Re: post topicality

[mem122a@lanl.gov (Milton McLain)]

Melissa,

1st:  Are you sure that the Dupont Aquasol won't work?  Creation of a
homogeneous gel (a single phase) may be OK.  

        Purpose of HCl is to avoid precipitation of nickel as hydrous oxide.
The maximum pH for which Ni solubility can be assured is probably about pH
4.  With the 0.1 N HCl, the pH is about 1.  It might be helpful to add base,
e.g. NaOH solution, to raise the pH to, let's say, 3 prior to cocktail
addition.  Also, how about limiting the volume of Ni-63 solution mixed with
the cocktail to 1 mL. Assuming that this Ni-63 solution is a standard, you
can still use it as such, provided that you keep up with aliquout values
removed, etc.
        Another approach, valid if the quantity of Ni-63 activity is
adequate, would be to dilute the 5 mL of Ni-63 to a larger volume, e.g. 25,
50, or 100 mL, and then count a 1 mL aliquot.  This will dilute the HCl, and
increase the pH.
        Another (a final suggestion) scheme might be to eliminate the HCl
entirely by boiling down the Ni HCl solution after addition of about 5 mL
conc. nitric acid.  Continue to evaporate the Ni nitrate solution to near
dryness, dissolve in water, dilute to known volume with water, and take
aliquot for LSC. This will remove chloride, which can be a significant
quenching agent.  A negative aspect of this procedure is that it can cast
serious doubt on the standard traceability.

Good luck!

Milton McLain

>
>Let's say you have Ni-63 in the form of nickel chloride (NiCl2) dissolved
>in approximately 5 mls of 0.1M HCl.  You have to use this as a standard in
>a liquid scintillation counter; therefore, you are constrained to a 20 ml
>scintillation vial for your chemical manipulations.
>
>There is not enough energy for Cerenkov here, so presumably some fluor has
>to be used.  Given that you have 5 mls of an aqueous solution and are
>constrained in regards to your total volume, what would you do?
>
>Aquasol (Dupont) does not appear to work; it results in a
>semi-opaque/semi-translucent gel.  Various proportions of HCl, Triton X-100
>and an organic fluor do not appear to work.  Since the NiCl2 will not
>volatilize, evaporation to reduce aqueous volume is a possible solution,
>but only as an extreme last resort.
>
>Comments?  Suggestions?
>
>-- 
>Melissa Woo                       | University of Illinois at Urbana-Champaign
>Health Physicist                  | Environmental Health & Safety Bldg., MC225
>office phone: 1.217.244.7233      | 101 S. Gregory St., Urbana, IL  61801
>m-woo@uiuc.edu                    | http://www.cso.uiuc.edu/ph/www/m-woo
>
>