RADIOACTIVE DECAY:

• understand radioactive decay.•describe alpha, beta and gamma radiation?

Atomic Theory and Radioactive Decay

Natural background radiation exists all around us. This radiation consists of high energy particles or waves being

emitted from a variety of materials. Radioactivity is the release of high-energy particles or

waves. Being exposed to radioactive materials can be beneficial or

harmful. X rays, radiation therapy, and electricity generation are beneficial. High-energy particles and waves damage DNA in our cells.

When atoms lose high-energy particles and waves, ions or even new atoms can be formed.

High-energy waves and particles are called radiation when they leave the atom.

The electromagnet

ic epectrum

Searching for Invisible Rays

Radiation is everywhere, but can be difficult to detect. Roentgen named X rays with an “X” 100 years ago

because they were previously unknown. Becquerel realized uranium emitted seemingly

invisible energy as well. Marie Curie and her husband Pierre named this

energy radioactivity. Early discoveries of radiation relied on photographic

equipment. Later, more sophisticated devices such as the Geiger-

Müller counter were developed to more precisely measure radioactivity. Radium salts, after being

placed on a photographic plate, leave behind the

dark traces of radiation.

RADIOACTIVITY:

Radioactivity: release of high-energy particles as a result of changes in the nuclei of atoms (nucleus of atom decays)

Radiation: high energy rays and particles that are released by radioactive sources found on the electromagnetic spectrum (as seen below).

Nuclear Reaction:

When the number of neutrons or protons in a nucleus change or when radiation is released from the nucleus.

Radioactive Decay: Results in formation of new atoms Caused by unstable nucleus: nuclei lose energy

and break apart. Radioactive decay releases energy from nucleus as

radiation Radioactive atoms release energy until stable, often as

different atoms.

Radioisotopes: Are natural or human-madeisotopes that decay into other Isotopes, releasing radiation.

Focus Questions:

What is a radioisotope?

What is meant by radioactivity?

What conditions in the nucleus cause decay?

What is a stable isotope?

Three Types of Radiation:

Rutherford identified three types of radiation using an electric field.1) Positive alpha particles were attracted to the

negative plate.2) Negative beta particles were attracted to the

positive plate.3) Neutral gamma rays did not move towards any

plate.

1) Alpha Decay Release of alpha particles from nucleus = Alpha

decay Positively charged particles Most massive of radiation types Are slow moving particles; a sheet of paper will stop

an alpha particle Same particles found in the Helium atom Alpha particle released, atomic # reduced by 2,

mass by 4.

Radium-226 releases an alpha particle and becomes

Radon-222. Radon has two less protons than radium.

88226 Ra 88

222 Rn + 24

or

88226 Ra 88

222 Rn + 24 He

24 or 2

4 He

24 or 2

4 He

2) Beta Decay

A beta particle is an electron that is negatively charged

Beta particles have a mass of 0, a charge of -1 Aluminum will stop beta particle Beta decay occurs when a neutron changes into

a proton + an electron. Proton stays in nucleus, atomic number

increases by one on the periodic table.

Iodine-131 releases a beta particle and becomes xenon-131. A neutron has turned into a proton and

the released electron.

53131I 54

131 Xe + –10

or

53131I 54

131 Xe + –10e

-10 or -1

0e

Atomic Mass does not change

3) Gamma Decay:

Gamma radiation is a ray of high-energy, short-wavelength radiation.

Highest energy form of electromagnetic radiation.

Only lead and concrete can stop gamma rays. No charge; no mass Gamma decay results from energy being

released from a high-energy nucleus

Gamma Ray-when the isotope changes from high-energy state to lower energy

00

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2860 Ni* 28

60 Ni + 00

Focus Questions:

What is an alpha particle? What is beta decay? What is gamma radiation?