Exciting New Developments in Photon Detection A Look into the Performance of the Silicon Photomultip

1
Exciting New Developments in Photon DetectionA
Look into the Performance of the Silicon
PhotomultiplierThe Replacement (?) for the
Phototube

• Elliot Smith
• Keith Drake
• Dr. Uriel Nauenberg
• University of Colorado

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Introduction

• EXCITING new developments for fields requiring
  photon detecting and photon counting
  capabilities!
• Silicon Photomultiplier (SiPM) development headed
  up by PULSAR/Moscow Engineering Physics Institute
  in Russia.
• Many other groups are interested in revolutionary
  SiPMs including but not limited to
• Fermi Lab/NICADD.
• Dutsches Elektronen-Synchrotron (DESY) and the
  CALICE detector collaboration in Europe and the
  U.S.
• Global Large Detector (GLD) Kobe, Japan.
• Institute for Theoretical and Experimental
  Physics, Russia
• University of Colorado

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Introduction

• New generations of silicon photomultipliers
  (SiPMs) have single photo-electron resolving
  capabilities and are superior to phototubes due
  to their
• Simplicity
• Small size
• Low power requirements
• Ease of calibration
• Cost effectiveness
• SiPMs will very likely replace the traditional
  phototube in many arenas.

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Outline

• Motivation
• International Linear Collider Calorimeter
• Phototube vs. New Generation Silicon
  Photomultipliers (SiPMs)
• Design
• Size
• Cost
• Functionality
• Methods and Measurements
• Apparatus
• Electronics
• Data Analysis
• Low Temperature Testing
• Cosmic Ray Data
• Conclusions
• Future Work

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Motivation International Linear Collider

• International Linear Collider (ILC) is an
  electron-positron collider that intends to reach
  energies as high as 1 TeV.
• The ILC requires a calorimeter to detect the
  shower of photons from pizero decays and must
  have the following properties
• Good directional and energy
  
  resolution 1.
• Reliable, mechanically sound,
• and operable inside a strong
• magnetic field 2.
• Many collisions per second
• require a detector that
• has a robust, high rate
• capability 3.
• Cost effective.

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Motivation International Linear Collider

• The calorimeter is a very large scale project.
• Will require millions of detector pieces, each
  requiring its own photo-detector.
• Price considerations are of the utmost importance.

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Motivation International Linear Collider

• Charged particles excite the dye molecules in the
  scintillation tiles which causes the them to emit
  photons at ?P 425nm.

• The wavelength shifting (WLS) fibers collect the
  blue light and shifts into the green ?P 476nm.
• The fiber feeds the collected light out of the
  tile to the face of an SiPM.
• The SiPM then sends the signal to our computer to
  be analyzed.

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Motivation International Linear Collider

• There are a number of different mounting options
  which are under consideration for the readouts of
  each tile.
• SiPM coupled directly to the scintillator tile.
• Fibers from each tile fed out of detector for
  final readout.
• SiPMs mounted directly to the top of each
  scintillating tile with no fiber.
• Things to keep in mind.
• Cross-Talk of wires.
• Ability to capture the full energy deposited in a
  tile.
• Coupling

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Motivation International Linear Collider

• Our full detector design is proposed by Dr. Uriel
  Nauenbergs group.
• Composed of millions of
• 5cm X 5cm scintillator tiles
• sandwiched with tungsten.
• Each tile will include a
• wavelength-shifting (WLS) fiber
• optic coupled to silicon
• photomultipliers (SiPMs) for
• readout.
• Offset geometry reduces the
• 5cm X 5cm tile size to an effective
• 2.5cm X 2.5cm for improved granularity.

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Phototube vs. SiPMs

• Photon counting devices such as phototubes have
  been used in many venues including, but not
  limited to, high energy physics, astrophysics,
  and the medical fields.
• These devices are often large and obtrusive and
  are not suitable for applications requiring
  compact size.

Single photon emission computed tomography (SPECT)
Japans Super Kamiokande Neutrino Detector
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Phototube vs. SiPMs Design

• Phototubes have a large face photocathode which
  is sensitive to low intensity light.
• These devices consist of a vacuum tube which, on
  its face, contains a light-sensitive,
  electron-emissive film which releases an electron
  when a photon hits its face.
• The film loses its photo-sensitive properties if
  the vacuum is lost inside the phototube.

