A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Decay
It is process of
disintegration of nucleus.
Decay
Constant
Decay
constant of radioactive nuclide describes the rate of decay i.e., its decay
probability in unit time.
or
The
probability that fraction of number of atoms of a radioactive nuclide decay in
unit time.
Decay
Energy or Q value
Decay energy is a
term used to quantify the energy released during the decay process. It can be
used to determine whether a certain decay mode for a nucleus is possible or
not.
Deceleration
Decrease in acceleration.
Deci
It is a prefix in
the metric system denoting a factor of one tenth.
Decibel
A unit used to
express relative difference in power or intensity, usually between two acoustic
or electric signals, equal to ten times the common logarithm of ratio of two
levels.
Deewar
Flask
Flask invented by
Scottish physicist, Sir James Deewar in 1892. It is an arrangement of double
walled vessel separated by vacuum. Vacuum greatly reduces the transfer of heat
preventing temperature change. Glass is used, as it is bad conductor of heat;
its surface is usually lined with a reflective material like silver to reduce
transfer of heat by radiation. This is encapsulated in plastic so that it will
further reduce loss of heat.
Degeneracy
It is a concept in
quantum mechanics as per which physical state having same energy can have
different arrangements.
Degenerate
States
The states of a
system with different Eigen functions but all corresponding to same Eigen
values are known as degenerate states.
Degree
of Degeneracy
Number of
linearly independent Eigen functions corresponding to same Eigen value.
Degrees
of Freedom
The number of
independent coordinates required to express the position and motion of a system
comprising one or more particles is called degrees of freedom of that
system.
Demagnetization
Process by which
magnetization is made zero for a material.
Demodulation
The process of
recovering the audio signal from modulated wave is known as demodulation.
Demodulation involves rectification of modulated wave and removing carrier
frequency to allow audio signal reach load i.e. speaker.
Densitometer
It is a device
that measures degree of darkness (optical density) of a photographic or semi-transparent
material or a reflecting surface.
Density
Operator
The quantum
analogue of classical density function is known as density operator.
Density
Mass per unit
volume of the substance.
Depleted
Uranium
Uranium having a
percentage of U235 smaller than 0.7% found in natural uranium is
called as depleted Uranium. It is generally obtained as by product from nuclear
reactor or as by product from uranium.
Depletion
Layer
When a P-N
junction forms and combines with holes to form negative ions on P-side and
electrons leave from N-type region there is formation of positive ions on
N-type side. This combined region on either side is also called space-charge
region. This region is an insulating region.
Derivative
The essence of calculus is the derivative.
The derivative is the instantaneous rate of change of a function with respect
to one of its variables. This is equivalent to finding the slope of tangent
line to the function at a point.
Derived
Air Concentration (DAC)
The Derived Air Concentration (DAC) for any
radionuclide, is that radioactive concentration in air, such that if a worker works
in such environment, for a year (50 weeks of 40 hour each for a total of 2000
hours per year), would result in the Annual Limit Intake (ALI) for
inhalation. The normal breathing rate, based on Reference Man, is 2,400 m3
per year at work. The Derived Air Concentration is the ALI divided by the
volume breathed in a year at work.
Destructive
Interference
Interference at
the points, where intensity of light is least is called as destructive
interference.
Deuteron
It is nucleus of
Hydrogen-2 atom, consisting of one Proton & one neutron bound together with
a total binding energy of 2.25MeV. The Hydrogen-2 atom, a stable isotope of
Hydrogen with a natural abundance of 0.015% is called Deuterium, which consists
of Deuteron (nucleus) and electron.
Deviation
The difference
between the measured value and the arithmetic mean is called as deviation.
Devitrification
It is the process
in which a glass (non-crystalline or vitreous solid) transforms into a
crystalline solid.
Dew
Point
It is the
temperature at which the present amount of humidity in air starts to
condensate.
Dextrorotatory
Those substances
which rotate the plane of polarization of the incident plane polarized light in
a clock wise direction when seen in the direction of light are called
dextrorotatory substances.
Diaphragm
It is a thin disk
which vibrates when receiving or producing sound waves as in microphone or
loudspeaker.
Diagnostic
Physics
It is the branch
of physics associated with diagnostic procedures that use X-rays, gamma rays,
ultrasound, radio frequency radiation and magnetic sources. In this field,
physicists advise on protocols & technology used for creation of images
that are generated by these diagnostic methods.
