radioactive wine?

From the mass of the neutrino to the dating of wine
Ph. Hubert, F. Hubert, V. Raffestin
Centre d’Etudes Nucléaires de Bordeaux-Gradignan (CENBG)
Domaine du Haut-Vigneau, BP 120, F-33175 Gradignan cedex
Tel : +33-5-57-12-08-62, Fax : +33-5-57-12-08-01, E-mail : hubertp@cenbg.in2p3.fr
How did a of group of research scientists, whose goal was to measure the mass of an
elementary particle, invent a precise mean of measuring the age of a fine wine, without
opening the bottle ?
It is no longer necessary to provide a lengthy introduction for neutrinos. Over the past
few years, they have formed the subject of numerous articles in non-specialist journals and
major newspapers. What accounts for such success? Because these particles, probably the
most numerous in the universe, interact only very weakly with the medium they are traveling
through. This makes it hard to study them. At present, their mass has not yet been measured.
This is not because the scientists looking for them have not displayed great ingenuity and
persistence in their research. To prove that the mass of the neutrino is different from zero has
been a long-term quest towards which many physicists have devoted themselves over the past
twenty or thirty years. For if the mass were indeed non-zero, this would have enormous
consequences in astrophysics, as well as in elementary particle physics. The most recent
results indicate that the mass of the neutrino is not zero, but they do not provide a precise
value.
With the aim of forcing the neutrino to reveal its closely guarded secrets, very large
and difficult experiments have been carried out or are currently being proposed. Some study
naturally occurring sources of neutrinos, such as the sun, while others use neutrinos from an
artificial source, such as a nuclear reactor. Still others attempt to demonstrate that the mass is
not zero by an indirect route.
All these experiments have one common feature: they are trying to find a needle in a
haystack ! The needle is the signal created by the passage of the neutrino in the medium,
while the hay is constituted by all the parasitic signals, which are grouped together under the
name of background noise. Those events being sought are so rare that the struggle to
eliminate all the various sources of background noise is sine qua non for any experiment. The
physicist ends up obsessed with the background noise. First of all, to reduce the effects of the
ever-present cosmic rays, he/she sets up the experiment far under ground, for example in a
mine or a mountain tunnel, when not at the bottom of the sea or deep in polar ice. Next, the
detector should be protected against the ubiquitous natural radioactivity, and this is
accomplished by surrounding it by shielding made of lead or iron. Finally, the detector itself
should be built out of materials countaining only infinitesimal quantities of naturally
occurring radioactive elements.
It was in response to these experimental requirements that the Centre of Nuclear
Studies of Bordeaux-Gradignan (CENBG) has been for several years working on the
development of ultra-low-background-noise gamma ray spectrometers. These spectrometers
should be able to detect activities about 100,000 times less than those which occur naturally in
most materials.
2
Cesium 137 activity in the Bordeaux
wine as a function of the vintage year
0,00
0,20
0,40
0,60
0,80
1,00
1,20
1950 1960 1970 1980 1990 2000
Cs-137 (Bq/l)
Such sensitivity in the detection of radioactive isotopes was of obvious interest for
other disciplines. Oceanography, geology and environmental science were the first to see the
interest of such developments, which for the most part, were carried out in close collaboration
with scientists from these disciplines. Well known among radioactive techniques is that of
dating. Why not try it on wine ?
Every wine connoisseur begins, before tasting, by reading the label to determine the
Château and the vintage year. The vintage year, or millésime, is of great consequence.
Certainly for the taster, but also for whoever bought the bottle. How can one be sure of the
year ? Did you mention dating through radioactive methods ? And that is how, in seeking to
determine the mass of the neutrino, one measures the radioactivity of fine old Bordeaux wine!