• This sensitive attribute leads to very expensive
  production costs.

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Phototube vs. SiPMs Design

• A string of dynodes are used following the film,
  causing an avalanche in order to amplify the
  emission of the initial electron.
• The tubes contain around 10-12 dynodes in order
  to achieve the desired amplification.
• These make the tubes rather oblong, but also
  reduce the need for external amplification.

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Phototube vs. SiPMs Design

• A large base is needed to power each of the
  dynodes in the phototube.
• Each dynode is given a different voltage in order
  for the signal to be sequentially stepped up.
• To create this effect, a series of voltage
  dividers are connected to the phototube,
  providing each dynode with a different voltage.
• Consequently even more
• space is needed for the
• already large phototube.

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Phototube vs. SiPMs Design
Dealing with Magnetic Fields

• Due to the need for tracking charged particles,
  the Hadronic and Electromagnetic Calorimeters
  will be placed in a large magnetic field.
• SiD Design 5T
• LDC Design 4T
• GLD 3T
• Because of the dynamics of the vacuum phototubes,
  in a magnetic field the electrons are deflected
  while avalanching to the next dynode in the
  series.
• Output decreases by 50 when B-field 2x10-4 T.
• Even earths magnetic field effects them,
  requiring additional shielding.
• Because of the Solid State dynamics of the SiPM,
  they are impervious to magnetic fields.
• This makes SiPMs a great choice over phototubes.

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Phototube vs. SiPMs Design

• Who are the manufacturers?
• Mephi/PULSAR, Moscow, Russia
• Obninsk/CPTA, Moscow, Russia
• Distributor-Photonique All of our data taken
  with Photonique SiPMs.
• Hamamatsu- Japan
• Distributor- Hamamatsu Currently negotiating
  purchases.
• SensL, Ireland
• Distributor- MarketTech Currently negotiating
  purchases.
• ITC-irst, Italy
• MPI, Germany
• JINR, Dubna, Russia

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Phototube vs. SiPMs Design

• An SiPM is a solid state photomultiplier with a
  1mm2 active area.
• SiPMs are the first commercial solid state
  photomultiplier providing single photon
  resolution and can act as a substitute for
  traditional vacuum photomultiplier tubes 4.

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Phototube vs. SiPMs Design

• SiPMs have 500 pixels, each sensitive to single
  photons allowing for a quick response time (lt
  2ns).
• SiPMs consist of a matrix of avalanche
  photodiodes built on a silicon substrate.
• The pixels are on the order of 20µm, each
  individually sensitive to single photons.
• The SiPMs have a gain ranging from 0.5x106 to
  1x106.

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Phototube vs. SiPMs Design

• Wavelength Sensitivity of the SiPM

• Green sensitive devices are the most developed
  SiPMs on the market at the moment.
• Peak wavelength of 560nm.
• Most have a gain around 8.0x105
• Blue sensitive SiPMs are less mature in their
  development but are soon to have comparable
  response to their green counterparts.
• Peak wavelength of 440nm.
• Most have a gain of 1.8x105

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Phototube vs. SiPMs Design
Noise Properties of SiPMs

• SiPMs have a very small noise count, making
  separating out the signal much easier.
• Noise occurs as single or double photo-electrons.
• A noise event occurs once every 100 counts.
• The rate of dark count is 50 KHz/mm2.
• Noise is negligible at or below
• -15 oC.

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Phototube vs. SiPMs Size

• The compact size of the SiPM allows for easier
  mounting and less obtrusive hardware.
• The SiPM is magnitudes smaller in size and has
  superior resolution than its phototube ancestor.

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Phototube vs. SiPMs Size

• 2.1x2.1mm SiPMs have been out for awhile but we
  have yet to study them.
• Immature in their development
• Low gain from 0.6-1.5x105.
• Operating voltage 20-35V
• ?P 580nm 440nm
• We are arranging our first purchase of these
  devices.
• 3x3mm and larger SiPMs are being developed.
• Have not been released yet.

