On a sunny day (Fri, 30 Mar 2012 12:30:45 -0700 (PDT)) it happened George Herold wrote in :
This I still have to find out exactly, when everything is mounted on the 'hotplate' it becomes easier to do a temperature run.
I think it is photocell current, as it was not 'absolute dark' either. I will store both the values from the blacked out photocell and those from the one looking at the tritium light, so later (after one year) different effects can be traced back, and hopefully systematic error can be removed mathematically. Of course there will be many test runs before gong for the very long one.. :-)
I can't find the TCL247 anywhere.. can't you look up the bias current on the spec sheet?
Hey I had an idea the other day. How about if you run two photodiode circuits one illuminated by the tritium lamp and the other from a lightbulb or LED. That might help take care of weird drifts that you haven't thought of. (Mind you I think the best you can expect is a null result.. but so what!)
On a sunny day (Tue, 3 Apr 2012 06:15:58 -0700 (PDT)) it happened George Herold wrote in :
That is because it is TLC274... For the input bias current only a typical value is given at 25 C: .7 pA. And at 70 C typical 50 pA and maximum 300 pA. So there is a huge spread from one chip to the other, and a huge dependence on temperature. Comparing 2 channels on the same chip in changing conditions may help eliminate any observed unexpected effects. For the photo diodes the story is very similar.
They do. How they age depends a lot on what the construction is. Whites (phosphor based) age the most by far. Other colors (peak lambdas) age differently.
Well I guess you don't care.. (too mcuh) The idea was to find 'common mode' fluctuations. If both outputs change in the same direction for a day, week.. you know there is something else happening.
On a sunny day (Wed, 4 Apr 2012 08:29:05 -0700 (PDT)) it happened George Herold wrote in :
Right, that is the idea, but if I use one sensor in 'darkness', and one in light, then I know it was not the LED :-)
So, for zero changes between opamps, and those are on the same chip, so expect little differences, it MUST be the photo diodes. One could then subtract the dark channel from the light channel. If you subtract the LED channel from the tritium light channel you have one more variable no?
"If you subtract the LED channel from the tritium light channel you have one more variable no?"
Hmmm... I'll have to think about it. (maybe it was a silly idea.) I was picturing running the LED to give the same light level as your tritium lamp. Then the difference signal is near zero and you've got more (potential) sensitivity. (I've seen some cute circuits that subtract two photodiode signals, but in practice I've just used two separate TIA's and an opamp differential circuit.) I don't know how much LEDs age. Is it any worse than the aging of your tritium lamp? Maybe you could have two LED references... three photodiodes.
On a sunny day (Thu, 5 Apr 2012 06:53:01 -0700 (PDT)) it happened George Herold wrote in :
Interesting then you can use the LED current as 'signal'!
An other solution would perhaps be a mechanical shutter so you get sequential dark and light signals, or maybe even a LCD shutter, I still have 2 Nvidia stereo goggles that will switch at 50 Hz... Should have thought about that earlier. They do not shut off 100%, but I expect little aging from them. Easy to drive with a 9V square wave.
formatting link
Some older LEDs leds to the point where they were hardly visible (instrument panels). Hopefully modern ones are better, I would have to look it up. High power LEDs do reduce in brightness,,, But I only need a very low light level.
Those led's are most likely driven from a voltage sorce through a resistor. (That's how I've always done it.) I bet an led is more constant if you drive it from a current source. At a low level it may last much longer than the tritium lamp.... What's the monthly decrease in the tritium light intensity? (I think I got a part per thousand... but it was just in my head and I can easily make a factor of ten mistake.)
On a sunny day (Thu, 5 Apr 2012 19:35:25 -0700 (PDT)) it happened George Herold wrote in :
If the forward voltage drop is more variable. It sure is more linear with the current.
Tritium has a half life of about 12.5 years IIRC. Assuming (always a bad thing to do) that the sum of light speckles from the phosphor in the tritium tube is proportional to the number of decaying nuclei, that it falls exponentially. The light intensity from the electron emitted by the decay of one nucleus hiting the phosphor is likely constant, as the electron always hits the phosphor with the same energy, Anyways I think I should be able to measure this decrease in light over much shorter periods of time than 1 year. We Will See. If not.. then back to the drawing board.
Somebody posted a formula somewhere in this thread..
Half life is around 12.32y according to NIST which translates to -155ppm /day or about -0.5% per month. It will be a test of your drift correction and signal processing skills if you *can* actually determine the half life reliably in under a month. BTW You are going to need to do orders of magnitude better to detect any seasonal variations.
True only if the phosphor is robust and not damaged by cumulative radiation dose. I think that is probably a safe assumption.
phosphor with the same
This is known to be untrue since the electron does have a spectrum of possible energies averaging 6keV but definitely variable. The electron energy spectrum is being used to put bounds on the neutrino mass.
See fig 1 in the following paper
formatting link
The only thing certain is that the energy of the electron is necessarily less than 18.60keV. Median value about 3keV or so.
A half decent experimental technique should get you an answer in about a month. Lets see if you are actually any good as an experimentalist.
What are some ways to increase sensitivity? If you could detect individual phosphor fluorescent events (one electron detection) and take the standard deviation of the event period maybe this would be better than measuring the averaged phosphor light intensity? For this type of detection the tritium source would have to be very weak so that a given area of phosphor is only hit at most once per phosphor fluorescent decay period probably.
On a sunny day (Fri, 06 Apr 2012 21:30:34 -0700) it happened Jamie M wrote in :
The alternative was counting 'ticks' with a geiger counter or scintillation detector, and that is a problem as cosmic rays also cause ticks, and maybe those depend on the 'earth orientation in the galactic plane' too, to quote a reference. At least the fluorescent flashes correspond only to decay events, There is too much overlap, I think a large area of the fluorescent layer lights up if hit by an electron to guarantee detection of 100 % individual decay events. The integrating function of the whole setup makes it interesting. It is designing and doing the whole experiment that makes it fun, and with the experience gained from it take the next step. I want to stay away from too much mathematical drivel without firm experimental data, the data will come and I will take it from there. As I am in control I can change anything I like if it needs it :-) Null results are great too, I'd settle for zero really quick :-) LOL
First rule of any experiment is to get as much raw signal as possible.
The main one is to surround the sensor and emitter with clever optics to capture as many as possible of the emitted photons. Passive gains of around 3-10x are not uncommon in non focussing neutrino detection kit.
The idea is to grab any photon that crosses the entrance aperture and cause it to eventually collide with the detector.
Classic 1-D non-focusing flux concentrator for a flat plate collector is a parabola with its focus at the base of matching parabola on the other side. A bit of ray tracing will show how it works.
They are finding favour these days for solar power applications too.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.