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Propagation Vector
Vector indicating the direction of wave propagation and the phase delay per unit length
Propellant
A
substance usually a mixture of fuel and oxide used for propelling a rocket.
or
A
compressed inert gas that serves to dispense the contents of an aerosol
container when the pressure is released is called as propellant.
Proper
Time
The time recorded
by a clock moving with a given system is called proper time for that system.
Proportional
Counter
It is type of radiation
detector which operates in proportional region. To a limited degree, the
fill-gas will determine what type of radiation the proportional counter will be
able to detect. Argon and helium are the most frequently used fill gases and
allow for the detection of alpha, beta, and gamma radiation. When detection of
neutrons is necessary, the detectors are usually filled with Boron-Tri-Fluoride
gas.
Proportional
Region
It is one of the
regions in which gas filled detectors are operated. When voltage applied to the
anode wire in gas filled detector is increased to a magnitude, the electrons
reaching anode wire gets increased due to gas multiplication. There is
exponential increase in the number of electrons reaching anode. The magnitude
of charge getting collected is proportional to the quantity of initial charge
generated during primary ionization created in the detector by incident
radiation.
Proton
Sub atomic
particle having positive charge of one electron unit and is a constituent of
nucleus.
Proton-Proton
Cycle
The proton-proton
cycle is a series of nuclear reactions which convert Hydrogen nuclei (protons)
into Helium nuclei (alpha-particles). All Main Sequence stars do this, in one
way or another. For stars like the Sun, the process almost always begins with
the collision of two protons, hence its name, the "proton-proton"
cycle.
Pseudo
Force
See fictious force
Pseudo
Vector
Any vector which commutes with parity
operator is a pseudo vector.
Pulse
Height Analyzer
Electronic device used to record amplitude
distribution of pulses produced by a pulse mode radiation detector. It is
helpful for analysis of energy resolution of the detector.
Pumping
It is a mechanism
used to achieve population inversion.
Pyro-Heliometers
Instrument used for the determination of solar
constant.
Pyrometer
Instrument used for measuring high
temperatures.
There
are two types of pyrometer. They are i) total radiation pyrometer ii) optical
or spectral pyrometer
i)
Total radiation pyrometer: The instruments that measure total radiation emitted
by the body under test are called as total radiation pyrometers. Temperature is
determined by making use of Stefan’s law.
ii) Optical or Spectral Pyrometer: The optical pyrometers compare the intensity of radiation of a certain wavelength emitted by the body with that of radiation of same wavelength emitted by a standard body at known temperature. The temperature of the body is obtained by applying Wien’s displacement law or planks law.
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