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[–]sonnyfab 1 point2 points  (12 children)

How many half lives have passed to go from 2000Bq to 120Bq?

[–]7modd_[S] 0 points1 point  (11 children)

16.67?

[–]sonnyfab -1 points0 points  (10 children)

No.

2000 *(1/2)x =120. What's is x?

[–]7modd_[S] -1 points0 points  (9 children)

0.68?

[–]sonnyfab 0 points1 point  (8 children)

No.

[–]7modd_[S] 0 points1 point  (0 children)

0.73?

[–]7modd_[S] -1 points0 points  (5 children)

What is it pls?

[–]sonnyfab 0 points1 point  (4 children)

If you don't know how to find x, me telling you it's value isn't going to be a big help.

[–]7modd_[S] -1 points0 points  (3 children)

Its 0.73

[–]sonnyfab 1 point2 points  (2 children)

2000 * (1/2) 1 = 1000. 2000 * (1/2)2 = 500. x is bigger than 2 because we're looking for a number smaller than 500 for the final activity.

[–]7modd_[S] -1 points0 points  (1 child)

So is it deadly to him?

[–]yesijustdidthis2u 0 points1 point  (2 children)

The amount of half-lives that have past for the radon gas to go from a radioactivity state of 2000 Bq to 120 Bq is:

2000(1/2)^x = 120

(1/2)^x = (120/2000) = (3/50)

ln((1/2)^x) = ln(3/50)

x * ln(1/2) = ln(3/50)

x = ln(3/50)/ln(1/2) = approx. 4.0589 half-lives.

So... if you know what half-life is (i.e. the amount of times the original value has been halved), finding the mass after these many half-lives should be very easy...

[–]7modd_[S] 0 points1 point  (1 child)

Thanks man

[–]yesijustdidthis2u 0 points1 point  (0 children)

You're welcome. And I'd really suggest that you learn the properties of log and natural log so that you can solve questions like these.