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Physics: Nuclear Physics - Nuclear Medicine, Cancer Treatment, and Nuclear Ethics

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Radioisotopes in Medicine: Radioisotopes are unstable isotopes that emit radiation. In nuclear medicine, tracers like Technetium-99m (99mTc^{99m}Tc) are injected into the body to visualize organs using gamma (γ\gamma) cameras.

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Radiotherapy (Cancer Treatment): High doses of ionizing radiation are used to destroy the DNA of cancer cells. This can be 'External Beam Radiation' (using γ\gamma-rays from Cobalt-60, 60Co^{60}Co) or 'Internal Radiation/Brachytherapy' (placing radioactive seeds inside the body).

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Half-Life (T1/2T_{1/2}): This is the time taken for the activity or the number of undecayed nuclei in a sample to reduce by half. For medical diagnostics, isotopes with short half-lives (e.g., hours) are preferred to limit radiation exposure to the patient.

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Ionizing Power vs. Penetrating Power: Alpha (α\alpha) particles have high ionizing power but low penetration; Gamma (γ\gamma) rays have low ionizing power but high penetration, making them suitable for external imaging and treatment.

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Nuclear Ethics and Safety: Ethical considerations include the 'ALARA' principle (As Low As Reasonably Achievable) regarding radiation dose, the environmental impact of radioactive waste disposal, and the risk-to-benefit ratio of treatment.

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Radioactive Waste: Medical nuclear waste must be stored in lead-lined containers until its activity reaches background levels before disposal.

📐Formulae

N=N0×(12)nN = N_0 \times (\frac{1}{2})^n

n=tT1/2n = \frac{t}{T_{1/2}}

A=A02nA = \frac{A_0}{2^n}

💡Examples

Problem 1:

A patient is injected with a dose of Iodine-131 (131I^{131}I) for thyroid treatment. If the initial activity is 400 MBq400 \text{ MBq} and the half-life of 131I^{131}I is 88 days, calculate the activity remaining in the patient after 2424 days.

Solution:

n=248=3n = \frac{24}{8} = 3 A=40023=4008=50 MBqA = \frac{400}{2^3} = \frac{400}{8} = 50 \text{ MBq}

Explanation:

First, we find the number of half-lives (nn) by dividing the total time (t=24t = 24) by the half-life (T1/2=8T_{1/2} = 8). Then, we divide the initial activity by 22 raised to the power of nn to find the remaining activity.

Problem 2:

Compare the use of Alpha (α\alpha) radiation and Gamma (γ\gamma) radiation in treating a deep-seated brain tumor.

Solution:

External γ\gamma radiation is used because α\alpha particles cannot penetrate the skull (blocked by paper/skin). However, if an α\alpha-emitter could be delivered directly into the tumor cells (Targeted Alpha Therapy), its high ionizing power would destroy the cancer cells with minimal damage to surrounding healthy tissue.

Explanation:

This involves understanding that penetration depth determines how radiation reaches a target, while ionizing power determines the level of cellular damage inflicted.

Problem 3:

Explain one ethical dilemma associated with the use of nuclear energy for medical purposes.

Solution:

One dilemma is the 'Waste Management' issue. While radioisotopes save lives, producing them generates radioactive waste that remains hazardous for years. Ethics dictates we must weigh the immediate benefit of saving a patient against the long-term environmental cost of storing toxic waste.

Explanation:

Nuclear ethics focuses on balancing human health benefits against environmental safety and potential risks to future generations.