He3 counter finalized

[Richard Hull]

Attached are four images of the finished He3 counter first shown in experimental mock up. See post

viewtopic.php?f=13&t=5517#p33961

AND

viewtopic.php?f=13&t=5519#p33963

The first image shows the finished moderator tube which was painted this weekend.

The second image shows the details of the track with milled slots and tube carriage. The track base is scribed with lines every centimeter. This arrangment allows the tube to be moved back and forth in the water to provide for more or less moderator between the tube and source. The moving assembly carries both the tube and attached preamp.

The third image shows the NIM configuration finally settled on. The preamp boosts the tube signal so that it can be sent to the equipment rack where it is fed into a linear amp for further boosting. This signal is then sent to a "windowed" SCA. The SCA output pulse is sent to a gated delay amp. This stretches the pulse a bit. The multiple output on the gated delay module allows the signal to be routed to an audio chirping annunciator module and two digital counters.

The final image shows the device in position and the preamplifier signal and HV cabling to the ceiling.

Following the addition of a water-antifreeze mix for winterization in my unheated lab, the entire system was tested in 12, (600 second/10 minute) runs for data collection. The average background was 6.1CPM while a small neutron source gave a background adjusted 118 CPM.

This is a very sensitive neutron counter.

Richard Hull

[StephenY]

A very timely addition and thread update for me, Richard! By next week I'll be in the process of setting up a NIM bin for a custom "tube" and this bring me to ask: How many NIM device of each type did you have to get on Ebay before you got one that did not smoke on power up, due to aged, and dormant, capacitors? Our ratio is 2 (bad ones) to 1 (good one), especially for amplifiers. The sturdiest parts of the system seem to be the rack power supply, still running with split open capacitors! (Yes, promptly replaced anyways), and the H.V. supplies, 'bought 3, all fine. But, generally speaking, Canberra devices do not appear to age well, IMHO.

[Steven Sesselmann]

Richard,

Nice picture of your NIM crate, can you tell us what the various modules are and what they are used for.

I have been looking for a NIM crate, but the shipping to Australia has always been a problem.

Steven

[Richard Hull]

I have a jig and I use it.

It is a custom made affair whereby a dummy module is placed in a bench mounted NIM crate ( I have 10 crates). The new e-bay or HEAS fleamarket purchased suspect module has both sides removed and is pluged into the dummy module that has a female NIM cable exiting it with NIM power. I did this because I have about 100 NIM pulg ins and need to test and diagnose frequently. I turn on the unit and look for smoke. No smoke? I them feel with my finger tips all of the stupid and often trashed tantalums sprinkled liberally over the boards. Any of them warm to the touch, get replaced. This is about 95% of all NIM module issues. Modules with severe issues not readily traceable or that are not that cool a module, get gutted and thrown on a pile of NIM module blanks to allow me to make up my own modules, as needed.

I am currently re-working this "servicing module assembly" to be even more versatile. (lined up with all the other crap jobs that I haven't got to yet)

A classic use for these blank "waste modules" is seen as the single NIM module in the pix mostly to the left in the bin. It has a biege front. This is an ennuciator with variable volume and settable duty cycle to the clicker via a 555 timer inside. It uses a 8000mcd green led. This allows it to be quite bright even at short duty cycle. Many of you have heard this annoying chirp to a tone when fusor IV is running at the HEAS events. I also included the obligatory mute switch that I rarely use.

My set up takes the high mv output of a Princeton Gammatech preamp and runs to an Ortec spectroamp to pump the neutron signal up to about 6 volts leaving the gammas at about 0.2volt. Its output is fed to an Ortec SCA for low level windowing out of the gamma signal. The NIM pulse signal is them fed a LeCroy signal conditioner module and shaped and timed to be fed to the annunciator and the counter/timer/scaler. I use a standard NIM HV bias supply as well for the HV tube bias on the He3 proportional tube which is currently fixed at 2100 volts.

You could actually do this with as few as three modules, But I got em to burn so why not process the crap outta' th' signal?

Richard Hull