The Three Rays

Why it matters

From one radioactive speck come three utterly different messengers: one stopped by paper, one by a metal sheet, one that shrugs at both. Meet them before you trust any wall.

The idea in plain words

The dossier on each ray. Tap them.

α = ⁴₂He²⁺ · β = e⁻ · γ = EM wave

In a magnetic field, which way does each ray bend?

Two curves, one straight line — the classic field-photo of all three

• the bulldozer: α — helium nucleus: +2 charge, mass 4u, slow, MOST ionising, LEAST penetrating (paper)
• the sprinter: β — fast electron from the nucleus: −1, ~1/1836 u, stopped by ~5 mm aluminium, deflects opposite to α in fields
• the ghost: γ — electromagnetic wave: no charge, no mass, LEAST ionising, MOST penetrating (thick lead only)
• α (+) and β (−) bend opposite ways (FLHR each)
• γ sails straight — nothing for the field to grab

Predict first

Which radiation is stopped by a mere sheet of paper?

The α particle (a helium nucleus) is a bulldozer: hugely ionising, so it burns out within centimetres of air or one sheet of paper. Penetration and ionisation are opposites.

• Alpha — big, heavy, doubly charged, spends its energy instantly — correct
• Gamma — weakest of the three
• Beta

What you do

Slide the barriers in and see which rays survive — then identify all three by behaviour alone.

Check yourself

Most PENETRATING and least ionising:

γ barely interacts — which is exactly why it travels farthest and needs lead.

A beta particle is…

The nucleus manufactures it on the spot: n → p + e⁻. That's why Z rises by 1 in β decay.

An electric field deflects…

Charge decides: +2 goes one way, −1 the other (and farther — it's light), neutral γ ignores the field.

• gamma — correct
• alpha
• beta
• an electron ejected FROM THE NUCLEUS (a neutron turned proton + electron) — correct
• an orbital electron knocked loose
• a helium nucleus
• α toward the negative plate, β toward the positive, γ not at all — correct
• all three equally
• only gamma