Download Alpha particle – a positively charged atom that is released in the

VOCABULARY TERMS
CHAPTER 4 ( SEC. 1) AND CHAPTER 9
Directions: Read Chapter 4 (section 1) and Chapter 9. Copy these terms into your
notebook. Do not write on this sheet.
1. Alpha particle – a positively charged atom that is released in the disintegration of
radioactive elements and that consists of two protons and two neutrons
2. Background radiation – the nuclear radiation that arises naturally from cosmic rays
and from radioactive isotopes in the soil and air
3. Beta particle – a charged electron emitted during certain types of radioactive decay,
such as beta decay
4. Critical mass – the minimum mass of a fissionable isotope that provides the number
Of neutrons needed to sustain a chain reaction
5. Electron – a subatomic particle that has a negative electric charge
6. Fission – the process by which a nucleus splits into two or more fragments and
releases neutrons and energy
7. Fusion – the process in which light nuclei combine at extremely high temperatures,
forming heavier nuclei and releasing energy
8. Gamma ray – the high-energy photon emitted by a nucleus during fission and
radioactive decay
9. Half-life – the time required for half of a sample of a radioactive substance to
disintegrate by radioactive decay or natural processes
10. Neutron – a subatomic particle that has no charge and that is found in the nucleus of
an atom
11. Nuclear chain reaction – a continuous series of nuclear fission reactions
12. Nuclear radiation – the particles that are released from the nucleus during
Radioactive decay, such as neutrons, electrons, and photons
13. Nucleus – an atom’s central region, which is made up of protons and neutrons
14. Orbital – a region in an atom where there is a high probability of finding electrons
15. Proton – a subatomic particle that has a positive charge and that is found in the
nucleus of an atom
16. Radioactivity – the process by which an unstable nucleus emits one or more particles
or energy in the form of electromagnetic radiation
17. Radioactive tracer – a radioactive material that is added to a substance so that its
distribution can be detected later
18. Rem – the quantity of ionizing radiation that does as much damage to human tissue
as 1 roentgen of high voltage X rays does
19. Valence electron – an electron that is found in the outermost shell of an atom and
that determines the atom’s chemical properties