SI19N Neutron Detector

[Sesselmann]

Hi All,

This weekend I have been busy making a neutron detector kit for a local client, it turned out good and I should probably add it to my range of products.

The detector is based on a Russion He3 corona tube called SI19N and according to the specs. it has an nvth (efficiency to thermal neutrons) of 70%. These Russian corona tubes are tricky to work with and require very high impedance load resistors up to 100 Mohm.

SI19N.jpg

For some reason many of the Russian tubes have a rather impractical design with anode and cathode at opposite ends, so I decided to make a new housing for it. I found some stock size 38x2 mm aluminium tubing which fitted the SI19N perfectly. I machined a slightly oversized plug for the bottom end for press fitting and a cap with a hole for an SHV connector at the top.

Housing.jpg

Not visible in the picture above, but the plug in the bottom has a nipple that holds a steel spring upright.

Spring.jpg

For the anode connection I 3D printed an insert to fit inside the pipe and fitted it with a brass connector, such that the tube when assembled is held in place between the spring against the cathode and the brass contact on the anode, hope that makes sense.

insert.jpg

I machined an aluminium cap and fitted it with an SHV connector.

cap.jpg

The completed detector looks great and is now a lot more compatible with standard lab electronics.

gs-neutron-si19n.jpg

Now if you are familiar with neutron detectors you will know that He3 only detects thermal (slow) neutrons, so for many experiments it is necessary to add a moderator. Such moderators are typically made from lightweight materials rich in hydrogen. Water is an excellent moderator because it contains a lot of hydrogen, but so does paraffin and most plastic materials, so for convenience HDPE is a popular choice. In this case I would have needed a 140 mm diameter HDPE bar which is not so easy to find and also quite expensive, so I turned to my favourite PVC plumbing pipes and made a container into which I filled HDPE beads. These are sold cheap eBay for dolls and weighted blankets.

hdpe-container.jpg

I made the moderator slightly oversized as the beads only stack around 75% as dense as a solid.

Now for the electronics my preferred method would have been to build the GS-SCHMITT-TRIGGER into the GS-USB-PRO, but in this case the professor also wanted to use the GS for gamma spectrometry, so I built the Schmitt trigger into a separate box with a 9V battery.

gs-schmitt-trigger.jpg

The GS-Schmitt-Trigger has two trimmer potentiometers, one for the volume and one for the trigger threshold, there are convenient outputs for both trigger and pulse on the board so it's easy to hook up a scope.

scope.jpg

Finally the whole project came together quite nicely and I ran it for a couple of hours with background neutrons, which varied between 1-4 neutrons per minute.

PRA.jpg

I look forward to building another one of these for my own use and if I add it to my products for sale. For the skilled DIY'ers out there it's a manageable project and I am happy to provide support, but for many who don't have the workshop or the skills it might just be easier to buy one.

Steven

[GigaBecquerel]

Nice build, steve!

I really like those russian corona tubes, they're far less noise sensitive than proportional detectrors, and their gamma rejection is amazing.
Some time ago I wrote a piece on my website about how to correctly use them: https://gigabecquerel.wordpress.com/201 ... snm-tubes/

Lukas

[Sesselmann]

Lukas,

Yes, I am aware of your web site, it's a really good source of information for all those confusing Russian tubes.

Nice work..

Steven

[Geoff]

Awesome work!

[James Luck]

Hay all

Soon i will be working on my own moderator, just picked up for quite cheap a NOS SI-14N He3 tube.
Smaller than the SI-19N so my moderator wont be as cluncky.

-size: 7x3/4 inch.

Planned to make her mobile, and if I can fit her to a Esp1 for neutron counting. Would be cool to see if I can try out a few scatter experiments, source depending of course.

Finally gave up on the SNM-12 as it works better for gamma I'll return one day.

Almost have to moderate the whole set up with low contaminant lead in order to isolate the neutron pulse. My attempts of separating the pulses have been unsuccessful, as many people who buy the Boron Corona tubes come to find out.

Hopefully my new tube works better, was tested by seller with 3in of polyethylene as being in working order. My plan is to do the same as Steve and moderate the tube with polyethylene pellets, maybe some metal for greater isolation.
-tests will be preformed with a 1mCi AmBe source.
( would love a Californium source

Well till I start work.
Take care all,
Luck