A hodoscope (from the Greek "hodos" for way or path, and "skopos" an observer) is an instrument used in
particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuc ...
s to detect passing charged particles and determine their trajectories. Hodoscopes are characterized by being made up of many segments; the combination of which segments record a detection is then used to infer where the particle passed through hodoscope.
The typical detector segment is a piece of
scintillating material, which emits light when a particle passes through it. The scintillation light can be converted to an electrical signal either by a
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
tube (PMT) or a
PIN diode
A pin is a device used for fastening objects or material together.
Pin or PIN may also refer to:
Computers and technology
* Personal identification number (PIN), to access a secured system
** PIN pad, a PIN entry device
* PIN, a former Dutch de ...
. If a segment measures some significant amount of light, the experimenter can infer that a particle passed through that segment. In addition to coordinate information, for some systems the strength of the light can be proportional to the deposited energy. By doing necessary calibrations, the deposited energy can be determined, which then can be used to infer information about the original particle's energy.
As an example: a simple hodoscope might be used to determine where a particle crossed a plane or a wall. In this case, the experimenter could use two segments shaped like strips, arranged in two layers. One layer of strips could be arranged horizontally, while a second layer could be arranged vertically. A particle passing through the wall would hit a strip in each layer; the vertical strip would reveal the particle's horizontal position when it crossed the wall, while the horizontal strip would indicate the particle's vertical position.
Hodoscopes are some of the simplest detectors for tracking charged particles. However, their spatial resolution is limited by the segment size. In applications where the spatial resolution is very important, hodoscopes have been superseded by other detectors such as
drift chamber
A wire chamber or multi-wire proportional chamber is a type of proportional counter that detects charged particles and photons and can give positional information on their trajectory, by tracking the trails of gaseous ionization. was located via ...
s and
time projection chamber
In physics, a time projection chamber (TPC) is a type of particle detector that uses a combination of electric fields and magnetic fields together with a sensitive volume of gas or liquid to perform a three-dimensional reconstruction of a particl ...
s.
Further reading
*http://www.scifun.ed.ac.uk/pages/pp4ss/pp4ss-hodoscope.html
External links
*
Particle detectors
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