GRAND Britni Bethune CROP 2002

G amma R ay A strophysics at N otre D ame The University of Notre Dame is located north of South Bend, Indiana The University of Notre Dame is located north of South Bend, Indiana –150km from Chicago –(86 o W, 42 o N, 222m elevation) The GRAND array was constructed on a field just north of campus; completed in the spring of 1996 The GRAND array was constructed on a field just north of campus; completed in the spring of 1996 Building costs totaled over $1 million; funded by the National Science Foundation, Notre Dame, and private contributors Building costs totaled over $1 million; funded by the National Science Foundation, Notre Dame, and private contributors

Purpose Original purpose: study stellar point sources of gamma rays Original purpose: study stellar point sources of gamma rays –This requires good angular resolution, good particle identification, adequate area, and sufficient running time to gather data New primary goal: measure composition of cosmic rays in the energy range of 100 to 100,000 TeV New primary goal: measure composition of cosmic rays in the energy range of 100 to 100,000 TeV

Change in Slope

The Array 100 x 100 meter field 100 x 100 meter field 64 stations arranged in 8 x 8 grid; 14 meters separating them 64 stations arranged in 8 x 8 grid; 14 meters separating them First southwest quadrant of stations constructed 0.6m underground First southwest quadrant of stations constructed 0.6m underground –Design purported for cooling in the summer –Led to moisture problems –Remaining stations built above ground

The Stations –2.4m x 2.4m x 0.9m high huts –Heaters maintain temperatures > 17 o C –Dehumidifiers maintain humidity < 55% –Each hut houses 8 planes of proportional wire chambers

Configuration of Detectors Four pairs of PWCs stacked vertically and separated by 200mm Four pairs of PWCs stacked vertically and separated by 200mm Each plane is 1.2m 2 Each plane is 1.2m 2 50mm thick steel absorber plate after top three pairs 50mm thick steel absorber plate after top three pairs Last pair identifies muons with 96% accuracy Last pair identifies muons with 96% accuracy

Proportional Wire Chamber First wire chamber: Geiger Muller counter, invented in 1908 First wire chamber: Geiger Muller counter, invented in 1908 Metallic cylinder; Ionizing gas; High voltage anode wire along axis Metallic cylinder; Ionizing gas; High voltage anode wire along axis When a particle passes through the cylinder When a particle passes through the cylinder –It ionizes gas molecules –Free electrons accelerate in electric field and produce secondary electrons –Electrons to anode wire; + ions to cylinder

Proportional Wire Chambers

Multiwire Proportional Chambers Primary electrons drift to nearest anode wire Primary electrons drift to nearest anode wire Avalanche begins about 50 μm from wire Avalanche begins about 50 μm from wire Positive signal from cathode planes; Negative signal from anode wires Positive signal from cathode planes; Negative signal from anode wires Cathode strips  to anode wires can locate passage of particle in two dimensions (X and Y) Cathode strips  to anode wires can locate passage of particle in two dimensions (X and Y)

Central Data Acquisition Trailer 80% Argon 20% CO 2 Gas bottles

Data Systems 80-cell planes 80-cell planes Each cell has amplifier, shift register, summer Each cell has amplifier, shift register, summer Station triggers from 3-fold coincidence in X or Y signal from top 3 pairs Station triggers from 3-fold coincidence in X or Y signal from top 3 pairs Trigger stores 640 cells of info in shift register memory Trigger stores 640 cells of info in shift register memory

Data Acquisition System Trailer coincidence circuit can be set for N simultaneous huts Trailer coincidence circuit can be set for N simultaneous huts Coincidence causes train of clock pulses to be sent to all stations Coincidence causes train of clock pulses to be sent to all stations Data is shifted from stations to trailer in 70 microseconds Data is shifted from stations to trailer in 70 microseconds Trigger time, accurate to 1 millisecond, is recorded along with trigger data Trigger time, accurate to 1 millisecond, is recorded along with trigger data Muon data processed separately (4-fold coincidences) Muon data processed separately (4-fold coincidences)

Setbacks Moisture problem in southwest quadrant Moisture problem in southwest quadrant –Remainder of array built above ground Ten stations flooded in summer of 1996 Ten stations flooded in summer of 1996 –Permanent drainage added on south and west NSF decides it cannot afford to operate array NSF decides it cannot afford to operate array –Major running expense: argon gas flowing through detectors ($200/week) –GRAND now seeking private contributions to be matched by university funding

Conclusions GRAND was constructed to study cosmic rays with energies from to eV GRAND was constructed to study cosmic rays with energies from to eV Upon completion of the array, the NSF decided against further funding Upon completion of the array, the NSF decided against further funding GRAND is inactive and has yet to collect any extensive air shower data beyond preliminary testing GRAND is inactive and has yet to collect any extensive air shower data beyond preliminary testing Sources: Sources: – (GRAND homepage) – de15.html (operational notes on PWCs)