one shot using nand gates

Hello from Australia!

I need to make a one-shot to reset a Programmable Unijuction Transistor for a Ramp Generator.

The reset is needed to syncronise with the other part of the circuit.

In theory ,all I have to do is put the incoming CLK through a NAND gate with the other input (2 inputs total),connected to the inverse

of the Q output through a charging capacitor which charges via Q through a resistor.

The 'Interlock' is suppose to stop the incoming CLK from holding to flip/flop high.

But the circuit 'Oscillates' at around 3Mhz and I don't know why?

It seems like a straight forward circuit.Does anybody know of an easier way to make a one-shot in a DIP package?

Thanks-Simon