RADIATION AND ATOM

RATIONALE

Atoms are far too small to see directly, even with the most powerful optical microscopes. It is through the "language of light" that we communicate with the world of the atom. This chapter will introduce you to the rudiments of this language.

1. THE ATOM

Atoms are mostly empty space, with a dense nucleus containing:

  • Protons (Z) → determines the element

  • Neutrons (A − Z) → adds mass

👉 Mass number (A) = protons + neutrons

Electrons orbit in shells:

  • Max electrons per shell = 2n²

  • Valence shell → chemical properties

  • Inner shells → involved in X-ray production

⚛ Fundamental Particles (Quick View)

Particle

Charge

Key Idea

Proton

+1

In nucleus

Neutron

0

In nucleus

Electron

−1

Orbiting

Positron

+1

Anti-electron

Alpha

+2

Heavy, helium nucleus

🔗 Binding Energy (VERY TESTABLE)

  • Binding energy = energy needed to remove particles

  • Nuclear binding energy >> electron binding energy (huge difference)

Key concepts:

  • Ionization → electron removed → ion pair formed

  • Excitation → electron moves to higher shell (not removed)

📌 Trend:

  • K-shell > L-shell > M-shell (inner = stronger binding)

🌊 2. WAVE–PARTICLE DUALITY

Radiation behaves as both:

  • Particle (photon)

  • Wave (electromagnetic)

Core Equations (MEMORIZE)

Energy–mass:
E=mc2E = mc^2E=mc2

Photon energy:
E=hfE = hfE=hf

Wave relationship:
c=λfc = \lambda fc=λf

💡 High yield:

  • ↑ Frequency → ↑ Energy

  • ↓ Wavelength → ↑ Energy

☢ 3. RADIATION

Radiation = energy traveling as waves or particles

Two Types:

1. Non-Ionizing

  • Not strong enough to remove electrons

  • Examples:

    • Radio waves

    • Microwaves

    • Infrared

    • Visible light

    • Most UV

👉 Causes vibration, NOT ionization

2. Ionizing (VERY IMPORTANT)

  • Has enough energy to remove electrons

  • Creates ions

Examples:

  • X-rays

  • Gamma rays

  • Alpha, beta, neutrons

☢ 4. TYPES OF IONIZING RADIATION

🔹 Particle Radiation

Alpha (α)

  • Heavy, + charge

  • ❌ Cannot penetrate skin

  • ⚠ Dangerous if inhaled/ingested

Beta (β)

  • Light, − charge

  • ✔ Penetrates skin slightly

  • Shield: aluminum

Neutron

  • No charge

  • ✔ Highly penetrating

  • Shield: hydrogen materials (water, plastic)

🔹 Electromagnetic Radiation

Gamma Rays

  • From nucleus

  • Highest energy

  • Deep penetration

X-rays

  • Outside nucleus

  • Used in imaging

Ultraviolet

  • Mostly non-ionizing

  • Shorter wavelengths can be ionizing

📏 5. INVERSE SQUARE LAW (SUPER HIGH YIELD)

I∝1r2I \propto \frac{1}{r^2}I∝r21​

Meaning:

  • If distance doubles → intensity becomes 1/4

  • If distance triples → intensity becomes 1/9

📌 Used in:

  • Radiation protection

  • Distance safety

📊 6. RADIATION MEASUREMENT

We measure:

  • Source strength

  • Energy

  • Environmental level

  • Dose (most important clinically)

📏 7. RADIOLOGIC UNITS (BOARD FAVORITE)

Unit

Measures

Key Idea

Roentgen (R)

Exposure

Air ionization

Rad

Absorbed dose

Energy absorbed

Rem

Biological effect

Adjusted for damage

Curie (Ci)

Radioactivity

Decay rate

eV

Energy

Photon energy

📌 Shortcut (for X-rays ONLY):
👉 1 R ≈ 1 rad ≈ 1 rem

⚖ 8. PRACTICAL DOSE UNITS

Absorbed Dose

  • Unit: Gray (Gy)

  • 1 Gy = 100 rad

  • Measures energy deposited

Equivalent Dose

  • Unit: Sievert (Sv)

  • Accounts for radiation type

Formula:

  • Dose × radiation weighting factor

📌 Example:

  • Alpha = more damaging than X-ray

Effective Dose

  • Also in Sievert (Sv)

  • Accounts for organ sensitivity

Formula idea:

  • Equivalent dose × tissue weighting factor

👉 Gives overall risk to the body

🔥 FINAL HIGH-YIELD TAKEAWAYS

  • Ionization = electron removal

  • Alpha = dangerous inside, not outside

  • Gamma/X-ray = highly penetrating

  • Inverse square law = distance is protection

  • Gy = absorbed dose, Sv = biological effect