Unit 6Radioactivity and Nuclear

Decay

Nuclear ChangesChapter 10.1

What is Radioactivity?

Radioactivity

Radioactivity• Radioactive decay is the disintegration of an

unstable atomic nucleus into one or more different nuclides.

• After radioactive decay, the element changes into a different isotope of the same element or into an entirely different element.

Radioactivity• Nuclear radiation is the release of

particles from the nucleus during radioactive decay.

• These particles can either be alpha, beta, or gamma particles.

Types of Radiation• Alpha particles can be stopped by paper.• Beta particles can be stopped by aluminum.• Gamma particles can be stopped by lead.

Alpha Decay• Alpha particle (α) is a positively charged

particle that consists of two protons and two neutrons and that is emitted from a nucleus during radioactive decay.

• This is a helium nucleus.

Alpha Decay

(Atomic Mass #)

(Atomic #)3. Since the atomic # = 82, then

Beta Decay• Beta particle (β) is an electron or

positron that is emitted from a nucleus during radioactive decay.

• A positron is a positively charged electron, NOT a proton.

Beta Decay

(Atomic Mass #)

(Atomic #)3. Since the atomic # = 84, then

Gamma Decay• Gamma ray (γ) is a high-energy photon

emitted by a nucleus during fission and radioactive decay.

• A photon is a packet of electromagnetic radiation or energy.

Gamma Decay

(Atomic Mass #)

(Atomic #)3. Since the atomic # = 84, then

Neutron Emission• Neutron emission consists of matter

that is emitted from an unstable nucleus• Neutrons have no charge, and therefore do

not want to interact with other particles.

How old are rocks?• If you were asked to determine the age of a

rock, you would probably not be able to do so easily.

• How, then, would you go about finding the rock’s age?

Radioactive Decay Rates• One way to find the age involves radioactive

decay.• It is possible to predict the time required for half of

the nuclei in a given radioactive sample to decay.• Half-life is the time required for half of the sample

of a radioactive isotope to break down by radioactive decay to form a daughter isotope.

Half-Life and Exponential Decay• The definition of half-life tells us that after the first half-life time of a

radioactive sample has passed, half of the sample remains unchanged.• After the next half-life, half of the remaining half decays, so only a

quarter of the original element remains.• Of that quarter, half will decay in the next half-life, so only one-

eighth will remain unchanged• This relationship is called exponential decay.

Half-life Time Frames

Half-Life Equations

Half- Life Fractions 1st = 1/2 # of 2nd = 1/4 HL’s 3rd = 1/8 4th = 1/16 5th = 1/32

1st = 1/2 2nd = 1/4 3rd = 1/8 4th = 1/16 5th = 1/32