Emulsion Detectors
University of BERN
Albert Einstein Centre for Fundamental Physics
LHEP
M.Fatih BAY
TextBooks for Emulsion Detector
• Nuclear Research Emulsions. Vol.1: Techniques and Theory Barkas, Walter H.
(Pure and Applied Physics, New York: Academic Press, 1963Walter)
• Nuclear Research Emulsions. Vol.2: Particle Behavior and Emulsion
Applications. Barkas, Walter H.
• The study of Elementary Particles by The Photographic Method: C. F. Powell,
P. H. Fowler and D. H. Perkins, (Pergamon Press, 1959. xvi–669 p. £12 10s.)
OUTLINE
• A Video of Pion Interaction inside Nuclear Emulsion
• Nuclear Emulsion.
• Physical and Chemical Constitution of Nuclear-Track Emulsions.
• History of Nuclear Emulsion.
• Emulsion Read-Out System.
• Modern Techniques of Nuclear Emulsion and their application.
.
Pion Interaction inside Emulsion Detector
~120 Micron
• Nuclear emulsion is a three-dimensional tracking detector for charged
particles having a spatial resolution of less than 1 μm
What is Nuclear Emulsion in Particle
and Nuclear Physics?
• Nuclear Emulsion particle detectors feature the
highest position and angular resolution in the
measurement of tracks of ionizing particles.
• Nuclear Emulsion, used to record the tracks of
charged particles, is a photographic plate.
• A photographic emulsion consists of a large
number of small crystals of silver halide, mostly
bromide.
• The sensitivity to light has allowed silver halides to
become the basis of modern photographic
materials.
Nuclear Disintegration
What is Nuclear Emulsion?(2)
• A silver halide is one of the compounds formed between
silver and one of the halogens — silver bromide (AgBr),
chloride (AgCl), iodide (AgI), and three forms of silver
fluorides.
• The method of recording tracks of charged particles in
photographic plates is based upon two achievements of
modern technology, the photographic emulsion and the
optical microscopes.
Pion Interaction
The Latent Image
• A latent image on photographic film is an invisible image produced by the
exposure of the film to light.
• The arrangement of atoms in a perfect silver-halide crystal is equivalent to
face-centered cubic lattices.
• The lattice is commonly not perfect.
It contains dislocations which are important
in promoting the growth of the crystal from the solution.
Latent Image Formation
• The absorption of energy in a sensitized
crystal of silver bromide leads to a
concentration of a few silver atoms of the
sensitizing layer, initially dispersed over
the surface, into an aggregate which can
act as a development centre, i.e. a Latent
Image
By Fuji Film
Electron micrograph of Silver Halide Crystals
The Development
• Photographic developer is a chemical amplifier acting
on the latent image.
• A rather complex physics-chemical process is able to
transform those grains with a suitable development
centre into metallic silver.
• After development, a silver halide emulsion is placed in
a second bath, called as fixer which dissolves the
unaffected grains of silver halide but leaves the small
black granules of silver.
• Finally, The plate is washed and dried.
Emulsion Films drying after development
The Mechanism of Development
Latent Images
The Silver Halide Grains (linear size of 0.2 micron)
by Fuji Film
the track left by a minimum ionizing particle in nuclear
Emulsion. About 35 grains/100 micron
Summary of Whole Process
Refresh
The Role of the Gelatine
• The Gelatine provides a three dimensional net-work which serves to locate
the small crystals of the halide and to prevent them migrating during
development and fixation.
• It is able to absorb large quantities of water.
• The gelatine molecules are adsorbed to the ions in the surface of the halide,
so that the grains are held fixed, like flies on a spider’s web.
• The gelatine also contributes to the sensitivity of the silver halide grains.
Nuclear Emulsion vs. Photographic Films
• Nuclear Emulsion differs from those of ordinary
photography in three respects.
1. The ratio of silver halide to gelatine is about eight times larger in the nuclear
emulsion.
1. The emulsion is commonly between ten and a hundred times thicker.
1. Developed silver grains are smaller and more uniform.
Fuji Nuclear Emulsion Film
• The development of the scanning system requires
good quality emulsion plates.
• Two layers are separated by a protection coat
(thickness of 1 micron).
•R&D project was jointly being carried out by Nagoya
University and the Fuji Photo Film Co., Ltd
Emulsion Refreshing (Memory Reset)
• A procedure to erase to a large extent
any previously recorded background
due to latent image tracks produced by
ionization.
• Emulsion refreshing is obtained by
keeping the films at high humidity (9599% RH) and high temperature (25-30◦
C) for a few days
Refreshing Apparatus
Emulsion Refreshing(2)
Scanning was done by the UTS automated scanning system at the Nagoya
University
Discovery of Radioactivity
• The first notable the use of the photographic emulsion(plates) is the
discovery of radioactivity by Henri Becquerel in 1896.
