Gamma-ray region

ELECTRON-HOLE PAIR See Charge carriers. ELECTRONVOLT (eV) Conventional unit of radiation energy in the X-ray and gamma-ray region. Energy gained by an electron as it passes through a potential difference of one volt. Also keV (1000 eV), and MeV (10 eV). 1 eV = 1.602 177 x 10 J. 

X-rays The portion of the electromagnetic spectrum between the ultraviolet (UV) region and the gamma-ray region. 

X-rays The fraction of the electromagnetic spectrum that is between the ultraviolet (UV) region and the gamma ray region. X-rays can penetrate substances that normally block Ught and are often used in medical diagnosis. 

A gamma-ray spectmm is produced nondispersively by pulse-height (multichannel) analysis using scintillation or semiconductor detectors. Resolving power, typically - 100 at 100 keV and - 700 at 2 MeV, is quite modest compared with that achievable in other spectral regions, but is sufficient to identify nucHdes unambiguously. 

Some detectors for the visible and UV spectral regions can detect individual photons. These detectors are shot-noise limited. X-ray and gamma-ray spectroscopy also detects... 

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

When a single gamma ray interacts with the gas in the chamber, it produces a rapidly moving electron which produces secondary electrons. About 10,000 electrons may be formed depending on the gas used in the chamber. The applied voltage can be increased until the amount of recombination is very low. However, further increases do not appreciably increase the number of electrons collected. This region in which all 10,000 electrons are collected is the ionization region. 

Astronomy s new eyes carry code names like HST (Hubble Space Telescope), XMM (X-ray Multi-Mirror) and GRO (Gamma-Ray Observatory). Each wavelength region has its own squadron, extended by future spacecraft that take us ever further towards sensitivity and detailed analysis of images and spectra. 

Nuclear incineration of the gluttonous white dwarf thus synthesises a considerable amount of nickel-56 (0.5-0.6 Mq) and radioactivity left over after its departure makes it shine with dazzling brilliance, like some lavish stellar requiem. This radioactive isotope is the source of the exceptional luminosity of type la supernovas, both in the optical region, as has already been observed, and in gamma rays, as yet only a prediction. 

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