Half Life Problems

[gibb0080]

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Could anybody help me me out. I am having trouble with half-life problems and radioactive decay. I know these should be easy problems, but I can't make sense of them. Is there an easy solution.

For example: If the half life is 24 hours, how long does it take 75% of the isotope to decay?


Thanks

 

[teefie]

Could anybody help me me out. I am having trouble with half-life problems and radioactive decay. I know these should be easy problems, but I can't make sense of them. Is there an easy solution.

For example: If the half life is 24 hours, how long does it take 75% of the isotope to decay?


Thanks

it would take 48 hrs. one half life is 24. at the 24th hour 1/2 will be left. for half of the 1/2 left to decay it will take another 24 hours. giving you 1/4 left or 75% decay. if this doesnt help i can give the equation but i think logic helps better and quicker.

 

[KOM]

Could anybody help me me out. I am having trouble with half-life problems and radioactive decay. I know these should be easy problems, but I can't make sense of them. Is there an easy solution.

For example: If the half life is 24 hours, how long does it take 75% of the isotope to decay?


Thanks

There's a formula you might be able to use but I just look at this and think...in 24 hours 50% of the sample will have decayed.

One more half life and 50% of what's left of the original sample (50%) will have decayed or 1/2 (50%) = 25%. Thus 50% + 25% = 75% after two half lives or 48 hours.

 

[RozhonDDS]

Could anybody help me me out. I am having trouble with half-life problems and radioactive decay. I know these should be easy problems, but I can't make sense of them. Is there an easy solution.

For example: If the half life is 24 hours, how long does it take 75% of the isotope to decay?


Thanks

24hrs*3/4=18

24hrs-18hrs=6

24hrs/2=12............12hrs/2=6

So, 2 half reactions=75% decay

2 half reactions= 24+24=48hrs

 

[gibb0080]

Will the decay problems get much harder than this on the real DAT?

 

[RozhonDDS]

Will the decay problems get much harder than this on the real DAT?

the problem is not hard, try it like this. What is 75% of 24 hrs? Answer=6

Now how many time do you have to take the half life of 24 to get 6?
24/2=12 24/2=6

So, you have to do the half life 2 times. Now all you do is multiply your 24hrs times 2 and you get 48 hrs.

 

[whiskeysour]

the problem is not hard, try it like this. What is 75% of 24 hrs? Answer=6

Now how many time do you have to take the half life of 24 to get 6?
24/2=12 24/2=6

So, you have to do the half life 2 times. Now all you do is multiply your 24hrs times 2 and you get 48 hrs.

75% of 24 hours is not 6, it is 18 lol

 

[dat_student]

Could anybody help me me out. I am having trouble with half-life problems and radioactive decay. I know these should be easy problems, but I can't make sense of them. Is there an easy solution.

For example: If the half life is 24 hours, how long does it take 75% of the isotope to decay?


Thanks

Use this formula:

N = Ni (1/2) ^ (t / t1/2)

N = remaining radioactive nuclei
Ni = initial amnt
t1/2 = half life
t = elapsed time

75% is lost. So, N = 25% of the initial amnt

25% Ni = Ni (1/2)^(t/24)
1/4 = (1/2)^(t/24)
(1/2)^2 = (1/2)^(t/24)
2 = t /24
t = 48 hrs 🙂

 

[RozhonDDS]

75% of 24 hours is not 6, it is 18 lol

opps forgot that step...

75% of 24hrs=18

than subtract 24-18=6 (6 represents what is left from 75% decay)

 

[dat_student]

opps forgot that step...

75% of 24hrs=18

than subtract 24-18=6 (6 represents what is left from 75% decay)

????

6 hrs left from 75% decay ????!!!!!! 😕

 

[teefie]

i think everyone is just confusing the kid more.

 

[gibb0080]

No, now that you point it out that problem was easy as hell! However, I'm sure there are others that are much more difficult then that on the DAT isn't there? On harder problems you actually have to know a formula, or in that case multiple formulas.

 

[teefie]

No, now that you point it out that problem was easy as hell! However, I'm sure there are others that are much more difficult then that on the DAT isn't there? On harder problems you actually have to know a formula, or in that case multiple formulas.

no dat science is cake compared to all of the practice test i ever took.

 

[whiskeysour]

OP,

there is no need to use a formula for this problem, just a lil common sense... don't listen to these other clowns 🙂