Why zinc sulphide screen is used inαscattering experiment?

 A zinc sulphide (ZnS) screen is used because it scintillates—producing tiny, bright flashes of visible light when struck by individual α‑particles—enabling precise visual counting and angular measurement in a dark room with a microscope.

ZnS acts as an efficient scintillator for heavy, charged α‑particles: each impact excites the crystal and yields a brief, localized flash, allowing single‑particle detection and angle readout without electronic detectors.

• High scintillation yield for α‑particles; flashes are bright enough for microscope observation in a dark room.
• Fast, point‑like flashes help resolve individual events and their scattering angles with minimal overlap.

Experimental role

In Rutherford’s setup, a movable ZnS screen was placed around the thin metal foil to record scintillations at different angles, including large‑angle and near‑backscattering positions that were crucial to the experiment’s conclusions.

A spherical or circular arrangement maximized solid‑angle coverage, ensuring even rare, large‑angle deflections were captured and could be counted reliably over time.

Why ZnS specifically

• High efficiency: Converts α‑particle kinetic energy into visible photons effectively, enabling single‑hit detection.
• Temporal response: Short scintillation duration limits afterglow, reducing event pile‑up during manual counting.
• Localization: Point‑like flashes give clear positional cues for measuring scattering angles under a microscope.
• Practicality (historical): Suitable before widespread electronic detectors; compatible with dark‑room, manual counting methods.

Consequences for conclusions

Most α‑particles produced forward scintillations, but a small fraction flashed at large angles; this pattern implied atoms are mostly empty space with a small, dense, positively charged nucleus.

Reliable ZnS scintillation counting enabled quantitative angular distributions consistent with Rutherford’s scattering law, validating single, Coulombic scattering from a concentrated nuclear charge.