Hello there!
The nuclear emanations 1, 2 and 3 are called, respectively:
1) Alpha, beta and gamma
Alpha Radiation consists of two protons and two neutrons, as protons are positive particles, they will be attracted to the negatively charged plate.
Beta Radiation is composed of a high-energy electron. As electrons are negative particles, they will be attracted to the positively charged plate.
Gamma Radiation is composed or photons. Photons don't have charge or mass, and they will not be attracted to the charged plates. This kind of radiation is more penetrating than the other two.
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