Lab 12: Radiation Only 0 more labs to go!! Nuclear reactions involve changes in the nucleus of an atom. Chemical reactions involve changes in the electron structure around the atom. Chemical reactions the same atoms are involved: Nuclear reactions the nucleus changes, resulting in an entirely new atom: There are three types of nuclear reactions we will talk about: 1.Alpha Decay (  - decay) – A reaction whereby a parent atom releases an  particle. An  particle consist of 2 protons and 2 neutrons. An  particle is basically a Helium nucleus atomic weight isotope # Atomic # # of protons

2. Beta Decay (  - decay) – A reaction whereby a parent atom releases a  -particle.  particles are simply free electrons. Since electrons have a charge of –1 proton a beta decay will have the following form: In lab today we will look at the  - decay of Strontium – 90: 3. Gamma Decay (  - decay) – A reaction whereby a parent atom releases a  -particle.  - decay is usually a result of an atom decaying from a higher energy state to a lower one. The emission of a  - particle is a mechanism by which an atom can get rid of excess energy. The neat thing about  - particles is that they are massless, it is a very high energy electromagnetic wave. Because of the high energy of the  - particle it also removes an electron from an atom. In lab today we will look at the  - decay of Cobalt – 60:

As these atoms undergo the nuclear reactions they will emit the radiation. Today we will measure this radiation using the Geiger counters. Also, we will look at how this radiation is affected by shielding. When dealing with radiation shielding we talk in terms of half-thickness – which is the thickness of a certain material that will stop half of the incident radiation. where, I 0 is the unshielded intensity, x is the thickness and x 1/2 is the half-thickness We can rearrange this equation: The equation that relates the intensity of the transmitted radiation to the thickness of the material is: thickness of shielding counts N N/2 x 1/2

Similar to the half-thickness there is a time when the original atom has been reduce by half. This is called it’s half-life. Let’s say I start with 100 g of some radioactive material with a half-life of 100 years. Remaining massTime 100 g00 50 g1 half-life100 years 25 g2 half-lives200 years 12.5 g3 half-lives300 years 6.25 g4 half-lives400 years time remaining amount N N/2 t 1/2

Mass – Energy: Let’s say we start with 100 grams of C-14, after one half-life it decays through the following reactions: How much C-14 do you have? 50 grams How about N-14? It turns out that you will wind up with less than 50 grams of N-14 because some of this mass is converted to energy