Geiger–Marsden α-scattering experiment (set-up)गाइगर-मार्सडन α-कण प्रकीर्णन प्रयोग (व्यवस्था)Geiger–Marsden α-scattering experiment (set-up)
NCERT Figs 12.1, 12.2 · Class 12 Physics · Chapter 12 · interactive diagram
Parts and what they mean
- Radioactive source ²¹⁴₈₃Bi (रेडियोऐक्टिव स्रोत ²¹⁴₈₃Bi) — Emits 5.5 MeV α-particles; kept inside a lead block.
- Lead bricks (collimator) (सीसे की ईंटें (समांतरित्र)) — Absorb stray α-particles and let only a narrow, parallel beam through.
- Collimated α beam (समांतरित α किरण-पुंज) — α-particles = helium nuclei (charge +2e, mass ≈ 4 u).
- Gold foil (thickness 2.1 × 10⁻⁷ m) (स्वर्ण पन्नी (मोटाई 2.1 × 10⁻⁷ m)) — So thin that an α-particle is scattered at most once while crossing it. Gold: Z = 79.
- Zinc sulphide (ZnS) screen (ज़िंक सल्फ़ाइड (ZnS) पर्दा) — An α-particle hitting it produces a tiny flash of light (scintillation).
- Microscope (सूक्ष्मदर्शी) — Used to see and count the flashes on the screen.
- Scintillation (light flash) (स्फुरण (प्रकाश की चमक)) — Each flash = one scattered α-particle arriving at that angle.
- Rotatable detector (घूमने वाला संसूचक) — Screen + microscope rotate around the foil to count particles at every angle θ.
- Scattered α-particles (प्रकीर्णित α-कण) — Most go almost straight; about 0.14% turn by more than 1°; about 1 in 8000 by more than 90°.
- Scattering angle θ (प्रकीर्णन कोण θ) — Angle between the original beam direction and the scattered direction.
Original diagram drawn by Simple Learning Hub, based on NCERT Figs 12.1, 12.2. Report a mistake