Physics Radiation Paper 1

Physics Radiation Paper 1

1. Structure of the atom

   • Atoms are very small, radius of 1*10^-10 metres
   • Contain a positive proton, neutral neutron in nucleus and surrounded by negative electron.
   • Have no overall charge
   • Nucleus contains most of the mass but is 1/10000 of the radius of an atom
   • If an atom loses an electron it becomes a positive ion, if it gains it becomes a negative ion.

2. Isotopes

   • All atoms of one element contain the same number of protons
   • Number of protons= Atomic number. Number of neutrons= Atomic mass.
   • Atoms of same element can have different number of neutrons

3. The Plum Pudding Model

   • Atoms were once thought to be tiny spheres that couldn't be divided
   • J.J. Thompson though the atom was a ball of positive chage wih electrons embedded in it

4. Rutherford and Marsden

   • Bombarded thin, gold foil with alpha particles.
   • Some of the particles were deflected
   • Showed them that the mass of the atom was concentrated in the middle nucleus and the electrons surround the nucleus.

5. Nuclear decay and Radiation

   • Some atomic nuclei are unstable and give out radiation to become more stable
   • The activity of a radioactive source is the rate at which it decays.
   • The count-rate is the number of days recorded each second by a detector

6. Alpha, Beta and Gamma decay

   • Alpha is the most ionising and gamma is the least
   • Gamma is the most penetrating, and alpha the least
   • Alpha is 2 protons and 2 neutrons. Beta is a high-speed electron and gamma is electromagnetic radiation

7. Radioactive contamination

   • The unwanted presence of materials containing radioactive atoms
   • The type of radiation effects the hazard
   • Irradiation
     • The process of exposing an object to nuclear radiation: accidental or on purpose
     • Does not cause the object to become a radioactive
     • Protect by using lowest activity sources possible, wear protective clothing and never handle with bare hands
   • Eating alpha particles would be more dangerous then gamma as alpha is more ionising. Entering an area full of gamma is more dangerous the alpha as it is more penetritive

8. Half Life

   • The half life is the average time it takes for half of the nuclei to decay
   • The time it takes for the count rate or activity to half
   • Short half life: Very unstable, emit radiation quickly, doesn't remain radiation for long
   • Long half life: More stable, emits radiation slowly and radioactive for longer

9. Uses of Nuclear Radiation

   • Medical Tracers: can be detected from the outside from within the body
   • Monitor kidney functions: If the tracer builds up in one kidney then one isnt functioning correctly
   • Look for damages in intestines: If the tracer passes out radiation to the rest of the body or cannot be detected then the intestine is damaged or blocked
   • Used to treat tumours: Radioactive iodine gathers at the tumour and destroys nearby cells. Also, a focused beam of gamma rays can be used to destroy some tumours.
   • Have to consider the half-life, activity and type of radiation

10. Background Radiation

    • All around us at all time
    • Varies depending on location and occupation
    • Some sources include radon gas, medical, nuclear industry, cosmic rays, gamma rays and from food.

11. Nuclear Fission and Fusion

    • Fission is the splitting of a large unstable nucleus. Absorbs a neutron and splits into 2 smaller nuclei and emits 2 or 3 neutrons, gamma rays and energy. This can start a chain reaction.
    • Fusion is the opposite of fission. Two light nuclei join together to form a heavier nucleus. Some mass is converted into energy and some energy is emitted as radiation. It requires high temp and pressure to overcome electrostatic repulsion and bring the positive nuclei together

12. Nuclear equations

    • Alpha particle represented by helium symbol and beta particle represented by an electron
    • With an alpha particle the mass number of an element is reduced by 4 and the atomic number is reduced by 2
    • With a beta particle, the mass doesn't change and the atomic number increases by 1 as the neutron becomes a proton.

13. Calculating energy changes

    • K.E=0.5 x Mass x (Speed)^2
    • GPE=Mass x Gravitational field strength x Height
    • Power=Energy transfer/Time
    • Power=Work done/Time

14. Specific heat capacity and Internal energy

    • Internal energy is the total kinetic and potential energy of all the particles in a system
    • Doing work in a system increases the energy stored in a system
    • Heating changes the energy stored by increasing the energy of the particles
    • As the energy increases, the temp will increase or a state of change will occur.
    • The specific heat capacity is the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius
    • Change in thermal energy=Mass x specific heat capacity x temp change