CHAPTER 3.4 & 24.1 Nuclear Chemistry RadioactivityRadioactivity

Radiation Radiation: The process of emitting energy in the form of waves or particles. Where does radiation come from? Radiation is generally produced when particles interact or decay. A large contribution of the radiation on earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial). Radiation is going through you at this very moment!

Man-made radiation sources that people can be exposed to include tobacco, television, medical x-rays, smoke detectors, lantern mantles, nuclear medicine, and building materials. Adding it all up, the average American is exposed to a total of about 360 millirems a year from natural and man-made radiation.

Isotopes What’s an isotope? Two or more varieties of an element having the same number of protons but different number of neutrons. Certain isotopes are “unstable” and decay to lighter isotopes or elements. Deuterium and tritium are isotopes of hydrogen. In addition to the 1 proton, they have 1 and 2 additional neutrons in the nucleus respectively*. Another prime example is Uranium 238, or just 238 U.

Definitions Radioactivity – emission of high-energy radiation from the nucleus of an atom Nuclide – nucleus of an isotope

Nuclear Decay Why nuclides decay… – to obtain a stable ratio of neutrons to protons Stable Unstable (radioactive)

Types of Radiation Alpha (  ) – helium nucleus paper 2+  Beta-minus (  )  electron 1- lead  Gamma (  )  high-energy photon 0 concrete

Where do these particles come from ?  These particles generally come from the nuclei of atomic isotopes which are not stable.  The decay chain of Uranium produces all three of these forms of radiation.  Let’s look at them in more detail…

Alpha Particles (  ) Radium R protons 138 neutrons Radon Rn 222 Note: This is the atomic weight, which is the number of protons plus neutrons 86 protons 136 neutrons + n n p p   He) 2 protons 2 neutrons The alpha-particle  is a Helium nucleus. It’s the same as the element Helium, with the electrons stripped off !

Beta Particles (  ) Carbon C 14 6 protons 8 neutrons Nitrogen N 14 7 protons 7 neutrons + e-e- electron (beta-particle) We see that one of the neutrons from the C 14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred: n  p + e ( +  And a neutrino is produced too.

Gamma particles (  ) In much the same way that electrons in atoms can be in an excited state, so can a nucleus. Neon Ne protons 10 neutrons (in excited state) 10 protons 10 neutrons (lowest energy state) + gamma Neon Ne 20 A gamma is a high energy light particle. It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum. A gamma is a high energy light particle. It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.

Gamma Rays Neon Ne 20 + The gamma from nuclear decay is in the X-ray/ Gamma ray part of the EM spectrum (very energetic!) Neon Ne 20

Nuclear Decay…the ones we care about Alpha Emission  Beta Emission TRANSMUTATIONTRANSMUTATION

Half-life Half-life (t ½ ) – time it takes for half of the nuclides in a sample to decay Example Half-lives polonium seconds lead hours iodine days carbon-145,370 years uranium billion years

Half-life Problem  How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours. GIVEN: total time = 30 hours t 1/2 = 15 hours original mass = 20 g WORK : number of half-lives = 2 20 g ÷ 2 = 10 g (1 half-life) 10 g ÷ 2 = 5 g (2 half-lives) 5 g of 24 Na would remain.

F ission splitting a nucleus into two or more smaller nuclei some mass is converted to large amounts of energy

F ission chain reaction - self-feeding reaction

Nuclear Weapons

Nuclear Power Fission Reactors Cooling Tower

Nuclear Power Fission Reactors

Nuclear Power Chernobyl

Nuclear power Three mile Island

Fusion combining of two nuclei to form one nucleus of larger mass produces even more energy than fission occurs naturally in stars

Nuclear Power Fusion Reactors (not yet sustainable)

Nuclear Power Fusion Reactors (not yet sustainable) Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment

Nuclear Power 235 U is limited danger of meltdown toxic waste thermal pollution Hydrogen is abundant no danger of meltdown no toxic waste not yet sustainable FISSIONFISSION FUSIONFUSION vs.

Cold Fusion?

Others Irradiated Food Radioactive Dating Nuclear Medicine Nuclear Weapons