Atomic Particles, Radiation & Nuclear Reactions – Comprehensive Study Notes

Major Atomic Particles – Quick Review

• Three fundamental particles discussed:
  • Proton (p⁺)
  • Neutron (n⁰)
  • Electron (e⁻)
• Everything that follows in the lecture is built on these three entities.

Beyond the Big Three – Hadrons, Leptons, Baryons, Quarks, Gluons

• Two grand families (test will expect only definitions):
  • Hadrons (“heavy”)
  • Composite particles made of quarks.
  • Sub-classes: baryons (e.g.
    protons, neutrons – 3 quarks) & mesons (quark + antiquark).
  • Leptons (“light/elementary”)
  • Cannot be broken down further in the Standard Model.
  • Includes electrons, muons, tau, neutrinos.
• Gluons
  • Exchange (force-carrier) particles that “glue” quarks together via the strong force.
  • Instructor anecdote: the whimsical name sparked a class contest to invent fake particles (e.g. “Pikachuon,” “Gokuon”) – these are fictional.
• Take-away for exam: know the definitions of hadron, lepton, baryon, quark, gluon; no deeper math required.

Core Properties Table (copy-worthy)

• Extra numeric tidbits:
  • m{\text{neutron}} \approx m{\text{proton}} + m_{\text{electron}} (by ~0.1%)
  • 1.6\times10^{-19}\,\text{C} absolute charge → simplified to +1, –1, 0 for chem notation.

Forces Operating Inside the Nucleus

• Electrostatic (Coulombic) Repulsion: F \propto \dfrac{q1q2}{r^2} — like charges repel (proton ↔ proton).
• Strong Nuclear Force (Binding Force):
  • Short-range, ~10^{-15}\,\text{m}.
  • Acts between p–p, n–n, p–n alike; always attractive.
  • No everyday analogue – unique to the nucleus.
• Role of Neutrons
  • Insert spacing (increase r) between protons → weaken Coulomb term while still participating in the strong force.
  • Too few neutrons → electrostatic repulsion wins (instability).
  • Too many neutrons → nucleus becomes overly massive; strong force cannot bind the excess → instability.

Radiation & the Drive Toward Stability

• Nature favors exothermic, lower-energy states.
• High-mass or unbalanced nuclei shed excess energy via radiation (particles/photons) until a stable n⁄p ratio is reached.
• “Heavy” = large Z (protons) and large N (neutrons).

Four Major Radiation Types (plus X-rays)

1. Alpha (α) Radiation

• Notation in text: α ; in equations: ^{4}_{2}He (helium nucleus).
• Properties
  • Mass = 4 AMU, charge = +2.
  • Low velocity ⇒ low KE despite high mass.
• Penetration / Hazard
  • Stopped by paper/skin; dangerous only if ingested (food, lungs).

2. Beta (β⁻) Radiation

• Neutron → proton + electron; electron ejected.
• Equation notation: ^{0}_{-1}e or \beta.
• Properties
  • Negligible mass, high velocity.
  • Charge = –1 ⇒ slowed by Coulomb attractions inside matter.
• Penetration
  • Passes through paper/wood, stopped by thin metal (Al).

3. Gamma (γ) Rays

• Pure electromagnetic energy, no mass, no charge.
• Notation in equations: γ (no isotope numbers).
• Very high E (higher than X-rays).
• Penetration
  • Passes through most materials; attenuated only by dense lead or several cm of concrete.
  • Primary health risk: deep tissue ionization → leukemia/cancers (Hulk fiction vs. reality).

4. Neutron Emission (n)

• Notation: ^{1}_{0}n.
• High mass and high velocity; neutral → no Coulomb slowing.
• Most penetrating / dangerous among listed particles.
• Practical role: triggers chain reactions in fission bombs & reactors.

5. X-Rays (for completeness)

• Same class as γ but lower energy; blocked by lead aprons in medical imaging.

Comparative Penetration Summary

Why Penetration Depends on KE and Charge

• KE = \tfrac{1}{2}mv^{2} — needs both mass and velocity.
• Charged particles lose KE via Coulombic interactions inside matter (ionization, excitation) → slow down.
• Neutral particles or photons have no such losses, so travel farther.

Nuclear Reactions Overview

1. Fission ("decay" ≈ decomposition)

• Large nucleus → smaller nuclei + particles + energy.
• Often spontaneous for very heavy isotopes or induced by neutron capture.

2. Fusion (synthesis)

• Small nuclei combine to form a larger one.
• Powers stars; requires extreme T/P to overcome Coulomb barrier.

Balancing Nuclear Equations – Rules & Examples

1. Conserve mass number (A) – sum of top numbers.
2. Conserve atomic number (Z) – sum of bottom numbers (protons).
3. Electrons are ignored (unless explicitly β in equation).

Simple Fusion Example

^{1}{1}H + ^{3}{1}H \;\longrightarrow\; ^{4}_{2}He

• A: 1+3=4 ✓
• Z: 1+1=2 ✓ (He)

Multi-step Fission/Decay Example

Given ^{238}_{92}U undergoes 2 α + 1 β⁻ decays, find product X.

Work:

• Subtract two α: A:238-2\times4=230, Z:92-2\times2=88
• Subtract one β⁻ (adds 1 to Z): Z=88+1=89
• Result: ^{230}_{89}Ac (actinium-230).

Fusion Puzzle Example (class exercise)

"What must merge with ^{12}{6}C to form ^{25}{12}Mg?"

• Need A: 25-12=13, Z: 12-6=6 ⇒ ^{13}_{6}C.

Average Atomic Mass – Weighted Mean of Isotopes

• General formula (n isotopes):
  \text{Avg Mass}=\sum{i=1}^{n} \left(\text{abundance}i \times \text{mass}_i\right)
  (abundance expressed as decimal, not %).

Worked Carbon Example (lecture numbers)

• Isotopes & abundances:
  • ^{12}C: 98.50 % (0.9850), mass = 11.998 AMU.
  • ^{14}C: 1.50 % (0.0150), mass = 13.987 AMU.
• Calculation:
  0.9850\times11.998 + 0.0150\times13.987 = 11.82 + 0.2098 \approx 12.03\,\text{AMU}
• Close to standard 12.011\,\text{AMU} (nat. abundances slightly different).
• Sig-fig protocol: multiply – look at total sig figs; add – align decimal places.

Ethical, Practical & Real-World Implications

• Radiation safety: alpha sources safe if sealed; beta/gamma require shielding; neutron/gamma relevant in nuclear reactors, space travel.
• Medical imaging: X-ray vs. γ-ray exposure, lead aprons, dose limits.
• Energy production vs. weapons: fission chain reactions, neutron moderation.
• Climate relevance: fusion research (ITER) aims for cleaner energy.

Instructor Anecdotes & Helpful Reminders

• You must memorize notation ^{4}{2}He, ^{0}{-1}e, ^{0}{0}\gamma, ^{1}{0}n for exam.
• Copy the properties table verbatim; simplest way to recall p/n/e data.
• Balancing nuclear equations is easier than redox: just add/subtract A & Z.
• Electrons do “weird things” – detailed electron behavior postponed to Chapter 5.
• Remember Dr. Checker’s maxim: “To prove something exists, you must first imagine it.” (Applies to theoretical physics & creative problem-solving.)