1. Current Status of Pepperpot Scintillator Screen
Simon Jolly
Imperial College
FETS Meeting, 11/10/06

2. Simon Jolly, Imperial College
Mk 1 Pepperpot Setup
11th October 2006
Simon Jolly, Imperial College

3. Scintillator Problems
High light yield expected from phosphor but never seen.
First screen (P46) shows severe damage from high beam power density – phosphor “explodes”!
Plastic scintillator also shows damage (burning/melting) – light yield also far too low.
Ruby scintillator gives better results:
Light yield closer to P46, but still low, and lots of internal reflection.
Ruby pieces are small (25 x 25 mm) and expensive (£300 per screen from Goodfellow).
But it survived! No beam impact markings.
11th October 2006
Simon Jolly, Imperial College

4. Simon Jolly, Imperial College
Scintillator Damage
Front plate
P46 phosphor
Plastic scintillator
11th October 2006
Simon Jolly, Imperial College

5. Simon Jolly, Imperial College
Ruby Scintillator
Shallow contrast
Deep contrast
11th October 2006
Simon Jolly, Imperial College

6. Scintillator For Mk II Pepperpot
Requirements:
High light output.
Fast response (< 1ms).
Extreme radiation hardness/structural integrity: need to absorb high beam power density and survive.
New size: 130x130mm to 150x150mm.
Options:
Ruby screen: large enough or tileable? Can we afford it?
Alternative scintillators: YAG:Ce, YAP:Ce, LuAG:Ce, BGO?
11th October 2006
Simon Jolly, Imperial College

7. Scintillator Comparison
Ruby
YAG:Ce
YAP:Ce
LuAG:Ce
BGO
Density (g/cm3)
3.98
4.57
5.37
6.73
7.13
Hardness (Moh) 9
8.5
8.6 - 5
Melting point (°C)
2050
1970
1875
1050
Coef. of thermal expansion (10-5/K)
0.58
0.7
Integrated light output (% NaI:Tl)
15/40
40/70 15
15-20
Wavelength of max. emission (nm)
550
370
535
480
Decay Constant (ns) 70 25
300
Afterglow (% at 6ms)
<0.005
Radiation length (cm)
3.5
2.7
1.1
Photon yield at 300 K (103 Ph/MeV)
8/35
10/25 10
2-3/8-10
Comments
No scintillation data
Test piece available
Emission wavelength too short
Available in 25mm pieces
Too small/
low light
11th October 2006
Simon Jolly, Imperial College

8. Simon Jolly, Imperial College
Scintillator Choices
We know ruby works, but no comparative data: will cost £10k to produce 150x150mm screen, tiling 36 pieces.
Currently trying to obtain larger ruby pieces from Goodfellow: no luck from St. Gobain, Roditi, Mellor Optics.
YAG:Ce looks like suitable alternative: emission in right wavelength range, not too dense, extremely radiation hard, fast, light output apparently higher than ruby.
Trying to obtain test piece from Crytur (Czech Republic) – recommended by PSI.
11th October 2006
Simon Jolly, Imperial College

9. Simon Jolly, Imperial College
Ruby vs. YAG:Ce
From C. Dujardin (Lyon):
“As far as I know, rubis is used as a screen as well at GANIL in order to perform visualization of heavy ion beams. As I understood, the experimental argument to use such crystal is effectively the radiation hardness, but the use is also the result of the history (it works so ...). For this reason, the literature is not very important as scintillator. Some teams work on Al2O3:Ti for cryogenic application, and since all the samples contain as impurities some Cr, some spectra can be found.
About the scintillator for such use, there are no specific requirements concerning the density, light yield (only to see the beam impact) and for the decay time: it can be "slow" (<1s for the afterglow). In general, users want visible emission in order to see the impact with eyes.
Recently some colleagues of mine broke their unique "screen" of rubis and for this reason they came to me in order to get another sample of rubis that I didn't have. Nevertheless, following the requirement for their experiment, I proposed to them to use YAG:Ce in order to check if it can be substitute to Rubis. It is a very stable crystal which has a good light yield in the visible region and easy to find. I lend a YAG plate to them 4-5 months ago. It seems to work perfectly and the light yield is far away better than Rubis. About radiation hardness, it survives. I’ll ask to my colleague about the status of the use of YAG as heavy particle beam screen.”
11th October 2006
Simon Jolly, Imperial College

10. YAG/LuAG Quotes From Crytur
YAG:Ce, both sides polished
Dimension: 50+0/-0.1 x 50+0/-0.1 x 0.1 +/-0.05mm
Quantity: pcs
Price: EURpc(EXW)
Delivery: 6 – 8 weeks
YAG:Ce sample available: 25x0.1mm disk on 25mm Al ring.
Delivery: 3 – 4 weeks
LuAG:Ce, both sides polished
Dimension: 25+0/-0.1 x 25+0/-0.1 x 0.1 +/-0.05mm
Quantity: pcs
Price: EURpc(EXW)
Delivery: 8 – 10 weeks
11th October 2006
Simon Jolly, Imperial College