Using Geiger tube in proportional mode...

P

Piotr Wyderski

Guest
Hi,

the literature says that avalanche gas detectors are capable of being
run in proportional mode where the voltage is below the Geiger plateau.
Would it make sense to operate a sufficiently undervolted Geiger tube
as a proportional detector for the purpose of simple gamma/beta
spectroscopy or is there some inherent property preventing it? E.g. the
gas composition?

If it can, then would a 10-way monster like the SBT10A be partly run in
proportional mode and partly in the usual avalanche?

Best regards, Piotr
 
Piotr Wyderski wrote:
Hi,

the literature says that avalanche gas detectors are capable of being
run in proportional mode where the voltage is below the Geiger
plateau. Would it make sense to operate a sufficiently undervolted
Geiger tube as a proportional detector for the purpose of simple
gamma/beta spectroscopy or is there some inherent property preventing
it? E.g. the gas composition?
Click to expand...

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

If it can, then would a 10-way monster like the SBT10A be partly run
in proportional mode and partly in the usual avalanche?
Click to expand...

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.

> Best regards, Piotr

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Phil Hobbs wrote:

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.
Click to expand...

Yes, this is for an entirely hobby project. No great spectral resolution
is required; in fact, anything resembling the right spectrum would be
very rewarding. It is an off-label application driven by curiosity.

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.
Click to expand...

By necessity I am going to use only the readily available weak sources
with pretty well-defined chemical composition: uranium and thorium,
perhaps americium too. So the dead time should not be a problem.

Best regards, Piotr
 
On 1/19/2022 17:52, Phil Hobbs wrote:
Piotr Wyderski wrote:
Hi,

the literature says that avalanche gas detectors are capable of being
 run in proportional mode where the voltage is below the Geiger
plateau. Would it make sense to operate a sufficiently undervolted
Geiger tube as a proportional detector for the purpose of simple
gamma/beta spectroscopy or is there some inherent property preventing
it? E.g. the gas composition?

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

If it can, then would a 10-way monster like the SBT10A be partly run
in proportional mode and partly in the usual avalanche?

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.

Best regards, Piotr

Cheers

Phil Hobbs
Click to expand...

Hi Phil, just related - have you experimented with NaI and some of the
photodiodes etc. you seem to do a lot of work with? My current
understanding is that PMT-s are still better by quite some margin
but then I don\'t give NaI much thought (although our netMCA is
HPGe grade we do have customers who use it with NaI though).

======================================================
Dimiter Popoff, TGI http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/
 
On Wed, 19 Jan 2022 15:56:46 +0100, Piotr Wyderski
<bombald@protonmail.com> wrote:

Hi,

the literature says that avalanche gas detectors are capable of being
run in proportional mode where the voltage is below the Geiger plateau.
Would it make sense to operate a sufficiently undervolted Geiger tube
as a proportional detector for the purpose of simple gamma/beta
spectroscopy or is there some inherent property preventing it? E.g. the
gas composition?

If it can, then would a 10-way monster like the SBT10A be partly run in
proportional mode and partly in the usual avalanche?

Best regards, Piotr
Click to expand...

Geiger tubes have a really tiny wire, to make very high e-fields close
to the wire for lots of multiplication. I recall that ion chambers
have more, bigger wires, or flat electrodes. That difference probably
affects pulse-height spectroscopy.

SBT10A is interesting, a multi-wire geiger tube. It would probably
work OK in proportional mode, with maybe a little multiplier gain.

Are the wires brought out to the connector individually? Looks like
it.



--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
Piotr Wyderski wrote:
Phil Hobbs wrote:

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

Yes, this is for an entirely hobby project. No great spectral resolution
is required; in fact, anything resembling the right spectrum would be
very rewarding. It is an off-label application driven by curiosity.

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.

By necessity I am going to use only the readily available weak sources
with pretty well-defined chemical composition: uranium and thorium,
perhaps americium too. So the dead time should not be a problem.

    Best regards, Piotr
Click to expand...

\"Lite salt\" sold in the supermarket is half KCl, which is a decent test
source too.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Dimiter_Popoff wrote:
On 1/19/2022 17:52, Phil Hobbs wrote:
Piotr Wyderski wrote:
Hi,

the literature says that avalanche gas detectors are capable of being
 run in proportional mode where the voltage is below the Geiger
plateau. Would it make sense to operate a sufficiently undervolted
Geiger tube as a proportional detector for the purpose of simple
gamma/beta spectroscopy or is there some inherent property preventing
it? E.g. the gas composition?

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

If it can, then would a 10-way monster like the SBT10A be partly run
in proportional mode and partly in the usual avalanche?

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.


Hi Phil, just related - have you experimented with NaI and some of the
photodiodes etc. you seem to do a lot of work with? My current
understanding is that PMT-s are still better by quite some margin
but then I don\'t give NaI much thought (although our netMCA is
HPGe grade we do have customers who use it with NaI though).
Click to expand...

Nothing can touch a PMT for dark counts per unit area--they\'re five or
six orders of magnitude better than an APD or SiPM / MPPC.

A typical 100-um diameter APD has about the same dark count rate as a
_four_inch_ PMT.

Plus you gain another factor of at least 2 by using coupling gel between
the crystal and the PMT face.

You\'d think it was right around 2 because you win etendue by the square
of the refractive index, but it\'s actually better than that--the extra
light at high angles gets totally internally reflected at the
photocathod/vacuum surface, so it gets at least two passes through the
PC, which raises the quantum efficiency considerably.

