Electron detectors and spectrometers 1) Gas detectors 2) Channeltrons 3) Semiconductor detectors 4) Electrostatic spectrometers 5) Magnetic spectrometers 6) Di-lepton spectrometers 7) Cherenkov detectors Detectors or combination of magnetic and electric fields and detectors are used Necessity of detection in the wide energy range: Atom physics meV - eV Auger electrons eV – 100 keV Beta and gamma decays keV – MeV Particle decays to e+e-, pair production MeV – 10 GeV Big spectrometer of „orange“ type (application center of Karlsruhe Institute and Technical University at Darmstadt)

Gas filled detectors 1) Geiger- Müler counters: work in the range of discharge (IV) Position sensitive: 1) Multi-wire proportional chambers – anode sensitive wires are placed between two cathode plates (signal is taken from anodes) 2) Drift chambers – drift of charge from ionization to anode, typical drift velocities ~ 5 cm/μs, it is possible determine from time distance 3) Time projection chambers – cylinder filled by gas end cap by multi-wire chambers, placed in homogenous magnetic fields, make possible 3D measurements Efficiency near to 100 % 2) Proportional detectors: work in the range of proportionality (III) (amplification ~ 10 7 ) 3) Ionization chambers: without amplification → weak output signal (II) Widely used in previous period, semiconductor detectors are used presently Wide application in high energy electron and positron spectrometry

Channeltron Channel from glass or ceramic Energie [eV] Účinnost [%] Small sensitivity to gamma detection Elektroda Primární elektron Výstupní elektrony Polovodičová vrstva Sekundární elektrony Skleněná stěna kanálku Channeltron scheme Dependency of detection efficiency on energy Amplification ~ 10 7 Channeltrons of BURLE Company Semiconductor surface layer Possibility of configuration to chaneltron plates – millions of miniature electron amplifiers working independently Amplification ~ 10 4 Two in cascade ~ 10 7 Distance of channels: 8 – 30 μm Small sensitivity to magnetic field Death time ~ 10 ns Position sensitive: Usage for energies 0,01 – 30 keV

Semiconductor detectors Usage of magnetic transporter – magnetic field transports electrons to place with smaller background Intensive exploitation of semiconductor silicon detectors Position sensitive detectors: 1) Silicon Strip Detectors – thin (1 μm) aluminum strips are on silicon wafer (thickness of 300 μm) and under them p + implantation (boron) - operate as separate electrodes 2) Silicon Pixel Detectors – structure of single cells 3) Silicon Drift Detectors – set of electrodes, charge afterwards drifts in electric field, one from coordinates is determined from drift time Energy resolution ~ 0,9 – 1,9 keV for energy 100 – 1000 keV Lower energies – very thin window is important → the smallest possible absorption SDD detector of experiment ALICE

Electrostatic and magnetic spectrometers Motion of charged particle in electric and magnetic fields: 2) Magnetic field – acting force: 1) Electric field - acting force: Ifhold valid where m – relativistic mass of electron: and then Resolution of magnetic spectrometer is given by momentum resolution: Resolution of electrostatic by energy resolution:where was taken : We determine relation E KIN = f(Br) ( ):

We determine relation between momentum and energy resolutions: and then: For nonrelativistic case: Agreement with nonrelativistic limit (E KIN << m e c 2 ) wanted relation between resolutions: For ultrarelativistic case: Agreement with ultrarelativistic limit (E KIN >> m e c 2 ) Relation between energy and momentum resolution

Basic characteristics of electron spectrometers 2) Already mentioned resolution R: 8·10 -8 – ) Transmission T – part of monoenergetic electron beam, which will reach detector 6) Total luminosity L = T·σ : – cm 2 7) Electron-optical quality: T/R or L/R 1) Range of measured energies: 0,01 – 1000 keV 3) Solid angle to which detected electrons are emitted Ω: 0,0001 – 20 % ze 4π 4) Sizes of source or irradiated target σ: ~ 0,5 mm 2 – 200 cm 2 8) Intensity of used magnetic fields B: 0,0001 – ~3 T Very important for source preparation– exclusion of electron energy losses in source material.

Electrostatic spectrometers Integral method of measurement – during every measurement (given decelerating potential) Magnetic fields – focuse electrons to measuring place, using slits makes possible selection of momentum (energy) Electric fields – produce potential barrier, which transmits only electrons, which energy is higher then given threshold Single channel method of measurement → big accent on time stability and continuous calibration 1) Channeltrons – suitable for low energies ~ keV Microchannel plate – position sensitive 2) Silicon detector – can measured also energy drift and pixel detectors – position sensitive Differential method of measurement - motion at magnetic field determines only definite energy range Usage up to energies 50 keV (too high voltage is necessary for higher energy and it is also problem with relativistic corrections) Used detectors: Electrostatic spectrometer ESA 12 (NPI ASCR Řež)

Magnetic spectrometers Resolution: R = Δp/p = ÷ Magnetic field is used for determination of electron momentum (energy) „Orange“ and „mini-orange“ type of spectrometer Compact device, magnets produce homogenous field – changes of magnet configuration make possible change of transmission maximum energy (by this also spectrometer efficiency) Energy [keV] Transmission [%] detector source beam lead absorber Spectrometer of miniorange type (University Bon) Many types were used during time: 1) Plane spectrometers – field has plane symmetry 2) Lens spectrometers – field has axial symmetry (Magnets are splitted to sectors – mostly six sectors placed around axis) Plane and lens type of magnetic spectrometers

Magnetic transporter and silicon detector Magnetic field is used for transport of electron outside place with background, electron energy is determined by silicon detector On beam measurement → intensive background of gamma photon and other particles Usage 1) toroidal magnetic field: → motion on cycloid „soft transition between magnetic spectrometers and transporters“ 2) magnetic field of solenoid: B z = B, B x = B y = 0 → motion on spiral Efficiency of system is given by transmission of transport system and also by efficiency of detector Some spectrometers of „orange“ and „miniorange“ types can be used also as transporters

High-energy physics – dilepton spectrometer Study of particle decay to e + e - or μ + μ - channels, production of such pairs through virtual photons → necessity of spectrometer of leptons with high energy Spectrometer composition: Necessary for momentum determination and identification of positive and negative particles: 1) Very intensive magnet (often superconductive) 2) Position sensitive detectors ahead magnet and under magnet (multiwire proportional chambers, Cherenkov detectors) Improvement particle identification (suppression of hadron background): 3) Detectors discriminating hadron and electromagnetic showers 4) Detectors measuring time of flight Scheme of di-lepton spectrometer NA50 and its wire chambers

Usage of Cherenkov radiation detectors Experiment CERES: Experiment HADES: