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
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.
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.
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
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
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
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
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).
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
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.
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?
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
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