INFN BO 1LNGS 4 Jul 2006

Grain analysis with High-Resolution microscope

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.

Bologna group (G.Sirri)

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

INFN BO 2LNGS 4 Jul 2006

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.

G. Sirri – INFN BO 3LNGS 25 May 2005

-8

4

-6

-4

-3

3

-2

-1

0

1

2

-3

3

-2

-1

0

1

2

ZEISS 100x

Z (micron)

Nikon 50x [custom setup: camera 50 mm below the specific coniugate]

Circle of least confusion

Z ≈ 1 micron

Circle of least confusion

Z ≈ 5 micron

X, Y ≈ 0.2 micron

X, Y ≈ 1 micron

NEGATIVE IMAGES

INFN BO 4LNGS 4 Jul 2006

Image formation

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.

The grain image is the space convolution between the grain surface and the P.S.F. .

INFN BO 5LNGS 4 Jul 2006

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

eZ0

eZz

ggrains

cluster

INFN BO 6LNGS 4 Jul 2006

Stability of the algorythm (Vertex Loc. nov04,br7,pl8)

Red = top

Blue = bottom

sublayer near the surface

sublayer near the base

INFN BO 7LNGS 4 Jul 2006

Mean grain area profile

100X

ESS (expansion filter)

ESS

Nov 2004

June 2006

INFN BO 8LNGS 4 Jul 2006

Cluster area profile (cut: area>2)(Vertex Loc. nov04, br7, pl8)

(cosmic rays, jun06, pl33)

Red = top

Blue = bottom

INFN BO 9LNGS 4 Jul 2006

Grey level horizontal profile

(cosmic rays, jun06, pl33)

X (1 pixel = 0.118 micron)

Gre

y level

FWHM ≈ 5 pixel ≈ 0.6 micron

INFN BO 10LNGS 4 Jul 2006

(Vertex Loc. nov04, br7, pl8)

Grey level vertical profile (negative image)

(cosmic rays, jun06, pl33)

Red = top sublayer near the surfaceBlue = bottom sublayer near the base

INFN BO 11LNGS 4 Jul 2006

Grain Size vertical profile(Vertex Loc. nov04, br7, pl8)

(cosmic rays, jun06, pl33)

Red = top

Blue = bottomØ 0.72 micron

Ø 0.62 micron

Ø 0.59micron

Ø 0.69 micron

INFN BO 12LNGS 4 Jul 2006

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.

INFN BO 13LNGS 4 Jul 2006

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) 4.9 (27’ development)