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Half-life
- the time it takes for half of the radionuclides in a sample of a given radioisotope to undergo decay
- Cannot predict the half-life of any thing on the table based on its position on the periodic table. Similarly, cannot determine based on halflifes of other isotopes. Can also not predict mode of decay (alpha, beta, gamma)
Ways to mesure
- Number of nuclides
- Changed to daughter nuclei - fission
- Also be aware when detecting radioactivity, you also may be detecting the radioactivity of radioactive daughter nuclei.
- Mass of the sample? NO!!! Mass is not consumed, so the mass of the sample will be the same. HOWEVER, the mass of the radioisotope will be different. Somehow you are magicaly sorting out these radioisotopes...
- But actual mass of entire sample will not change significantly since little actual mass is lost, most is converted into mass of other isotopes.
- Activity - measured disintegrations per second (dps)
Flaws of the Geiger counter
- Can't discriminate between two or more decays being measured simultaneously, i.e. two decays produce one click.
- IF daughter nuclides is also radioactive then decays from these nuclides will result in an overestimate.
Half-life graph
- LOB - can be curved
- Do multiple half-lives on a graph to show average: 2 is perfectly fine, 3 is sure, but don't have to do it!
Math
$N=N_{0}( \frac{1}{2} )^{n}$
Here:
- $N \implies \text{Final units of sample}$
- $N_{0} \implies \text{Initial units of sample}$
- $n \implies \text{Number of \textbf{half lifes! NOT Number of time units!}}$
