b

EDEXCEL

I. Physics, 8540/9540
Unit 1: Mechanics and radioactivity
- 1.19 Stable and unstable nuclei.
Nucleon number and proton number. The balancing of nuclear equations. Isotopes.
- 1.20 Radioactivity as a random process. Exponential decay: decay constant and half-life. Activity and the becquerel. The constant ratio property of exponential curves. The experimental determination or modelling of half-life. Measure half-life of protactinium.

Unit 3d: Medical physics (option)
- Radioisotopes for nuclear medicine; metastable radionuclides. Production by neutron irradiation and elution methods: in particular 123I, 131I and 99mTc. Radionuclides as tracers. Dilution studies; measurement of body fluids. Uptake studies; use of model or ‘phantom’. Imaging body parts. Physiological effects of radiation.
- Range and effects of alpha, beta and gamma radiation.
- Radioactive and biological half lives; effective half lives.
- Gamma camera. Principles of collimator, scintillation counter and photomultiplier.
- X-ray production. The rotating anode X-ray tube. Energy of accelerated electrons in eV. Efficiency.
- MeV X rays for therapy. Absorption not strongly dependent on proton number.
- Multiple beams and rotational treatment. Alignment devices. Criticality of dose.
- keV X-rays for diagnosis. Absorption strongly dependent on proton number. Detection with photographic plates. Radiographs of bones, tissues and air spaces.
- X-ray geometry. Point source, shadows, use of a lead anti-scatter grid. Inverse square law.
- Ultrasonics in medicine. The sonar principle. Small wavelengths give rise to better resolution. Scanning methods for ultrasonic diagnosis. Basic principles only. A-scans and B-scans. Reflection and absorption. Acoustic impedance Z. Dependence of Z on speed of wave and density of medium; Reflection coefficient = (Z1 – Z2)2/(Z1 + Z2)2
- The need for a coupling medium. Comparison of ultrasonic and X-ray techniques in diagnosis.
- Health and safety aspects of the use of ultrasound and X-rays.