To zinc or not to zinc (i.e. to cad?)

[Ralph Florentin]

Dear Jim,
	You can use either zinc or cadmium arc lamps for UV flooding.
There is no big difference between the two. We use the Cd for a few
not very important reasons:
1. it is the same as used by Mike Lesser. Works according to recepie.
2. the lamp is compact and fits into tight space as the DFOSC and at
   the same time only dissipates 5 watts of heat (which we even suck
   out with a small ventilator), so no harm is done to the optics
   /coatings.
However, both Zn and Cd lamps can be used. Both of them are harmful
to the eyes, so one should not look at them directly without protective
goggles. Cd have its dominant emission lines at about 2200 Angstroem.
Personally I think that cleanliness and use of proper dry, clean and
oil free gas for the UV flooding is the most important part of the
process. 
	Also, access to proper cleanroom facilities for the opening
up of cryostats and/or handling of the CCD chips is very desirable.
I do suspect that the poor holding time that we experienced with
our DFOSC cryostat at La Silla could well be due to Atacama dust
settling on one of the O-rings, when Preben opened the cryostat
there.
Best wishes and in appreciation of the help extended to us by
Peter Sinclaire.
Ralph.
> 
> 
> Johannes et al,
> 
>     We are still trying to decide whether to flood with zinc or
> cadmium.  In Garching, we have a zinc lamp, at La Silla we have
> a cadmium lamp.  Since we want to have a repeatable recipe, we
> wish to stick with a single type of lamp.  I understand that you
> use cadmium.  Any arguments for one lamp type or the other will
> fall on thankful ears here.  Please include O. Iwert, S. Deiries,
> J.-G. Cuby, P. Sinclaire and N. Haddad in this discussion.
> 
>     I got your message about your detector system status.  Good
> luck with everything.
> 
>                                         Cheers,
> 
>                                           Jim
> 
> 
> P.S. We will probably end up testing both lamps to see if they get the
>      same results, although the optimal flood time may be different.
> 
> J. Beletic
> E.S.O.
> Head of Optical Detector Group
> Tel: +49-89-32006-520
> 
>