Detectors in Particle Astrophysics

8/19/2019 Detectors in Particle Astrophysics

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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

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Detectors in Particle Astrophysics