Schott Radiation Resistant Glasses
Peter R Hobson, IPES, Brunel University UK
Introduction
Schott Glaswerke1 make a series of radiation resistant glasses based on their standard
optical glass products. All of these glasses have had CeO2 added in varying amounts
to give them increased resistance to gamma irradiation. Some of these stabilised
glasses also have significant resistance to other ionising particles and to neutrons.
Glasses for VPT faceplates in the CMS endcaps
Ideally we need glasses with radiation resistance to more than 105 Gy, no attenuation
of the scintillation light from the lead tungstate crystals, a good match of thermal
expansion and glass transition temperature to the standard borosilicate glass used for
low-cost windows in normal vacuum photodetectors. It would be desirable to have a
moderately high refractive index at the peak of the lead tungstate scintillation
spectrum to increase the light collection from the end of the crystal. Available optical
adhesives limit the gain that can be made to a maximum refractive index of around
1.70.
Glass availability and properties
Schott have made a number of radiation resistant glasses; their current printed
catalogue list 16 as normally available with a further 15 as special order items.
However their UK agents2 state that in 1998 only four glass types are readily
available, with the likelihood that another two (LaK9G15 and BK7G25) will also be
melted for existing customers. The key properties of these six glasses are listed in
table 1.
Glass name
nF (480 nm)
Coeff. of thermal
d
Tg (C)
expansion (10-6K-1)
BK7G18
1.525
63.7
7.0
570
K5G20
1.530
56.8
8.9
503
SF6G05
1.834
25.3
7.8
427
SF8G07
1.711
30.7
8.4
428
LaK9G15
1.670
54.7
6.2
650
BK7G25
1.527
63.2
7.0
570
The catalogue also gives the internal transmittance, for 10 mm thick samples, for the
glasses before and after Co60 irradiation for total doses of 10, 100, and 1000 kGy. This
data is shown, for the four readily available glasses, in figure 1.
It can be seen, by reference to the lead tungstate emission spectrum, in figure 2 (taken
from the ECAL TDR3), that only the BK7G18 and K5G20 glasses are really suitable.
1
Schott Glasswerke, Geshaftsberiech Optik, Verkaut Optishes Glas, Postfach 2480, D-6500 Mainz 1
H.V. Skan Ltd., 425/433 Stratford Road, Shirley, Solihull B90 4AE
3
ECAL TDR Reference
2
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Schott BK7G18
Internal Transmittance
1
0.9
Unirradited
10 kGy
0.8
100 kGy
1 MGy
0.7
0.6
400
500
600
700
Wavelength (nm)
Figure 1a
Internal transmittance for a 10mm thick block of BK7G18 glass
Schott K5G20
Internal Transmittance
1
0.9
Uniradiated
10 kGy
0.8
100 kGy
1 MGy
0.7
0.6
400
500
600
700
Wavelength (nm)
Figure 1b
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Internal transmittance for a 10mm thick block of K5G20 glass
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Internal Transmittance
Schott SF6G05
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Uniradiated
10 kGy
100 kGy
1 MGy
400
500
600
700
Wavelength (nm)
Figure 1c
Internal transmittance for a 10mm thick block of SF6G05 glass
Internal Transmittance
Schott SF8G07
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Uniradiated
10 kGy
100 kGy
1 MGy
400
500
600
700
Wavelength (nm)
Figure 1d
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Internal transmittance for a 10mm thick block of SF8G07 glass
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Lead tungstate scintillation spectrum
Relative Intensity
100%
75%
50%
25%
0%
350
400
450
500
550
600
Wavelength (nm)
Figure 2
Scintillation emission spectrum of lead tungstate crystals in CMS
Comments
Although a wide range of glasses with radiation resistance have been produced by
Schott, only four are readily available commercially (a special melt , producing about
180 kg of glass, would cost of the order of £25000). Of these four only BK7G18 and
K5G20 have a transmission far enough into the blue to be useful. Samples of these are
being sent to Brunel for
 Co60 radiation damage tests at LHC rates and total dose in the endcaps
 Tests to see whether these glasses are themselves scintillators (this is true for
some radiation resistant glasses containing cerium)
It should be ascertained from vacuum photodetector manufacturers whether the poor
match of thermal expansion coefficient of these glasses to borosilicate (???) will allow
them to be attached to standard VPT bodies without graded seals.
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