296 ScintiPack Photomultiplier Base with Preamplifier and HV Supply
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296 ScintiPack™ Photomultiplier Base with Preamplifier and HV Supply • For scintillation detectors employing 10-stage PMTs that fit standard 14-pin sockets • Internal, adjustable, high-voltage bias supply eliminates high-voltage cables • Integral spectroscopy preamplifier avoids dangling boxes • Active bias network minimizes peak shifts at high countingrates • Anode timing output for coincidence measurements • Low power consumption (240 mW) for portable applications • Convenient, single-cable connection for most applications The ScintiPack Photomultiplier Base (Model 296) includes everything needed for scintillation detectors in one compact package: a low-power, adjustable, high-voltage supply, an active bias network, and a spectroscopy preamplifier. Incorporating the bias supply in the photomultiplier base eliminates high-voltage cable connections to bulky, external, HV supplies. As a result, the ScintiPack operates with extremely low power consumption (240 mW). This makes the ScintiPack attractive for portable applications, as well as for high-density detector arrays. Because the preamplifier output signal is bundled into the power cable, only a single cable is required between the photomultiplier base and the main amplifier location. The optional Signal Break-Out Adaptor can be used with amplifiers that do not offer signal interfacing through the preamplifier power plug. The adaptor attaches to the preamplifier power plug at the amplifier, and supplies the preamplifier signal on a coaxial cable for connection to the front-panel input of the amplifier. This approach maintains a singlecable connection from the ScintiPack to the amplifier location. The ScintiPack biases the cathode of the associated photomultiplier tube at ground potential, and the anode at a positive voltage. The voltage applied to the anode can be optimized within the range of +600 V to +1100 V via a 20-turn screwdriver adjustment. This provides a cost-effective means of adjusting and matching photomultiplier gains in large arrays of scintillation detectors. The dynode bias network applies 1/6 of the anode voltage between the cathode and first dynode, and 1/12 of the anode voltage between the remaining pairs of electrodes. To provide excellent gain stability at high counting rates, the voltages applied to dynodes 8, 9, and 10 are transistor regulated. Feedback regulation is also applied to the anode voltage to achieve optimum gain stability for the entire photomultiplier tube. The signal from dynode 10 is integrated on a 500-pF capacitor at the preamplifier input, amplified by the preamplifier gain, and presented as a positive-polarity pulse at the PREAMP output. A jumper on the printed circuit board allows selection of a preamplifier gain of X1 or X6. The preamplifier output signal can be accessed on pin 3 of the power connector, or at the BNC connector on the rear panel of the ScintiPack. The anode signal is available on a rear-panel BNC connector to facilitate high resolution timing in coincidence measurements. This output is intended to drive a 50-fi coaxial cable to a timing amplifier or a timing discriminator. By moving a jumper on the printed circuit board, the anode output connector can be converted to a test input for the preamplifier. A pulser can be applied to the test input to check the operation of the entire chain of electronics, starting from the preamplifier input. The PMT socket is a standard JEDEC B14-38 socket that fits 10-stage photomultiplier tubes with 14 pins. Figure 1 defines the pin assignments, and Figure 2 illustrates the connections. The Model 296 ScintiPack Photomultiplier Base is compatible with the photomultiplier tubes listed in Table 1. Compatibility with tubes not listed in Table 1 can be checked by reference to Figures 1 and 2, and by comparison with the photomultipliers listed in the table. Specifications PERFORMANCE PMT Bias CATHODE-TO-ANODE VOLTAGE Adjustable from +600 V to +1100 V (grounded cathode, positive anode) with feedback regulation. BIAS DISTRIBUTION 1/12 of the cathode-to-anode voltage is applied between: the cathode and focus electrode, the focus electrode and the first dynode, each pair of dynodes, and between the tenth dynode and the anode. Voltages on dynodes 8, 9, and 10 are transistor regulated for improved stability at high counting rates. TEMPERATURE SENSITIVITY The cathode-to-anode voltage changes <100 ppm/°C over the operating temperature range of 0 to 50°C. BIAS VOLTAGE DECAY TIME Nominally 3 minutes, when the HV switch is turned off. Preamplifier OUTPUT POLARITY Positive. OUTPUT RISETIME <100 ns for a fast pulser at the TEST input, or for a fast scintillator. OUTPUT DECAY TIME CONSTANT Nominally a 50-ps exponential time constant.

Table 1. Compatible Photomultiplier Tubes. Fig. 1. JEDEC B14-38 PMT Pin Base, with Pin Assignments CONVERSION GAIN Typically 1 pV/eV or 6 pV/eV (jumper selectable) for a 3-in. x 3-in. Nal(TI) crystal and a PMT gain of 106 OUTPUT NOISE <300 pV rms. Measured using an ORTEC Model 671 Amplifier under the following conditions: HV on, no PMT installed, X6 preamplifier gain, and a 1-ps amplifier shaping time constant. INTEGRAL NONLINEARITY <±0.1% from 0 to +6.5 V into a 1-kQ load; measured via the TEST input. Maximum output is +7 V into an open circuit, or +3 V into a 93-Q load. Overall linearity...

PREAMP A rear-panel, BNC connector delivers the preamplifier output signal for applications where a separate signal cable is desired. The same signal is also available on pin 3 of the power cable connector for systems that accommodate a single-cable connection to the spectroscopy amplifier. Both outputs have a common, ac-coupled, 93-Q, output impedance, and are short-circuit protected. The signal from dynode 10 is integrated on a 500-pF capacitor at the preamplifier input, amplified by the preamplifier gain, and presented as a positive-polarity pulse at the PREAMP output. PMT SOCKET TRW...