What is radioactivity? What types of particles are emitted by

radioactive substances? What is radioactivity used for? What dangers are associated with

radioactivity?

Isotopes – different numbers of NEUTRONS

Some isotopes more stable than others

Shows the ratios of protons to neutrons in a stable nucleus

Radioisotope – isotope with unstable nucleus

Radioactivity or Radioactive Decay- describes the spontaneous change(s) that radioisotopes undergo to become stable

Gives off EM radiation ALWAYS results in a more stable

nucleus ALWAYS results in a new element

Transmutation- the change in the identity of the element after it undergoes radioactive decay

Radioactive Decay is represented with an equation

Protons and masses on both sides of the equation MUST balance

Alpha Beta Gamma Positron Emission Electron Capture

An Alpha particle is a helium nucleus 2 protons; 2 neutrons The release of an ɑ particle makes the

original nucleus smaller Relatively low energy particles Easily shielded by paper or clothing

Notice:1.Masses add up to 238 on both sides of the arrow2.The number of protons on both sides of the arrow are also equal

The result of a neutron breaking down 1 neutron is converted to 1 proton and

1 electron The beta particle is the electron More energy than alpha, but still easily

shielded by Al foil or wood

Same idea here. Masses balanceProtons balance

High energy photon, usually released with alpha or beta particles

What are photons?

Gamma rays have very high energy, and must be shielded using lead or concrete

Happens when the ratio of protons to neutrons is too high

Positrons are positively charged particles with the mass of an electron

Turns a proton into a neutron and a positron

Atomic number goes down – one less protonMass number stays the same – protons and neutrons weight the samePositron is written like a beta particle (electron) but now the charge is +1

Also happens when the ratio of protons to neutrons is too high

The nucleus takes in an electron from its own atom

The electron being brought into the nucleus makes a proton into a neutron

Add electronAtomic number goes down - 1 less protonMass stays the same - protons and neutrons weigh the same

Nuclei combine to make a nucleus with greater mass

Releases a LOT of energy Nuclear Fusion is responsible for the

energy we get from the sun

Nuclear fusion is used in Hydrogen Bombs

It “boosts” the fission reaction, and ensures all material is used

Hydrogen bombs are the most common type of nuclear weapon

Occurs when a radioisotope is bombarded by neutrons, causing it to split into smaller pieces

Releases a large amount of energy (but not as much as fusion)

Results in a chain reaction

Used in nuclear power plants Fission creates heat, which boils water Steam spins turbines, creating

electricity The water must then be cooled off

Nuclear Fission produces about 20% of our energy in the US

Heat

Steam produced

Steam

Turbine

Generator

Electricity

The worst nuclear accident in US history occurred on Three Mile Island in PA 1979

The reactor meltdown was caused by several mechanical errors as well as human error creating a coolant leak

The reactor that had the melt down is no longer in use. The other reactor is slated to remain in use until 2034

“London Calling” by The Clash is about this accident

Chernobyl Nuclear Power Plant– Pripyat, Ukraine; April 1986

During a test, the reactor received a power spike, causing several explosions

Radiation was picked up several hundred miles away, prompting the Soviet Union to admit the accident, 3 days after it happened

During clean-up workers could spend a max of 40 seconds at a time

A concrete sarcophagus was built around the reactor

Today the sarcophagus needs to be replaced, unfortunately the funds are not available

It is difficult to say how many people were affected, because the Soviet Union doesn’t release much information

We do know that radioactive material was detectable over all of Europe

Film Badges – exposure of film measures radiation exposure

Geiger Counters- detect radiation through electric pulses in ionized gas

Scintillation Counters- measure radiation from substances that emit visible light when energy is absorbed

Radioactive dating can determine the approximate age of an object

There are many uses of radiation in the medical field› Detect and kill cancerous cells› X-Rays› Many others

Disinfect foods

What is half life? How do we determine the length of

radioactive decay?

No two radioisotopes decay at the same rate

Half Life (t1/2) is the time required for half the atoms of a radio isotope to decay

Can be as short as a few seconds or take billions of years

To calculate the amount of a radioisotope remaining:

Nt = No X (0.5)number of half lives

Nt is the amount remaining

No is the amount you started with

# of ½ lives = total time/length of 1 ½ life

Manganese-56 is a beta emitter with a half life of 2.6 hours. What is the mass of manganese-56 in a 1.0 mg sample of the isotope at the end of 10.4 hours?

To calculate the ½ life

t1/2 = (.301)T

log(No/Nt)

Nt is the amount remaining

No is the amount you started withT is the time of decayt1/2 is the half life

A 15 g sample of cesium-137 is allowed to decay for 450 years. After this time, 0.9375 g of the sample remain. What is the half life of cesium-137?