FEATURES:
? Noise Slope:1.8 x 10-17 coulombs RMS/pF
| Input Characteristics | |
| Threshold | Model A121 has a nominal threshold referred to the input of 8 x 10-15 coulomb. This is equivalent to 5 x 104 electrons. |
| Threshold Stability vs. Temperature | 0.5% per °C |
| Threshold Stability vs. Power Supply Variations (Vs) | -0.1% per mV |
| Unit-to-Unit Threshold Variation | ±8% |
| Noise (typical) | 15 x 10-16 coulombs RMS; 9,650 e- RMS; 19% of threshold |
| Noise Slope (typical) | 1.8 x 10-17coulombs RMS/pF |
| Output Characteristics (At Threshold)Input Test: 4 mV through 2 pFQ = CV = 0.008 pC = 5 x 104electrons | |
| Analog Output (Pin 5) Sensitivity | 120 mV (15V/pC) |
| Analog Output Risetime | 10 ns |
| Output (Pin 9) | 5 V; 35 ns minimum |
| General | |
| Dead Time | Fixed Dead Time.Minimum Dead Time 80 ns.See figure A. |
| Count Rate | 12 x 106CPS periodic |
| Operating Voltage | +5 to +7 VDC (25 mW) |
| Operating Current (typical) | 5 mA quiescent, plus 1.5 mA/MHz |
| Temperature | -55 to +85 oC operational |
| Screening | Amptek High Reliability |
| Warranty | One year |
| Weight | 3.5 g |
| Package | 9-pin SIP |
| Accessories | PC-121 test board |
Pin 1 should be AC coupled to the detector.The High Voltage coupling capacitor should have adequate voltage rating in order to prevent breakdown which could damage the A121.
An anode at ground potential needs a DC path to ground to maintain a fixed potential.This can be provided by DC coupling to the input of the A121, which will hold the anode at about 1.2 V.Alternatively, you can AC couple, but use a higher value resistor (1 MEG) to ground at the anode side of the capacitor.
2. Protection to the A121 can be provided as follows:
Threshold to the A121 can be changed remotely by changing the voltage level on Pin 3. A resistor from Pin 3 to Vs can be added in order to raise the threshold on the A121.The impedance at Pin 3 is about 10k ohms. (See Figure B)
Pin 5 provides a positive analog pulse output from the preamplifiersection just prior to the discriminator with a rise time of about 10 ns. At maximum sensitivity (Pin 3 = 0 volts) the amplitude of this pulse is proportional to the input charge, A= 15V/pC.At threshold this will correspond to a 120 mV pulse.If a voltage is present on Pin 3, the size of the analog pulse will be divided by the same threshold attenuation factor the voltage produced.Example: If 1.3 volts is present on Pin 3(6 dB attenuation is a factor of 2), the size of the analog pulse will be 60 mV.This output must be capacitively coupled to external circuitry and can be used to monitor detector gain variations by performing pulse height analysis.
The final output stage of the A121 is produced from a 74AC00 gate with a 200 ohm series resistor
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