Temperature effects in the ATIC BGO calorimeter
Section snippets
Flight conditions
The ATIC Balloon instrument was designed to measure Cosmic ray spectra in the energy range from 100 GeV to 100 TeV for particles ranging from Hydrogen to Iron (Guzik et al., 1996). To cover this range the energy deposited in the BGO calorimeter ranges from a few MeV (Muons) to about 13 TeV (shower maximum at the largest angle). Cosmic ray muons are used to calibrate the absolute energy scale of the BGO calorimeter. A change in light output due to temperature changes would shift that scale.
The
The calorimeter trays
The individual BGO crystals of the ATIC Calorimeter, each 2.5 cm by 2.5 cm by 25 cm in size are wrapped in 25-μm-thick Teflon, and 25-μm aluminized Mylar foil for light tightness and viewed by a single photomultiplier tube, a Hamamatsu R5611-01 seen in the back of Fig. 2. A tray holds 40 crystals, six can be seen pointing towards the pmts. The top and bottom of each tray is lined with 0.5-mm thick latex to protect the crystals against shock and provide some thermal resistance. Once a tray is
The BGO calorimeter
The BGO calorimeter is made of ten stacked trays, covering an active area of 51 cm × 51 cm with alternating layers rotated 90° relative to each other forming X and Y layers. Fig. 3 shows the frames of the ten trays.
This design minimizes the thermal gradients so that the temperature variations during flight effect all BGO crystals uniformly as shown by the bottom curve in Fig. 1.
The set-up
In order to determine the temperature sensitivity of the ATIC calorimeter the ATIC instrument was taken to the CSBF in Palestine, TX and set up in their thermal vacuum chamber. Unfortunately, the chamber was too small to fit the entire instrument; the top two scintillators and the carbon target section were too wide to fit in. So the BGO calorimeter, two scintillator panels and the readout electronics including the entire flight electronics was set up on a cart and moved into the chamber. Fig. 4
The temperature calibration
The calorimeter was held at various temperatures (35, 23, 15, 1 °C) to within ±0.5 °C and cosmic ray muon data were collected for a duration of at least 2 h. The energy calibration of the ATIC calorimeter is derived from the pulse height measurement of the energy deposit of cosmic ray muons passing through the BGO crystals. The temperature sensitivity is derived in the same way. The position of the muon peak is determined for each crystal at each temperature. Fig. 5 shows the pulse height
Conclusions
The temperature sensitivity of the BGO calorimeter was calibrated by utilizing the thermal vacuum chamber at the Columbia Scientific Balloon Facility in Palestine, Texas. This calibration is used to correct the Energy scale for the ATIC calorimeter at the temperatures experienced during its balloon flight in McMurdo, Antarctica. The calibration is for the BGO crystals in combination with readout electronics, an end-to-end calibration. Since the electronics was not calibrated separately it was
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