Topic Physics 2 a Dose and Dose equivelent

Topic – Physics 2 a Dose and Dose equivelent • Prior learning – Half life- [t ½ ] • Key words – Half life, ionising, dose, absorb, quality factor

Topic – Physics 2 a Detecting radiation By the end of this lesson we should be able to: • Describe term absorbed dose • Explain dose equivalent in terms of body damage • Know and use absorbed dose and dose equivalent equations

Topic – Physics 2 a Absorbed Dose • The energy cells absorb from radiation is called absorbed dose • Radiation damage depends on 2 factors: – The energy the cell absorbs – The time over which the cell absorbs the energy – Absorbed does = energy absorbed / mass of body part • This is measured in joules per kg of tissue • The unit for absorbed dose = Gray (Gy) • 1 Gy = 1 joule per kg (JKg-1)

Topic – Physics 2 a Task 1: Read pg 86 STAWA Answer following questions 1. What is absorbed dose? 2. What 2 factors affect absorbed dose? 3. What is the equation for absorbed dose? 4. What is a GRAY?

Topic – Physics 2 a Task 1: Answers 1. What is absorbed dose? Energy cells absorb from radiation 2. What 2 factors affect absorbed dose? Energy and time 3. What is the equation for absorbed dose? Energy / mass 4. What is a GRAY? Unit for absorbed dose 1 -J per kg

Topic – Physics 2 a Dose equivalent • Absorbed dose is only useful if comparing different amounts of the same type of radiation • Dose equivalent is much better as it takes into account absorbed dose and a weighting factor called the QUALITY FACTOR. This factor is much bigger for alpha as it reflects the amount of damage done to living cells by the large alpha particle.

Topic – Physics 2 a Dose equivalent • • • Dose equivalent = absorbed dose x Quality factor Dose equivalent measured in Sieverts 1 Sievert(Sv) = 1 joule per kg (1 Jkg-1) Radiation type Quality factor Gamma 1 Beta 1 Slow neutrons 3 Fast neutrons 10 Alpha particles 20

Topic – Physics 2 a Task 2: Read pg 86 STAWA Answer following questions 1. What is dose equivalent? 2. Why is it a better measure than absorbed dose? 3. Draw the table for weighing factor 4. Why is weighting factor higher for alpha particles? 5. What is lethal dose?

Topic – Physics 2 a Task 2: Answers 1. 2. 3. 4. 5. What is dose equivalent? Absorbed dose x quality factor Why is it a better measure than absorbed dose? Takes into account the damage done by alpha particles Draw the table for weighing factor Why is weighting factor higher for alpha particles? More ionising and larger – greater damage done to living tissues What is lethal dose? LD dose that results in death LD-50 kills 50% of exposed people

Topic – Physics 2 a Task 3: body damage Dose equivelent Sv Body Damage 0. 25 Reduction in t(WBC) 1 Possible nausea / vommiting 4 Nausea, diarrhoea, drop in blood count – 50% die in weeks from failure of blood forming organs 5 Loss of hair 50% die 6 Damage to stomach, intestines, loss of fluids, radiation sickness, death within 3 weeks 10 Severe damage to nervous system – death in days.

Topic – Physics 2 a Summary task • Read summary 5. 4 in text pg 178 • Try questions 5. 4 task 1 -4

Topic – Physics 2 a What have I learnt? ? ? I can: • Describe term absorbed dose • Explain dose equivalent in terms of body damage • Know and use absorbed dose and dose equivalent equations