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Phototube vs. SiPMs Size

• Common phototubes require a driving voltage of
  approximately 2000V.

• The SiPM requires a driving voltage of 40-60V!
• New SiPMs on the market require as little as 20V!
• The SiPM power supply is also an order of
  magnitude smaller.

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Phototube vs. SiPMs Cost
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Phototube vs. SiPMs Functionality

• As shown in the plots below, the SiPM easily
  resolves individual photo-electrons while the
  phototube falls behind.
• This is essential in applications where high
  levels of accuracy and photon counting is
  necessary.
• Single photo-electron resolution also allows for
  simple calibration which is not as readily
  available with phototubes.

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Phototube vs. SiPMs Functionality

• Phototubes have to be calibrated with a
  independent light source with well-known
  characteristics.
• SiPMs are self calibrating due to their single
  photo-electron resolution.
• The DESY group has worked out a scheme for
  calibrating multiple SiPMs at once.

• Any low-light source can be used for the
  calibration.
• 15 SiPMs are pulsed simultaneously with a single
  LED.
• The gain of each SiPM is determined by measuring
  the distance between each peak.

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Methods and Measurements Apparatus

• The setup consists of various custom Lucite
  brackets (depending on measurement being taken).
• One side of the bracket generally contains a
  mount for an ultraviolet LED, and the other a
  mount for the SiPM. These are connected via a
  wavelength-shifting (WLS) fiber optic.

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Methods and Measurements Electronics

• For single photo-electron measurements, the
  ultraviolet LED is illuminated with a 2.47V
  10.6ns pulse.
• Neutral density filters are used at the face of
  the LED to further reduce the intensity of the
  light.
• The SiPM signal is amplified with a 200X
  amplifier.

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Methods and Measurements Electronics

• At the linear fan-out the signal is multiplexed
  and delayed with respect to each other by 2.5ns.
• SiPM and Phototube is data acquired using two
  National Instruments 14-bit 100MS/s digitizers.
• Utilizing the two digitizers full capabilities
  at 400MS/s we can sample the pulse every 2.5ns
  enabling us to observe the pulse train with high
  accuracy.

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Methods and Measurements Electronics

• We currently use a 200X amplifier but for future
  uses this is inefficient.
• 60X amplifiers are available from Photonique
  which mount directly to the SiPM.
• These integrated circuits are stable and
  inexpensive.
• They also allow for options of complete
  integration of electronics (amplifier, power
  supply, and read-out).

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Methods and Measurements Electronics

• Traditionally pulses are analyzed with expensive
  CAMACs while losing valuable time information.
• The National Instruments digitizer preserves time
  distribution of the pulses associated with the
  event.

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Methods and Measurements Electronics

• The pulse train lasts for an average of 50ns.
• The pulse width for a single photoelectron has
  been found to be 10ns.
• Pulses with more than 5 photoelectrons become too
  complicated to separate with our current sampler.

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Methods and Measurements Electronics

• We have observed cross-talk from other sources in
  our system, including LED and power supply
  cables, destroy the resolving power of the SiPMs.
• Keeping the cables fully shielded or using an
  interference-free circuit board is essential for
  obtaining clean signals as demonstrated above.

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Methods and Measurements Data Analysis

• Once acquired, the digitized data is analyzed
  with ROOT 5, a programming-based data analysis
  tool.
• The program determines what qualifies as a
  pulse, based on the slope of the line, then
  integrates over the pulse region (shown in red
  below).
• The result is a histogram of charge distribution
  (in Coulombs). From this, the SiPM can easily be
  calibrated based on the charge of a single
  electron.

Special thanks to Joseph Proulx for programming
support
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Methods and Measurements Low Temps

• These solid state devices produce a larger gain
  (2x) when brought to lower temperatures.
• With this higher gain it is possible to attain an
  optimal region in which the peak to valley ratios
  for the photoelectrons are at their highest.
• We found this to happen around -30 C.
• Lower than this, we found the gain to remain
  unchanged.
• The manufacturer rates the operating temperature
  from 40 to -40 degrees C.
• Weve taken data within a range of 25 to -60
  degrees C and have found the SiPMs to continue to
  function normally at these low temperatures.
• Gain increases.
• Noise decreases dramatically.

