Just to make sure we start off on same page I include what I know about the photon line
geometry.
Summary of photon line geometry. It should be understood that that these are not survey
measurements. They are Bugg tape measurements.
Photon Line Geometry
Coordinate system—beam in z direction y is up and x is to left (rhs)
Beam elements
Z(meters)
-0.15
Beginning of collimator1 (undulator protection collimator) C1
0.0
Beginning of undulator
1.45
bpm6130
32.16
front of collimator counters colt,colR.colB,colL
32.17
Front of collimator 2 (C2)
32.42
Pb wall with large hole(2.5 cm diameter) and 0.406m thick(16’’)
34?
Target and lens/spectrometer system. Target is 0.81mm Densalloy 170.
36.7
S1
36.75
A1
37.0825
Beginning of analyzing magnet Iron
37.2325
End of analyzing magnet Iron
37.30
Front of Pb brick collimator 8” long with 5mm diameter hole(C4)
37.53
Front of A2
37.815
Front of GCAL box
37.865
S2
38.015
Beginning of GCAL
Item description
Collimator 1 (densalloy170),5.08cm diameter, length 15cm,central hole 750micron
diameter
Undulator 1 meter long, inner diameter hole 890 micron. Wall thickness 100 micron
stainless steel. Enclosed in a copper tube inner diameter 1090 micron and outer diameter
3380 micron.
Bpm6130 no material
Collimator counters 3.7mm densalloy170
300micron Si
900 micron G-10
backed by 1.59mm G-10 except in collimator hole. They are immediately followed by
collimator 2 and they surround the edges of collimator hole tangential to aperture. See
photo in long paper Fig 36. It also shows trapezoidal shape (M1) of detectors. All
detectors have this shape.
Collimator 2
Like collimator 1 except hole is 3mm diameter. Length 15 cm.
S1
555 micron Densalloy170
300 micron Silicon
900 micron G-10
Lateral shape is M1. It is located in center of a box with 1.59mm Al walls front and b
ack. Box is 4” high, 3’’ wide and 2” deep.
A1
Has 2 cm aerogel, n=1.0096 preceded by
1.52mm Aluminum and followed by 9.17 mm Aluminum. Lateral and longitudinal size
not measured but probably not important.
Magnet Iron is cylinder 2” in diameter and 15cm long.
C4 Pb brick collimator is 8” high, 4”wide and 8” long. A 5mm diameter hole is drilled
thru long axis to allow beam to pass thru.
A2
Identical to A1
S2/GCAL box is 8” wide, 6” high and 15” long. Its walls are 3.175 mm Al and it
contains the S2 counter and the GCAL calorimeter.
S2
Identical to S1 (M1) but not in box of its own.
GCAL
Consists of 9 elements, each element composed of 3 layers:
3.7mm Densalloy170
300 micron Si
900micron G-10
Elements are separated by 0.5mm air.
M1 Shape of all Silicon detectors.
Peter this is a complicated description as the geometry is not simple The detectors S1,S2,
Col and GCAL all have the same transverse shape. Imagine a wedge of a circle of radius
46.917 mm and angular width 45 degrees. Cutoff the inner portion an isosceles triangle of
height 18.45 mm. The remaining region is the detector sensitive area. The tungsten and
G10 are same size and shape as Si sensitive area. .
Materials.
Al
Pb
Si
Stainless steel
Densalloy 170
Density 17 g/cm3
Weight fraction
W=90%
Ni=4%
Fe=3%
Cu=2.5%
Co,Mn,Cr,Mo each 0.125%
Average Z=69.3725
G-10
Density 1.7g/cm3
Weight fraction
Si=44.0235%
O=44.0235%
C=11.0248%
weight
H=0.928206%
Average Z=10.35594
E166 Aerogel
Density=0.033g/cm3. This is taken from PDG. I asked Kirk for actual value but haven’t
received answer.
Weight fraction
O=66.5845%
Si=29.2208
H=4.19473
Average Z=9.459615