Re: what wavelenght is the light generated by cerenkov effect?

Fred, 

This was a remarkably challenging question and unfortunately, it has no 
direct answer.  The Cerenkov light is polychromatic ranging from about 300 
to 600nm with a strong peak of about 470nm in water.  That peak gives the 
traditional blue glow.  I've checked with a large number of experts and 
there seems to be no data concerning the exact spectra.  I hate to say it, 
but this may need to become a part of your thesis.  On the bright side, I'm 
sure it's at least another paper on it's own and possibly several. 

There is a strong dependence of light output to the density of the material 
and the energy of the electrons are entering the medium.  I'll provide you 
with all the references I could find on the topic, but several may prove 
difficult to find.  

Incidently, I've seen a pulseable reactor and that flash is actually nearly 
white light.  (Not to mention very, very cool.)

References:

Radiation Detection and Measurement, Glenn F. Knoll, Wiley 1989. 
Chapter 19 Miscellaneous Detector Types: Cerenkov Detectors, p.682-684

Interesting chapter section, includes two graphs for photon yield and 
threshold energy. 

Classical Electrodynamics, J.D. Jackson, Wiley 1962.
p. 499, Fig. 14.16

Reference courtesy of Dr. H.B. Knowles. Good classical description of 
Cerenkov light.  

NCRP 58, A Handbook of Radioactivity Measurements and Procedures.
P. 59-6? several tables on Cerenkov light. 
(NCRP: National Council for Radiation Protection, USA)
Ref. courtesy of D. Whitfill, Kansas Dept. of Health and the Environment. 

Cerenkov Light Production, Madey, 1964.
Ref courtesy of Dr. Barlow at Yale. 

Cerenkov Radiation and its Applications, J.V. Jelly, Pergamon 1958. 

B.D. Sowerby, Nucl. Instrum. Meth. 97, 145 (1971)

W. J. Gelsema, et. al., Int. J. Appl. Radiat. Isotopes 26, 443 (1975)

These last three are in the references of Ch 19 in Knoll.

I'm sorry I couldn't be of more help, but this was all that I could find in 
over a week of looking.  If you do get a paper out of the Cerenkov stuff, 
I'd like a copy!  Thanks for an interesting challenge and good luck on 
your PhD.