Atomic Glossary
Abundance
See Natural
Abundance
Alpha
Decay
(click
here for animation)
Nuclear decay by emission of an alpha particle (4He nucleus
).
Atomic Mass (Atomic Weight)
The mass of a neutral atom of a nuclide. The atomic weight of an atom is the
weight of the atom based on a scale where 12C = 12. The atomic weight of an
element is the weighted average of each isotope.
Atomic Number
The number of protons
in the nucleus
Beta
Decay
(click
here for animation)
Nuclear decay by emission of an electron
or a positron. Positron decay is always accompanied by electron
capture
decay.
Beta-Delayed
Particle Emission
(click
here for animation)
When a large amount of decay energy is available, the nucleus
may emit:
NeutronsAlpha particles following the beta decay.
Bremsstrahlung
X-rays
produced when fast electrons
pass through matter. The bremsstrahlung (German for "slowing-down
radiation") energy varies from 0 to the energy of the electron.
Carbon-Nitrogen-Oxygen
Cycle (see
also hot CNO cycle)
In stars more massive than the sun (>1.1 Solar masses), this cycle is the
primary process which converts hydrogen into helium. 12C serves as a
catalyst, an ingredient which is necessary for the reaction but is not consumed.
Listing
of the steps
Compton
Scattering
Collision process between a gamma
ray and a bound atomic electron
where only part of the gamma-ray energy is transferred to the electron. The
probability for Compton scattering is approximately proportional to Z, and for
energies greater than 500 keV approximately proportional to 1/Egamma
Conversion Electron
An alternate process to x-ray
emission during the de-excitation of an excited atom.
Decay Branching %
The nuclide decay rate by a particular decay mode. Some nuclides decay by
only one mode (100%), and others by more than one mode. For example, 187Pb decay
by beta
decay (98%) and alpha
decay (2%).
Decay Mode
Disappearance of a radioactive substance due to nuclear emission of an alpha
or beta
particle, capture
of an atomic electron,
neutrinos,
spontaneous
fission, and the emission of bremsstrahlung,
x-rays, and conversion
electrons. In rare instances proton,
neutron,
or light element (for example 14C) emission can occur. When a large
amount of decay energy is available, beta-delayed
emission of neutrons, protons, and other particles may occur.
Decay
Scheme
A drawing depicting the decay of a parent nucleus
to a daughter nucleus.
The betas
or alphas
are shown as arrows from the parent level to daughter level(s). Gamma
rays de-exciting daughter levels are shown on the decay scheme.
Electromagnetic radiation
Radiation consisting of electric and magnetic waves that travel at the speed
of light. Examples: light, radio waves, gamma
rays, x-rays.
Electron
An elementary particle with a unit electrical charge and a mass 1/1837 of
the proton.
Electrons surround the atom's positively charged nucleus
and determine the atom's chemical properties. In our diagrams, an electron is
represented by this:
Electron
Capture Decay
Nuclear decay by capture of an atomic electron.
If the decay energy is greater than 1022 keV, positron
emission can also occur in competition with electron
capture.
Energy Scale
The energy scale used by most nuclear scientists is electron volts (eV),
thousands of electron volts (keV), and millions of electron volts (MeV). An
electron volt is the energy acquired when an electron
falls through a potential difference of 1 volt. 1 eV=1.602*1012ergs.
Masses are also given by their "mass-equivalent" energy (E=mc2).
The mass of the proton
is 938.27231 MeV.
E=mc2
Where: e is energy, m is mass, and c is the speed of light. Einstein's
famous equation describes how energy and mass are related. In our animated
decays, mass is lost. That mass is converted into energy in the form of electromagnetic
waves. Because the speed of light is so great, a little matter can transform
into large amount of energy.
ENSDF
The Evaluated Nuclear Structure Data File is evaluated by an international
collaboration of nuclear scientists. ENSDF is a database of nuclear structure
and decay data.
Gamma
Rays
A highly penetrating type of nuclear radiation, similar to x-rays and light,
except that it comes from within the nucleus
of an atom, and, in general, has a shorter wavelength. Gamma rays emission is a
decay mode by which excited state of a nucleus
de-excite to lower (more stable) state in the same nucleus.
In our diagrams, a gamma ray is represented by this:
Geiger Counter
A radiation detector consisting of two electrodes with a low-pressure gas in
between. A voltage is maintains such that if radiation passing through the
counter ionizes the gas, an avalanche of electrons
will occur. Geiger counters can count radiation but cannot distinguish either
the energy or kind of radiation.
Ground State
A lowest energy state of the nucleus.
Half-Life
Used to measure the rate of radioactive decay of disintegration. The time lapse
during which a radioactive mass loses one half of its radioactivity.
Helium
Burning (triple alpha process)
When temperature in the core of a star reaches 100 million degrees, three
colliding helium nuclei fuse to form a carbon nucleus. This process occurs when
the star is a red giant.
Hot
Carbon-Nitrogen-Oxygen Cycle (see
also C-N-O cycle)
Complete
Listing of the
Steps
Hydrogen
Burning
Hydrogen burning is the fusion of four hydrogen nuclei (protons) into a
single helium nucleus (two protons and neutrons.) The process is a series of
reactions. The type of reactions depend on the mass of a star and its core
temperature and density. In our Sun, the process is a proton-proton chain. In
more massive stars, the C-N-O
cycle (Carbon-Nitrogen-Oxygen) serves to fuse hydrogen into helium.
Intensity Branching(%)
The intensity of a radiation emitted during radioactive decay.
