If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi, this is intriguing. Took apart a ZP1313, 1314 and some similar looking tube to see if the tube sensitivity was poor due to the lead shield. Turns out the problem may be fixable on one of these, they use either a metal shield (ZP1313/14) or glass mantle (unidentified tube) and once this is removed the tube responds to even low level radiation, much more sensitive than an SBM21.
For drone use these tubes are very lightweight, certainly under a gram and are compact enough to put in a wristwatch.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Without the compensating filter, which you have removed, the energy response of the tubes will be wildly non-linear below about 150 keV.
All uncompensated GM tubes have fairly sharp response peaks at 70 - 80 keV, giving up to 10 times the count rate that would be recorded at, typically, ~50 keV or ~150 keV.
Without knowledge of the energy response characteristics of a tube, dose rate estimates at these lower energies will be grossly in error.
Above ~150 keV, the energy response of GM tubes mellows out and tends to flatline out to 1MeV and beyond.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Yeah, figured as much. I am looking at detecting very low level radiation here, every particle lost in the filter is one less detected. In fact, something interesting I did notice with the SBM20 tubes is that they consistently detect the weak radiation from 40K (20 grams recrystallised from solution) whereas none of my other tubes will.
An interesting note here is that putting a meter in series with the ground connection on low volts range (ie 200mV) shows that the tube is detecting particles even though the counter does not record a count. These signals range from just above the start point of 1.2mV to about 90mV with many in the 30mV range with lo-salt near the tube.
This effect suggests that the sense amplifier needs redesigning and may be responsible for missed counts on some designs.
I recall reading somewhere that a high power magnetic field near Geiger tubes can increase sensitivity, perhaps by raising the "noise floor" to a point that the sense amplifier can detect the ionization ?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The γ sensitivity of GM tubes is very low - often less than 0.1% - so you'll be doing well if you detect 1 in 1000 of the γ-photons that pass through it. The γ-photons hardly interact at all with the counting gas, so γ counting depends on electrons knocked out of the tube wall to initiate the Townsend Avalanche.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
I did have a thought about using a graphite bismuth layered composite as a monochromatic filter as both are relatively easy to get and mixing bismuth and indium allows low temperature printing.
EDIT: Would also work as a collimator if put side-on in layers.
Wonder if Bi:Mg or Bi:Na would work for the same reason, a light metal sandwiched between two heavier ones ?
EDIT: PM, would you be able to proof read/comment on a physics paper if I mailed you a draft please? Or for that matter, anyone else who wants to have a look.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Geiger tube hacks
