Fano noise is a fluctuation of an electric charge obtained in a detector (in spite of constant value of the measured quantity, which is usually an energy), arising from processes in the detector. It was first described by

Ugo Fano Ugo Fano (July 28, 1912 – February 13, 2001) was an Italian American physicist, notable for contributions to theoretical physics. Biography Ugo Fano was born into a wealthy Jewish family in Turin, Italy. His father was Gino Fano, a professo ...

in 1947, as a fluctuation of amount of ion pairs produced by a charged particle of high energy in a gas. The amount of the ion pairs is proportional to the energy the particle loses in the gas, but with some error - due to the Fano noise. Surprisingly, the noise is usually smaller than a

Poisson distribution In probability theory and statistics, the Poisson distribution is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time or space if these events occur with a known co ...

noise (in which the

variance In probability theory and statistics, variance is the expectation of the squared deviation of a random variable from its population mean or sample mean. Variance is a measure of dispersion, meaning it is a measure of how far a set of numbers ...

is equal to the value - note the variance is average squared distance from the expected value), showing there is an interaction between ionization acts. A

Fano factor In statistics, the Fano factor, like the coefficient of variation, is a measure of the statistical dispersion, dispersion of a probability distribution of a Fano noise. It is named after Ugo Fano, an Italian American physicist. The Fano factor is d ...

was introduced to describe it, and the factor is almost independent of the energy measured (Fano computed it to change from 0.43 to 0.47 for ionization of atomic hydrogen by electrons of energy from 1keV to 100keV). Fano expected it to be between 1/3 and 1/2 for gases, for moderate energies of ionizing particles. The Fano noise applies as well to other processes in which an energy is converted to an electric charge - solid state detectors of charged particles and gamma radiation, and even semiconductor light detectors like

image sensors An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of curr ...

. E.g. it is a limiting factor in the noise characteristics of CCDs and

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...

image sensor An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of curr ...

s. The Fano factor achieveable is an important parameter of the detector material – the smaller it is the better.

References

* {{cite conference , last=Janesick , first=James , last2=Elliott , first2=Tom , last3=Bredthauer , first3=Richard , last4=Chandler , first4=Charles , last5=Burke , first5=Barry , editor-last=Golub , editor-first=Leon , title=Fano-Noise-Limited CCDs , publisher=SPIE , date=1988-12-21 , doi=10.1117/12.948704 , bibcode= 1988SPIE..982...70J

References

See also