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Date: | Wed, 31 Jan 2001 11:28:28 -0800 |
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Bhaskar,
The 2.09E7 atoms/L is for 1 pCi of tritium, not 1 TU. The error came when
I mixed up pCi and TU in my first message (we agree now that 1 TU = 3.2
pCi/L).
You can come by this number couple different ways:
1 pCi = 3.7E-2 dps
and the tritium decay constant (lambda) = 1.767 E-9 s-1
So, for the decay eqn:
-dN/dt = (lambda)N
3.7E-2 = (1.767E-9)*N
N = 2.09 E7 atoms
(multiply by 3.2 to get the number of 3H atoms per TU = 6.69 E7 atoms)
Alternatively, use the definition for 1 TU as noted by Axel Suckow.
1 TU = (1 atom 3H/ 1E18 atoms H)*(6.022 E23 atoms H / mol H)*(2 mol H /18 g
H2O)*1000 g/L = 6.69 E7 atoms 3H per L.
Converting to g/L, I obtain 1 TU = 3.3 E-16 g tritium per liter, or a
factor of two different from the number Axel reported. You should check
this yourself - clearly I've been wrong before.
If you want values in Bq, then 1 pCi = 37 mBq (or 1 Bq = 27 pCi).
I am not a modeler, and cannot appropriately respond to Axel's comment
about what units you should use in your model. However, I hope this helps
clarify the "units" issue.
- Tim
At 09:14 AM 1/31/01 -0800, you wrote:
>Hello Tim:
>
>I shall be very grateful if you can review the following calculation for me.
>It is based on the input received from you
>
>3.2 pCi/L =1 TU = 2.09E7 atoms/L (Am I right here?? How do you get
>the atoms/L)
>
>Now 3g Tritium = 6.023E23 atoms
>
>So 1 atom of Tritium = (3/6.023E23) g
>
>So 1TU = (2.09E7*3/6.023E23) g/L = 1.04E-16 g/L
>
>Now 1 TU = 0.118 Bq/ L (from Clark & Fritz pp. 175)
>
>so 1 TU = 1.04E-16 g/L = 0.118 Bq/L
>
>Can we then say that
>
>
>1.04E-16 g of Tritium = 0.118 Bq ????
>
>Even though Bq is a frequency unit (dps)it appears that it can be
>equivalenced to mass of tritium.
> I have to convert TU into a mass unit for a contaminant transport
>simulation and this is the way I found
>
>But is this valid??
>
>I shall be very grateful for your help
>
>Regards
>
>Bhaskar Joshi
>
>
>
>
>
>
>
>:
>
>
>
>-----Original Message-----
>From: Timothy P. Rose [mailto:[log in to unmask]]
>Sent: Tuesday, January 30, 2001 10:21 AM
>To: [log in to unmask]
>Subject: [ISOGEOCHEM] errata
>
>
>Bhaskar,
>You are correct that 1 TU = 3.2 pCi/L, not the other way around. Sorry for
>the misinformation. I'll go a little slower before I hit the reply button
>next time.
>- Tim
>
>
>*****************************************************************
>Timothy P. Rose
>Analytical and Nuclear Chemistry Division, L-231
>Lawrence Livermore National Laboratory
>Livermore, CA 94550
>Phone: 925-422-6611
>Fax: 925-422-3160
>email: [log in to unmask]
>*****************************************************************
>
>
*****************************************************************
Timothy P. Rose
Analytical and Nuclear Chemistry Division, L-231
Lawrence Livermore National Laboratory
Livermore, CA 94550
Phone: 925-422-6611
Fax: 925-422-3160
email: [log in to unmask]
*****************************************************************
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