7.2+B+-+RADIOACTIVITY+EFFECTS,+STABILITY+AND+HALF-LIFE

Back to HOME > IB PHYSICS > ATOMIC AND NUCLEAR There is a lot of information in 7.2, so it is split in two sections on this wiki. 7.2 A RADIOACTIVITY: PROPERTIES OF ALPHA, BETA AND GAMMA
 * 7.1 ATOM || 7.2 RADIOACTIVE DECAY || 7.3 NUCLEAR REACTIONS ||

**7.2 B RADIOACTIVITY: EFFECTS, STABILITY AND HALF-LIFE**
VIDEO FROM VERITASIUM - Is there dangerous radiation in the environment? media type="youtube" key="wQmnztyXwVA" width="560" height="315" 7.2.4 Outline the biological effects of ionizing radiation. Students should be familiar with the direct and indirect effects of radiation on structures within cells. A simple account of short ‑ term and long ‑ term effects of radiation on the body is required. media type="custom" key="23202676"

7.2.5 Explain why some nuclei are stable while others are unstable.

An explanation in terms of relative numbers of protons and neutrons and the forces involved is all that is required.

NUCLEAR STRONG FORCE: The force that holds the particles of a nucleus together. It is strong enough to overcome electrostatic repulsion of protons and very short range so that nuclei don’t attract each other. STABILITY: The nucleus is under the effect of strong nuclear attraction and proton-proton repulsion. It is therefore more stable with an excess of neutrons.

HALF-LIFE 7.2.6 State that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentially with time. Exponential decay need not be treated analytically. It is sufficient to know that any quantity that reduces to half its initial value in a constant time decays exponentially. The nature of the decay is independent of the initial amount.

EXPONENTIAL DECAY: The number of particles AND the rate of decay reduce by half in a constant time. Thus the gradient of the decay curve (rate) is proportional to the number of remaining nuclei.

7.2.7 Define the term //radioactive half// // ‑ life // . RADIOACTIVE HALF-LIFE: The time taken for half of the nuclei in a sample to decay. AND/OR The time taken for the activity to reduce to half of its original value.

7.2.8 Determine the half-life of a nuclide from a decay curve.
 * [[image:nothingnerdy/decay curve particles.jpg caption="Graph showing nuclei remaining"]] || [[image:decay curve activity.gif caption="Graph showing activity"]] ||
 * [[image:RadonDecay.gif caption="Estimate the half-life"]] || [[image:half life.jpg caption="Find half life and nuclide"]] ||

7.2.9 Solve radioactive decay problems involving integral numbers of half-lives 1 The activity of a nuclide reduces from 1000 to 125 in 51 days. What is its half life? 2 At 3:00 pm, a radioactive sample with a half life of 90 minutes contains 500 thousand nuclei. At what time did it contain 8 million nuclei? 3 A sample contains 0.003% of a particular isotope with a half life of 70 years. What percentage did it contain 140 years ago?

SOLUTIONS HERE 17 days 9:00 am 0.012%