• The radiation emitted by uranium shared certain characteristics with X-rays
but, unlike X-rays, could be deflected by a magnetic field and therefore must
consist of charged particles. For his discovery of radioactivity, He was
awarded the 1903 Nobel Prize for physics.
Measurement of α-Particles
• S.Kinoshita found record of alpha-particle
radiation detected as tracks by means of optical
microscopes.(in 1910)
Experimental Apparatus.
Tracks Produced by Cosmic-Rays
• The Balloon, Explorer II in 1935, was the first
attempt to employ photographic method to
detect tracks due to cosmic radiation. (73.000ft
for more than two hours.)
• The balloon carried photographic plates for
Rumbaugh and Locher (1936) who found no
tracks in their plates and for Wilkins and
Helens who found of long tracks some of which
appeared to be involved in nuclear collissions
(1936,1938).
• Long tracks of Protons were also observed by
Tokio Takeuki (1937).
Discovery of Heavy Mesons
• The Emulsion technique greatly improved during
30’s and 40’s thanks to the group of the Bristol
University lead by POWELL.
• Developing of electron sensitive Nuclear
Emulsions.(Produced by ILFORD and KODAK)
Cecil Frank Powell
• In parallel, dedicated microscopes were
developed.
• The Cosmic-Ray Pion was detected through its
decay into muon.(by Powell)
• Powell was awarded the Nobel Prize for physics
in 1950 for his discovery using nuclear
emulsion.
The contributions to Discovery of Elementary Particles
The Discovery of new particles by
using Nuclear Emulsions
• In 1947, π+and π- were discovered
by Powell.
• In 1947, K+and K- were
discovered.
• In 1953,
Bonetti.
Σ+
was discovered by A.
• In 1958, Anti Λ0 was discovered
by Baldo Ceolin.
• In 2001, ντ was discovered by
DONut collabration.
The Discovery of new particles by
using Various Detectors
Particle
Instrument
π+ and π-
Nuclear Emulsion
π0
Counters and Emulsion
Λ
Cloud Chamber
K+and K-
Nuclear Emulsion
K0
Cloud Chamber
Σ+
Nuclear Emulsion
Σ-
Cloud Chamber
Σ0
Bubble chamber
Ξ-
Cloud Chamber
Ξ0
Buble Chamber
Anti Λ0
Nuclear Emulsion
Emulsion Cloud Chamber(ECC) Detectors
• A major breakthrough in the emulsion
technique was the introduction of the ECC.
• The ECC technique was first introduced in
1951 by Kaplon to study heavy primaries in
cosmic ray interactions.
A Schematic Structure of ECC.
• Sandwiching emulsion films with passive
material layers, usually made of plastic,
metal or lead plates.
• Spatial resolutions down to 1 micron with
3D Capabilities, reconstruction of the
cascade showers in the Detector.
A Reconstructed νμ CC Event inside ECC.
• ECC detectors were first applied to the
study of the cosmic-ray spectrum and to
very-high energy interaction process.
Nuclear Emulsion Applications
•
•
•
•
•
•
•
•
•
Medical Application with Nuclear Emulsions(Proton Radiography).
Emulsion Hybrid Telescope for Cosmic Gamma-Ray Observation.
Cosmic-Ray Muon Radiography of Volcanos with ECC.
Radiation Monitoring around Accelerator.
The Detection of Dark Matter.
Application to Neutrino Experiments.
Muon Monitoring at Muon Pit at J-PARC.
Electron/Pion Separation.
OPERA Experiment.
Particles for Medical Application
• Proton therapy : very high local control
of the pathology with minimal secondary
effects.
• A particle accelerator is used to target the
tumor with a beam of protons.
• The dose delivered to tissue is maximum
just over the last few millimeters of the
particle’s range; this maximum is called the
Bragg peak
• To treat tumors at greater depths, a beam
with higher energy.
Proton Radiography with Nuclear
Emulsions at LHEP
•
To obtain medical images of the patient’s body (proton
radiography).
•
Proton radiography allows obtaining images directly
proportional to the average density of the traversed
material.
•
Emulsion detector is cheaper and easier to install and
remove.
Emulsion Hybrid Telescope for Cosmic
Gamma-Ray Observation.
• Telescope observes
• Emulsion Measures
1. Brightness (Magnitute)
2. Color (Wavelength)
3. Direction of the light
1. Event Rate (Flux)
2. Energy (Momentum)
3. Direction of gamma-ray
photon
2 mrad
Ultra Violet
(UIT)
Visible
(Palomar)
Reconstructed
Tracks
Gamma
Shower
Cosmic-Ray Muon Radiography of Volcanos
with ECC.
muon
ECC
• Muon source with a well-known energy
spectrum for different zenith angles.
•A well-understood muon detector.
•The information from counting muon events
at different arriving angles can be used to
infer on the matter profile.
