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SASP – Radioactivity Karen Fisher – Helena Romanes School

SASP – Radioactivity Karen Fisher – Helena Romanes School. 27 th May 2010. Learning Outcomes. Provide evidence for the structure of atoms Explain radioactivity in terms of the instability of nuclei Describe properties of alpha, beta and gamma radiation

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SASP – Radioactivity Karen Fisher – Helena Romanes School

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  1. SASP – RadioactivityKaren Fisher – Helena Romanes School 27th May 2010

  2. Learning Outcomes • Provide evidence for the structure of atoms • Explain radioactivity in terms of the instability of nuclei • Describe properties of alpha, beta and gamma radiation • State and use units of activity and of radiation dose • Interpret and use nuclear equations, A and Z, isotopes • Teach ‘How Science Works’ skills through radioactivity • Appreciate why teaching should start with macroscopic phenomena before moving to microscopic descriptions and explanations • Use a range of models and examples to illustrate radioactive phenomena.

  3. Plan

  4. What do we need to know about radioactivity? • In groups, sort statements into topics/year groups • There are some gaps! • How do ideas progress across KS4 & Post-16? • Where do you feel confident/what looks like the biggest challenge? • 10 minutes!

  5. What makes teaching radioactivity difficult? Conceptual Difficulties • Too small to see • Abstract ideas Teacher concerns • What is safe? • Handling sources Student perceptions • Radioactivity is bad • Nuclear weapons/pollution

  6. Conceptual difficulties Everything is made of atoms Atoms are almost unimaginably small – you can’t see them even with a really good microscope because they are smaller than the wavelength of light. An atom is almost entirely empty space with nearly all it’s mass in a tiny central nucleus. This tiny central nucleus is made up of even smaller bits – these do stuff we can term radioactivity Richard Feynman Stylised lithium atom Electron micrograph of carbon atoms

  7. Addressing conceptual difficulties • Research shows mid and lower ability students find the particle model of matter difficult. • So introducing radioactivity in terms of atomic and nuclear structure is unhelpful! • Start from the phenomena you can demonstrate, e.g. effects getting smaller with distance from source or which materials radiation can and can’t penetrate. • Models of microscopic processes can help students develop understanding but may also add to misconceptions – important that students question the model.

  8. ‘Radiation is bad’ • Students (and the population in general) perceive radiation as a bad thing: • Undetectable by human senses • Serious consequences • Cancers (time delayed) • Contamination (long lasting) • Unaware of background radiation • Media scares • Secrecy – industrial, military and political interests

  9. What do you think of radiation?

  10. Addressing fears… • Consider the concepts you use to teach about radioactivity. • Medical Physics; IoP Inside Story site is excellent - http://www.insidestory.iop.org/insidestory_flash1.html • Other uses of radioactivity: industry, archaeology, smoke detectors • Nuclear electricity – how do fission reactors work, might fusion be a future energy source • But students are interested in nuclear weapons, nuclear waste and the stories about weapons proliferation and assassinations with Po-210 that they here in the media

  11. Background Radioactivity • Many students are unaware that radiation occurs naturally around us all the time. • The nucleonica site is a useful resource: http://www.nucleonica.net/naturalra.aspx

  12. Teacher concerns • What practical work can I do? • How do I handle sources to keep risk to my students and myself to a minimum? • When can students handle sources? • What are the legal requirements? • Where can I get more help?

  13. Sources of support • Your school will have a radiation protection supervisor – they will have been on external training and be able to explain safe practice to you. • They will be responsible for checking the sources and ensuring protocols are followed. • An RPS course is not expensive and is only one day – but it does not focus on classroom practice. • www.practicalphysics.org – Atoms and nuclei • IoP Teaching Radioactivity DVD • Teachers TV – Demonstrating Physics: Radioactivity • Several excellent ICT resources & simulations

  14. Radiation Dose • Activity of a source is measured in Becquerels (Bq) • Absorbed dose is the amount of energy that cells absorb and is measured in Grays (Gy) • 1 gray = 1 Joule absorbed per kg of tissue • Dose equivalent is a measure of the possible harm from radiation and is measured in Seiverts(Sv) • UK annual average dose is 2.6mSv • Maximum allowable dose for employees is 20mSv • Diagnostic medical radiation gives an average dose of 0.37mSv • A teachers hand receives a 0.01mSv dose during a standard school demonstration

  15. Radioactivity - an historical context • History of atoms, ideal example of how scientific idea evolve over time. • In 1896, Henri Becquerel discovered radioactivity when invisible rays from fluorescent salts (potassium uranyl sulfate) were detected by photographic film. • Research carried out my Marie and Pierre Curie, discovery of Polonium and Radium • Six experiments that changed the world

  16. Rutherford Scattering • Before radioactivity could be explained the structure of the atom needed to be understood A cosmic onion RSCL clip http://www-outreach.phy.cam.ac.uk/camphy/nucleus/nucleus1_1.htm

  17. ‘Nucleons’ (protons and neutrons) are held together by the strong force.

  18. Radioactive decay • Radioactivity is a random process – this means the chance of any particular atom decaying is constant with time. • We can’t make predictions for individual atoms. • However, over large numbers of atoms we can identify patterns because of the statistics involved. • This allows us to talk about half-life for a radioactive isotope, which can be modelled in a number of ways; • Dice • Drawing Pins • Coins

  19. Data from drawing pins Original data

  20. Mathematical model of decay • Each nucleus in an isotope has a certain chance of decaying in a unit of time. • This is called the decay constant (λ) and has units of s-1 • The activity (A) of a sample is a measure of how many atoms decay each second and has units of Becquerels (Bq) also dimensionally s-1 • A = -λN • Half-life and decay constant are related by the equation • t1/2 = ln2/λ

  21. Mathematical model of decay Equation of line: N = N0 e-λt

  22. Nuclear Stability A nucleus can only be stable if there is a balance between the repulsive (coulombic) force and the attractive (strong) force. http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/page_8325.html

  23. More on alpha, beta and gamma • Alpha decay • Beta decay

  24. Cloud Chamber Evidence Alpha Particle Tracks

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