The Alpha-Beta Mystery

TEKS Par 112.35 #12a

Becquerel's Mysterious Rock

Henri Becquerel (Beck-uh-REL) owned a rock of Uranium ore. It appeared to give off a small amount of heat.

He took an unexposed photographic plate and wrapped it so no visible light could get to it.

He put the rock on top of it and left it in a desk drawer overnight.

Wikipedia

When he developed the plate, this is what he saw:

Discussion: what do you think had happened?

We Infer What Must Have Happened

Visible light could not get through But some kind of light rays did get through

to cause the chemical reaction to occur and the image to develop

Later experiments showed that the radiation was high energy, high frequency, and short wavelength.

The Uranium ore was RADIOACTIVE.

Marie & Pierre Curie. . .meanwhile

Polish scientist Marie Curie and French scientist Pierre Curie also worked with uranium, radium, and thorium.

They discovered a lower-energy ray they called “alpha” rays, that could not penetrate a sheet of paper.

Later work showed the alpha rays actually were helium ions.

Becquerel's Radiation

Becquerel's rays DID penetrate paper. Could they be alpha rays/helium?

Alpha rays do not penetrate paper Becquerel's rays can be bent by a

magnetic field, or electric field. So they must be charged particles

Becquerel's rays are negatively charged and very small, very fast.

What particle of the atom could they be?

What Are They?

Beta rays are fast-moving electrons Alpha rays are slow-moving helium ions Both types of radiation are charged Both types can be harmful

“Radium Girls”

The Radium Girls were female factory workers who contracted radiation poisoning from painting watch dials with glow-in-the-dark paint at the United States Radium factory in Orange, New Jersey, around 1917.

The women, who had been told the paint was harmless, ingested deadly amounts of radium by licking their paintbrushes to give them a fine point.

Many became sick; we don't know how many died.

Story in NY Times, Oct 6, 1998

Wikipedia photo

Extension: what kind of radiation made the young women sick?

Another Radium Ray

About 1898, French scientist Paul Villard (Vil-AHRD) found that even after all the alpha and beta radiation was blocked, radium still exposed X-ray film.

He had discovered a third kind of radiation from the atom.

It was called gamma radiation, and can only be shielded by several cm of lead, or thick concrete.

Radiation SummaryType of

RadiationWhat

IsIt?

Massamu

Charge ProtectionFrom

Effects

Alphaα

HeliumIon

(nucleus)

4 +2 Sheet of paper(don't

ingest!)

Betaβ

Electron(e-)

1 1800

-1 Sheet of metal (don't

ingest!)

Gammaγ

High energy,Short

wavelengthLight

0 0 Thick lead or

concrete