Charged particles (atomic nuclei, electrons, positrons, protons, muons, etc.) can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. These particles must be moving at relativistic speeds to reach the required kinetic energy. Even photons (gamma rays and X-rays) can ionize atoms directly (despite they are electrically neutral) through the Photoelectric effect and the Compton effect, but secondary (indirect) ionization is much more significant.
Detection of Alpha Particles
Detection of alpha radiation is very specific, because alpha particles travel only a few centimeters in air but deposit all their energies along their short paths, thus the amount of energy transferred is very high.
In order to describe principles of detection of alpha radiation, we have to understand the interaction of radiation with matter. Each type particle interacts in a different way, therefore we must describe interaction of alpha particles (radiation as a flow of these particles) separately.
Detection of Alpha using Semiconductors – Silicon Strip Detectors
Silicon-based detectors are very good for tracking charged particles. A silicon strip detector is an arrangement of strip like shaped implants acting as charge collecting electrodes.
Silicon strip detectors 5 x 5 cm2 in area are quite common and are used in series (just like planes of MWPCs) to determine charged-particle trajectories to position-accuracies of the order of several μm in the transverse direction. Placed on a low doped fully depleted silicon wafer these implants form a one-dimensional array of diodes. By connecting each of the metalized strips to a charge sensitive amplifier a position sensitive detector is built. Two dimensional position measurements can be achieved by applying an additional strip like doping on the wafer backside by use of a double sided technology. Such devices can be used to measure small impact parameters and thereby determine whether some charged particle originated from a primary collision or was the decay product of a primary particle that traveled a small distance from the original interaction, and then decayed.
Detection of Beta Particles
Detection of beta radiation is very specific, because beta particles are more penetrating than alpha particles. On the other hand a thin aluminum plate can stop them.
In order to describe principles of detection of beta radiation, we have to understand the interaction of radiation with matter. Each type particle interacts in a different way, therefore we must describe interaction of beta particles (radiation as a flow of these particles) separately.
Detection of Beta Radiation using Scintillation Counter
Scintillation counters are used to measure radiation in a variety of applications including hand held radiation survey meters, personnel and environmental monitoring for radioactive contamination, medical imaging, radiometric assay, nuclear security and nuclear plant safety. They are widely used because they can be made inexpensively yet with good efficiency, and can measure both the intensity and the energy of incident radiation.
Scintillation counters can be used to detect alpha, beta, gamma radiation. They can be used also for detection of neutrons. For these purposes, different scintillators are used.
- Beta Particles. For detection of beta particles, organic scintillators can be used. Pure organic crystals include crystals of anthracene, stilbene and naphthalene. The decay time of this type of phosphor is approximately 10 nanoseconds. This type of crystal is frequently used in the detection of beta particles. Organic scintillators, having a lower Z than inorganic crystals, are best suited for the detection of low-energy (< 10 MeV) beta particles.
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