18WuD2x

486 n-type material • null detector
n-type material Semiconductor material that has
been doped with a donor-type impurity and, consequently,
conducts a current via electrons. Germanium,
for example, when doped with arsenic,
becomes n-type. Compare P-TYPE MATERIAL.
n-type semiconductor See N-TYPE MATERIAL.
nuclear battery See ATOMIC BATTERY.
nuclear bombardment In nucleonics, the bombarding
of the nucleus of an atom with subatomic
particles, usually neutrons.
nuclear charge The net positive charge of the nucleus
of an atom.
nuclear clock A chronometer based on the rate of
disintegration of a radioactive material.
nuclear energy Energy resulting from the splitting
of the nucleus of an atom or from the fusion of
nuclei. Also see ATOMIC ENERGY, ATOMIC
POWER, NUCLEAR FISSION, NUCLEAR FUSION,
NUCLEAR REACTOR, and NUCLEUS.
nuclear fission A nuclear reaction resulting from
the bombardment of nuclei in the atoms of certain
radioactive materials. The bombardment
with neutrons creates two new nuclei (by splitting)
and several new neutrons that split several
other nuclei, producing still more nuclei and neutrons,
etc. The result is a chain reaction that can
lead to a violent explosion if not checked. Compare
NUCLEAR FUSION.
nuclear force A strong attraction that holds together
pairs of nucleons in an atomic nucleus.
This prevents an electric charge of protons from
driving the nucleus apart. Nuclear force acts only
over very minute distances. At greater distances,
electrostatic repulsion is stronger.
nuclear fusion A nuclear reaction resulting from
the violent collision of the nuclei of the atoms of a
hydrogen isotope (such as deuterium) at extremely
high temperature. The process produces
more energy than does NUCLEAR FISSION, and
leaves no hazardous radioactive waste.
nuclear magnetic resonance An atomic phenomenon
in which a particle, such as a proton, in
a steady magnetic field “flips over” when an alternating
magnetic field is applied perpendicular to
the steady field.
nuclear magnetic resonance imaging Abbreviation,
NMRI. The use of NUCLEAR MAGNETIC
RESONANCE effects to produce a picture of internal
body organs. Using computers, threedimensional
renditions can be generated. It is
useful in medicine as a diagnostic aid.
nuclear medicine A branch of medicine involving
the use of radioactive isotopes in diagnosing and
treating disease. A radioactive isotope is put
inside the body and it tends to accumulate in
certain areas. Abnormal concentration of
radioisotopes might indicate abnormal body activity
in a certain area.
nuclear pile See NUCLEAR REACTOR.
nuclear power plant A power-generating plant using
a NUCLEAR REACTOR.
nuclear reaction 1. A reaction in which a heavy
atomic nucleus is split into two or more lighter nuclei,
with an accompanying release of radiant energy.
Also called NUCLEAR FISSION. 2. A reaction
in which two or more light nuclei combine to form
a heavier nucleus, accompanied by the release of
radiant energy. Also called NUCLEAR FUSION.
nuclear reactor 1. A device in which nuclear fission
can be initiated and controlled. At the center
of the reactor is a core of nuclear fuel, such as a
fissionable isotope of uranium. The core is surrounded
by a graphite moderator jacket that is, in
turn, surrounded by a coolant jacket; the whole
is surrounded by a thick concrete shield. Neutron-absorbing
rods are inserted through various
walls to different depths in the fuel to control the
reaction. Also called atomic pile. 2. A controlled
nuclear fusion device, not yet perfected, but under
development. It would provide all the benefits
of an atomic pile (fission reactor), but would be
more efficient and would not produce hazardous
radioactive waste.
nuclear recoil An observable vibration of an
atomic nucleus when it disintegrates.
nuclear resonance The condition wherein a nucleus
absorbs a gamma ray emitted by an identical
nucleus.
nuclear service robot A remotely controlled (teleoperated)
robot used for general work in environments
where the level of radioactivity is too high
for humans (e.g., the maintenance of a nuclear
reactor). It could also be used, if necessary, for
such tasks as disarming nuclear warheads and
cleaning up after a nuclear accident.
nucleon A proton or neutron in the nucleus of an
atom.
nucleonics The branch of physics concerned with
nucleons and nuclear phenomena. The name is
an acronym for nuclear electronics.
nucleon number See MASS NUMBER.
nucleus The center or core of an atom. Contains
neutrons, protons, and other particles. The net
electric charge of the nucleus is positive, and is
equal to the sum of the negative charges of the orbital
electrons of the atom.
null 1. The condition of zero output current or voltage
resulting from adjusting or balancing a circuit,
such as a bridge. 2. A local minimum in an
interference pattern or directivity pattern.
null balance In potentiometric-measuring circuits
for comparing one voltage to another, the balance
condition in which no current flows through the
galvanometer.
null current In potentiometric-measuring circuits
for comparing one voltage to another, the galvanometer
current remaining at null when the
null point is not fully zero.
null detection Direction finding by means of an
antenna with a bidirectional or unidirectional
null response.
null detector See BRIDGE DETECTOR.