suppose a sample of a certain substance decayed to 77.8% of its original amount after 300 days. (round your answers to two decimal places.) (a) what is the half-life (in days) of this substance? days (b) how long would it take the sample to decay to one-third of its original amount?



Answer :

The half life of the substance is 828.37

What is Half life?

The period of time it takes for one-half of a radioactive isotope to decay is known as the half-life. An individual radioactive isotope's half-life is unaffected by environmental factors and is independent of the isotope's starting concentration.

The amount of time needed for half of a radioactive sample's atomic nuclei to decay

Given:

As, The amount of a substance after t days is given by:

p(t)= [tex]p(0)[/tex][tex]e^{-kt[/tex]

Original amount after 300 days.

p(300)= 0.778p(0).

p(t)= [tex]p(0)[/tex][tex]e^{-kt[/tex]

0.778 = p(0)[tex]e^{-300k[/tex]

-300k= log (0.778)

-300k= -0.109020

k = 0.0003634

So, p(t)= [tex]p(0)[/tex][tex]e^{-0.0003634t[/tex]

This is t for which P(t) = 0.5P(0). So

0.5p(0)=  [tex]p(0)[/tex][tex]e^{-0.0003634t[/tex]

[tex]e^{-0.0003634t[/tex] = 0.5

log ( [tex]e^{-0.0003634t[/tex]) = log 0.5

-0.0003634 t = log 0.5

t= -0.30102999566/ -0.0003634

t= 828.37

Hence, the half life of the substance is 828.37

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