Physical Science – Ms. Oster - 2015 Radiation Notes Physical Science – Ms. Oster - 2015

Monday 12/7 Please grab a new bellringer sheet Don’t forget to be completing and turning in any late work- every point counts! Work through the exam review sheet in order to make a “cheat sheet” for the midterm! Today’s Bellringer: What do you think of when you hear the term radiation? https://www.youtube.com/watch?v=wQmnztyXwVA

Radiation Radiation is dangerous energy or particles given off by radioactive materials.

Sources of Radiation Radiation is released in large amounts by atomic bombs and nuclear power plants https://www.youtube.com/watch?v=sehKAccM8p0

Effects of Radiation Burns the Skin Cancer Birth Defects in Children

Chernobyl https://www.youtube.com/watch?v =ldYeFLZqh3Q

What Causes Radioactivity? Atoms are radioactive when the nucleus has too many protons “packed together” The positive charges push against each other and make the atom unstable This instability causes the nucleus to break apart (decay) by throwing off particles / energy https://www.youtube.com/watch?v=TJgc28csgV0

Rates of Decay Radioisotope: Radioactive isotope of an element Nuclear decay is the deterioration of a radioisotope The types of decay are alpha, beta, and gamma Half-life: The amount of time required for half of a sample of a radioisotope to decay https://www.youtube.com /watch?v=tzM6aK5QbSU

Rates of Decay After 1 half-life, half of the atoms of a radioactive sample have decayed and the other half remains radioactive After 2 half-lives another half of the material decays and ¼ of the original amount remains

Rates of Decay Calculations: Half lives can vary from fractions of a second to billions of years Nuclear reaction rates are constant, whereas chemical reaction rates can vary Calculations: Half lives elapsed = Total time of decay Half Life

Half Life Practice Half lives elapsed = Total time of decay Half Life You have one gram of iridium-182, which decays to osmium-182. The half life is 15 minutes. How much iridium will remain after 45 minutes? Half lives elapsed = 45 minutes 15 minutes

Rates of Decay Half lives elapsed= 3 That means we cut the sample in half 3 times: ½ x ½ x ½ = 1/8 If we have 1/8 of one gram then we have 1/8 x 1 gram= .125 grams

Practice Problems An isotope of cesium-137 has a half life of 30 years. If 5.0 mg of cesium-137 decays over a period of 90 years, how many grams of the sample remain? Half lives elapsed = Total time of decay Half Life 3 half lives have elapsed Half lives elapsed = 90 years 30 years 3 half lives= ½ x ½ x ½ or 1/8 of the original sample 1/8 x 5.0 mg= .625 mg cesium-137

Assignment 5 half life problems