There are tricks to do even better, e.g. by using prism coupling to make
light rattle round inside the faceplate till it gets absorbed. With a
negative electron affinity (NEA) photocathode, that\'ll get you almost
100% QE over a wide bandwidth.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 1/19/2022 21:20, Phil Hobbs wrote:
Dimiter_Popoff wrote:
On 1/19/2022 17:52, Phil Hobbs wrote:
Piotr Wyderski wrote:
Hi,

the literature says that avalanche gas detectors are capable of being
 run in proportional mode where the voltage is below the Geiger
plateau. Would it make sense to operate a sufficiently undervolted
Geiger tube as a proportional detector for the purpose of simple
gamma/beta spectroscopy or is there some inherent property preventing
it? E.g. the gas composition?

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

If it can, then would a 10-way monster like the SBT10A be partly run
in proportional mode and partly in the usual avalanche?

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.


Hi Phil, just related - have you experimented with NaI and some of the
photodiodes etc. you seem to do a lot of work with? My current
understanding is that PMT-s are still better by quite some margin
but then I don\'t give NaI much thought (although our netMCA is
HPGe grade we do have customers who use it with NaI though).

Nothing can touch a PMT for dark counts per unit area--they\'re five or
six orders of magnitude better than an APD or SiPM / MPPC.

A typical 100-um diameter APD has about the same dark count rate as a
_four_inch_ PMT.

Plus you gain another factor of at least 2 by using coupling gel between
the crystal and the PMT face.

You\'d think it was right around 2 because you win etendue by the square
of the refractive index, but it\'s actually better than that--the extra
light at high angles gets totally internally reflected at the
photocathod/vacuum surface, so it gets at least two passes through the
PC, which raises the quantum efficiency considerably.

There are tricks to do even better, e.g. by using prism coupling to make
light rattle round inside the faceplate till it gets absorbed.  With a
negative electron affinity (NEA) photocathode, that\'ll get you almost
100% QE over a wide bandwidth.

Cheers

Phil Hobbs
Click to expand...

Thanks Phil.
 
On Wed, 19 Jan 2022 17:15:43 +0100, Piotr Wyderski
<bombald@protonmail.com> wrote:

Phil Hobbs wrote:

A proportional counter is a fairly heartbreaking thing to use for
spectroscopy--even a sodium iodide scintillator is much much better.

OTOH for a hobby project, it would probably work OK.

Yes, this is for an entirely hobby project. No great spectral resolution
is required; in fact, anything resembling the right spectrum would be
very rewarding. It is an off-label application driven by curiosity.

ISTM that you\'d need to prevent ions from migrating around inside
somehow, unless you\'re okay with a fairly long dead time after each
Geiger pulse.

By necessity I am going to use only the readily available weak sources
with pretty well-defined chemical composition: uranium and thorium,
perhaps americium too. So the dead time should not be a problem.

Best regards, Piotr
Click to expand...

There are liquid scintillators too.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
John Larkin wrote:

SBT10A is interesting, a multi-wire geiger tube. It would probably
work OK in proportional mode, with maybe a little multiplier gain.

Are the wires brought out to the connector individually? Looks like
it.
Click to expand...

Yes, they are. It opens several interesting possibilities, e.g.
shielding half of it to get beta and gamma signals separately or running
some part of it in avalanche mode and the rest in proportional mode.
Spectral sensitivity is also much better than typical metal tubes --
some specs say it should react to gamma as low as 15keV.

The digital part would be boring, just a bunch of counters. But it is
the analog front-end that could make it possible to go way beyond the
specs. Looks like a lot of fun in my spare time.

Best regards, Piotr
 
On Wednesday, January 19, 2022 at 6:57:05 AM UTC-8, Piotr Wyderski wrote:
Hi,

the literature says that avalanche gas detectors are capable of being
run in proportional mode where the voltage is below the Geiger plateau.
Would it make sense to operate a sufficiently undervolted Geiger tube
as a proportional detector for the purpose of simple gamma/beta
spectroscopy or is there some inherent property preventing it? E.g. the
gas composition?
Click to expand...

There\'s gas recipe differences, but that\'s because you want fat (time-duration)
pulses for proportional but not Geiger. The big irritation, is that the
proportional region is relatively small, it takes regulated V source, and
only part of the (usually cylinder-around-wire) field region has best sensitivity.

But, the construction, if not the gas mix and bias, are about the same.
There\'s a lot of literature available online, like <https://archive.org/details/arxiv-1509.02379>
and spectroscopy is possible... as long as your gas mix is dense enough to actually
stop some of the rays in question. Some variant of multichannel analyzer is needed, of
course, and a test source for calibration.

Not sure about beta spectroscopy, unless you put the beta emitter inside the gas-containing tube.
 
On Wed, 19 Jan 2022 21:12:07 +0100, Piotr Wyderski
<bombald@protonmail.com> wrote:

John Larkin wrote:

SBT10A is interesting, a multi-wire geiger tube. It would probably
work OK in proportional mode, with maybe a little multiplier gain.

Are the wires brought out to the connector individually? Looks like
it.

Yes, they are. It opens several interesting possibilities, e.g.
shielding half of it to get beta and gamma signals separately or running
some part of it in avalanche mode and the rest in proportional mode.
Spectral sensitivity is also much better than typical metal tubes --
some specs say it should react to gamma as low as 15keV.

The digital part would be boring, just a bunch of counters. But it is
the analog front-end that could make it possible to go way beyond the
specs. Looks like a lot of fun in my spare time.

Best regards, Piotr
Click to expand...

I designed some wire chamber electronics for CERN. Each chamber was a
big thing made of parallel sheets of aluminized mylar or something,
with a zillion collector wires inside. I think there was some ion
multiplication but not geiger mode. The wires were close enough that
we could measure the pulses and interpolate the track locations
between wires

It was a massive flood of data from multiple planes, the object being
to tease out particle tracks. We did \"progressive enrichment\" of the
data: ecl gates, then FPGAs, then software. The final output was a
single bit, PUBLISH.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
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