7/27/2019 Radioactivity For IB1(2).docx

1/3

7/27/2019 Radioactivity For IB1(2).docx

2/3

Radiation Relative

Charge

Relative

Mass

Nature Penetration Deflection

By Electric

Field

Alpha

particles

+2 4 2 protons and 2

neutrons (He

2+

ion)

Stopped by

a few sheetsof paper

Low

Betaparticles

-1 1

1836

Electron Stopped bya few mm

of plastic

High

Gammarays

0 0 Electromagneticradiation of

very high

frequency

Stopped bya few cm of

lead

None

The rate at which nuclei undergo radioactive decay varies between chemical elements.It is an exponential process and decay rates are compared using the half-life (time

taken for half of the radioactive nuclei to undergo decay)

1. Alpha Decay An particle is released from the nucleus. Mass number (A)decreases by 4, and the atomic number (Z) decreases by 2. Every elementheavier than lead (Pb) and a few lighter ones, exhibit alpha decay.

22688Ra

22286Rn +

42He

2. Beta (Decay Involves the ejection of a particle from the nucleus. A particle is an electron that is expelled from the nucleus during beta-decay The

particle is first formed in the nucleus by the conversion of a neutron into a

proton and a particle. The particle is expelled immediately and is

symbolized by0

1e

.

146C

147N +

0

1e

Note: During beta decay an atom of the next higher atomic number is formed.

7/27/2019 Radioactivity For IB1(2).docx

3/3

3. Gamma ( ) Emission Involves the radiation of high energyelectromagnetic radiation from a nucleus. Often, gamma radiationaccompanies either alpha or beta particle emission. Following emission of analpha or beta particle, the nucleus is in a high energy (excited) state, when it

relaxes, gamma radiation is emitted.

Gamma radiation is symbolized by

0

0 . An example of a nuclear equationinvolving gamma radiation looks as follows:

137 137 0 0

55 56 1 0Cs Ba e

Review uses of radioactivity in text. You are responsible for C-14, Co-60, I-131.

Simulation: Half-life and Radioactive Dating

http://phet.colorado.edu/en/simulation/radioactive-dating-gamehttp://phet.colorado.edu/en/simulation/radioactive-dating-gamehttp://phet.colorado.edu/en/simulation/radioactive-dating-game