alpha particle

a positively charged particle that is the nucleus of the helium atom; emitted from natural or radioactive isotopes

लेकिन चूंकि रेडियम से निकले ऐल्फा कणों की गति बड़ी तेज़ होती है इसलिए यह आशा हुई कि शायद वे आसानी से दूर न हटेंगे।

But since alpha particles given off by radium moved at a high speed, it was hoped that they might not be pushed away easily.