Mnemonics: Nuclei | Physics Class 12 - NEET PDF Download

Constituents of the Nucleus

Types: Protons, Neutrons

Mnemonic: "Priya ​Negotiates "

Breakdown:

• Priya - Protons
• Negotiates - Neutrons

The nucleus of an atom is made up of two types of particles:

• Protons are positively charged particles that determine the atomic number and identity of an element.

• Neutrons are neutral particles that add mass to the nucleus and help stabilize it by reducing repulsive forces between protons.

Together, protons and neutrons are called nucleons, and they are held together by strong nuclear forces within the nucleus.

Nuclear Properties

Types: Mass Number, Atomic Number, Size

Mnemonic: "Mona Adds Shiny Zingers"

Breakdown:

• Mona - Mass Number
• Adds - Atomic Number
• Shiny Zingers - Size

These three properties are essential to understanding the characteristics of any nucleus:

• Mass Number (A): Total number of nucleons (protons + neutrons) in the nucleus. It represents the mass of the atom (approximately).

• Atomic Number (Z): Number of protons in the nucleus, which determines the identity and position of the element in the periodic table.

• Size: Refers to the nuclear radius, which increases slightly with mass number, roughly following the formula $R\propto A1/3R\; \backslash propto\; A^\{1/3\}$R∝A1/3. The nucleus is incredibly small—about 10⁻¹⁵ meters.

Radioactive Decay Types

Types: Alpha, Beta, Gamma

Mnemonic: "Amit Blasts Glass"

Breakdown:

• Amit - Alpha
• Blasts - Beta
• Glass - Gamma

Alpha Decay (α/He²⁺): Emits 2 protons + 2 neutrons → Z ↓ by 2, A ↓ by 4.
Example: U-238 → Th-234.

Beta Decay (β⁻/β⁺): Neutron → proton + electron (β⁻) or proton → neutron + positron (β⁺) → Z changes ±1, A unchanged.
Example: C-14 → N-14.

Gamma Decay (γ): Emits high-energy photon → No change in Z or A, just energy release.
Often follows α or β decay.​​​​

Nuclear Forces Characteristics

Types: Short Range, Strong, Charge Independent

Mnemonic: "Sara Strikes Chair"

Breakdown:

• Sara - Short Range
• Strikes - Strong
• Chair - Charge Independent

The nuclear force binds protons and neutrons in the nucleus.

• Short Range: Acts only within ~1–2 femtometers; negligible beyond.

• Strong: Strongest fundamental force; overcomes proton repulsion.

• Charge Independent: Same effect between p–p, n–n, or p–n.

Radioactive Decay Law Components

Types: Activity, Half-Life, Decay Constant

Mnemonic: "Acids Have Dangerous Consequences "

Breakdown:

• Acids - Activity
• Have - Half-Life
• Dangerous consequences  - Decay Constant

Activity (A): Rate of decay → A = λN

Half-Life (T₁/₂): Time for half the nuclei to decay → T₁/₂ = ln2 / λ

Decay Constant (λ): Probability of decay → λ = ln2 / T₁/₂

Nuclear Reactions

Types: Fission, Fusion

Mnemonic: "Farah Fuses Fireworks"

Breakdown:

• Farah - Fission
• Fuses Fireworks - Fusion
  

Fission:
Heavy nucleus splits → smaller nuclei + neutrons + energy
Example: U-235 + neutron → splits + energy
Used in: Reactors, bombs

Fusion:
Light nuclei combine → heavier nucleus + more energy
Example: H + H → He + energy (in the Sun)
Releases more energy than fission

Particles in Nuclear Physics

Types: Alpha Particle, Beta Particle, Neutrino

Mnemonic: "Always Be Neat"

Breakdown:

• Always - Alpha Particle
• Be - Beta Particle
• Neat - Neutrino
  

Alpha Particles (α):
2 protons + 2 neutrons (He nucleus), + charge, low penetration.
Stopped by paper/skin
Example: U-238 → Th-234 + α

Beta Particles (β⁻/β⁺):
High-speed electrons or positrons, – or + charge, moderate penetration.
Example: C-14 → N-14 + β⁻

Neutrinos (ν):
Neutral, tiny mass, weakly interacting, very hard to detect.
Emitted with beta particles
Example: Neutron → Proton + Electron + Neutrino (β⁻ decay)

Applications of Nuclear Physics

Types: Power Generation, Medical Uses, Radiocarbon Dating

Mnemonic: "Power Makes Radiations Durable"

Breakdown:

• Power - Power Generation
• Makes - Medical Uses
• Radiations Durable - Radiocarbon Dating
  

• Power Generation:
  Nuclear reactors use fission (e.g., U-235) to produce heat and generate electricity.
  Example: Nuclear power plants.

• Medical Uses:
  Radioactive isotopes for imaging (PET, CT scans) and cancer treatment (radiation therapy).
  Example: Tc-99m for scans, Co-60 for cancer therapy.

• Radiocarbon Dating:
  Uses C-14 decay to date ancient organic materials.
  Example: Dating fossils and archaeological artifacts.