vuantum ?fficiency
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Vuantum ?fficiency
Some catho%es no+ reach efficiencies of 68 or more2 irstP1T ha% an efficiency of "29
?lectron 1ultiplication
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?lectron 1ultiplication
Alkali antimo%e;erylium o'i%e ;eO1agnesium o'i%e secon%ary electronemission> only a fe+ of the electronsmake it out of the %yno%e
Typically 9>8