Cosmic-Ray Muon Radiography of Volcanos
with ECC.
pg
Cosmic-Ray Muon Radiography of Volcanos
with ECC.
Result in USU
Particle Identification.
The PEP4/9-TPC
energy deposit
measurements
The Bethe-Bloch
Formula
β2=p2/(p2+m2)
e
• In Emulsions, the grain density is proportional to
energy loss by ionization(Bethe-Bloch)
• If the momentum known, dE/dx allows the particle
identification.
• If the Momentum unknown, the combined
measurement of momentum(βP by MCS) and
grain density allows particle identification.
μ
π
Bethe-Bloch for Different Materials
Horizontal Exposure
Two modules (5cmx5cm) were prepared,
each module has 2 OPERA films inside.
 They were exposed horizontally at
different angles and at different
momentums
(500MeV/c, 1 GeV/c, 1.5 GeV/c,, 2GeV)/c,
~104/cm2
 Developed at CERN.
1GeV/c
Prepared
And
Exposed at
CERN
0.5GeV/c
Grain Counting
-Tracks are selected as depending on angle.
-Track Grains are counted unit by unit.
-Unit length not yet calibrated.
-Pion Tracks are found by looking pion interactions
Results and Discussion
•The results fit perfectly with theory.
•OPERA Films allow to separate at low momentum
of particles.
The OPERA Experiment
• Mainly designed for the direct search of ντ
appearance in the pure νµ CNGS beam from
CERN to Gran Sasso(732km).
• Based on the use of Emulsion Cloud
Chambers (ECCs) and of electronic
detectors(Hybrid Detector).
• In an ECC the nuclear emulsion films act as
very high precision tracking detectors, and are
interleaved with plates of lead.
Emulsion Cloud Chamber
• The brick, is made of 57 emulsion films
interleaved with 56 lead foils of 1 mm
thickness. It has 128x102x79mm3, and weighs
8.3 kg.
The OPERA Experiment
•
The distinctive feature of ντ charged-current
interactions is the production of a short-lived τ
lepton (cτ =87 µm).
•
This is achieved in OPERA using the Nuclear
Emulsion technique that features an unrivaled
spatial resolution (≤ 1 µm).
•
OPERA Detector is a hybrid (emulsion+electronics)
with a modular structure.
2 SuperModules=2*(31walls+1spectrometer)
Total Mass: 1766 Tons. # of Bricks=206336
•
ECC measures: Kink of Tau, Momentum(via MCS),
Electromagnetic Shower, dE/dX, e/π separation,
Event Kinematics,Vertex Location, τ ID,
•
Magnetic Spectrometer: μ ID, charge and
momentum.Target tracker: Trigger and localiza ν
interactions.
Electromagnetic
shower
reconstruction
The OPERA Experiment
• The required area of emulsion is of
order of 100,000 m2 s
• It is needed high-speed automatic
scanning systems.
• Scanning power is 10cm2/h at
LHEP
• Emulsions are scanned at Europe
and Japanese scanning Labs.
Hybrid Detectors(Emulsion+Electronic
Detectors)
• Hybrid experiments combining ECC
and Electronic detectors.
• To provide time resolution to the
emulsion stack (trigger signal).
• To pre-select the region of interest for
the event occuring in the ECC.
• The ECC is removed from the detector
for reconstruction and analysis of the
events.
Emulsion Cloud Chamber
Changeable Sheets (CS) Detectors
• Used as interfaces between Target
Tracker detectors and Emulsion Cloud
Chambers.
• They are placed to the downstream
face of the ECC.
• It confirms neutrino interaction signals
obtained from TT detector.
• To find neutrino-related interactions for
the ECC brick.
• To decrease useless scanning load,
useless film handling and processing
Automated Emulsion Read-out System
• The first microscopes to scan emulsion
detectors were Human-eye based.
(difficult to increase speed for data
acquisition)
• The first automated scanning system
wasTrack Selector(TS) developed by
Nagoya University in 1974 (Invented
by K.Niwa)
• Japanese and European groups have
separately developed new automatic
high-speed scanning systems.(SuperUltra Track Selector,S-UTS and
European Scanning System ESS)
Digitizing Grains inside Emulsion
Microscope
Z-axis
Image
sensor
Image
sensor
Resolution :
512x512 pixels
FOV :
160x160mm2
Eff. Pixel size :
~0.3mm
Objective lens : 50x
~3mm DOF (effective)
Nuclear emulsion film
Emulsion (topside)
typ. 45-100 mm
Film base
200-800 mm
Emulsion （
backside)
• The images are collected at
different gray levels.
• The micro-tracks are
reconstructed
• Base-tracks and Volume tracks are
reconstructed for event analysis.
LHEP Emulsion Scanning LAB. At University
of BERN.
Data Acquisition and Plate Changer
System developed by I.Kreslo