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Conundrum

Fri Feb 19 2016, 08:51AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Interesting, although a bit tricky to make it accurate unless you spend $$$ on the UV LED and photo-diode detectors.

Proud Mary

Wed Feb 24 2016, 06:26PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

These Ag doped phosphate glass detectors are designed for use at nuclear installations and such, and a sophisticated machine is required to extract the dose information from them. Unlike the quartz fibre pen dosimeters, and devices that use mini GM tubes, phosphate glass detectors and the related thermoluminscent detectors (TLD) can not be read by the (anxious!) worker or soldier. They must hand in the dosimeter at the end of the week, or what have you, and it is then read in a sophisticated machine. You sometimes see wrist-watch style military TLD detectors on sale on ebay for a few pounds, but they are of no use without the reader machine. Trying to measure accurately the miniscule light output of the phosphate glass with DIY equipment looks very difficult to me, compared with making your own ionisation chamber, or having fun with GM tubes, or the gold leaf electroscope (good enough for Marie Curie!) which most folk can get up and running without breaking the bank, or lying awake at night worrying about nanoLux.

I'll put up pix of some of my own detectors over the next few days, when I have time to photograph them nicely. :)

Conundrum

Sat Feb 27 2016, 10:50AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I have the crystal and diode from one of the Bull Electrical ones..

Proud Mary

Wed Mar 09 2016, 05:29PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've just bought this end-window GM tube, type SI-3B, from a man in Moscow, and paid him Â£14 for it, tested and working.

According to the datasheet the mica window is < 3 mg/cm2, a middle of the road thickness, but not so thin you'd wake up sweating in the night worrying that you'd put a hole in it.

The operating voltage is quite high - 1650-1800V - so I guess that the fill gas pressure is quite high by modern GM standards, no doubt to place as little stress on the window as possible.

The guy had another (much more expensive but otherwise identical) end window tube with a 1.5mg/cm2 window, which had a Geiger plateau between 2 and 3 kV, which seems to bear out my theory about the gas pressure. Too much vacuum and the thin window would implode. I remember there was an American GM tube, the Victoreen 1B85, that went with those Civil Defense brick-like yellow monstrosities and the aluminium alloy that if was formed from was so thin that sometimes the tubes would collapse in on themselves like a tractor had driven over it if you dropped it or flicked it with your finger. It had quite a high voltage for such a skinny little tube - about 900V if I remember right - so I guess a trade-off had to be made somewhere between the fill gas pressure and the strength of the walls.

Meanwhile, I can't wait for my SI-3B to arrive from Russia! :)

Conundrum

Thu Mar 10 2016, 01:41PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

In other news, I found that the APDs can be found on Ebay for around the Â£15-Â£22 mark if you buy from Shenzen, China.
They are new old stock but as is often the case this is less of a problem if you can measure accurately the diode's characteristics.

Proud Mary

Thu Mar 10 2016, 02:53PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Conundrum wrote ...

Would there be any interest in a group buy of silicon photomultipliers?

What's a silicon photomultiplier?

Bjørn

Thu Mar 10 2016, 05:56PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Conundrum wrote ...

Would there be any interest in a group buy of silicon photomultipliers?

This belongs in a separate thread with some data and an approximate price.

klugesmith

Tue Mar 15 2016, 11:33AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Well I just received a proportional counter tube filled with boron trifluoride at pressure of "70 cm Hg".
Firing it up on the bench will be a learning experience, as my first use of a raw detector tube.
Now where did those two little radioactive test sources go?
The BF3 tube is strong metal, with no window, 'cause made for detecting neutrons.

Proud Mary

Tue Mar 15 2016, 12:47PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

klugesmith wrote ...

Well I just received a proportional counter tube filled with boron trifluoride at pressure of "70 cm Hg".
Firing it up on the bench will be a learning experience, as my first use of a raw detector tube.
Now where did those two little radioactive test sources go?
The BF3 tube is strong metal, with no window, 'cause made for detecting neutrons.

Is there some especial reason why you think your neutron detector is of the BF3 type? Had you not said that, I'd have assumed that the walls had been coated in the usual way with unenriched boron deposited by high temperature decomposition of diborane, and that the fill gas in which the corona occurs was argon. The gas pressure you cite is typical of an argon-filled corona discharge detector.

Does your datasheet specify the anode or quench resistor? If not it is likely to be of the order of 100 -150Mâ€ŽÎ© to maintain a stable low-noise corona.

Will you mount your tube coaxially inside concentric layers of lead and paraffin wax or ultra high molecular weight polythene?

Or are you just going to put your test source in a block of moderator for now?

Conundrum

Fri Mar 18 2016, 09:46AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Heh, my thinking too.
If its of any help I worked out how to hack a TV 38kHz (thanks to Dave.Hadley of CES) to decode 60kHz no-longer-in-rugby MSF signals.
It works for a GM counter so should work fine for this, just use the well known heterodyne method and a weak sinewave source imposed on the rod with a critically biased infrared emitter diode.
EDIT: also works for some radiation sensor applications, for this a 32 kHz crystal connected to a simple Pierce oscillator with IRED in its emitter circuit will work even though it is slightly off frequency.

EDIT 2: My APDs showed up, 3 of them.

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