Problem 45 - Chemistry The Molecular Science

Question

There are two isotopes of americium, both with half-lives sufficiently long to allow the handling of large quantities. Americium-241, an alpha emitter, has a half-life of 433 years; it is used in gauging the thickness of materials and in smoke detectors. This 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

Pu-239 absorbs 2 neutrons and undergoes beta decay to form Am-241.

Step 1: Identify the Initial Nucleus

The process begins with plutonium-239, denoted as \[ \text{Pu-239:} \quad ^{239}_{94} \text{Pu} \]

Step 2: Neutron Absorption

Two neutrons are absorbed by plutonium-239. Each neutron adds 1 to the mass number but does not change the atomic number. The resulting isotope is:\[ ^{239+2}_{94} \text{Pu} + 2 \times ^{1}_{0} n \rightarrow \, ^{241}_{94} \text{Pu} \]

Step 3: Beta Decay

A beta particle \((\beta^-)\) is emitted. This converts a neutron to a proton, increasing the atomic number by 1:\[ ^{241}_{94} \text{Pu} \rightarrow \, ^{241}_{95} \text{Am} + \beta^- \]

Step 4: Write the Balanced Equation

Combine the neutron absorption and beta decay to write the overall balanced equation:\[ ^{239}_{94} \text{Pu} + 2 \times ^{1}_{0} n \rightarrow \, ^{241}_{95} \text{Am} + \beta^- \]

Key Concepts

Americium-241

Americium-241 (\(^{241}_{95}\text{Am}\)) is a radioactive isotope of the element americium. Known for its alpha particle emission, it has a relatively long half-life of 433 years.
This attribute makes it particularly useful in applications where longevity is an advantage.
One of the most common uses of Americium-241 is in smoke detectors.

• It ionizes air particles, allowing the detector to sense smoke through a change in electrical conductivity.
• It's also used industrially to gauge the thickness of materials by measuring how much radiation passes through them.

It's important to handle Americium-241 carefully, given its radioactivity. However, it safely remains in low quantities in household devices due to its long half-life minimizing the risk of decay and subsequent radiation exposure.

Beta Decay

Beta decay is one of the radioactive decay processes where a beta particle is emitted from an atomic nucleus. In the case of beta-minus \((\beta^-)\) decay, a neutron is converted into a proton within the nucleus, releasing an electron (the beta particle) and an antineutrino.
This process increases the atomic number of the element.

• For instance, when \(^{241}_{94}\text{Pu}\) undergoes beta decay, it transforms into \(^{241}_{95}\text{Am}\)
• The neutron-to-proton conversion results in the formation of a new element with a higher atomic number on the periodic table.

Beta decay alters the nature of the element, thus making it a critical process in nuclear chemistry and transmutation of elements.

Neutron Absorption

Neutron absorption is a nuclear reaction where an atomic nucleus captures a neutron. This process leads to the formation of an isotope.
When plutonium-239 absorbs two neutrons, it becomes plutonium-241 without changing its element identity, but increases its total mass number.

• The neutrons added in this process do not alter the atomic number but increase the mass number, transitioning it to a higher isotope.
• In many nuclear applications, neutron absorption is crucial for isotopic adjustment, which can alter nuclear properties like stability and decay rates.

This process is essential in nuclear reactors and atomic synthesis, highlighting its importance in understanding nuclear reactions like the formation of Americium.

Isotopes

Isotopes are variants of a particular chemical element that share the same number of protons but have different numbers of neutrons.
They have identical atomic numbers but distinct mass numbers, which differentiate them.

• Americium-241 and plutonium-239 are examples of isotopes with different neutron counts.
• Each isotope presents unique properties, which can be exploited in various industrial and scientific applications.

The concept of isotopes is central to nuclear chemistry as it explains variations in nuclear stability and radioactivity. Understanding isotopes allows scientists to predict the behavior of elements under various nuclear reactions, helping in applications ranging from medicine to energy production.