Radioactivity A2 AQA unit 5 syllabus Radioactivity revision points 2.5 / 5 based on 2 ratings ? PhysicsRadioactivityA2/A-levelAQA Created by: Kirsty JonesCreated on: 04-06-10 19:39 Rutherford study Beam of positively charged alpha particles directed at gold film. A detector is placed on the radius of a circle outlining the experiment. This detector is moved manually around the circle to allow it to detect either: particles that go striaght through particles that are deflected at an angle particles that reflect back off the gold foil. Results: most go straight through or are deflected at an angle less than 90 degrees very few bounce back Explanation: most of atom's mass is cincentrated in the centre, the nucleus. nucleus is positiveky charged because the positively charged alpha particles are deflected. 1 of 5 Alpha partical properties Easily absorbed positive charged Causes strong ionisation (100000 ions per mm at standard pressure) Easily deflected Leaves stright tracks in cloud chamber Few cm range in air stucture consists of 2 protons and 2 neutrons stopped by paper of thin metal foil energy per particle is constant for a given source. 2 of 5 Beta properties more penetrating than alpha negative charge weaker ionisation ability than alpha (100 ions per mm in air at stand pressure) Deflected in opp direction than alpha particles Less easily dieflected than alpha particles +ve beta emission = electron -ve beta emission = positron Leaves wispy tracks in cloud chamber range up to 1m in air structure: fast moving electron stopped by 5mm aluminium energy per particle varies up to a max for a given source 3 of 5 Gamma properties Most penetrating uncharged very weak ionising effect magnetic field have no effect No tracks in cloud chamber high energy particle unlimited range in air (inverse square law) consists of photons stopped by several cm of lead constant energy per particle for a given source. 4 of 5 Ionisation experiment Experiment setup: a source emits into an ionisation chamber, surrounded by an insulated electrode wall. Opposite the source is a central electrode which is wired up to a picoammeter. The chamber air at atm pressure ions created in chamber are attracted to the opp charged electrode where they are discharged current produced is proportional to the no of ions per second created in chamber. Results: Alpha strong ionisation source has to be within a few cm of detector beta weaker ionising effect produces fewer ions per mm along its path than alpha particle gamma weaker ionising effect photons carry no charge so less effect than alpha and beta cells. 5 of 5
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