Compton suppression
Encyclopedia
Electronic anticoincidence is a method (and its associated hardware) widely used to suppress unwanted, "background" events in high energy physics, experimental particle physics
, gamma-ray spectroscopy, gamma-ray astronomy
, experimental nuclear physics
, and related fields. In the typical case, a high-energy interaction, or event, that it is desired to study occurs and is detected by some kind of electronic detector, creating a fast electronic pulse in the associated nuclear electronics
. But the desired events are mixed up with a significant number of other events, produced by other particles or other processes, which create indistinguishable events in the detector. Very often it is possible to arrange other physical photon or particle detectors to intercept the unwanted background events, producing essentially simultaneous pulses that can be used with fast electronics to reject, or veto, the unwanted background.
Compton scattering
out of the target before depositing all of its energy. The effect is to minimize the Compton edge
feature in the data.
The high resolution solid state germanium detectors used in gamma ray spectroscopy are very small, typically only a few centimeters in diameter and with thickness ranging from a centimeters to less than a centimeter. Since the detectors are so small, it is likely that the gamma ray will Compton scatter out of the detector before it deposits all of its energy. In this case, the energy reading by the data acquisition system will come up short: the detector records an energy which is only a fraction of the energy of the incident gamma ray.
In order to counteract this, the expensive and small high resolution detector is surrounded by larger and cheaper low resolution detectors, usually sodium iodide scintillators
. The main detector and the suppression detector are run in anti-coincidence, which means that if they both detect a gamma ray then the gamma ray has scattered out of the main detector before depositing all of its energy and the data is ignored. The much larger suppression detector has much more stopping power than the main detector, and it is highly unlikely that the gamma ray will scatter out of both devices.
, where the enormous Atlas and CMS detectors must reject huge numbers of background events at very high rates, to isolate the very rare events being sought.
HEAO 1
HEAO 3
INTEGRAL
Uhuru (satellite)
Gamma-ray spectroscopy
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, gamma-ray spectroscopy, gamma-ray astronomy
Gamma-ray astronomy
Gamma-ray astronomy is the astronomical study of the cosmos with gamma rays. Gamma-rays are the most energetic form of "light" that travel across the universe, and gamma-rays thus have the smallest wavelength of any wave in the electromagnetic spectrum.Gamma-rays are created by celestial events...
, experimental nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
, and related fields. In the typical case, a high-energy interaction, or event, that it is desired to study occurs and is detected by some kind of electronic detector, creating a fast electronic pulse in the associated nuclear electronics
Nuclear electronics
Nuclear electronics is a subfield of electronics concerned with the design and use of high-speed electronic systems for nuclear physics and elementary particle physics research, and for industrial and medical use....
. But the desired events are mixed up with a significant number of other events, produced by other particles or other processes, which create indistinguishable events in the detector. Very often it is possible to arrange other physical photon or particle detectors to intercept the unwanted background events, producing essentially simultaneous pulses that can be used with fast electronics to reject, or veto, the unwanted background.
Gamma-ray astronomy
Early experimenters in X-ray and gamma-ray astronomy found that their detectors, flown on balloons or sounding rockets, were corrupted by the large fluxes of high-energy photon and cosmic-ray charged-particle events. Gamma-rays, in particular, could be collimated by surrounding the detectors with heavy shielding materials made of lead or other such elements, but it was quickly discovered that the high fluxes of very penetrating high energy radiations present in the near-space environment, created showers of secondary particles that could not be stopped by reasonable shielding masses. To solve this problem, detectors operating above 10 or 100 keV were often surrounded by an active anticoincidence shield made of some other detector, which could be used to reject the unwanted background events. Plastic scintillators are often used to reject charged particles, while thicker CsI, bismuth germanate ("BGO"), or other active shielding materials are used to detect and veto gamma-ray events of non-cosmic origin. A typical configuration might have a NaI scintillator almost completely surrounded by a thick CsI anticoincidence shield, with a hole or holes to allow the desired gamma rays to enter from the cosmic source under study. A plastic scintillator may be used across the front which is reasonably transparent to gamma rays, but efficiently rejects the high fluxes of cosmic-ray protons present in space.Compton suppression
In gamma-ray spectroscopy, Compton suppression is a technique that improves the signal by preventing data which has been corrupted by the incident gamma rayGamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
Compton scattering
Compton scattering
In physics, Compton scattering is a type of scattering that X-rays and gamma rays undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy of an X-ray or gamma ray photon, called the Compton effect...
out of the target before depositing all of its energy. The effect is to minimize the Compton edge
Compton edge
In spectrophotometry, the Compton edge is a feature of the spectrograph that results from the Compton scattering in the scintillator or detector. When a gamma-ray scatters off the scintillator but escapes, only a fraction of its energy is registered by the detector. This leads to a spectrum of...
feature in the data.
The high resolution solid state germanium detectors used in gamma ray spectroscopy are very small, typically only a few centimeters in diameter and with thickness ranging from a centimeters to less than a centimeter. Since the detectors are so small, it is likely that the gamma ray will Compton scatter out of the detector before it deposits all of its energy. In this case, the energy reading by the data acquisition system will come up short: the detector records an energy which is only a fraction of the energy of the incident gamma ray.
In order to counteract this, the expensive and small high resolution detector is surrounded by larger and cheaper low resolution detectors, usually sodium iodide scintillators
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
. The main detector and the suppression detector are run in anti-coincidence, which means that if they both detect a gamma ray then the gamma ray has scattered out of the main detector before depositing all of its energy and the data is ignored. The much larger suppression detector has much more stopping power than the main detector, and it is highly unlikely that the gamma ray will scatter out of both devices.
Nuclear and particle physics
Modern experiments in nuclear and high-energy particle physics almost invariably use fast anticoincidence circuits to veto unwanted events. The desired events are typically accompanied by unwanted background processes that must be suppressed by enormous factors, ranging from thousands to many billions, to permit the desired signals to be detected and studied. Extreme examples of these kinds of experiments may be found at the Large Hadron ColliderLarge Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
, where the enormous Atlas and CMS detectors must reject huge numbers of background events at very high rates, to isolate the very rare events being sought.
See also
Nuclear electronicsNuclear electronics
Nuclear electronics is a subfield of electronics concerned with the design and use of high-speed electronic systems for nuclear physics and elementary particle physics research, and for industrial and medical use....
HEAO 1
HEAO 3
INTEGRAL
INTEGRAL
The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
Uhuru (satellite)
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
Gamma-ray spectroscopy