levo
Log inStart

Medical Physics

Half-life

  • 3 things to know
  • Paper 3, section B

Overview

Physical, biological and effective half-life, and the formula relating them.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

What determines physical half-life, and what processes give the biological one?

Numbers

How does effective half-life compare with the other two, and what formula links them?

Numbers

What is the formula for effective half-life, and what do its terms represent?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by the physical half-life of a radioactive isotope?

    Model answer

    The time taken for half the radioactive nuclei in a sample to decay, determined solely by the nuclear properties of the isotope.

  2. 2

    What factor determines the physical half-life of a radioisotope?

    Model answer

    The nuclear properties of the isotope itself; it is independent of external conditions.

  3. 3

    Define biological half-life.

    Model answer

    The time taken for half of a substance to be removed from the body by biological processes such as metabolism and excretion.

  4. 4

    Which processes contribute to the biological half-life of a substance in the body?

    Model answer

    Metabolism and excretion.

  5. 5

    What is the effective half-life of a radioactive substance in the body?

    Model answer

    The time taken for the activity of a radioactive substance in the body to fall to half its original value, accounting for both radioactive decay and biological removal.

  6. 6

    Why does effective half-life account for two separate processes?

    Model answer

    Because both radioactive decay (physical) and biological removal occur simultaneously, each contributing to the reduction in activity.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book
2Open book
3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Measurements and Their Errors
Particles and Radiation
Waves
Mechanics and Materials

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Q is .
positivenegativezero

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AP = 4πr²σT⁴.
BThe surface area of a spherical star is 4πr².
CP₁/P₂ = (r₁²/r₂²) × (T₁⁴/T₂⁴).

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Speed means rate of change of distance.
TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Medical Physics, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a monthSee how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.