To improve the sensitivity of the gamma detection, the first measurements were
carried out with wine samples reduced to ashes. They have shown that wine contains
essentially the isotope potassium 40 at the level of about 30 becquerels per liter (Bq/l), which
corresponds to about 0.9 g of naturally occurring potassium in each liter of wine. Nothing
surprising about that, since wine contains a fair amount of the chemical potassium bitartrate,
so that the presence of the radioactive potassium 40 is quite natural (remember that you have
in your body about 60 Bq/kg of potassium 40). But far more interesting is the fact that certain
bottles of wine contain also the isotope cesium 137, a man-made radioactive element (mainly
from nuclear weapons testing in the atmosphere). This fact was sufficient to excite the
curiosity of the Interregional Laboratory at Bordeaux of the DGCCRF (a French government
agency charged with protecting consumers, assuring fair competition and preventing fraud),
which was in fact looking for a quick and simple way to verify the millésime, and which -very
important- knows how to get hold of some old Bordeaux wine whose years are precisely
known, a crucial element of the story.
All that remained was to carry out the measurements of the radioactivity of the wine as
a function of the years, and the opposite curve was
readily obtained. First, amateurs of wine can
reassure themselves, the activities observed are
quite small, less than 1 Bq/l. The most interesting
aspect is the presence of peaks of activity, which
show that the wine keeps in memory the
atmospheric nuclear testing (years 1950-1963) and
the accident of Chernobyl (1986), which in both
cases led to the presence on French soil of
measurable amounts of cesium 137.
There is a strong correlation between the
rate of cesium 137 decay and the year the wine
was produced. It is obvious that such a curve can
be exploited as of now to estimate the age of a
given wine, and to detect any possible anomalies.
For example, a 1930 vintage wine should not
contain cesium 137. Conversely, an unknown wine
in which activities of about 1 Bq/l or more of
cesium 137 are measured can only correspond to
the year 1963.
3
Being able to date the wine was thus very satisfactory, but reducing it to powder,
especially for “grands crus” or old vintages, was almost a
crime ! The ideal was thus to determine the amount of
cesium 137 without opening the bottle. This appeared to
be possible, as the gamma radiations emitted during the
disintegration of the cesium 137 can easily escape from the
wine, pass through the glass of the bottle and interact with
the gamma spectrometer (see photograph). After a new
series of measurements, and especially after having
checked that the cork and the glass of the bottle did not
contain notable quantities of cesium 137, the feasibility of the nondestructive dating was
established. Dating a wine without opening the bottle is thus possible and the method is now
validated. The improvement of this technique is currently under study, in particular to develop
complementary methods to date young wines.
In conclusion, one can notice that with the current level of sensitivity of radioactivity
measurements, around 1 mBq/l, a whole series of radioactive isotopes could be detected in the
wine. Suppose that the distribution of these activities is specific of a given wine ? Then
different distributions could be expected for a Bordeaux, a Burgundy or an Australian wine,
leading to a possible identification of the origin. However, this is a long term objective and
many measurements remain still essential before this concept can be validated.
Bibliography :
· Pour la Science, n°295, Mai 2002, In neutrino veritas, p.10.
· Science et Vie, n°1017, Juin 2002, Vin : la radioactivité contre la fraude au millésime,
p.46.
· Ph. Hubert, F. Hubert, H.Ohsumi, J. Gaye, B. Médina et J-M. Jouanneau, Application de
l’analyse par spectrométrie gamma bas bruit de fond à la datation des vins d’origine
française, Annales des falsifications, de l’expertise chimique et toxicologique, n°957,
2001, pp. 357-368.
· De la masse des neutrinos à la datation du vin, CNRS Info, n°400, Mars 2002.
· Ph. Hubert, Datation des vins et radioactivité ou Comment valider l’authenticité d’un
millésime ?, 7ème Journée Technique du Conseil Interprofessionnel du Vin de Bordeaux
(CIVB), 6 Février 2003, Arcachon, France.
· Ph. Hubert, F. Hubert, From the Mass of the Neutrino to the Dating of Wine, Nuclear
Physics News International, Vol. 13, No. 1, 2003.
· Ph. Hubert, Datation des vins, neutrino et radioactivité, Bulletin de la Société Française
de Physique, mai 2003.