Diapositiva 1 - INFN

Diapositiva 1 - INFN

Study of UV absorption and photoelectron emission in RPC (Resistive Plate Counters) detector with an UV source Carlo Gustavino (INFN-LNGS) RPC and their applications RPC working principle Afterpulses Gas mixture UV photoelectron emission from the cathode plate Experimental set-up Preliminary tests Conclusions RPCs are widely used as active elements in large experiments (CMS, ATLAS, BABAR, BELLE, ARGO, OPERA, etc) for their good resolution in both timing (~1 ns) and position (~1 cm) measurements over large areas (thousands of m2).

Example: THE OPERA EXPERIMENT (~3400 m2 of Adriano RPCs) Di Giovanni 7 rows RPC sub-detectors under construction 3 RPC/row Bakelite RPC (spectrometers) Float Glass RPC (Veto System) RPC is composed of two plates with high volume resistivity (1010-1012 cm), that generate a uniform electric field. When a crossing particle ionizes the gas between the electrodes, an avalanche process occurs, eventually developing into a streamer. The streamer discharges only a

limited area, because of the high-volume resistivity of the electrodes. The time to recover the electric field is proportional to the electrode resistivity and must be long enough to allow the full ion recombination, to prevent self-sustaining discharges. Secondary avalanche/discharge between the electrodes can be generated by the UV photons produced during the avalanche process. The gas mixture contains organic components to quench the UV photons. Tipical gas mixture: argon + IsoC4H10 + C2H2F4 + SF6. The isobuthane is added to the noble gas to limit the amount of secondary streamers by absorbing UV photons which are radiated from the deexcitation of molecules. Freons have high electron affinity and are used to reduce the streamer size by capturing the outer electrons. The smaller streamer limits the number of UV photons produced. Probably, Freons are also effective in capturing UV photons. Electrodes (float glass or bakelite coated with linseed oil) Gas ionization

Primary ionization Streamer HV Electron photoextraction Afterpulse UV photons HV Best performance is obtained by minimizing the afterpulses. This is achieved by using a proper gas mixture. The RPC used in the experiments have elecrodes of Float Glass electrodes or bakelite.

Single streamer afterpulses Multiple streamer (afterpulses) Gas Mixture argon/TFE/IsoC4H10/SF6=48/47/4/1 % argon/TFE/IsoC4H10/SF6=49/47/4/0 % argon/TFE/IsoC4H10/SF6=50/47/2/1 % argon/TFE/IsoC4H10/SF6=79/16/4/1 % Big charge reduction with a small percentage of SF6. The streamer size does not depends on the TFE/ IsoC4H10 percentage TFE40 %, IsoC4H104 % to minimize afterpulses.

Full dots: streamer charge Empty dots: total charge N.B. High Voltage values are rescaled to superimpose the efficiency curves RPC electrodes Electrode properties: Planarity, smooth surface =1010-1012 cm High surface resistivity Low electron photoextraction efficiency N.B. RPC operation (ageing) can change the initial values. Float Glass: It is produced by putting the glass on a Tin bath. The glass float on Tin bath to obtain a perfect planarity. Therefore, the two sides of the glass are not equivalent. Tin side: surface resistivity: 109-1011 /square

Excellent planarity Air side: resistivity: ~1012 /square. good planarity Tin/Air surfaces photoemission properties? In the RPC, the surface facing the gas is the air one. Bakelite: without linseed oil treatment the bakelite RPC is very noisy. It is commonly believed that the treatment improve the bakelite smoothness. Maybe the oil is effective because it prevents UV photoemission. Electron photoemission The The absorption band of Buthane is limited to about 170 nm. Beyond this value UV are able to produce electrons from the cathode, that can generated a discharge.

