Radiation Detectors

In particular,Silicon Microstrip

Detectorsby

Dr. Darrel Smith

Silicon Microstrip Detectors

• Introduction• Charged Particle Detectors• Silicon Microstrip Detectors• Their use in remote sensing

Introduction• Since the discovery of radioactivity (1890’s), scientists have designed detectors to record and measure the appearance of new particles.

, , and radiation ( +, -)• n radiation (neutrons)• p radiation (protons)

Detectors• Photographic Film• Emulsions• Bubble Chambers• Wire Chambers• Scintillators• Cerenkov Detectors• Solid-State Detectors

Ionization Radiation

• In the case of searching for charged particles, most of these detectors work on the principle of energy loss, namely dE/dx.

• The Bethe-Bloch equation:

• The slower a particle moves, the more ionization that occurs.

Ionization Radiation

• β = v / c• v velocity of the particle• E energy of the particle• x distance travelled by the particle• c speed of light• z particle charge• e charge of the electron• me rest mass of the electron• n electron density of the target• I mean excitation potential of the target o permittivity of free space

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Bragg Curve

• Stopping Power– Type of particle– Energy of the particle– Properties of the material

Ions Slowing Down

• A typical ion slowing down in material due to the dE/dx energy loss.

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Two Basic Interactions• Electromagnetic Interactions

– electrons, and photons lose most of their energy through these processes.

• Hadronic Interactions– particles containing quarks, tend to lose a greater fraction of their energy through nuclear interactions.

Electromagnetic Interactions

• Electrons and Photons• A “figure of merit” describing the interaction of electrons in materials is called the radiation length, Xo.

• Energy loss is primarily through bremsstrahlung, and pair production down to 10’s of MeV.

• Below a few 10’s of MeV, the energy loss I primarily through ionization.

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Hadronic Interactions

• The figure of merit is called the “nuclear interaction length.”

Detector Resolutions• Bubble Chamber 10-150 m• Streamer chamber 300 m• Drift Chamber Scintillator50-300

m• Emulsion 1 m• Silicon Strip pitch/(3-7)• Silicon Pixel 2 m

Early Tests (CERN)

Early Tests (CERN)

Vertex Reconstruction

Simulation of a topquark decay into a B meson.

Vertex Reconstruction

• Short-lived particles (b-decays)

• Lifetime = 1.54 x 10-12 seconds

• c o = 462 m

• Lo = co

Vertex Reconstruction

Next Generation Detectors

• CCDs in layers• Pixel readout• 3 dimensional reconstruction