TEST OF LEAD GLASS SHOWER COUNTERS* K. Ogawa, R. Sugabara, K. Takabssbi, F. Takasaki and T. Taucbi KEK, Japan N. Awaji, H. Hayasbii, S. Iwata, H. Ozaki and S. Suzuki Nagoya University, Japan R. A. Gearhart, A. Miyamoto and T. Sbimomura Ston$ord Linear Aeecleralor Center Stanjord University, Stanford, Calijornia Q&l05 SLAGPUB (Rev.) October 1983 (1) Abstract Lead glass counters made of wedge shaped blocks of SF6 were tested with positrons at SLAC. The beam energy ranged from 2-17.5 GeV. Energy dependenceand beam position de pendence of pulse beigbt‘and energy resolution were studied with lead glass blocks of various lengths. The effect of a BK-7 light guide on pulse height was clearly observed. Degradation of the energy resolution due to aluminum absorbersof various lengths was investigated. A mesh type photomultiplier was also tested. 1. Introduction : ,*-array of a new type of lead glass SF6, radiation length x0 = 1.7 cm, has been tested in a positron beam at SLAC. The glassis intended to be usedin barrel calorimeters for TRIS TAN experiments at KEK. Some 10,000piecesof lead glass ul- timately will be required. The block segmentsare to be wedge shaped to better fill the annular volume of the barrels. 2. Experimental Procedure A 3 x 3 array of the glass was exposed in a secondary positron beam, with beam energy of 2 to 17.5 GeV. The beam bad a spot size of about 2 mm diameter and a beam energy spread, AE/E, of less than 0.5%. The experimental layout is shown in Fig. 1. The lead glass block array was positioned and moved transverse to the beam with a precision of less than EXPERIMENTAL I 1 SETUP =k Tngger Absorber (Al-plate) ‘/ Wooden Box zocm Momg Table Fig. 1. Experimental layout. l Work supported in part by the Department of Energy, con- tract DE-AC03-76SFOO515, and by the Japan-U.S. Cooperative Program on Detector R&D. 1 mm. A coincidence signal of defining counters, Sl (3 mm in diameter and 2 cm long) and S2 (2 cm X 5 cm), was used as a trigger. The beam intensity was set to be an averageof 0.1-0.3 particles per pulse with beam repetition rate of 10 Hz. Pulse length was about 150 nsec. Data from pulses with more than 1 positron were rejected by imposing a tolerance on the pulse height from S2. The lead glass block to be measured was placed at the center of the 3 x 3 array and pulse height data for all 9 blocks were digitized, collected and written onto magnetic tape for every event. The surrounding 8 counters were each of 20X0 with a cross section of 9.0 cm X 10.3 cm at the beam entrance and 10.3 cm x 10.3 cm at the rear surface (the horizontal side faces were tapered by 1’). Whenever the beam position dependence was studied, the top middle block wss also replaced by one of the same type as the center block and the beam was scannedvertically from the center block through the top block. Lead glass blocks of 15X0, 18X0 and 20X0, and a wedge- shaped block of 18X0, were tested. The effects of a 4 cm long light guide (3 inches in diameter) of BK-7 glass were also measured. To each block was attached a 3-inch diameter pb+ tomultiplier, Hamamatsu R59402, using an ultra high vacuum greaseof excellent transparency to attach the tube. Each lead glass block was wrapped with aluminized mylar and black tape to ensure light tightness. The signals from the lead glass blocks were digitized by an II-bit ADC, Lecroy 224QW, using a gate width of 200 nsec. The linearity of the ADC’s was checked in advance and was found to be linear to within 2 counts throughout the entire dynamic range. By means of an LSI-11 mini-computer, data was collected, analyzed and written onto magnetic tape to per- mit further off-line analysis. To adjust the gain constant for each channel (including the ADC’s), the nine counters of the array were successively exposed to 10 GeV positrons. The high voltage for each counter was then adjusted to give roughly the same mean amplitude in pulse height. After adjusting the high voltages, the mean amplitudes for 10 GeV positron signals were used to generate normalization constants for the off-line anal- ysis. Figure 2 showsthe typical pulse height spectrum for a 20x0 lead glass block array exposed to a 17.5 GeV positron beam. The pulse heights for the nine blocks has been summed. The energy resolution was obtained by fitting the Gaussian shape to the spectrum as shown with the solid line in the figure. For those circumstances in which the spectra was asymmetric, independent Gaussian distributions were fitted separately to the upper and lower halves and the average sigma was used to determine the energy resolution. - --dslm Contributed to the Nuclear ScienceSymposium, San Francisco, California, October 1821, 1983.