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Methods and Measurements Low Temps

• Our initial low temperature measurements were
  made using dry ice in a custom insulated box.
• We were able to achieve the temperatures desired
  but, for only short periods of time.
• The temperature was unstable for any longer than
  10-20 minutes.
• We took data at RT down to -60o C at ten degree
  decrements.

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Methods and Measurements Low Temps

• Using a Peltier cooler allowed us to reach colder
  temperatures for long periods of time.

• Our water cooled system allows the Peltier cooler
  to keep the SiPM at a steady within 0.2
  degrees.
• Currently able to reach -20 degrees C and working
  on reaching lower temps.

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Methods and Measurements Low Temps

• The temperature stability of the Peltier cooler
  allows for a more precise charge distribution for
  each photo-electron.
• The higher peaks in the Peltier plots are due to
  the narrower charge distributions.

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Methods and Measurements Cosmic Rays
Cosmic Ray Apparatus
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Methods and Measurements Cosmic Rays

• We have obtained data of the energy deposition
  left in a single scintillating tile from cosmic
  rays.
• The result is a record of the the energy left by
  muons and high energy photons.
• We intend to take at lower temperatures with our
  Peltier cooler.
• Have yet to produce and measure showers

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Conclusions

• In many applications, a decrease in the size of
  detectors could be made possible with the use of
  SiPMs instead of phototubes.
• These low cost SiPMs have much higher resolution
  capabilities than their phototube predecessor.
• This could lead to the phasing out of phototubes
  from many arenas in high energy physics,
  astrophysics and medical fields.
• Larger area SiPMs will only increase the areas in
  which they will be used in future detectors.
• The fact that they are impervious to radiation
  and magnetic fields also allows them to be used
  in many applications.

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Future Work

• Optimize coupling to various materials including
  fiber optics and scintillator.
• 1GS/s sampler - separate photons within a pulse.
• Test beam/Fermi.
• Characterize large batches of SiPMs from various
  developers.
• Larger Calorimeter arrays.
• The Study of Larger Surface SiPMs.
• 2.1mm X 2.1mm have been developed.
• 3mm X 3mm are in the works.
• Investigate coupling a number of tiles to a
  single SiPM.

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References

• 1 U. Nauenberg, E. Erdos, and E. G. Gollin, A
  University Program of Accelerator and Detector
  Research for the Linear Collider, p. 549, Apr.
  2005.
• 2 D. Chakraborty, Snowmass scintillator-based
  HCAL for ILC, in ILCW2005, Snowmass, CO, Aug.
  2005.
• 3 F. Sefkow, HCAL DESY CALLICE collaboration
  ALCPG workshop, in ILCW2005, Snowmass, CO, Aug.
  2005.
• 4 Blue sensitive solid state photomultiplier
  with 1mm2 active area, Photonique SA, Geneva-1
  Switzerland, Data Sheet, 2004.
• 5 R. Brun and F. Rademakers, ROOT -an object
  oriented data analysis framework, in AIHENP '96
  Workshop. Lausanne Nucl. Inst. Meth. in Phys.
  Res. A 389, Sept. 1997, pp. 81-86.

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Abstract

• New generations of silicon photomultipliers
  (SiPMs) have single photo-electron resolving
  capabilities and will consequently phase out
  phototubes, their larger, more expensive
  counterparts. The silicon photomultiplier will
  lead to significantly more economical detectors
  for scintillator calorimetry and for devices in
  other scientific arenas such as space and
  medicine. The International Linear Collider (ILC)
  is an electron-positron collider that intends to
  reach energies as high as a terraelectronvolt,
  five times that of current colliders. These high
  gain, low bias devices are impervious to
  radiation and magnetic fields, making them an
  optimal choice for photon detecting devices. We
  have been examining and evaluating the
  performance characteristics of silicon
  photomultipliers and have shown that the
  resolution surpasses that of phototubes. Due to
  their simplicity, low power requirements,
  cost-effectiveness, and ease of calibration,
  silicon photomultipliers are an inevitable
  replacement for the outdated phototube.