Re: I-129&127

[Franz Schoenhofer <schoenho@via.at>]

At 07:50 30.03.99 -0600, you wrote:
>1 - Can anyone guide me to a reference for "chemical technique" for
>quantitative and qualitative determination of Iodine-129 and Iodine-127?
>
>2 - What is the range of the background level of these two isotopes?
>
>Your help is appreciated.
>
-----------------------------------------

Iodine-127 is the only stable isotope of Iodine, therefore its abundance is
100%. I-129 is a fission product with an extremely long half life of
1.57*10E7 years. The natural background originates from spallation of xenon
in the atmosphere after collision with particles from cosmis rays. The
concentration of I-129 is usually given by the socalled R-value, which is
the ratio of the amount of I-129 to I-127. The natural background R-value
is in the range of 10E-13. I have some values at hand from 1984 and 85: In
airfilters R-values between 0.5 and 4.5*10E-8 were found. In thyroids of
animals (iodine is accumulated in thyroids) R-values were measured between
o.7 to 4.2*10E-8, in wild animals the highest value was 39*10E-8.

For I-127 usual non-radiometric analytical methods are used. For I-129 at
environmental levels the classical method is neutron activation by an
n,gamma reaction to I-130, which decays by beta-decay and a half-life of
12.4 hours to Xe-130, which is stable. Since it is so long- lived a
relatively high mass is associated with this isotope. Therefore to my
knowledge also ICP-MS methods are increasingly used, also because the
number of research reactors is steadily declining. I-129 cannot be measured
directly or after easy sample preparation by radiometric methods.

Best regards,

Franz




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