Radioactive Banana Math

Quote of the Day

I never did a day's work in my life. It was all fun.

— Thomas Edison

Introduction

I have been reading about the hazards of space travel to Mars. During this reading, I occasionally see references to space radiation hazards in terms of Banana Equivalent Dose. I find this a strange unit. Then today I read a blog post by Anne Marie Helmenstine that discussed how bananas are slightly radioactive. I liked her discussion and I thought I would go through the math here.

Background

Why are Bananas Radioactive?

Bananas are radioactive because they contain potassium and potassium has an isotope (⁴⁰K) that is radioactive. This same isotope is present in humans, which means that humans are also slightly radioactive.

Banana Data

Figure 2 shows the data that Google puts out when you type in "Amount of Potassium in a Banana".

Figure 2: Banana Characteristics from Google Search.

While there is a lot of data here, I will only use the amount of potassium (422 mg) in a typical banana (118 gm) to estimate the rate of radioactive decay.

Measuring Banana Radiation

Here is a Youtube video of a person measuring the radiation from a banana. You can hear the sound of the Geiger counter. Ignore his comments about bananas being dangerous because of radiation levels. We are always exposed to low-level radiation.

Analysis

Figure 3 shows my quick analysis of Anne's results.

Figure 3: My Analysis of the Radiation Emission from a Banana.

Conclusion

Numbers all confirmed. I also read that Brazil nuts are relatively radioactive.