Half-life L/O;- To understand radioactive half-life

 Half life is the time taken for a radioactive substance to reach half its radioactivity  In other words the time it takes for half of the atoms to have decayed!!

Half life The decay of radioisotopes can be used to measure the material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay… At start there are 16 radioisotopes After 1 half life half have decayed (that’s 8) After 3 half lives another 2 have decayed (14 altogether) After 2 half lives another half have decayed (12 altogether) = radioisotope= new atom formed

Modelling Half-life Collect 20 cubes in a tray. Collect 20 cubes in a tray. Shake all 20 cubes in your hand and let them fall into the tray – remove all the cubes that land black side up. Shake all 20 cubes in your hand and let them fall into the tray – remove all the cubes that land black side up. Count the number of cubes left – record this number Count the number of cubes left – record this number Continue until there are no dice left Continue until there are no dice left Draw a graph of your results Draw a graph of your results Work out the half-life Work out the half-life

Throw Number of Dice Left Start Number of Throws Number of dice Half the number of Dice HALF LIFE

Compare your results to other members of the class Were the results of the class reliable ? Were your own results accurate ? Half Life Average

Swap your graph with the person next to you and mark it using these criteria The X axis starts from 0 The X axis starts from 0 The X axis has a scale The X axis has a scale The X axis is labelled The X axis is labelled The Y axis starts from 0 The Y axis starts from 0 The Y axis has a scale The Y axis has a scale The Y axis is labelled The Y axis is labelled The points are plotted correctly The points are plotted correctly They have drawn a line/curve of best fit They have drawn a line/curve of best fit The have drawn an accurate line of best fit The have drawn an accurate line of best fit They have given the graph a title They have given the graph a title Give your partner a mark out of 10 and set them a target for next time Can you think of anything which is usually really important in a graph but is not important for this graph?

Hospitals use Barium ‘meals’ and Thallium as tracers to look at the digestive system and blood flow. Why do you think the radioactive material Barium and Thallium are used instead of other radioactive substances?

Hydrogen-3 (tritium)12 years Hydrogen-3 (tritium)12 years Beryllium-101 million 600 thousand years Beryllium-101 million 600 thousand years Carbon-145 thousand 700 years Carbon-145 thousand 700 years Silicon years Silicon years Potassium-401 thousand million years Potassium-401 thousand million years Calcium-4214 thousand yearsIron-553 years Calcium-4214 thousand yearsIron-553 years Cobalt-605 yearsNickel-5975 thousand years Cobalt-605 yearsNickel-5975 thousand years Nickel-6310 years Nickel-6310 years Krypton thousand years Krypton thousand years Krypton-8310 years Krypton-8310 years Strontium-9029 yearsYttrium-902 days Strontium-9029 yearsYttrium-902 days Zirconium-931 million 500 thousand years Zirconium-931 million 500 thousand years Niobium-93m14 years Niobium-93m14 years Niobium-9420 thousand years Niobium-9420 thousand years Molybdenum-933 thousand 500 years Molybdenum-933 thousand 500 years Technetium thousand years Technetium thousand years Ruthenium-1061 year Ruthenium-1061 year Palladium-1076 million 500 thousand years Palladium-1076 million 500 thousand years Cadmium-113m14 years Cadmium-113m14 years Tin thousand years Tin thousand years Antimony-1253 years Antimony-1253 years Antimony days Antimony days Tellurium-125m58 days Tellurium-125m58 days Iodine million 700 thousand years Iodine million 700 thousand years Cesium-1342 years Cesium-1342 years Cesium-1352 million 300 thousand years Cesium-1352 million 300 thousand years Cesium years Cesium years Cerium-1443 hundred days Cerium-1443 hundred days Promethium-1473 years Promethium-1473 years Hafnium-1829 million years Hafnium-1829 million years Rhenium thousand million years Rhenium thousand million years Lead million 300 thousand years Lead million 300 thousand years Lead years Lead years Bismuth thousand years Bismuth thousand years Bismuth-2105 days Bismuth-2105 days Bismuth-210m3 million years Bismuth-210m3 million years Polonium daysRadon-2224 days Polonium daysRadon-2224 days Radon days Radon days Actinium days Actinium days Actinium years Actinium years Thorium daysThorium-2282 years Thorium daysThorium-2282 years Thorium-2297 thousand 300 years Thorium-2297 thousand 300 years Thorium thousand years Thorium thousand years Thorium-2311 day Thorium-2311 day Thorium thousand million years Thorium thousand million years Thorium days Thorium days Uranium years Uranium years Uranium thousand years Uranium thousand years Uranium thousand years Uranium thousand years Uranium million years Uranium million years Uranium million years Uranium million years Uranium-2384 thousand million years Uranium-2384 thousand million years Neptunium-2372 million years Neptunium-2372 million years Plutonium years Plutonium years Plutonium thousand 100 years Plutonium thousand 100 years Plutonium-2406 thousand 500 years Plutonium-2406 thousand 500 years Plutonium years Plutonium years Plutonium thousand years Plutonium thousand years

What is the half-life of Sodium-24? What is the half-life of Sodium-24? What would you expect the count rate of this sample to be after 20hours? What would you expect the count rate of this sample to be after 20hours? How long should it take for this sample to fall to 50cps How long should it take for this sample to fall to 50cps

What is the half-life of this sample? What is the half-life of this sample? How long will it take for this sample to fall to 25 cps? How long will it take for this sample to fall to 25 cps? What will the cps be after 3 half-lives? What will the cps be after 3 half-lives? What will the cps be after 10 days? What will the cps be after 10 days? What will the cps be after 3 half-lives? What will the cps be after 3 half-lives? Strontium - 90 has a half-life of 28.1 years. A sample has an initial activity of 400 MBq. 1. What will the activity be after one half life? 2. How long will it take the sample to fall to 100 MBq? 3. What will be the activity after 92 years?

What is the half-life of Caesium 137? What is the half-life of Caesium 137? How long will it take this sample to fall below 10 cps How long will it take this sample to fall below 10 cps What will the cps be after 3 half-lives? What will the cps be after 3 half-lives? What will the cps be after 100 years? What will the cps be after 100 years?

A radioactive decay graph Time Count 1 half life

An exam question… Potassium decays into argon. The half life of potassium is 1.3 billion years. A sample of rock from Mars is found to contain three argon atoms for every atom of potassium. How old is the rock? (3 marks) The rock must be 2 half lives old – 2.6 billion years

Hospitals use Barium ‘meals’ and Thallium as tracers to look at the digestive system and blood flow. Why do you think the radioactive material Barium and Thallium are used instead of other radioactive substances?