2 Radioactive ElementsRadioactivity – release of energy and matter from changes in an atom’s nucleusSome elements or some of their isotopes (atoms w/ different mass #’s) are radioactiveA new way to write an atomic symbol:mass number Atomic Symbolatomic number12C6Try Sodium on your own….
3 II. Transmutation of Elements Transmutation or Radioactive Decay – change of one element to another (e.g., U changing to Pb)Decay Series – series of steps by which a radioactive nucleus changes to a nonradioactive one (Fig 11-6)Alpha Decay – when a nucleus releases 2 protons and 2 neutrons together ( a He nucleus)Beta Decay – when a nucleus releases an electron…“But wait Mrs. O’Gorman, you told us that electrons are not in the nucleus…”Well, scientists believe that a neutron is nothing but a proton and an electron that are hooked up and disguised as a neutral charge…
4 III. Transmutation of Elements (Cont’d) Gamma Decay – release of energy in the form of gamma rays that accompanies α (alpha) and β (beta) decayDecay or die! (try these)Illustrate the alpha decay of Polonium – 216Illustrate the beta decay of Bismuth – 210
5 III. Transmutation of Elements (Cont’d) To sum up, the “rules” of radioactive decay are:Alpha Decay – nucleus loses 2 P’s and 2 N’sBeta Decay – nucleus loses an electron (the electron was produced by the breakdown of a neutron)Gamma Decay – accompanies Alpha and Beta Decays – nucleus releases a HIGH energy wave called a Gamma ray
6 II. Transmutation of Elements Half-life – amount of time it takes half the atoms in a sampleof radioactive material to decay into a stable, non-radioactive element (Fig )Half-life of Polonium-215 is secondHalf-life of Uranium-218 is 4.5 billion years!!Suppose you have 100 grams of Po-215…How much Po is left after seconds?After sec?After sec?Suppose you are given 600 g of U-238…How large was the sample 2.25 billion years ago?In how many years would I expect to see ONLY 300 g of U-238 left in my sample?How much, and what decay material, would I have along with my 300 g of U-238 (see your textbook) ?
7 III. Transmutation of Elements Nuclear FissionSplitting of a large atom into two smaller ones by a neutron bulletReleases energyCan be controlled so it’s used for nuclear powerINDIAN POINT = FISSION235 U + 1 n Kr Ba nNuclear Fusionfusing of two smaller atoms to form a larger oneTREMENDOUS Release of energyDifficult to control so we don’t use it as an energy sourceThis is how the SUN produces so much heat and radiation energyFUSION = SUN
8 IV. Detecting & Measure Radioactivity Electroscope (Fig )Separated foil leaves collapse if a radiation source is nearGeiger Counter (Fig )Makes a click every time a radiation particle hits it# of clicks per unit time indicates the radiation strengthCloud chamber (Fig )Radiation particles leave visible trails through alcohol vaporBubble chamber (Fig )Similar to a cloud chamber
9 V. Uses of Radioactivity Radioisotopes – artificially produced radioactive isotopes of common elementsUsed as tracers whose paths can be followed with instrumentsIodine-131 collects in the thyroid gland so doctors can observe any problems that a person my be having with their thyroid.Iron-59 collects in bloodSome food is “irradiated” to kill bacteria so it will stay safe to eat for long periods of
10 Practice of Half-Life Calculations Fill in this chart of the half-life decay of Carbon-14Half Life # Time Elapsed Am’t of C14 Remainingggggg- In what year will you have half of the amount of radioactive material than what you started with (assuming that the decay process starts today)?- 7737How many years will it take to have 25% of what you started with?11,460 years