GRANDGRANDBritni BethuneBritni Bethune

CROP 2002CROP 2002

GGamma amma RRay ay AAstrophysics at strophysics at NNotre otre DDameame

The University of Notre Dame is located north of The University of Notre Dame is located north of South Bend, IndianaSouth Bend, Indiana– 150km from Chicago150km from Chicago

– (86(86o o W, 42W, 42o o N, 222m elevation) N, 222m elevation)

The GRAND array was constructed on a field just The GRAND array was constructed on a field just north of campus; completed in the spring of 1996north of campus; completed in the spring of 1996

Building costs totaled over $1 million; funded by Building costs totaled over $1 million; funded by the National Science Foundation, Notre Dame, the National Science Foundation, Notre Dame, and private contributorsand private contributors

PurposePurpose

Original purpose: study stellar point Original purpose: study stellar point sources of gamma rayssources of gamma rays– This requires good angular resolution, good This requires good angular resolution, good

particle identification, adequate area, and particle identification, adequate area, and sufficient running time to gather datasufficient running time to gather data

New primary goal: measure composition of New primary goal: measure composition of cosmic rays in the energy range of 100 to cosmic rays in the energy range of 100 to 100,000 TeV100,000 TeV

The Cosmic Ray Energy Spectrum

FERMILAB’s protonsFERMILAB’s protons

Bounced Superball

Bounced Superball

Pitched baseballPitched baseball

Hockey PuckHockey Puck

Energy (eV)

Change in Slope

The ArrayThe Array

100 x 100 meter field100 x 100 meter field 64 stations arranged in 8 x 8 grid; 14 meters 64 stations arranged in 8 x 8 grid; 14 meters

separating themseparating them First southwest quadrant of stations First southwest quadrant of stations

constructed 0.6m undergroundconstructed 0.6m underground– Design purported for cooling in the summerDesign purported for cooling in the summer– Led to moisture problemsLed to moisture problems– Remaining stations built above groundRemaining stations built above ground

The StationsThe Stations

– 2.4m x 2.4m x 0.9m 2.4m x 2.4m x 0.9m high hutshigh huts

– Heaters maintain Heaters maintain temperatures temperatures > 17> 17oo C C

– Dehumidifiers Dehumidifiers maintain humidity maintain humidity < 55%< 55%

– Each hut houses 8 Each hut houses 8 planes of proportional planes of proportional wire chamberswire chambers

Configuration of DetectorsConfiguration of Detectors

Four pairs of PWCs Four pairs of PWCs stacked vertically and stacked vertically and separated by 200mmseparated by 200mm

Each plane is 1.2mEach plane is 1.2m22

50mm thick steel 50mm thick steel absorber plate after absorber plate after top three pairstop three pairs

Last pair identifies Last pair identifies muons with 96% muons with 96% accuracyaccuracy

Proportional Wire ChamberProportional Wire Chamber

First wire chamber: Geiger Muller counter, First wire chamber: Geiger Muller counter, invented in 1908invented in 1908

Metallic cylinder; Ionizing gas; High Metallic cylinder; Ionizing gas; High voltage anode wire along axisvoltage anode wire along axis

When a particle passes through the cylinderWhen a particle passes through the cylinder– It ionizes gas moleculesIt ionizes gas molecules– Free electrons accelerate in electric field and Free electrons accelerate in electric field and

produce secondary electronsproduce secondary electrons– Electrons to anode wire; + ions to cylinderElectrons to anode wire; + ions to cylinder

Proportional Wire ChambersProportional Wire Chambers

Multiwire Proportional ChambersMultiwire Proportional Chambers

Primary electrons drift to nearest anode Primary electrons drift to nearest anode wirewire

Avalanche begins about 50 Avalanche begins about 50 μμm from wirem from wire Positive signal from cathode planes; Positive signal from cathode planes;

Negative signal from anode wiresNegative signal from anode wires Cathode strips Cathode strips to anode wires can locate to anode wires can locate

passage of particle in two dimensions passage of particle in two dimensions (X and Y)(X and Y)

Central Data Acquisition Trailer

80% Argon20% CO2

Gas bottles

Data SystemsData Systems 80-cell planes80-cell planes Each cell has Each cell has

amplifier, shift amplifier, shift register, summerregister, summer

Station triggers from Station triggers from 3-fold coincidence in 3-fold coincidence in X or Y signal from top X or Y signal from top 3 pairs3 pairs

Trigger stores 640 Trigger stores 640 cells of info in shift cells of info in shift register memoryregister memory

Data Acquisition SystemData Acquisition System

Trailer coincidence circuit can be set for N Trailer coincidence circuit can be set for N simultaneous hutssimultaneous huts

Coincidence causes train of clock pulses to be sent Coincidence causes train of clock pulses to be sent to all stationsto all stations

Data is shifted from stations to trailer in 70 Data is shifted from stations to trailer in 70 microsecondsmicroseconds

Trigger time, accurate to 1 millisecond, is Trigger time, accurate to 1 millisecond, is recorded along with trigger datarecorded along with trigger data

Muon data processed separately (4-fold Muon data processed separately (4-fold coincidences)coincidences)

SetbacksSetbacks Moisture problem in southwest quadrantMoisture problem in southwest quadrant

– Remainder of array built above groundRemainder of array built above ground Ten stations flooded in summer of 1996Ten stations flooded in summer of 1996

– Permanent drainage added on south and westPermanent drainage added on south and west NSF decides it cannot afford to operate NSF decides it cannot afford to operate

arrayarray– Major running expense: argon gas flowing Major running expense: argon gas flowing

through detectors ($200/week)through detectors ($200/week)– GRAND now seeking private contributions to GRAND now seeking private contributions to

be matched by university fundingbe matched by university funding

ConclusionsConclusions

GRAND was constructed to study cosmic rays with GRAND was constructed to study cosmic rays with energies from 10energies from 101414 to 10 to 101717 eV eV

Upon completion of the array, the NSF decided Upon completion of the array, the NSF decided against further fundingagainst further funding

GRAND is inactive and has yet to collect any GRAND is inactive and has yet to collect any extensive air shower data beyond preliminary testingextensive air shower data beyond preliminary testing

Sources:Sources:– http://www.nd.edu/~grand/index.htmlhttp://www.nd.edu/~grand/index.html

(GRAND homepage)(GRAND homepage)– http://www.physik.unizh.ch/~twalter/diploma_thesis/http://www.physik.unizh.ch/~twalter/diploma_thesis/

node15.html (operational notes on PWCs)node15.html (operational notes on PWCs)