1) If the background is constant for your sample, why bother to subtract it from

Question

1) If the background is constant for your sample, why bother to subtract it from each reading prior to the regression analysis? 2) Under what circumstances would the effect of the background be less/more noticeable? 3) Apart from the magnitude of the energies involved, in what 'mechanistic' sense does the reaction (decay) of your sample (cesium -137 to barium -138m) differ from the reactions occurring in an exploding atomic weapon, or controlled nuclear reactor? 4) Why are 'lifetime values' always longer than their corresponding 'half-life' values?

Explanation / Answer

1)

I will try to explain the answer with an exaple.

suppose we want to measure the half life of a radio active sompound present in a pond. the pond already contains traces of carbon C-14 carbon. So when we measure the half life of that compound, we will get an increased reading of half life than it should be as there was already C-14 present in the surrounding.

So to measure exact half life of the sample we need to subtract the the surrounding value from each of our samples before we measure them.

2)

If the concentration of C-14 in the surroundings is very less as compared to the sample, then the affect of the surrounding would be negligble. (normally for samples which have just died, as content of C-14 is maximum in them). For samples which have died many years ago, the content of C-14 would be very less, and hence even small traces of C-14 in the surrounding would affect the measurement of Half life of the sample.

3)

The reaction occuring in the decay is a very slow process as compared to fast and highly exthermic reactions occuring during the atomic blast and nuclear reactors. And radio active decay is a natural process, which occurs for every living substance.

4)

Half life values are calculated using logarthemic equation. Hence to exactly predict the age of a very old sample is impossible as slight change in the concentration can change the life of the sample by many years. Thus, the value of total life is never accurate and is generally considered to lesser than the actual value.

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