If you google "gate effect propellerhead reason", you'll find these three videos that make up a quick how-to on gating. In the video, the synth used was Subtractor.

I'm using a Thor in my current composition and have had partial success using the method described in the video. Basically you add a Matrix sequencer and tie the gate output CV to the Amp Level CV input on the synth, and crank the knob next to the input up to 127 (Max).

Since I'm new here, I can't post a link to a sample clip but hopefully the following will be enough of a description:

The clip starts with the matrix running a strait 16 steps, untied, resulting in the steady chopping of the gate you hear for the first few seconds. After a bit, steps are tied, but the gate is closed for all steps. So, what I was expecting was for Thor to be silent, but instead, the really low-end sound coming through. I have this repeat a couple times for emphasis so you can hear the difference. The kind of gate I was aiming for was for the sound to be absolutely silent when the gate is closed so the stuttering would be more pronounced/noticeable.

The patch being used is called "Underwater Agard Pad" if you feel like playing with it on your own.

After experimenting a while, I discovered a way to get the sound I wanted. Instead of routing the Gate CV from Matrix to Thor, I routed it to the Level CV on one of the channels on the big mixer board, and cranked up the knob next to it to 127. Then run the audio-out from Thor to that channel.

At first, when I did this, I discovered that I was still getting the same problem. The gate sound was happening, but when the gate was closed, some of Thor was still sneaking through. Then I turned the level slider on the mixer all the way down and started the gate back up again. The CV input took over, and sure enough, it produced exactly the crisp gate sound I was looking for, albeit a little quieter than I wanted. Taking care of that was simply a matter of either increasing the Master Output knob on Thor up until it sounded loud enough, post mixer board.

Lesson learned: Use a mixer panel for an effective gate effect and make sure you turn the volume slider on the channel you're working with all the way down and let the CV input from the Matrix do the driving from there.