The emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.
Radioactivity
The process of energy and particles being spontaneously emitted from the nucleus of atoms; also known as radioactive decay.
Alpha Decay
The nuclear process that emits alpha particles, reducing the atomic number by two and the mass number by four.
Beta Decay
The nuclear process during which a beta particle is emitted when a neutron changes to a proton (beta minus decay) or a proton changes to a neutron (beta plus decay).
Gamma Decay
The nuclear process during which gamma rays are emitted as nuclei transition from an excited state to lower states.
Half-Life (t1/2)
The time that it takes for half the radioactive atoms in a sample to decay.
What is Radiation?
Roentgen discovered the presence of a previously unknown type of ray, or energy, which he called x-rays.
Becquerel discovered that x-rays not only cause fluorescence, but may also be emitted during fluorescence.
Marie Curie discovered both polonium and radium and coined the term radioactivity.
Short-term rates of emission of radiation have been found to be stable, depending only on the kind and number of atoms present.
Kinds of Radiation
Alpha radiation: The nuclear process that emits alpha particles.
Beta minus radiation: The nuclear process during which a beta particle is emitted when a neutron changes to a proton.
Beta plus radiation: The nuclear process during which a beta particle is emitted when a proton changes to a neutron.
Gamma radiation: The nuclear process during which gamma rays are emitted as nuclei transition from an excited state to lower states.
Radioactive Decay Law
Naturally radioactive nuclei emit radiation at predictable rates.
The decay rate is proportional to the amount of original material present.
The factor λ is called the decay constant, with units of inverse time, such as s-1 or y-1.
The number of nuclei remaining at a certain time after an initial number of nuclei begin to decay can be found from N = N0e-λΔt.
Relating half-life to the decay constant: t1/2 = 0.693 / λ.
Radiometric Dating
Radiometric dating compares the parent and daughter nuclides from a naturally occurring decay event.
By comparing the present ratio of daughter to parent nuclides with the rate that nuclides should change, scientists can estimate the time at which the object was formed.
Assumptions include constant half-life, activity of the nuclide at A0, and no contamination or escape of nuclides.
Questions for Students
Define radiation and radioactivity. How are they related?
Describe the discoveries of Roentgen, Becquerel, and Marie Curie in the context of radiation.
Explain the differences between alpha, beta, and gamma radiation.
What is the radioactive decay law and how is it used to determine the half-life of a substance?
How is radiometric dating used to estimate the age of an object?