Simple half-life question (1 Viewer)

[davidbarnes]

"Calculate the percentage of original parent isotope left in a 3800 million year old rock by using the K/Ar isotope with a half-life of 1300 million years."

It seems very simple, but I'm not sure if I've got the right answer. The answer I got was 13.46%. Can anyone concur or disagree?

 

[Forbidden.]

In short, agreed.

Working:

Let:
m(0) = 1, for 100% of the mass of the parent isotope originally
t = 3800x10⁶, the current time of recording the amount of the isotope left.
t_1/2 = 1300x10⁶, the half-life of the isotope.
m(t) = ?, the amount of the isotope left after 3800x10⁶ in question.

m(3800x10⁶) = 1 . 0.5 ^{(3800x106)/(1300x106)}
m(3800x10⁶) = 0.1318457596 ...

13.18% is left after 3800 million years

 

[Undermyskin]

Gosh is it the decay formula for Maths Ex1? Crap. I haven't touch it.

 

[rooeys2]

is this maths or chemistry =S
half-life is NOT in the syllabus dont waste ur time doin those questions

 

[Undermyskin]

It is! (I suppose....so....hang on...let me check)

Anyway, half-life is asked in any radioactivity relating questions.

 

[Forbidden.]

is this maths or chemistry =S
half-life is NOT in the syllabus dont waste ur time doin those questions

Agreed.
Leave extended knowledge to university, where it will be much more useful there than in high school.