Problem 28 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

If a radioactive element is placed in an evacuated container, its rate of disintegration (a) will be increased (b) will be decreased (c) will change very slightly (d) will remain unchanged

Step-by-Step Solution

Answer

The rate of disintegration of a radioactive element will remain unchanged when placed in an evacuated container.

Step 1: Understanding Radioactive Decay

The rate of radioactive disintegration (decay) of an element is determined by the properties of the element itself, such as the half-life, and is independent of environmental factors like air pressure or the presence of other substances.

Step 2: Analyzing the Impact of an Evacuated Container

Placing a radioactive element in an evacuated container means that the element is in a vacuum. A vacuum has no effect on the nuclear processes that cause radioactive decay. Thus, the rate of disintegration will remain the same.

Step 3: Selecting the Correct Answer

Since the rate of radioactive disintegration is unaffected by external physical conditions such as being in an evacuated container, the correct answer is that the rate of disintegration will remain unchanged.

Key Concepts

Radioactive Disintegration

Radioactive disintegration, or decay, is a spontaneous process where unstable atomic nuclei lose energy by emitting radiation. This transformation leads to the conversion of one element into another, a process fundamental to radioactive substances.

At its core, radioactive decay is driven by the quest for stability. Unstable isotopes, or nuclides, that have an imbalance in their number of protons and neutrons, seek a more balanced state. This can result in the emission of alpha particles (two protons and two neutrons), beta particles (high-energy electrons or positrons), or gamma rays (high-energy electromagnetic radiation).

• Alpha decay: Loss of an alpha particle from the nucleus.
• Beta decay: A neutron changes into a proton with the emission of an electron or positron.
• Gamma decay: Release of energy from the nucleus without changing the number of protons or neutrons.

The exercise at hand demonstrates that the rate of radioactive disintegration is intrinsic to the isotope and remains constant over time, regardless of environmental changes such as being placed in an evacuated container.

Half-Life

The half-life of a radioactive element is the time required for half the atoms of the radioactive isotope in a sample to undergo decay. It is a characteristic constant for each isotope, reflecting how quickly it transforms into a more stable form.

Understanding half-life is crucial for grasping the longevity and behavior of radioactive substances. If a radioactive isotope has a half-life of one year, then after one year, only half of the original quantity of the isotope will remain; after two years, only a quarter will be left, and so on. The concept of half-life helps us to answer many practical questions, from determining ages of archaeological finds through carbon dating to managing nuclear waste. The step-by-step solution reinforces that half-life is unaffected by external factors, much like the overall rate of disintegration.

Nuclear Processes

Nuclear processes are the actions that occur within the nucleus of an atom and include a broad range of phenomena, from radioactive decay to nuclear fission and fusion. The stability of an element's nucleus determines its susceptibility to undergo these processes and dictates whether it will emit radiation as a form of decay.

For example:

• Nuclear fission: Splitting of a heavy nucleus into lighter nuclei, often releasing a significant amount of energy, as in nuclear reactors or atomic bombs.
• Nuclear fusion: The combining of light nuclei to form heavier ones, releasing tremendous energy, which powers the stars, including our sun.

In our exercise context, the evacuated container has no bearing on these nuclear processes because they are only affected by the forces within the atomic nucleus itself, and not by environmental conditions such as air pressure or temperature. This reinforces the idea that nuclear processes and the rates of nuclear reactions are inherent to the material and its structure.