Glossary of "Biology (3rd ed.)" by Hardin & Bajema (1978)
- a helium nucleus emitted in radioactive decay.
Glossary of "Environmental Science: Earth as a Living Planet (2nd ed.)" by Botkin & Keller (1998)
- One of the major types of nuclear radiation, consisting of two protons and two neutrons (a helium nucleus).
- Hardin, G. & Bajema, C. 1978. Biology, its Principles and Implications, third edition. -x + 790 pp. W. H. Freeman and Company, San Francisco.
- Botkin, D. B. & Keller, E. A. 1998. Environmental Science: Earth as a Living Planet, 2nd ed. -xxxxii + 649 pp. John Wiley & Sons, Inc., New York.