NUCLEAR CHEMISTRY Text Reference – Chapter 25 SOL CH.2i - The student will demonstrate an understand of the current atomic model, including nuclear stability and patterns of decay

RADIOACTIVITY Unstable nuclei can decompose into different more stable elements. When nuclei change spontaneously and release radiation are said to be “radioactive” All elements heavier than bismuth (Bi) on periodic table will decay into more stable elements.

3 TYPES OF DECAY alpha decay – helium nucleus emitted α or W hat nuclide remains after 226Ra loses an α particle? Balance decay reactions by making sure atomic mass and atomic # on one side of equation equals atomic mass on other

3 TYPES OF DECAY beta decay – electron emitted from unstable atom β or What nuclide remains after 131I loses a β particle?

3 TYPES OF DECAY gamma decay – high energy photon . high energy, short wavelength radiation always accompanies other types of decay, represented by symbol above looking something like ‘y’.

DECAY SUMMARY Decay Type Particle Change in Mass Change in atomic # Example alpha -4 -2 beta +1 gamma photon of light

SHIELDING FROM NUCLEAR DECAY

RATES OF RADIOACTIVE DECAY Radioactive substances decay over time; rate of decay measured in half-lives. Half-life is the amount of time it takes for half of the original quantity to decompose. Half-lives of radioactive materials can vary from millionths of a second to billions of years – all of which factors into the way various radioactive waste materials are handled.

HALF-LIFE CALCULATIONS ½ life problems can vary greatly. Here are some tips: Determine # of ½ lives elapsed first Divide initial mass by 2 for how ever many half-lives you determine

PRACTICE PROBLEMS If Bi-210 with a ½ life of 5 days had an initial mass of 100 g, how much mass would it have after: 1 half-life? ____ 2 half-lives? ____ 3 half-lives? ____ The ½ life of iodine-131, commonly used in medicine, is 8.0 days. If a nurse orders 15.0 g, how much will be left in 24 days? # half-lives = _______ 15.0 g = 1.88 g 23 50 g 3 25 g 12.5 g