  Aims: To measure the beryllium abundance in two TO stars of the Globular
Cluster NGC 6752, one oxygen rich and sodium poor, the other presumably oxygen
poor and sodium rich. Be abundances in these stars are used to put on firmer
grounds the hypothesis of Be as cosmochronometer and to investigate the
formation of Globular Clusters. Method:We present near UV spectra with
resolution R$\sim 45000$ obtained with the UVES spectrograph on the 8.2m VLT
Kueyen telescope, analysed with spectrum synthesis based on plane parallel LTE
model atmospheres. Results:Be is detected in the O rich star with
log(Be/H)=-12.04 $\pm$0.15, while Be is not detected in the other star for
which we obtain the upper limit log(Be/H)$<$-12.2. A large difference in
nitrogen abundance (1.6 dex) is found between the two stars. Conclusions:The Be
measurement is compatible with what found in field stars with the same [Fe/H]
and [O/H]. The 'Be age' of the cluster is found to be 13.3 Gyrs, in excellent
agreement with the results from main sequence fitting and stellar evolution.
The presence of Be confirms the results previously obtained for the cluster NGC
6397 and supports the hypothesis that Be can be used as a clock for the early
formation of the Galaxy. Since only an upper limit is found for the star with
low oxygen abundance, we cannot decide between competing scenarios of Globular
Cluster formation, but we can exclude that 'polluted' stars are substantially
younger than 'unpolluted' ones. We stress that the Be test might be the only
measurement capable of distinguishing between these scenarios.
