Since the last post, the neutron generator has been set-up and checked to see that it works. So what to do with it next? Throw it into a swimming pool!
We plan to run the neutron generator under 5 metres (16ft) of water next to XENON1T, see the figure. For XENON1T, the water acts for two purposes: to shield the detector from environmental neutrons, and to veto any highly energetic cosmic ray muons that interact near the detector.
When we ordered the generator, we of course specified that it should be water tight to this depth. However, it’s obvious that we should test it ourselves before putting it next to the detector. This is to see if it leaks under water, if any of the attached cables and hoses are not perfectly sealed. This is also to test that it sinks unaided, as it could have been that air in the hoses made the generator set-up too buoyant.
So we contacted the Boilermaker Aquatic Center, the nearest clean body of water we could think of, and they said they would be happy to help. The deep end of the diving pool is 17ft deep, which was more than enough for us. To check for leaks, we put colour saturation desiccant crystals inside the end of each cable, at the point where each cable attaches to the generator. These crystals would then change colour if they were in contact with water. We then went down when the pool was closed, with all cables and hoses attached to test the water tightness and buoyancy. Needless to say, the generator itself was not powered at any point, and so could not produce any neutrons during the test. We then left the generator underwater for an hour, to make completely sure that there was not even a small leak.
The results of the test were very positive. The generator sank, and the dessicant remained dry inside all cables. In short, everything looks good
We would like to thank David Fraseur, Terry Huntley and James Barnett at the Boilermaker Aquatic Center for all their help in this test, we couldn’t have done it without you!