7.10 to 7.12

·         

Smoke detectors use ²⁴¹Am to emit alpha particles which pass through a small air gap before being detected.  If smoke particles are present they interrupt the beam of alpha particles and this triggers the alarm to go off

·         Tomorrow, will the ²⁴¹Am still be as radioactive?

·         Next year, will the ²⁴¹Am still be as radioactive?

·         In a thousand years, will the ²⁴¹Am still be as radioactive?

Answers

·         To answer the questions, we need to know the half life of Americium-241which is 432 years

·         Tomorrow and even next year its activity will hardly have changed at all (sensible for a smoke detector - you don't want it to suddenly stop working!)

·         In a thousand years its activity will have dropped to about a quarter

·         

7.10 understand that the activity of a radioactive source decreases over a period of time and is measured in becquerels

·         7.11 recall the term ‘half-life’ and understand that it is different for different radioactive isotopes

·         7.12 use the concept of half-life to carry out simple calculations on activity

Half-life of Different Isotopes

·         

Half life.pptx Download this file

interactive simple half life calculations.swf Download this file

Decay of Balonium - exponential graph.swf Download this file

PhET animation - alpha decay

31 January 2012

13:34

<<alpha-decay_en.jar>>

Website

http://phet.colorado.edu/en/simulation/alpha-decay

PhET animation - beta decay

31 January 2012

13:34

<<beta-decay_en.jar>>

Website

http://phet.colorado.edu/en/simulation/beta-decay