Isobars
Nuclides
of the same atomic mass but different atomic
number.
Isomers
A long-lived excited state of the nucleus.
Arbitrarily defined in as the Table
of Isotopes as having a half-life greater than 1 ms.
Isotopes
Two or more nuclides having the same atomic
number, thus constituting the same element, but differing in the mass
number. Isotopes of a given element have the same number of nuclear protons
but differing numbers of neutrons.
Naturally occurring chemical elements are usually mixtures of isotopes so that
observed (non-integer) atomic weights are average values for the mixture.
Mass Number
The sum of the number of neutrons
and protons
in a nucleus.
Natural Abundance
Percentage of an element occurring on earth in a particular stable isotopic
form.
Neutrino
An electrically neutral particle with negligible mass. It is produced in many
nuclear reactions such as in beta
decay. In our diagrams, it is represented by this:
Neutron
One of the basic particles which make up an atom. A neutron and a proton
have about the same weight, but the neutron has no electrical charge. In our
diagrams, a neutron is represented by this:
Neutron Decay
Nuclear decay by emission of a neutron.
Neutron-Induced
Fission
Bombardment with a neutron
resulting in splitting the nucleus
into two parts (fission fragments), neutrons,
and gamma
rays.
Neutron-induced
fission movie by Encylopedia Brittanica
Neutron Separation Energy
The energy required to remove a neutron
from a nucleus.
Nuclear
Reaction
Reaction between an energetic incident projectile (neutron,
proton,
or nucleus
) from a reactor or particle accelerator and a target nucleus
producing product nuclides, gamma
rays, particles, and other radiations.
FusionCoulomb Excitation
When two nuclei pass each other, the electrostatic repulsion can excite a nucleus enough to release gamma rays.Particle Transfer
Cold fusion should not be confused with the other cold fusion which was debunked several years ago.
Nucleus
The core of the atom, where most of its mass and all of its positive
charge is concentrated. Except for hydrogen, it consists of proton
and neutrons.
NSR
The Nuclear Science Reference file is a compilation of about 160,000 references
relevant to nuclear structure and decay.
Pair
Production
A collision process for gamma
rays with energies greater than 1022-keV (two electron
masses) where an electron
/positron pair is produced. A heavy nucleus must be present for pair
production. For high-energy gamma
rays the pair production process is proportional to Z2 and
ln(gamma).
Parity
A nucleus
or particle has odd (-) or even (+) parity according to whether or not its wave
function changes sign when all of the space coordinates are changed.
Photoelectric
effect
Collision process between an x-ray
or gamma
rays and a bound atomic electron
where the photon disappears, the bound electron is ejected, and the incident
energy is shared between the ejected electron and the remaining atom. The photon
energy must be greater than the atomic binding energy. The probability for the
photoelectric effect is approximately proportional to Z5 of the
absorber and falls of by about E(gamma)3.5.
Positron
Annihilation
Positron decay in matter by annihilation with an electron.
Usually and "atom" of positronium (e+e-) forms which annihilates to
produce two 511-keV photons. Occasionally, the positron will annihilate in
flight to produce on or more photons sharing the total rest mass and kinetic
energy of the positron and electron.
Proton
One of the basic particles which makes up an atom. The proton is found in the nucleus
and has a positive electrical charge equivalent to the negative charge of an electron
and a mass similar to that of a neutron.
A proton is a hydrogen nucleus.
In our diagrams, a proton is represented by this:
Proton-Proton Chain
In the Sun and other less massive stars, this chain is the primary source of
heat and radiation. The proton-proton chain converts hydrogen into helium
releasing energy in the form of particles and gamma-rays.
Hydrogen is converted into helium in a chain of reactions. The first reaction
takes an average of 1 billion years to occur while the others are much shorter.
One step is only 1 second long. In the Sun, there are so many hydrogen nuclei
that the 1 billion year waiting period does not stop it from producing
tremendous radiation.
List
of the steps
Proton Separation Energy
The energy required to remove a proton from a nucleus.
Proton
Decay
Nuclear decay by emission of a proton.
Q-value
The energy available for decay. This energy is released by the nucleus
mainly as gammas,
betas,
neutrinos,
and/or alpha
particles.
Scintillation Counter
A scintillation counter consists of a material that emits light when radiation
passes through it. Various liquid, plastic, and crystalline materials have
scintillation properties. Scintillation light is measured with photomultiplier
tubes. In general the amount of scintillator light detected is proportional to
the energy of the radiation.
Semiconductor Detector
Radiation striking very pure Ge and Si semiconductor detectors can excite a
large number of electrons
into the conduction band leading to a measurable current. This current is
proportional to the energy of the radiation. Semiconductor detectors can be used
to accurately measure the energy and intensity of radiation.
Spin
Used to describe the angular momentum of the nucleus.
Spontaneous
Fission
Nuclear decay by splitting the nucleus
into two parts (fission fragments), neutrons,
and gamma
rays.
Triple Alpha Process (see helium burning)
X-rays
A type of radiation of higher frequency (or energy) that visible light but lower that gamma rays. Usually produced by fast electrons going through matter or by the de-excitation of excited atoms. In our diagrams, a x-ray is represented by this:
*The background image is a chart of the nuclides. Each box represents an nuclide. The neutron numbers increase to the right on the x-axis and the proton number increases vertically in the y-axis. Each color represents different decay modes. The white band in the middle is for stable nuclides. The nuclides farther from the stable band are more unstable.