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Particle Detectors

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Title: Particle Detectors


1
Particle Detectors
  • By Cigdem Ozkan
  • December 2004

2
Why?
  • Matter (smallest scale) made of elementary
    particles. Over the past century studies on the
    atom have revealed the smallest things human
    beings have ever found. How were these particles
    found?

3
Three Steps
  • Accelerators Collision of particles at high
    energies to look at what's inside these
    particles, but also to use the energy of their
    collisions to create different particles of
    matter.
  • DetectorsUnveiling the tiniest constituents of
    matter with accelerators is only half the battle.
    An extraordinary particle detector to observe
    what happens in high-energy collisions.
  • Computing Data Acquisition Tonnes of data -gt
    computer farms to sift thru and analyse data.

4
Second Step Particle Detectors
  • Instruments to count particles, visualise tracks,
    measure particle energies, record time-of-flight
    and identify different particles
  • Depending on the type of accelerator and the
    particles and forces to be studied, various
    detection devices are arranged in intricate
    configurations.

5
Types of Detectors
  • Cloud Chambers The tracks of charged particles
    can be made visible with vapour, which condenses
    as charged particles travel through it

Wilsons Cloud Chamber (c. 1912)
6
Types of Detectors
  • Photography Not used at all. Charged particles
    leave marks as they cross photographic plates.
    Roentgen gt X-rays
  • Geiger Counter Gas-filled tube with a central
    wire at high voltage to collect the ionisation
    produced by incident radiation. Detects alpha,
    beta, and gamma radiation although it cannot
    distinguish between them. Very limited.

7
Types of Detectors
  • Bubble Chamber Filled with a superheated liquid,
    creates a track of small bubbles when a charged
    particle crosses the chamber, locally bringing
    the liquid to boil. Data acquisition and analysis
    is rather slow, bubble chambers are no longer
    used for research purposes.

Alan and the bubble chamber
8
Types of Detectors
  • Wire Chambers Charged particle traverses a
    gas-filled chamber, ionises the gas atoms along
    its path. Installing planes of thin wires inside
    the chamber and applying high voltage to the
    wires, can record the signals caused by gas ions
    attracted to the wires. The data reveal the
    arrival time of a particle as well as its track.

A Wire Chamber for the GLAST (Gamma Ray Large
Area Telescope) project
9
Types of Detectors
  • Transition Radiation Detectors (TRD) When a
    charged particle crosses the boundary between two
    media with different dielectric properties (that
    is to mean, with different index of refraction),
    it can emit an electromagnetic radiation, known
    as transition radiation. Radiation intensity is
    approximately linear with the Lorentz ? factor
    (E/m0c2) of the particle. TRD can be employed as
    a mean of identifying particles measuring their
    ?, or as a threshold detector, to distinguish
    between particles which emit or not transition
    radiation.

10
Types of Detectors
  • Calorimeters - Most particles interact with
    matter when they travel through it and can lose a
    fraction or all of its energy. Calorimeters
    measure the energy lost and determine the total
    energy of the incoming particle. Electromagnetic
    gt the energy of leptons and photons as they
    interact with the electrically charged particles
    inside matter. Hadronic gt monitor the energy of
    particles containing quarks as they interact with
    atomic nuclei.To build calorimeters, a wide
    variety of materials including solid lead glass,
    cesium iodide, liquid argon and silica aero gel
    are used.

11
Types of Detectors
  • Scintillators Based on electronic detection of
    the scintillation light - the flash of light
    produced when a fast charged particle passes
    through certain fluorescent materials. Energetic
    neutral particles such as gamma rays and neutrons
    can also be counted by detecting the charged
    secondary particles which result from their
    interaction with matter. The first scintillation
    counting was done by eye (Rutherford, early
    1900's) gt Geiger counter gt photomultiplier tube.
    Since that time, a number of highly efficient
    scintillator materials (organic and inorganic)
    and special photomultipliers have been developed
    for this purpose.

12
Types of Detectors
  • Photomultiplier Tubes detect photons by first
    producing electrons in a photo-cathode (by the
    photoelectric effect). These electrons are
    collected by a shaped electric field and then
    multiplied.

13
Types of Detectors
  • Silicon Detectors A semiconductor with a voltage
    applied across its junction constitutes a
    sensitive, high-precision tracking device.
    Consist of layers of small pads with many tiny
    silicon strips a fraction of a millimetre wide.
    Charged particles passing through the silicon
    create electric signals that exactly indicate
    which strips the particles have crossed. As the
    particles pass through many layers of silicon,
    can obtain information on the directions the
    particles travel.

14
Types of Detectors
  • Cerenkov Detectors The resultant polarization of
    local atoms as the charged particles travel
    through the atmosphere results in the emission of
    a faint, bluish light known as "Cerenkov
    radiation. In a transparent medium, blue light
    can escape and transmit the information that a
    fast charged particle has passed through. Various
    media to optimise the size of the light cone
    around the particle's direction. Also contain
    light-sensitive devices called photomultipliers.
    Cosmic Ray detection

15
Types of Detectors (Cerenkov)
Whipple Air Cerenkov Detector
16
After all is said an done
  • Unfortunately all does not end with being able to
    detect particles. A lot of effort goes into the
    up keep of the detectors, data storage and of
    course data analysis
  • New detectors mean new problems but also new
    horizons
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