Problem 50 - Chemistry and Chemical Reactivity

Question

There are two isotopes of americium, both with half-lives sufficiently long to allow the handling of large quantities. Americium-241, with a half-life of 432 years, is an \(\alpha\) emitter used in smoke detectors. The isotope is formed from \(^{239} \mathrm{Pu}\) by absorption of two neutrons followed by emission of a \(\beta\) particle. Write a balanced equation for this process.

Step-by-Step Solution

Answer

The balanced equation is: \[ ^{239}_{94} \text{Pu} + 2(^{1}_{0} n) \rightarrow ^{241}_{95} \text{Am} + ^{0}_{-1} \beta \]

Step 1: Understand the Reaction

Americium-241 is formed from plutonium-239 by absorbing two neutrons and then emitting a beta particle. We need to represent how these transformations occur in a nuclear equation.

Step 2: Initial Nucleus Formation

Start with the plutonium-239 nucleus: \[ ^{239}_{94} \text{Pu} \]Absorb two neutrons: \[ n + n \] A neutron has a mass number of 1 and an atomic number of 0: \[ ^1_{0} n \] Therefore, absorbing two neutrons does not change the atomic number but increases the mass number by 2. This forms:\[ ^{241}_{94} \text{Pu} \]

Step 3: Beta Decay

In beta decay, a neutron is converted into a proton, increasing the atomic number by 1 while the mass number stays the same. The beta particle is an electron: \[ ^0_{-1} \beta \]Thus, one of the reactions for this step is: \[ ^{241}_{94} \text{Pu} \rightarrow ^{241}_{95} \text{Am} + ^{0}_{-1} \beta \]

Step 4: Combine Reactions

Combine the initial formation and beta decay to write the full balanced equation:\[ ^{239}_{94} \text{Pu} + 2(^{1}_{0} n) \rightarrow ^{241}_{94} \text{Pu} \xrightarrow[\beta]{\text{decay}} ^{241}_{95} \text{Am} + ^{0}_{-1} \beta \]

Step 5: Final Balanced Equation

The complete balanced nuclear equation, representing the formation of Americium-241 from Plutonium-239 through neutron absorption and beta decay, is:\[ ^{239}_{94} \text{Pu} + 2(^{1}_{0} n) \rightarrow ^{241}_{95} \text{Am} + ^{0}_{-1} \beta \]

Key Concepts

Isotope Decay

Isotope decay is a process all about change. Nuclear isotopes, versions of elements with different numbers of neutrons, undergo transformations to become more stable. This is often achieved through processes like alpha decay, beta decay, and gamma decay. As isotopes decay, they transform into different elements or isotopes by losing particles from their nuclei. This change can be mapped through something called a nuclear equation. A wonderful example is the decay of Americium-241, which we can break down step by step. Initially formed from Plutonium-239, Americium-241 undergoes decay in a sequence. This leads to the emission of different particles. Over time, through these sequences of decay, isotopes may completely transform into a more stable form or another element. This gradual transformation is the essence of isotope decay.

Beta Decay

Beta decay is a fascinating type of radioactive decay where a beta particle is emitted. Beta particles can be electrons or positrons. In this process, a neutron in the nucleus is transformed into a proton, accompanied by the emission of a beta particle and a neutrino. Let's take Plutonium-239 as an example. When it absorbs neutrons, it becomes Plutonium-241, which then undergoes beta decay. One neutron in the Plutonium-241 nucleus changes into a proton. This increase in atomic number transforms the atom into Americium-241. The key characteristic of beta decay is the increase of the atomic number by one unit. This alteration results in a different element creation while the mass number remains constant. It showcases how energy within an atom’s nucleus can lead to remarkable transformations.

Neutron Absorption

Neutron absorption is an essential process in nuclear reactions. When a nucleus captures one or more neutrons, it often changes to a more massive isotope of the same element. This is because neutrons add to the mass number but do not affect the atomic number. In our earlier example, two neutrons are absorbed by Plutonium-239. This reaction increases its mass number from 239 to 241, resulting in Plutonium-241. The original plutonium atom remains the same element since the atomic number does not change during neutron absorption. This absorption is crucial in various applications like nuclear reactors where controlling the number of neutrons can manage chain reactions. Neutron absorption can lead to subsequent decay processes such as beta decay, showcasing the interconnected nature of nuclear transformations.