RAD
(Radiation Absorbed Dose)
It is the unit
for measure of energy deposited by ionizing radiation per unit mass of
material. One RAD is equal to energy absorption of 100 ergs per gram of
material.
RADAR
Radar is acronym
for "Radio Detection And Ranging." A radar system usually operates in
the ultra-high-frequency (UHF) or microwave part of the radio-frequency (RF)
spectrum, and is used to detect the position and/or movement of objects. Radar
can track storm systems, because precipitation reflects electromagnetic fields at certain frequencies. Radar can also render precise maps. Radar
systems are widely used in air-traffic control, aircraft navigation, and marine
navigation.
Radian
It
is the angle subtended at the centre of a circle by an arc whose length is
equal to the radius of that circle.
1radian
= 57o 17’44”; 2π radian=360o
Radiant
Energy (Heat)
The heat energy
transferred by the mode of radiation is called radiant energy.
Radiant
Energy
It is defined as
energy of particles (excluding rest energy) emitted, transferred or received.
(As per ICRU, 1980).
Radiation
Absorbed Dose
It is the unit for measure of energy
deposited by ionizing radiation per unit mass of material. One RAD is equal to
energy absorption of 100 ergs per gram of material.
Radiation
Exposure
It is defined by ICRU(1980) as “the
quotient of dQ/dm, where the value of dQ is absolute value of total charge of
the ions of one sign produced in air when all the electrons liberated by
photons in air of mass ‘dm’ are completely stopped in air”.
Radiation
Length
Radiation length
is a physical quantity in nuclear physics which describes overall attenuation
of electrons and photons passing through matter. It is defined as thickness of
a material that an electron travels such that it loses about 63% of its energy
in Bremstrahlung.
Radiative
Capture
A particle may
combine with a nucleus to produce a new nucleus or a compound nucleus which is
in an excited state. The excess energy is emitted in the form of γ-ray photons. This type of process is known as radiative
capture.
Radiator
(Thermal)
If the
temperature of the body is higher than the temperature of its surroundings, the
body emits thermal radiations all around from its surface.
Radio
Frequency
Frequency of
radio waves or signals in the range of about 3KHz to 300GHz.
Radio
Waves
They are type of
electromagnetic waves with frequencies ranging from 300GHz to as low as 3 KHz.
Radioactive
Decay
When nuclei emit
subatomic particles, their configuration, state, and even identity may change.
Except for gamma decay, in which nucleus retains its identity, all other decays
transform the nucleus into a totally different one. This process is called
radioactive decay.
Radioactive
Disintegration
Spontaneous breaking up of nucleus is known as
radioactive disintegration.
Radioactive
Transformation
The disintegration of an unstable nucleus
resulting in another nucleus is called as radioactive transformation.
Radio
Waves
Waves having wave
length in range of 106 to 10-3 meters are called as radio
waves. Sources of radio waves are electrons vibrated by electronic circuits,
radio, stars, and galaxies including pulsars and quasars.
Radium
Radium was discovered by Marie Curie and
her husband Pierre in 1898. Radium is an alkaline earth metal. Radium has a
melting point of 700°C, boiling point of 1140°C, specific gravity estimated to
be 5, and valence of 2. Pure radium metal is bright white when freshly
prepared, although it blackens upon exposure to air. The element decomposes in
water. Radium emits alpha, beta, and gamma rays. It produces neutrons when
mixed with beryllium. A single gram of Ra-226 decays at the rate of
3.7x1010 disintegrations per second. A gram of radium produces around
0.0001 ml (STP) of radon gas (emanation) per day and about 1000 calories per
year. Radium loses about 1% of its activity over 25 years, with lead as its
final disintegration product. Radium is a radiological hazard. Stored radium
requires ventilation to prevent the build-up of radon gas.
Radius
of Gyration
It is that
distance from the axis of rotation, where the whole mass of body can be placed
to get same moment of inertia which the body actually does possess.
Radius
Vector
When a particle
describes circular path, the line joining centre of circle and position of that
particle at any instant is called as radius vector.
Rainbow
It
is a phenomenon due to combination of refraction of sunlight by spherical
wavelet droplets behaving like prism (dispersion) and of “Total internal
reflection”.
or
The
spectrum formed due to dispersion of sunlight by water drops settling down
after rain.
Raman
Effect
When a
monochromatic beam of light is passed through a gas, liquid or transparent
solid body, a small fraction of light is scattered in all directions. The
scattered light consists of frequencies greater and smaller than incident beam
frequency in additional to original, the phenomenon is known as Raman Effect.
Ramsden
Eye Piece
It consists of
two plano-convex lenses of same focal lengths with a separation of two third
the focal length of either lens. The two lenses are placed with their surfaces
facing each other.
Random
Errors
Random errors
refer to the errors that are statistical in nature.
Rank
of a Tensor
The rank of a tensor only indicates the
number of indices attached to its per component. The rank of Tensor gives the
number of mode of changes of a physical quantity when passing from one system
to other which is in rotation relative to the first.
Rayleigh
Scattering
When a scattering occurs with molecules
which are smaller than the wavelength of incident radiation is called Rayleigh
scattering.
