Zero Cross Pulse Shape Discriminator
The Model ZCPSD2027 is a fully dc-coupled Unit with a dynamic range of up to 500:1. The Model ZCPSD2027 provides optimum pulse shape separation for liquid scintillation counters.


  • Particle separation for scintillators detectors (NE213, BC501, BC505, . . .)
    • Neutron-Gamma Separation
    • Alpha-Proton Separation 
    • Electron-Alpha Separation 
    • Electron-Alpha-Gamma Separation
  • 500: 1 dynamic range 
  • Z-identification for thick surface-barrier detectors 
  • Needs anode signal only 
  • Particle identification with proportional counters and Phoswitch detectors Count rate capability over 50KHz- with pile up rejection > 500KHz Multicolor Count Rate Indicator 
  • Full DC coupling 
  • Full adjustable module


The Model ZCPSD2027 is a fully dc-coupled Unit with a dynamic range of up to 500:1. The Model ZCPSD2027 provides optimum pulse shape separation for liquid scintillation counters. However the applications are not limited to n-g separation, the 2027 can also be used for particle separation with inorganic scintillators, phoswitches, thick SSB detectors and proportional counters.
The Model has a dc-coupled 50 ohm input which accepts negative pulses. The dc coupling allows high statistical count rate without affecting resolution, a major problem of conventional designs. The single width module is easy to use, since only the anode signal is required from PM tubes.
The ZCPSD2027 can be used to generate identification spectra with a TAC2038 and MCA or an identification signal for one species of particle (see application diagrams).
Four simultaneous, independent output signals are provided. The two positive outputs are adjustable in width, the width duration sets the internal dead time required to suppress spurious outputs due to input signal anomalies. The two negative outputs are fixed-width pulses keyed to the start of the dead time period. The front panel CROSS OVER permits the user to trim the zero cross time characteristics of the experimental setup for optimum timing resolution. A novel front panel LED indicates count rate by color change.

Electrical and Mechanical Power Required:

  • Standard version +6 V - 150mA, - 6 V - 450mA, 12 - 30mA Physical
  • Size: Single width NIM module 
  • Weight: Net Weight - 0.9kg (2.0lbs.) &  Shipping Weight - 2.2 kg (4.9 lbs.)


  • Input: Accepts -5mV to -5V linear pulses: Zin= 50 Ohms, dc coupled; 2 front panel BNC connectors.
  • Strobe Input: 50 ohm Negative FAST-NIM signal from CFD2017, front panel BNC connector. 


  • Inspect: Displays signal of zero crossing discriminator for use in trimming time characteristics.
  • Outputs (-): Two independent negative current outputs, each providing -32mA into 50 Ohm; rise time < 3 ns, pulse width 5 ns nominal, dc coupled.
  • Outputs (+): Two independent positive voltage outputs providing 2 V (minimum) into 50 Ohm, rise time< 5 ns, width adjustable by adjacent width trimming potentiometer, which also determines internal dead time.
  •  Clip Cable (Rear Panel): 2 BNC connectors accept 50 Ohm delay cable to adjust width of the negative output pulses: controlled by adjacent IN EXT switch.


  •  Strobe Delay - Front panel 10-turn locking dial potentiometer to set strobe of Zero Crossover discriminator acceptance.
  •  Adjust - Front panel trim pot to adjusting time characteristics.
  •  Output Width - Front panel 10-turn screwdriver adjustable potentiometer to set width of slow positive output pulse, which is equal to the internal dead time of the discriminator. Min setting: 500nsec.
  •  N—N+G - Toggle switch allows use of N and N+G.
  •  Position N: generates an identification signal.
  •  Position N+G: generates identification spectrum. 
  •  IN—EXT (Rear Panel) - Toggle switch allows use of external cable to widen negative outputs. 
File Format TypicalApplication.pdf en 3/17/2016 8:38:19 AM
File Format ZeroCrossPulseShapeDiscriminator-Model-ZCPSD2027-Catalog.pdf en 3/15/2016 8:56:19 AM
File Format NIM-MODULE-Mechanical.pdf en 7/28/2016 10:14:24 AM
n/Gamma Discriminator Block Diagram:
n/Gamma Discriminator Block Diagram
Electron/Alpha/Gamma Separation with Proportional Counter:
Electron/Alpha/Gamma Separation with Proportional Counter
Electron/Alpha Separation with Phoswitch:
Electron/Alpha Separation with Phoswitch
Alpha/Proton Separation with Silicon Surface Barrier {SSB} detector:
Alpha/Proton Separation with Silicon Surface Barrier {SSB} detector
Typical 2 parameter n/Gamma Discriminator Block diagram:
Typical 2 parameter n/Gamma Discriminator Block diagram
  • Dynamic Range - 500:1
  • Walk - <2n (typically 1.5n) for 30mV to -3V range with <2nsec rise time. Counting Rate up to 500 KHz, limited by dead time (OUTPUT WIDTH setting).
  • Temperature Range - 0 to +50oC
  • Typical Power Requirements: 
  • PHYSICAL: Size: Single width NIM module, Net weight - 0.9kg (2.0lbs.) - Shipping weight - 2.2 kg (4.9 lbs.)


NIM standard module connector pin assignments (required by DOE/ER-0457T):

Pin# Function Pin# Function Image
1 Reserved [+3 V] 2 Reserved [−3 V]  
3 Spare bus 4 Reserved bus 
5 Coaxial 6  Coaxial
7 Coaxial 8 200 V DC 
9 Spare 10 +6 V 
11  −6 V 12  Reserved bus
13  Spare 14  Spare
15 Reserved  16  +12 V
17 −12 V  18 Spare bus 
19  Reserved bus 20  Spare
21 Spare  22 Reserved 
23 Reserved  24  Reserved
25  Reserved 26  Spare
27  Spare 28  +24 V
29  −24 V 30 Spare bus 
31  Spare 32 Spare 
33  117 V AC (hot) 34  Power return Gnd
35  Reset (scaler) 36 Gate 
37  Reset (aux) 38 Coaxial 
39 Coaxial  40  Coaxial
41 117 V AC (neutral)  42 High-quality Gnd 
G  Gnd guide pin