 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 arrow 2.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 balance Protons 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 proton Mass number stays the same – protons and neutrons weight the same Positron 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 electron Atomic number goes down - 1 less proton Mass 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 (t 1/2 ) 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: N t = N o X (0.5) number of half lives N t is the amount remaining N o 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 t 1/2 = (.301)T log(N o /N t ) N t is the amount remaining N o is the amount you started with T is the time of decay t 1/2 is the half life

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