Radiation astronomy/Detectors

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This tree diagram shows the relationship between types and classification of most common particle detectors. Credit: Wdcf.{{free media}}

Radiation detectors provide a signal that is converted to an electric current. The device is designed so that the current provided is proportional to the characteristics of the incident radiation.

There are detectors that provide a change in substance as the signal and these may be automated to provide an electric current or quantified proportional to the amount of new substance.

Absorptions[edit | edit source]

This is an overview of electromagnetic radiation absorption. Credit: Jon Chui.
An example of applying Absorption spectroscopy is the first direct detection and chemical analysis of the atmosphere of a planet outside our solar system in 2001. Sodium filters the alien star light of HD 209458 as the hot Jupiter planet passes in front. The process and absorption spectrum are illustrated above. Credit: A. Feild, STScI and NASA website.{{free media}}

Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.

This example in the image at center discusses the general principle using visible light as a specific example. A white beam source – emitting light of multiple wavelengths – is focused on a sample (the complementary color pairs are indicated by the yellow dotted lines). Upon striking the sample, photons that match the energy gap of the molecules present (green light in this example) are absorbed in order to excite the molecule. Other photons transmit unaffected and, if the radiation is in the visible region (400-700nm), the sample color is the complementary color of the absorbed light. By comparing the attenuation of the transmitted light with the incident, an absorption spectrum can be obtained.

Backgrounds[edit | edit source]

The main components of background noise in neutron detection are high-energy photons, which aren't easily eliminated by physical barriers.

Noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits.[1] Noise generated by electronic devices varies greatly, as it can be produced by several different effects. Thermal noise is unavoidable at non-zero temperature (see fluctuation-dissipation theorem), while other types depend mostly on device type (such as shot noise,[1][2] which needs steep potential barrier) or manufacturing quality and semiconductor defects, such as conductance fluctuations, including 1/f noise.

Noise is an error or undesired random disturbance of a useful information signal, introduced before or after the detector and decoder. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources. Noise is, however, typically distinguished from interference, (e.g. cross-talk, deliberate jamming or other unwanted electromagnetic interference from specific transmitters), for example in the signal-to-noise ratio (SNR), signal-to-interference ratio (SIR) and signal-to-noise plus interference ratio (SNIR) measures. Noise is also typically distinguished from distortion, which is an unwanted alteration of the signal waveform, for example in the signal-to-noise and distortion ratio (SINAD). In a carrier-modulated passband analog communication system, a certain carrier-to-noise ratio (CNR) at the radio receiver input would result in a certain signal-to-noise ratio in the detected message signal. In a digital communications system, a certain Eb/N0 (normalized signal-to-noise ratio) would result in a certain bit error rate (BER).

Spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) in an electrical circuit.

Fast, short duration electrical transients (overvoltages) in the electric potential of a circuit are typically caused by

  • Lightning strikes,
  • Power outages,
  • Tripped circuit breakers,
  • Short circuits,
  • Power transitions in other large equipment on the same power line,
  • Malfunctions caused by the power company,
  • Electromagnetic pulses (EMP) with electromagnetic energy distributed typically up to the 100 kHz and 1 MHz frequency range, or
  • Inductive spikes.

For sensitive electronics, excessive current can flow if this voltage spike exceeds a material's breakdown voltage, or if it causes avalanche breakdown. In semiconductor junctions, excessive electric current may destroy or severely weaken that device. An avalanche diode, transient voltage suppression diode, transil, varistor, overvoltage crowbar, or a range of other overvoltage protective devices can divert (shunt) this transient current thereby minimizing voltage.[3]

Meteors[edit | edit source]

The white spot on this image of the Earth side of the Moon is the impact site of a meteor from March 17, 2013. Credit: NASA.{{free media}}
This is a Hubble Space Telescope image taken on July 23, 2009, showing a blemish of about 5,000 miles long left by the 2009 Jupiter impact.[4] Credit: NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team.{{free media}}

Usually, a meteor detector is designed for another form of radiation that the meteor may radiate.

In the image at right, a 0.3 m meteor has impacted a meteor detector, in this case the Moon, and created a scintillation event that in turn is detected by a photoelectronic detector system.

In the image at left, a meteor has impacted another detector, here Jupiter, but instead of a scintillation event has created a lowering of albedo as detected by the photoelectronic system, the Hubble Space Telescope.

Protons[edit | edit source]

This is an image of the alpha particle X-ray spectrometer (APXS). Credit: NASA/JPL-Caltech.{{free media}}
The stopping power of aluminum for protons is plotted versus proton energy. Credit: H.Paul.

Some of the alpha particles are absorbed by the atomic nuclei. The [alpha,proton] process produces protons of a defined energy which are detected. Sodium, magnesium, silicon, aluminium and sulfur can be detected by this method. This method was only used in the Mars Pathfinder APXS.

At right, the second figure shows the stopping power of aluminum metal single crystal for protons.

"Choosing materials with the largest stopping powers enables thinner detectors to be produced with resulting benefits in radiation tolerance (which is a bulk effect) and lower leakage currents. Alternatively, choosing smaller stopping powers will increase scattering efficiency, which is a requirement for polarimetry, or say, the upper detection plane of a double Compton telescope."[5]

Hypotheses[edit | edit source]

  1. The use of satellites should provide ten times the information as sounding rockets or balloons.

A control group for a radiation satellite would contain

  1. a radiation astronomy telescope,
  2. a two-way communication system,
  3. a positional locator,
  4. an orientation propulsion system, and
  5. power supplies and energy sources for all components.

A control group for radiation astronomy satellites may include an ideal or rigorously stable orbit so that the satellite observes the radiation at or to a much higher resolution than an Earth-based ground-level observatory is capable of.

See also[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 C. D. Motchenbacher; J. A. Connelly (1993). Low-noise electronic system design. Wiley Interscience. 
  2. L. B. Kish; C. G. Granqvist (November 2000). "Noise in nanotechnology". Microelectronics Reliability (Elsevier) 40 (11): 1833–37. doi:10.1016/S0026-2714(00)00063-9. 
  3. Transient Protection, LearnEMC Online Tutorial. http://www.learnemc.com/tutorials/Transient_Protection/t-protect.html
  4. Dennis Overbye (2009-07-24). Hubble Takes Snapshot of Jupiter’s ‘Black Eye’. New York Times. http://www.nytimes.com/2009/07/25/science/space/25hubble.html?ref=science. Retrieved 2009-07-25. 
  5. Alan Owens; A. Peacock (September 2004). "Compound semiconductor radiation detectors". Nuclear Instruments and Methods in Physical Research A 531 (1-2): 18-37. doi:10.1016/j.nima.2004.05.071. http://www.msri.org/people/staff/levy/files/ToPrint/owens-compound.pdf. Retrieved 2013-05-24. 

External links[edit | edit source]

{{Radiation astronomy resources}}{{Repellor vehicle}}