Joint International Conference on Long-term Experiments ...

concentration measurements of the radium how much radon-222 is formed in a unit of
time. The measurements effectuated in the mixed layer present a deficiency relative
to the quantity at which we should expect. The flux to the atmosphere can be estimated
from this deficiency and the gas exchange coefficient is found from the rapport of the
flux to the air–water concentration gradient. We will present a simple estimation, but we
will firstly consider the process of a series of decays, which imply radium-226 and
radon-222. Radiu-226 has a half value life time much longer than radon-222. These two
isotopes are put in isolation until when they reaches equilibrium, where the exchange
rates for which the two isotopes are decayed are equal. It is better to give the
concentration of these radioisotopes by the activity, noted as A, which is equal with the
product between the decay constant λ and the atoms number that are present in a
volume unit:
A Rn-222 = λ⋅CRn-222 (13)
where CRn-222 represents the atom concentration per volume unit. In the case of our
considered isotopes the concentration is given in dpm ⁄100 Kg, where dpm is the
number of decays in a minute. The decay constant is given as a rapport between ln(2)
and the mean half value life time. The equilibrium activity of Rn-222 is of the form A Rn-
222 Ra-226
= A .
The radon deficiency due to the gas exchange is given by:
Φ = h(A Ra-226 - A Rn-222 ) (14)
where h is the Radon-222 layer depth and the activities are the values on this layer. The
flux will be of the form:
Φ = - kapă(CRn-222)aer - (CRn-222)water =
k
= −
water
[ A ) − ( A ) ]
(15)
λ Rn−222
air Rn−222
water
The concentration of the atmospheric radon Rn-222 is much lower than that from the
ocean. Then we can ignore the activity of Rn-222air and we make equal the last two
equations, obtaining the following result:
⎛ A ⎞
k = λ h⎜
Ra − 226
− 1⎟
(16)
water ⎜ A ⎟
⎝ Rn − 222 ⎠
From the made measurements it was obtained (in a mixed layer of 40 m in depth) that
the rapport of Ra-226 to Rn-222 is 1,6, giving a pushing velocity kappa of the form:
ln( 2)
−1
k
water
= 40 m(
1,
6 − 1)
= 4,
4 m d = 10 cm / hour (17)
3,
85d
(c) Applications
One of the advantages of in situ researches is that they have permitted a better
understanding of the role played by organic films for determination of the gases
exchanges. After obtaining such results more types of models for this phenomenon of
the gas exchange were been given. It is not the aim of this paper to develope models,
which were only used in the next discussion and could be given in the Table nr.3. We
wish that, on these models base to answer at some questions that were been not
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