# I'm stuck on a Nuclear Decay question

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I'm given the initial activity to be 3000Bq with a half life of 6 hours. It's asking me for the number of unstable nuclei.

It also asked me for decay constant which I got to be 3.2x10^-5 by using ln2/(6x3600) which was correct.

I'm on IsaacPhysics so when I type the answer in and I'm told if my answer is correct or not. Can anyone help with finding the number of unstable nuclei?

It also asked me for decay constant which I got to be 3.2x10^-5 by using ln2/(6x3600) which was correct.

I'm on IsaacPhysics so when I type the answer in and I'm told if my answer is correct or not. Can anyone help with finding the number of unstable nuclei?

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#2

(Original post by

I'm given the initial activity to be 3000Bq with a half life of 6 hours. It's asking me for the number of unstable nuclei.

**NatKH**)I'm given the initial activity to be 3000Bq with a half life of 6 hours. It's asking me for the number of unstable nuclei.

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(Original post by

Unless I'm being silly, this doesn't seem to be a complete question. Can you put up the original wording please?

**atsruser**)Unless I'm being silly, this doesn't seem to be a complete question. Can you put up the original wording please?

Initial Activity = 3000Bq

Half Life = 6 Hours

Decay Constant = ?

Number of unstable nuclei left after 6 hours = ?

Activity after 6 hours = ?

What is the initial number of unstable nuclei

The ones with the question marks are the ones I have to work out.

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#4

(Original post by

Initial number of unstable nuclei = ?

Initial Activity = 3000Bq

Half Life = 6 Hours

Decay Constant = ?

Number of unstable nuclei left after 6 hours = ?

Activity after 6 hours = ?

What is the initial number of unstable nuclei

The ones with the question marks are the ones I have to work out.

**NatKH**)Initial number of unstable nuclei = ?

Initial Activity = 3000Bq

Half Life = 6 Hours

Decay Constant = ?

Number of unstable nuclei left after 6 hours = ?

Activity after 6 hours = ?

What is the initial number of unstable nuclei

The ones with the question marks are the ones I have to work out.

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#5

(Original post by

I'm given the initial activity to be 3000Bq with a half life of 6 hours. It's asking me for the number of unstable nuclei.

It also asked me for decay constant which I got to be 3.2x10^-5 by using ln2/(6x3600) which was correct.

I'm on IsaacPhysics so when I type the answer in and I'm told if my answer is correct or not. Can anyone help with finding the number of unstable nuclei?

**NatKH**)I'm given the initial activity to be 3000Bq with a half life of 6 hours. It's asking me for the number of unstable nuclei.

It also asked me for decay constant which I got to be 3.2x10^-5 by using ln2/(6x3600) which was correct.

I'm on IsaacPhysics so when I type the answer in and I'm told if my answer is correct or not. Can anyone help with finding the number of unstable nuclei?

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(Original post by

If that is the literal and complete wording of the question, then I have no idea. Surely there must be more to it than that?

**atsruser**)If that is the literal and complete wording of the question, then I have no idea. Surely there must be more to it than that?

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(Original post by

The relationship A = lambda N is included in the formula booklets for Physics A Levels (where A = activity, lambda = decay constant, N = number of nuclei) - this is what you need!

**Pangol**)The relationship A = lambda N is included in the formula booklets for Physics A Levels (where A = activity, lambda = decay constant, N = number of nuclei) - this is what you need!

But it says 9.4x10^7 is wrong.

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#8

**Pangol**)

The relationship A = lambda N is included in the formula booklets for Physics A Levels (where A = activity, lambda = decay constant, N = number of nuclei) - this is what you need!

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#9

(Original post by

That's what I've been using but it keeps saying it's the wrong answer. I'd do 3000/3.2x10^-5 = 9.4x10^7

But it says 9.4x10^7 is wrong.

**NatKH**)That's what I've been using but it keeps saying it's the wrong answer. I'd do 3000/3.2x10^-5 = 9.4x10^7

But it says 9.4x10^7 is wrong.

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#10

(Original post by

Ah right. This is a problem of terminology then (to me at least). I wouldn't typically refer to N as the "number of unstable nuclei".

**atsruser**)Ah right. This is a problem of terminology then (to me at least). I wouldn't typically refer to N as the "number of unstable nuclei".

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#11

(Original post by

Out of interest, what would you describe that N as meaning?

**Pangol**)Out of interest, what would you describe that N as meaning?

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(Original post by

What does it claim that the answer is? This looks OK to me.

**Pangol**)What does it claim that the answer is? This looks OK to me.

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#13

(Original post by

I would just refer to it as the number of atoms remaining of the radioactive species in question. Or maybe "parents", depending on the context.

**atsruser**)I would just refer to it as the number of atoms remaining of the radioactive species in question. Or maybe "parents", depending on the context.

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#14

(Original post by

But if they are the atoms of the radioactive sample we are considering, then by definition, they are unstable...

**Pangol**)But if they are the atoms of the radioactive sample we are considering, then by definition, they are unstable...

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