Neutron Trigger Discussion


The Neutron Trigger Module processes multiple PMT signals from the Neutron Scintillator which are converted to NIM logic levels and passed through a multiple OR function to the input of the Trigger Module. Pulse events are qualified by selecting only pulse trains having a defined number of events within a specified time window following the initial event. The interesting pulse time sequence might be 4 pulses occurring within a 40 us period, when this sequence is detected a Global Trigger will be generated which starts the data acquisition process. In order to generate a global trigger the Trigger Module must be enabled set to LIVE. Following the data acquisition, the A/D converter system generates a TRIGGER ENABLE pulse which arms the Trigger Module for the next event.


The time window and the pulse tally requirements are set through a USB interface to a PC which uses a LabView application. The ranges are listed in the table below, any combination.

TIME WINDOW: 10, 20, 30 . . . 150 uS


EVENT COUNT: 1, 2, 3. . . . 15





Pulse In: NIM Logic, Lemo connector, 50 ohms, 10 ns minimum pulse width. 90 Mhz max rate. For multiple pulse inputs the separation must be greater than 20 ns.

Trigger Enable: 5v CMOS Logic, front Lemo connector, 1000 ohm, 100 ns minimum pulse width

Trigger Enable Switch: Used to enable or disable the Trigger Enable feature, with two settings; USE and IGNORE (Label Reversed)

External Trigger In: 5v CMOS Logic, front Lemo connector, 1kohm, 100 ns minimum pulse width

USB Control: PC Interface, USB9


Trigger Out\: 5v CMOS Logic low level, front Lemo connector, 50 ohm, Global-Trigger stays high until Trigger Enable.



TRIGGER: Red LED, 0.5 second pulse upon generation of a trigger

LIVE: Green LED indicating that the trigger module is enabled.

POWER: Red LED +5v power indicator


5volts taken from QuickUSB Module which uses PC power, 37 mA


TRIGGER: Raw Trigger Signal

COUNT: Pulse counter AND gate output, pulse counter set by labview VI

GATE: Output of Gate Flip Flop, gate width set by labview VI

+5V: 5 volt power

GND: Common or ground connection