Two tracers are named in the OCR specification.Technetium-99m is the most widely used tracer. The m means metastable: the nucleus is in an excited state and drops to its ground state by emitting a gamma photon only.99m43Tc → 9943Tc + γ • it emits gamma photons of 140 keV, energetic enough to leave the body but easy to detect in a gamma camera
• it emits no alpha or beta particles, so the dose is low
• its half-life is 6.0 h
• it is made on site from molybdenum-99 (half-life 66 h) in a generator, so hospitals keep a steady supply
• it binds to many different compounds, so it can target bone, heart, kidneys, thyroid and moreFluorine-18 is a β+ (positron) emitter with a half-life of about 110 minutes.189F → 188O + 0+1e + νe It is attached to glucose to form fluorodeoxyglucose (FDG), which is taken up most by very active cells such as cancer cells and the brain. It is used in PET scanning. Its short half-life means it must be made in a cyclotron close to the hospital.Worked example: the energy of a 140 keV photon in joules isE = 140 × 103 × 1.60 × 10−19 = 2.24 × 10−14 J
• it emits no alpha or beta particles, so the dose is low
• its half-life is 6.0 h
• it is made on site from molybdenum-99 (half-life 66 h) in a generator, so hospitals keep a steady supply
• it binds to many different compounds, so it can target bone, heart, kidneys, thyroid and moreFluorine-18 is a β+ (positron) emitter with a half-life of about 110 minutes.