Smoke detectors use a very small quantity of the element americium-241 - Leaving Cert Physics - Question 12(d) - 2009

Alpha particles are produced during the radioactive decay of americium-241. This process occurs as americium-241 is unstable and undergoes alpha decay, disintegrating to achieve a more stable state. The equation for this decay can be represented as:

$_{95}^{241}Am \rightarrow _{93}^{237}Np + _{2}^{4}He + \text{energy}$

Here, americium-241 disintegrates, emitting an alpha particle (helium nucleus) in the process.

Alpha particles have a very short range and are poor penetrators, meaning they cannot penetrate human skin. When trapped within the smoke detector, they do not escape into the environment, which minimizes exposure. Additionally, any potential risk is neutralized as they can recombine to form helium.

The half-life ($T_{1/2}$) can be calculated using the decay constant ($\lambda$):

$T_{1/2} = \frac{0.693}{\lambda} \quad \text{where} \quad \lambda = 5.1 \times 10^{-11} s^{-1}$

Substituting the values:

$T_{1/2} = \frac{0.693}{5.1 \times 10^{-11}} \approx 1.36 \times 10^{10} s$

To convert seconds into years:

$T_{1/2} \approx \frac{1.36 \times 10^{10} s}{3.1536 \times 10^7 s/year} \approx 430.6 years$

Americium-241 does not exist naturally because it is not a member of the decay series of isotopes in nature. Its existence is synthetic and artificial, as it was produced during the Manhattan Project, and it has a relatively short half-life compared to the age of the universe, which implies it does not persist in natural settings.