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Alpha Particle

a particle with two protons and two neutrons, has a 2+ charge, is equivalent to a helium-4 nucleus. Is emitted during radioactive decay.

Alpha Radiation

radiation that is made up of alpha particles; is deflected toward a negatively charged plate when radiation from a radioactive source is directed between two electrically charged plates


the smallest particle of an element that retains all the properties of that element

Atomic Mass

the weighted average mass of the isotopes of that element

Atomic Mass Unit (amu)

one-twelfth the mass of a carbon-12 atom

Atomic Number

the number of protons/electrons in an atom

Beta Particle

a high-speed electron with a 1- charge that is emitted during radioactive decay

Beta Radiation

radiation that is made up of beta particles; is deflected toward a positively charged plate when radiation from a radioactive source is directed between two electrically charged plates

Cathode Ray

radiation that originates from the cathode and travels to the anode of a cathode-ray tube


a negatively charged, fast-moving particle with an extremely small mass that is found in all forms of matter and moves through the empty space surrounding an atom's nucleus


a pure substance that cannot be broken down into simpler substances by physical or chemical means

Gamma Rays

high-energy radiation that has no electrical charge and no mass, is not deflected by electric or magnetic fields, usually accompanies alpha and beta radiation, and accounts for most of the energy lost during radioactive decay


atoms of the same element with different numbers of neutrons

Mass Number

the number after an element's name, representing the sum of its protons and neutrons


a visual, verbal, and/or mathematical explanation of data collected from many experiments


a neutral, subatomic particle in an atom's nucleus that has a mass nearly equal to that of a proton

Nuclear Equation

a type of equation that shows the atomic number and mass number of the particles involved

Nuclear Reaction

a reaction that involves a change in the nucleus of an atom


the extremely small, positively charged, dense center of an atom that contains positively charged protons and neutral neutrons

Periodic Table

a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number


a subatomic particle in an atom's nucleus that has a positive charge of 1+


the rays and particles - alpha and beta particles and gamma rays - that are emitted by radioactive materials

Radioactive Decay

a spontaneous process in which unstable nuclei lose energy by emitting radiation


the process in which some substances spontaneously emit radiation


an explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered valid if it can be used to make predictions that are proven true

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