Problem 69 - Chemistry Matter and Change

Question

Smoke Detectors Americium-241, a radioisotope used in smoke detectors, is produced by bombarding plutonium-238 with neutrons to produce plutonium-240, which is bombarded with neutrons to produce plutonium-241. The plutonium-241 decays to americium-241. Write the balanced nuclear equations for each reaction.

Step-by-Step Solution

Answer

The balanced nuclear equations for the production of Americium-241 are as follows: 1. \( {}^{238}Pu + {}^{1}n \rightarrow {}^{240}Pu \) 2. \( {}^{240}Pu + {}^{1}n \rightarrow {}^{241}Pu \) 3. \( {}^{241}Pu \rightarrow {}^{241}Am + β^{-} \)

Step 1: Reaction 1: Bombardment of Plutonium-238 with neutrons to produce Plutonium-240

In this reaction, we have Plutonium-238 and a neutron as the reactants, and Plutonium-240 as the product. To balance this equation, we can represent plutonium with the symbol \(Pu\) and the neutron with the symbol \(n\). The equation is: \[{}^{238}Pu + {}^{1}n \rightarrow {}^{240}Pu\] The mass numbers are conserved (238 + 1 = 240).

Step 2: Reaction 2: Bombardment of Plutonium-240 with neutrons to produce Plutonium-241

In this reaction, we have Plutonium-240 and a neutron as the reactants, and Plutonium-241 as the product. To balance this equation, we can represent plutonium with the symbol \(Pu\) and the neutron with the symbol \(n\). The equation is: \[{}^{240}Pu + {}^{1}n \rightarrow {}^{241}Pu\] The mass numbers are conserved (240 + 1 = 241).

Step 3: Reaction 3: Decay of Plutonium-241 to produce Americium-241

In this reaction, we have Plutonium-241 as the reactant and Americium-241 as the product. Plutonium-241 decays through beta decay, in which a neutron is converted into a proton, releasing an electron (also known as a beta particle, represented by the symbol \(β^{-}\)). To balance this equation, we represent plutonium with the symbol \(Pu\) and americium with the symbol \(Am\). The equation is: \[{}^{241}Pu \rightarrow {}^{241}Am + β^{-}\] The mass numbers are conserved (241 = 241), and the atomic numbers are also conserved because a neutron is converted into a proton, increasing the atomic number by 1.

Key Concepts

Radioisotopes

Radioisotopes are atoms that have an unstable combination of protons and neutrons. This instability causes them to decay over time, releasing radiation in the form of particles or energy. These are not just theoretical; they play practical roles in our daily life.

• The term "radioisotope" combines "radioactive" and "isotope," meaning isotopes that are radioactive.
• Each element can have multiple isotopes. For example, carbon has three naturally occurring isotopes: Carbon-12, Carbon-13, and the radioactive Carbon-14.
• Their decay process leads to the emission of radiation, such as alpha particles, beta particles, or gamma rays.

A great example of a useful radioisotope is Americium-241, which is cleverly utilized in smoke detectors. The Americium-241 decay provides a steady source of alpha particles in smoke detectors that detect smoke particles by triggering an alarm. This is a practical application of radioisotopes, demonstrating how the decay of unstable atoms can be harnessed to serve everyday safety needs.

Beta Decay

Beta decay is a type of radioactive decay where an unstable nucleus transforms by converting a neutron into a proton. This transformation results in the emission of a beta particle, which is, in essence, an electron or a positron.

• In beta minus (\(β^{-}\)) decay, a neutron is converted into a proton, and the emitted beta particle is an electron.
• This process increases the atomic number by 1, as a neutron turns into an additional proton in the nucleus.
• Common examples of beta decay can be seen when isotopes of elements like Carbon-14 and Plutonium-241 decay.
• The equation for beta decay is often written as: \[n ightarrow p + β^{-} + \bar{ν_e}\]
  where \(\bar{ν_e}\) is an antineutrino, which is also emitted during the decay.

Beta decay is an essential concept for understanding processes like the decay of Plutonium-241 to Americium-241, crucial for the production of radioisotopes used in various applications, including smoke detectors.

Neutron Bombardment

Neutron bombardment is a process where atomic nuclei are targeted and penetrated by neutrons. This results in the formation of a new isotope or even a different element.

• This method is widely used in nuclear reactors and can transmute one element into another or create new isotopes.
• Neutron bombardment is fundamental for nuclear synthesis, as seen in our earlier example where Plutonium-238 is bombarded with neutrons to produce Plutonium-240.
• When a neutron collides with a nucleus, it does not possess a charge, making it ideal for penetrating the electron cloud surrounding the nucleus without being repelled.
• This technique can create isotopes that may undergo further reactions, such as decay or further bombardment, as witnessed in subsequent transformations of Plutonium isotopes.

By using neutron bombardment, scientists can create specific isotopes with useful properties, such as those that fuel plutonium-based energy sources or radioactive isotopes like Americium-241 used in smoke detectors. This showcases the versatility and power of neutron bombardment in modern scientific and practical applications.