Nuclear Chemistry25.1 Radiation25.2 Nuclear Transformations

• Difference between radioactivity, radiation, radioisotopes

• Learn the three main types of radiation• What is the band of stability?• Radioactivity and half-life

Radioactivity

Discovered by Antoine Henri Becquerel in 1896– He saw that photographic plates developed bright spots

when exposed to uranium metals

The Experiment That Started it All

Marie Curie and Antoine Becquerel-1896

They were studying effect of uranium salts that were exposed to sunlight and fogged photographic film. On cloudy day, he left uranium on film and it made this image.

Definitions

• Radioactivity - Process by which substances give off the rays that fogged the photographic film

• Radiation - What the actual rays are called

• Radioisotopes - Unstable isotopes that become stable by emitting energy and radiation

Marie Sklodowska Curie

Shared Nobel Prize 1903

Radiation Phenomenon

Nobel Prize 1911

Discovery of Po and Ra.

The Radium Girls

Grace Fryer and the other women at the radium factory in Orange, New Jersey, naturally supposed that they were not being poisoned. It was a little strange, Fryer said, that when she blew her nose, her handkerchief glowed in the dark. But everyone knew the stuff was harmless. The women even painted their nails and their teeth to surprise their boyfriends when the lights went out. They all had a good laugh, then got back to work, painting a glow-in-the-dark radium compound on the dials of watches, clocks, altimeters and other instruments.

Three Main Types of Radiation

• Alpha• Beta• Gamma

Alpha Radiation

Loss of an -particle (a helium nucleus)

He42

U23892 Th234

90 He42+

Alpha Radiation

Alpha radiation occurs when an unstable nucleus emits a particle composed of 2 protons and 2 neutrons. The atom giving up the alpha particle has its atomic number reduced by two. Of course, this results in the atom becoming a different element. For example, Rn undergoes alpha decay to Po.

Beta Radiation

Beta Decay

Loss of a -particle (a high energy electron)

0−1 e0

−1or

I13153 Xe131

54 + e0−1

0−1+1

0n p11

Beta Radiation

Beta radiation occurs when an unstable nucleus emits an electron. As the emission occurs, a neutron turns into a proton.

Gamma Radiation

Loss of a -ray (high-energy radiation that almost always accompanies the loss of a

nuclear particle)

00

Radiation Comparisons

Band of Stability

• Nuclei above this belt have too many neutrons.

• They tend to decay by emitting beta particles.

Stability of Nuclei

•There are no stable nuclei with an atomic number greater than 83.•These nuclei tend to decay by

alpha emission.

Half-LifeHalf Life (t1/2) is the time required for half the atoms of a radioactive nuclide to decay.

Carbon-14 has a half life of 5715 years. If you had 20 mg of C-14 the following would be true …

Years Amount C-14 left (mg)

5715 1011430 517145 2.522860 1.2528575 0.625