Purpose
To measure the uniformity of the Energy Resolution, Gas Gain, and Efficiency over the face of the IPC.
Testing Setup and Procedure During the uniformity tests, a collimated 55Fe source is put in 50 different positions over the IPC face. At each position, data is acquired for 30 seconds resulting in the collection of about 4000 events per position. The Cathode voltage is set to 400 V and the Anode voltage is adjusted to produce a Gas Gain of about 5000. The collimated 55Fe source is designed to produce an x-ray spot size less than 3 mm in diameter. To ensure that the source positioning is reproducible, a plastic mask was made which covers the IPC face and can be attached to the IPC. The 55Fe source is inserted into 50 different holes which were drilled into the plastic mask. The labeling of the holes is as follows: Looking at the face of the IPC so that the E-box is on the left, the columns are labeled from A to K from left to right and from 1 to 8 from bottom to top. Analysis and Results Figures 5.6-1a to 5.6-1d display histograms of the measured Gas Gain, Energy Resolution, and Efficiency for the 50 source positions. The means and the standard deviations ("SIGMA") of the distributions are shown in the plots. The normalization forces the mean to be 1.00 for the efficiency plot. A measure of the uniformity of the three quantities over the IPC face is provided by calculating the ratio of the standard deviation to the mean in each case. The fractional standard deviations for Gas Gain, Energy Resolution, and Efficiency for the four IPCs are given in Table 31.Figures 5.6-2a to 5.6-2l are two-dimensional histograms showing the variation of the three quantities over the IPC face. As shown in the figures, the x-coordinates are the A-K hole indices, while the y-coordinates are the 1-8 hole indices. Data was acquired for 50 of the 72 holes. The z-axis quantity is set to zero for the holes for which no data was acquired. The data used in making these plots is in the appendix.
Table 31: Fractional Standard Deviations for Gas Gain, Energy Resolution, and Efficiency over the IPC Face| IPC | Gas Gain | Energy Resolution (%) | Efficiency (%) | ||||||
| LE1 | 3.7 | 3.9 | 1.9 | ||||||
| LE2 | 3.3 | 4.2 | 2.2 | ||||||
| HE1 | 3.6 | 3.5 | 2.1 | ||||||
| HE2 | 2.7 | 5.0 | 2.1 |