Why the preference of the SBM-20?

Support forum for the mightyohm.com Geiger Counter.
http://mightyohm.com/geiger
User avatar
mightyohm
Site Admin
Posts: 1064
Joined: Fri Apr 03, 2009 10:29 pm
Location: Seattle, WA
Contact:

Re: Why the preference of the SBM-20?

Post by mightyohm »

Those specs are nearly identical to the SBM-20. I'll have to get one and check it out. Thanks for the info!
ei8htohms
Posts: 4
Joined: Mon Nov 07, 2011 9:30 am

More sensitive tube?

Post by ei8htohms »

I am a watchmaker and built the kit with the intention of identifying radioactive dials and hands. Many older watches used Tritium and VERY old watches used Radium to make the dials and hands glow in the dark. The SBM-20 tube is able to pick up Radium (the stuff gives off alpha, beta and gamma radiation so it's not too surprising I guess...) but doesn't make a peep for Tritium. Tritium gives off low energy beta radiation, so I'm guessing the tube is just not sensitive enough. Any suggestions for alternatives?

Thanks!
_john
User avatar
mightyohm
Site Admin
Posts: 1064
Joined: Fri Apr 03, 2009 10:29 pm
Location: Seattle, WA
Contact:

Re: Why the preference of the SBM-20?

Post by mightyohm »

See if you can find an LND-712 tube, it should work with the kit and has an end window for alpha/low energy beta.
ei8htohms
Posts: 4
Joined: Mon Nov 07, 2011 9:30 am

Re: Why the preference of the SBM-20?

Post by ei8htohms »

Thanks for the tip, I'll try to track one down and give it a shot.

Regards,
_john
NGinuity
Posts: 9
Joined: Sat Sep 24, 2011 11:43 am

Re: Why the preference of the SBM-20?

Post by NGinuity »

Thanks, I will design this into my surface mount design as a capable alternative. I'm almost there!
wbp
Posts: 13
Joined: Mon Nov 14, 2011 1:58 pm

Re: Why the preference of the SBM-20?

Post by wbp »

I picked up an Anton 6107 on fleaBay for around $52 with shipping. Modified the kit, reversing the terminals so it can poke out on the left side. Replaced the anode resistor with 1 M ohm, and the VR with a 20 ohm pot so I could get it up to 700 V. Seems to work quite well. With an AM241 source (from smoke detector) held close it beeps almost continuously. It does pick up something from a small tritium tube, but just barely. Background rate is much lower than the SBM-20.

William
ei8htohms
Posts: 4
Joined: Mon Nov 07, 2011 9:30 am

Re: Why the preference of the SBM-20?

Post by ei8htohms »

mightyohm wrote:See if you can find an LND-712 tube, it should work with the kit and has an end window for alpha/low energy beta.
OK, I got the LND-712 tube; is there anything special I need to think about when modifying the kit for it? Is there a positive and negative to the connections (I'd guess not)? Can anyone recommend a clip or good way to mount the tube to the board?

Thanks again!

_john
User avatar
mightyohm
Site Admin
Posts: 1064
Joined: Fri Apr 03, 2009 10:29 pm
Location: Seattle, WA
Contact:

Re: Why the preference of the SBM-20?

Post by mightyohm »

John,

There is a positive and negative terminal on all geiger tubes. The negative side of the LND-712 is the wire connected to the outside metal tube.

Take a look at the Sparkfun Geiger Counter kit, they use an LND-712. That kit might give you some mounting ideas.
ei8htohms
Posts: 4
Joined: Mon Nov 07, 2011 9:30 am

Re: Why the preference of the SBM-20?

Post by ei8htohms »

Great, thanks! I surely would've noticed the + and - on the circuit board after removing the SBM-20, but thanks for clarifying the polarity of the LND-712.

SparkFun's "mount" looks, um... functional, but I guess it'll work if I can't come up with anything better. Thanks again!

_john
Post Reply