Problem 76 - Master Resource Book in JEE Main Physics

Question

Assertion \({ }_{38} \mathrm{Sr}^{90}\) from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells. Reason The energy \(\beta\)-particle emitted in the decay of \({ }^{90} \mathrm{Sr}\) damage to bone marrow.

Step-by-Step Solution

Answer

Both Assertion and Reason are true, and the Reason explains the Assertion.

Step 1: Understanding Strontium-90

Strontium-90 ( { }_{38} ext{Sr}^{90} ) is a radioactive isotope that can be released into the environment during nuclear fallout. It has a half-life of approximately 29 years and can mimic calcium, which means it can be absorbed by bones.

Step 2: Analyzing the Assertion

The assertion states that { }_{38} ext{Sr}^{90} from nuclear fallout ends up in human bones via milk consumption and impairs red blood cell production. Since { }^{90} ext{Sr} is chemically similar to calcium, it can replace calcium in bones when consumed through contaminated milk.

Step 3: Identifying the Reason

The reason explains that the \(\beta\)-particles emitted from the decay of { }^{90} ext{Sr} cause damage to bone marrow, which can indeed impair red blood cell production. This is because bone marrow is responsible for producing blood cells, and radiation can damage its ability to do so.

Step 4: Evaluating the Link Between Assertion and Reason

The reason logically supports the assertion; if { }^{90} ext{Sr} deposits in bone and emits \(\beta\)-particles, it can damage bone marrow, leading to reduced red blood cell production as claimed in the assertion. Both the assertion and the reason are correct, and the reason explains the assertion.

Key Concepts

Radioactive Isotopes in Nuclear Fallout

During a nuclear event, such as a bomb explosion, various radioactive isotopes are released into the environment. These isotopes are tiny, charged particles that can travel long distances from the site of detonation. One such harmful isotope is Strontium-90, denoted as \(_{38} \text{Sr}^{90}\). It is crucial to understand that even if we are far from the explosion, we can still be affected by these particles.
Radioactive fallout tends to settle on the ground and surface water, contaminating everything in its path. \(_{38} \text{Sr}^{90}\), with its 29-year half-life, is particularly concerning because it can persist in the environment for decades.

• It can be absorbed by plants we then consume or feed to livestock, entering the food chain.
• Continual accumulation in the environment means long-term exposure risks.

Beta Decay and Bone Marrow Damage

Strontium-90 undergoes a radioactive process called beta decay, wherein it loses energy by releasing beta particles. These are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei. Strontium-90, by mimicking calcium, is easily absorbed into bones, substituting for calcium in the bone structure.
When it decays, the beta particles can cause significant damage to bone tissue, including the bone marrow.
Bone marrow is where red and white blood cells are formed. Damage here can disrupt normal blood cell production, leading to several health issues.

• The high-energy emissions can directly harm the cells or DNA in the bone marrow.
• Such damage can increase the risk of developing blood disorders or even leukemia.

Impairment of Red Blood Cell Production

Healthy red blood cell production is essential for carrying oxygen throughout the body. When Strontium-90 causes damage, it disrupts this vital process, leading to a condition called anemia. Anemia results in symptoms like fatigue, weakness, and paleness because tissues and organs get less oxygen.
The beta particles emitted during decay target the bone marrow cells that produce blood cells.
Damage here means:

• Fewer red blood cells get produced, which affects oxygen transport.
• There can be an increased susceptibility to infections due to impaired white blood cell production.

This impairment underscores the extended health risks posed by radioactive isotopes in fallout.

Contamination through Milk Consumption

Milk is a critical source of calcium for both children and adults. Unfortunately, it can also become a pathway for Strontium-90 to enter the human body. After nuclear fallout, \(_{38} \text{Sr}^{90}\) settles on grass and other plants. Cows and other milk-producing animals eat this contaminated fodder. Over time, Strontium-90 accumulates in their bodies and is subsequently excreted in the milk they produce.
This means that consuming such milk can lead to ingestion of Strontium-90, which then deposits into the human bone.

• Once it is in the body, it mimics calcium and becomes part of the bone tissue.
• This poses immediate and long-term health risks, especially for growing children whose bone development is essential for healthy growth.

Avoiding contaminated milk sources post-fallout is critical in mitigating exposure to this hazardous isotope.