How to build a probe to detect Cerenkov's radiation?

For an engineering class, we are to construct a probe to detect the power level of a nuclear reactor. My design thus far is using PVC pipe, encase a set of photo diodes to detect Cerenkov's radiation and hook that up to a voltmeter. However, I can't think of what to encase the diodes in that would allow light to pass through but not leak under 10 ft of water pressure.|||My first answer is to use a standard canning jar, drilling a hole in the lid and using a CGB connector (cord grip bulkhead) connector for the cable. One other important note: make the jar heavier than neutrally buoyant-calculate the volume of the jar, and then the weight of that volume of water. Add weights inside the jar to make the entire jar weight a little more than the equivalent amount of water. If you don't add weights, your jar will just float on top of the water!