RadioactiveElements

Radioactivity: An Imbalance of Forces in the Nucleus

Radioactivity: An Imbalance of Forces in the Nucleus

Strength of Force depends on distance !

Radioactivity: An Imbalance of Forces in the Nucleus

• Strength of force depends on distance

• SO.. Larger nuclei are less stable• Strong force less effective in

holding nucleus together• Electrical (repulsive) forces

have greater impact

• Elements DECAY (come apart) over time

Radioactivity: Definition

Radioactivity: the process by which certain elements emit particular forms of radiation.

Radioactive: any element that emits any of these forms of radiation.

Half Life: Measures Decay Rate

Half life refers to amount of time it takes for ½ of the radio active sample to decay

Half life for a particular isotope is always the same

Half Life

Half life measures decay rateEx. Every1620 years ½ of a sample of

radium-226 will have decayed.

Start1620 years

3240 years

6480 years

Application: Carbon Dating

Reaction in a Nuclear Reactor

RadioactiveElements

Part 2Jan 9, 2014

Different Ways to Decay –Types of Radioactive Particles

Alpha Particles (α)– 2 protons and 2 neutrons

Beta Particles (β)– split 1 neutron into 1 proton and 1 electron

Gamma Particles (ɣ) – emits a photon

Half-life: Exponential Decay

Decay of 238U: Natural Decay Chain

Decay of 238U: Natural Decay Chain decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234 which decays, through beta-emission, with a half-life of 24 days to protactinium-234 which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234 which decays, through alpha-emission, with a half-life of 240 thousand years to

thorium-230 which decays, through alpha-emission, with a half-life of 77 thousand years to radium-

226 which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-

222 which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218 which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214 which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214 which decays, through beta-emission, with a half-life of 20 minutes to polonium-214 which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210 which decays, through beta-emission, with a half-life of 22 years to bismuth-210 which decays, through beta-emission, with a half-life of 5 days to polonium-210 which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is

a stable nuclide.

Types of Radioactive Particles

Alpha Particles – 2 protons and 2 neutrons

Beta Particles – split 1 neutron into 1 proton and 1 electron

Gamma Particles – emits a photon

Types of Radioactive Particles

Alpha Particles – 2 protons and 2 neutrons• Lowest Energy

• Still fast enough to do damage• Easily stopped

• Relatively large size and mass• Large enough to do damage• Easily stopped

• +2 Charge. • Tends to pick up electrons

& convert to Helium

Types of Radioactive Particles

Alpha Particles

Emits: 2 p + 2 n

Example:Uranium-238 Thorium-234 + Helium-4

Element Atomic #(# protons)

Mass # (# p + # n)

# neutrons

Uranium 92 238 146

Thorium 90 234 144

Helium 2 4 2

Types of Radioactive Particles

Beta Particles - 1 n 1 p + 1 e- (emits e-)• Higher Energy

• Harder to stop than α particle• Becomes part of material when stopped• -1 Charge.

• Proton joins nucleus• Electron (-1 charge) is emitted

Types of Radioactive Particles

Beta Particles

Loses: 1 nGains: 1 pEmits: 1 e-

Example: Thorium -234 Protactinium – 234 + electron

Element Atomic #(# protons)

Mass # (# p + # n)

# neutrons

Thornium 90 234 144

Protactinium 91 234 143

Types of Radioactive Particles

Gamma Particles – emits a photon• Highest Energy

• Can do significant damage• Hard to stop

• No charge• Doesn’t combine with other materials

• No mass• Hard to stop

Types of Radiation: Energy (Resistance to being stopped)

Types of Radiation: Charges

Types of Radiation: Charges