AIIMS 2007 Physics Radioactivity Assertion Reason Question

To analyze the given question, we need to understand both the assertion and the reason in the context of nuclear physics, specifically focusing on radioactivity and its biological impacts.

Explanation of the Assertion and Reason

Assertion: It states that strontium-90 ($^{90}\text{Sr}$), a radioactive isotope released from nuclear fallout, can accumulate in human bones through the consumption of milk. This is true because strontium is chemically similar to calcium, which is a major component of bone. As a result, when humans consume milk (which contains calcium), they may inadvertently also ingest strontium-90, leading to its deposition in the bones. The impairment of red blood cell production results from damage to the bone marrow, where blood cells are produced.

Reason: The reason provided states that the beta particles ($\beta$-particles) emitted during the decay of $^{90}\text{Sr}$ can damage the bone marrow. This is also true. When $^{90}\text{Sr}$ decays, it emits beta particles, which are high-energy, high-speed electrons or positrons. These particles have sufficient energy to cause ionization in nearby biological tissues, including the sensitive cells in the bone marrow responsible for producing red blood cells. This damage can lead to various hematological disorders, including anemia.

Why the Correct Answer is A

Both the assertion and the reason are true, and the reason correctly explains the assertion. The radioactive decay of $^{90}\text{Sr}$ indeed leads to the emission of beta particles that damage the bone marrow, which in turn impairs the production of red blood cells. Thus, option A is correct because:

• The mechanism (beta particle emission) is indeed responsible for the effect (impairment of red blood cell production).
• Both statements accurately reflect scientific understanding.

Clarification of Incorrect Options

• Option B: This option claims both statements are true, but the reason does not explain the assertion. This is incorrect because the reason does explain the assertion, as discussed.

• Option C: This option states the assertion is true but the reason is false. This is incorrect because both the assertion and reason are true.

• Option D: This option claims both the assertion and reason are false. This is incorrect because both statements are true based on established scientific knowledge regarding $^{90}\text{Sr}$, its biological effects, and the mechanism of beta decay.

Relevant Concepts and Formulas

While there are no direct formulas needed for this question, understanding the decay process is crucial. The decay of $^{90}\text{Sr}$ can be represented as:

$$^{90}\text{Sr} \rightarrow ^{90}\text{Y} + \beta^-$$

where $^{90}\text{Y}$ is the daughter isotope, and $\beta^-$ represents a beta particle (electron) being emitted.

In summary, the correct answer is A because both the assertion and reason are true and the reason correctly explains the assertion. Understanding the biochemical and physical behavior of radioactive isotopes in biological systems is essential for comprehending the implications of nuclear fallout on human health.