Above ~170 nm no buthane absorbtion Preliminary measurements: Experimental set-up Very preliminary measurements have been done to measure the photoextraction of a float glass sample Filters band pass: from 160 to 260 nm (FWHM=104 nm) Poor Xenon lamp stability, unknown transmission (GaAs cathode as reference) Murphys law: Vacuum pump broken just after the preliminary tests Optical Filter Compound (cathode) Fiber

Mirror Anode Xenon Lamp Trigger Vacuum chamber Signal RC Filter Oscilloscope HV

Photoemission Vs Wavelength (Float Glass) 185 160 nm NO 260 210 200 230FILTER nm Signal is visible also above 170 nm (preliminary measurements). Photoemission Vs sample material Photoextraction efficiency Vs Wavelength

1000 GaAs Bakelite Oiled Bakelite 100 Float Glass 10 Amplitude (mV) 1 GaAs

Bakelite Oiled Bakelite Float Glass Cathode material N.B. Preliminary! Strongly affected by the Xenon lamp instability Conclusion and outlook In spite of their large use in High Emergy Physics, the RPC still need investigations. A better understanding of afterpulsing is needed to address the RPC thecnology and to improve its long term stability. A dedicated study of electrode properties have been started by using UV sources.

=160-260 nm High stability, absolute calibration Pulsed (~ 1 Hz) Electrode material Surface treatment RPC Aging (deposits, gas polymerization) UV gas absorption coefficient

Recently Viewed Presentations

  • Chapter Five - International Business Styles

    Chapter Five - International Business Styles

    Chapter Five - International Business Styles Gladys Hung Vocabulary - paragraph 5-8 Condensed: narrower than usual for a particular height Compare Virtually: practically; nearly Sensitive: Susceptible to the attitudes, feelings, or circumstances of others.
  • Binomial Nomenclature

    Binomial Nomenclature

    All living things are assigned a two-word name in order to classify them. This is similar to us giving each child that is born a first and a last name. The Genus is similar to a last name. It is...
  • Control the - cdn.ymaws.com

    Control the - cdn.ymaws.com

    Lansing Core Values - Diversity, Exemplary Customer Care, Affordability, Health & Fitness, Professionalism - created by the staff, asked each to write down what values they believe the department has, combined all thoughts to these.
  • Diapositiva 1 - Le Baobab Bleu

    Diapositiva 1 - Le Baobab Bleu

    J'ai monté les valises au grenier. DESCENDRE intransitif transitif direct Je suis descendu(e) à la cave. J'ai descendu les escaliers à toute vitesse. ENTRER intranstif transitif direct Je suis entré(e) dans la maison. J'ai entré un mot-clé dans le moteur...
  • TGn Opening Report September 06 - Welcome to Mentor

    TGn Opening Report September 06 - Welcome to Mentor

    Proceed 2-3 miles to I-84 West (follow signs to Portland city center). Follow signs to Beaverton, Hwy 26 West & I-405 (left two lanes). You will be crossing the Marquam Bridge. As you come off the bridge, stay in the...
  • Best Practices for DemandDriven Acquisition of Monographs: Recommendations

    Best Practices for DemandDriven Acquisition of Monographs: Recommendations

    Develop a flexible model for DDA that works for publishers, vendors, aggregators, and libraries. Model should allow for DDA programs that. Meet local budget and collection needs . Allow for consortial participation. Support cross-aggregator implementation. Account for how DDA impacts...
  • ACUTE PANCREATITIS Severity Classification, Complications and ...

    ACUTE PANCREATITIS Severity Classification, Complications and ...

    Pathophysiology. Due to many causes, pancreatic pro-enzymes will be activated, and not released to the duodenum, so they will return back to the pancreas in the active form and cause autodigestion of the pancreas, which in turn will lead to...
  • Sullivan Algebra and Trigonometry: Section 7.1

    Sullivan Algebra and Trigonometry: Section 7.1

    Sullivan Algebra and Trigonometry: Section 6.1 Angles and Their Measures Objectives of this Section Convert Between Degrees, Minutes, Seconds, and Decimal Forms for Angles Find the Arc Length of a Circle Convert From Degrees to Radians, Radians to Degrees Find...