How Radioactive Is Your Banana?

Abstract

This exercise uses a banana to illustrate the level of radioactivity (in this case, from 40K) in an everyday object.

Periodic Table Target: A Game That Introduces the Biological Significance of Chemical Element Periodicity

“…Incorporating these topics increases students' interest and engages them in the lesson (1,3). so that similar physical and chemical properties and periodic trends may be explored.…”

How Radioactive Are You?

“…A 70-kg person's body contains 140 g of potassium (interestingly, the sodium content is less: 100 g)( 2). Hence, a person's body contains approximately 0.0164 g of 40 K, which is 230 times more than in a big banana (1). Thus, the activity of a body will be 230 × 18.4 ≈ 4230 Bq, and during one year, there will occur about 1.33 × 10 11 (130 billion!)…”

“…In the October 2004 issue, David W. Ball published a paper entitled "How Radioactive Is Your Banana?" (1). He calculated that the activity of a big banana equals 18.4 Bq (decays per second).…”

“…Potassium, one of the elements most abundant in the Earth crust (2.1%), has three isotopes (1,2): The relative atomic mass of natural potassium A r = 39.0983. One of its isotopes, 40 K, is radioactive with half-life of t 1/2 = 1.26 × 10 9 y.…”