Grain analysis with High-Resolution microscope
Bologna group (G.Sirri)

An High Resolution microscope was developed in parallel with the ESS
and is working in BOLOGNA (MIC1 – PROTO).

The microscope is used for manual checks, fog measurements and
(recently) scanning with sysal.

The microscope is equipped with :


ZEISS 100x objective | n.a. 1.3

ZEISS tube lens hosted in a custom tube

Stage with higher load capacity
[MICOS HPS-170]

Legs with air suspension mechanisms to reduce vibrations.

Custom CMOS camera (same sensor as mikrotron mc1310)
Illumination, horizontal stage, motor controller, frame grabber, workstation
are the same as ESS
LNGS 4 Jul 2006
INFN BO
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Measurements of the optical resolution: star test
Star test: diagnostic tool which consists in the observation of the image of a point source of
light (also known as Point Spread Function (PSF) of the objective) from the specimen
projected by the microscope objective onto the camera sensor plane.
In a perfect aberration-free optical system the
image will be a very close approximation to
the diffraction pattern rings
Aberrations enlarge the Airy disk and produce a spot with variable form and
photometric profile (circle of least confusion). This enlargement reduces the
resolving power both in the lateral and in the axial directions.
LNGS 4 Jul 2006
INFN BO
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Nikon 50x
ZEISS 100x
Z (micron)
4
3
3
2
2
1
1
0
Circle of least
confusion
0
-1
-1
Z ≈ 1 micron
-2
-2
-3
-3
[custom setup: camera
50 mm below the specific
coniugate]
Circle of least
confusion
Z ≈ 5 micron
X, Y ≈ 1 micron
-4
X, Y ≈ 0.2 micron
-6
NEGATIVE IMAGES
LNGS 25 May 2005
-8
G. Sirri – INFN BO
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Image formation
The grain image is the space convolution between the grain surface
and the P.S.F. .
If our “object” size (grain Ø ≈0.6-0.8 micron) is smaller than the “circle of
least confusion” :
 the geometrical image of the grain is smaller than the “circle of least
confusion” and consequeltely its size is not proportional to the object
(impossible to observe little differences in size)
 as smaller the object, as brighter the image
Since the horizontal dimension of the circle of least confusion is 0.2 microns,
this microscope is able to measure the grain size.
LNGS 4 Jul 2006
INFN BO
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Acquisition, analysis … and credits


We used libACQ, a test library developed by I. Kreslo (Bern)
and installed with the help of V. Tioukov (Naples).



Each image grabbing is triggered by stage controller
Output in libEdb format (FEDRA)
Mean grey level of the clusters is also stored




100 levels per emulsion layer
Image size: 0.5 Megapixel
Magnification: 0.118 micron/pixel
Several views in the whole emulsion sheet
Analysis with an improved version of the Fedra Grain Analysis
library (by V. Tioukov).



limit for the clusters area >= 5
Vertical length of a grain >= 3 layers
Two samples:


Nov. 2004 (vertex location CERN test beam)
June 2006 (cosmic rays exposure at LNGS)
Grain Size = cluster area at center grain
LNGS 4 Jul 2006
INFN BO
z
cluster
eZ
eZ0
grains
g
5
Stability of the algorythm (Vertex Loc. nov04,br7,pl8)
sublayer
near the
surface
sublayer
near the
base
Red = top
Blue = bottom
LNGS 4 Jul 2006
INFN BO
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Mean grain area profile
100X
ESS (expansion filter)
ESS
 Nov 2004
 June 2006
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Cluster area profile (cut: area>2)
(Vertex Loc. nov04, br7, pl8)
Red = top
Blue = bottom
(cosmic rays, jun06, pl33)
LNGS 4 Jul 2006
INFN BO
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Grey level horizontal profile
Grey level
(cosmic rays, jun06, pl33)
FWHM ≈ 5 pixel
≈ 0.6 micron
X (1 pixel = 0.118 micron)
LNGS 4 Jul 2006
INFN BO
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Grey level vertical profile (negative image)
(cosmic rays, jun06, pl33)
(Vertex Loc. nov04, br7, pl8)
Red = top
Blue = bottom
LNGS 4 Jul 2006
 sublayer near the surface
 sublayer near the base
INFN BO
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Grain Size vertical profile
Ø 0.72 micron
(Vertex Loc. nov04, br7, pl8)
Red = top
Blue = bottom
Ø 0.62 micron
Ø 0.69 micron
(cosmic rays, jun06, pl33)
Ø 0.59micron
LNGS 4 Jul 2006
INFN BO
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Conclusions

The grains of two sample were measured with a high resolution
microscope equipped with 100x Zeiss objective.


Nov. 2004 (vertex location test beam exposure at CERN)
June 2006 (cosmic rays exposure at LNGS)

Grain size: maybe -5% smaller, but we shuold better estimate
the uncertainty related to threshold set-up and illumination
uniformity )

At present the only evidence is for different thickness of the
emulsion layers (35-40 micron for nov. 2004 and 55-60 for
june 2006). Further investigation are needed.
LNGS 4 Jul 2006
INFN BO
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Further test with sysal
MIC3 (sysal):
Thr
400
500
600
700
800
900
GS (2004) 6.2
5.7
5.3
5.0
4.7
4.3
GS (2006) 5.8
5.4
5.0
4.7
4.4
4.1
GS (2004)
11.3 10.3
9.7
9.1
8.5 (expansion filter)
GS (2006)
LNGS 4 Jul 2006
4.9
INFN BO
(27’ development)
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