RadToolz Practical Exercise #1 - Solution

Practical Exercise #1 dealt with ionization type smoke detectors that contain about 1 microcurie (μCi) of the radioactive isotope Am-241 in the form of americium oxide (AmO2). You were asked to calculate the following:

1. How much does the Am-241 weigh in the smoke detector?
2. How much does the AmO2 weigh?

Here's how we did it using RadToolz in Excel(R):

Given

Isotope is Am-241
Activity is 1 μCi or 1E-06 Ci
Chemical form is AmO2
Atomic Mass of Am-241 is 241.056829 grams/mole
Atomic Mass of O is 15.9994 grams/mole

Calculate

1. Weight of 1E-06 Ci of Am-241 in grams

Divide the activity by the RadToolz function for specific activity with Am-241 as the input. Enter the following into an empty cell:

=0.000001/SpA("AM-241")

The result is 2.9163E-07 grams.

2. Weight of 1E-06 Ci of americium oxide in grams

Add the atomic masses of americium-241 and 2 oxygen. This is the gram molecular weight for americium oxide. Then multiply by the ratio of the mass of Am-241 from above and the atomic mass of americum-241. This is the moles of Am0241. Enter the following into an empty cell:

=(241.056829+(2*15.9994))*(0.00000029163/241.056829)

The result is 3.30342E-07 grams, or about one-one-thousand-five-hundredth the mass of a grain of sand. In other words, it would take about 1,500 times that amount of americium oxide to equal the mass of a grain of sand!