Re: [Phys-l] thorium-228

[ludwik kowalski <kowalskil@mail.montclair.edu>]

On Dec 25, 2009, at 7:21 PM, Bernard Cleyet wrote:

> Ludwik!
>
> ppb moles, atoms, molecules, etc.???

a) My understanding is that ppb stands for the number of ions of  
thorium per one molecule of water. Is this correct? If so then one  
liter of water contains 10^15 atoms of Th-228, as shown by Bernard.

b) That was the first part of the problem. The second part is how many  
alpha particles are emitted by these atoms each second. My answer,  
based on the given half-life is 1.15*10^7. Is this correct?

c) Yes, by definition, 1 Ci is 3.7*10^10 decays/second. Therefore, the  
activity is 1.15*10^7/3.7*10^10 = 3.57*10^-4. That is my answer. Is  
this correct?

Ludwik
= = = = =

> Plugging and chugging W/O much thought:
>
>
> Activity = decay constant times number of nuclei
> decay constant = half life / Ln(2)
> 37 GBq / Ci
>
> Therefore N = 1.15 E+15   nuclei.   Compare this to A = 6.022 E+ 23  
> nuclei per mole.   I doubt very much you used Th metal.  Th is most  
> commonly? (IV),  e.g ThCl(4)
>
> bc missing something?
>
>
>
> On 2009, Dec 25, , at 15:01, ludwik kowalski wrote:
>
> > Not trusting myself, I would like someone to confirm that the  
> > answer below is correct.
> >
> > Question: Th-228 (half-life 1.913 years) is dissolved in water, at  
> > the concentration of 0.03 ppb. What is the activity of that  
> > isotope? (ignore activity of daughters).
> >
> > Answer: 3.57*10^-4 Ci.
> >
> > Thanks in advance,
> >
> > Best wishes to all,
> >
> > Ludwik
> > = = = = =
> >
> > Ludwik's new book (AUTOBIOGRAPHY) see:
> >
> > > http://pages.csam.montclair.edu/~kowalski/mybook2.html
> >
> >
> > Share this link with those who might be interested. Thanks in  
> > advance.
> >
> >
> >
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>
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Ludwik Kowalski, a retired physics teacher
5 Horizon Road, Apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist.

                                            Food for thought:  
"Absence of proof is not proof of absence."

Updated links  to his selected publications are at:
http://csam.montclair.edu/~kowalski/cf/  ,   http://csam.montclair.edu/~kowalski/my_opeds.html 
  and  http://csam.montclair.edu/~kowalski/revcom.html