Needing more than a spark test?

[WobblyHand]

Look for Teensy SPI info from the data sheet. Even disregard what other folk posing on the net get up to. I won't be using Teensy, but I know it is fast enough to manage quite fine. The bottleneck is not Teensy.

If you have ever had the displeasure of reading an NXP processor datasheet, you would rapidly find all the parameters are in terms of others. So far all I can find is f_sclk = f_peripheral/2 Hz. Now I have to find what the heck f_peripheral is... Every other device, including Flex SPI has an actual frequency, (60MHz) but the normal SPI bus is in terms of f_peripheral, but nowhere on the sheet do they define what it is and what rate it runs at. 3522 pages of wordy documents and not there... Obviously have the wrong docs.

 

[graham-xrf]

Breaking away for a minute from the (intense) discussion on the very tech stuff, and software, would simply cutting off about the lower third of a aluminium beer can serve as a mold to pour molten lead into? Maybe my ex paint primer rattle can?
I know it's cheaper than cheapskate, but it does not matter if it won't drop out. We just cut the can away!

None of my speculative forays into borrow-able kitchen stuff will result in anything except an outraged veto!
No little ladles, no big spoons, nor any kind of a defunct saucepan in stainless steel.
I guess I am going to have to peruse the £1 store, trying to feign a non-tightwad demeanor.

 

[WobblyHand]

You could probably cast lead into an beer can, although I'd be really careful about it. Lead melts roughly 300C and aluminum at 660C, if I recall. The aluminum at 300C will lose a bit of whatever strength it has. I'm not sure I'd do it. If it tips over, maybe due to softening or wall collapse, you better be able to move quick!

I wouldn't try melting lead in that aluminum can, you need some sort of better container for that. A tiny kids cast iron cook pot might work. Or some second hand sort of small pot. You want to keep the surface area down - minimizes oxidation, and heat loss. Ideally the pot would be cast iron and maybe two tuna tins high.

Nothing you use (for lead casting) should ever go back to the kitchen... No ladles, spoons, whatever. Keep that stuff out in the shed or car park, far from the house.

 

[graham-xrf]

You could probably cast lead into an beer can, although I'd be really careful about it. Lead melts roughly 300C and aluminum at 660C, if I recall. The aluminum at 300C will lose a bit of whatever strength it has. I'm not sure I'd do it. If it tips over, maybe due to softening or wall collapse, you better be able to move quick!

I wouldn't try melting lead in that aluminum can, you need some sort of better container for that. A tiny kids cast iron cook pot might work. Or some second hand sort of small pot. You want to keep the surface area down - minimizes oxidation, and heat loss. Ideally the pot would be cast iron and maybe two tuna tins high.

Nothing you use (for lead casting) should ever go back to the kitchen... No ladles, spoons, whatever. Keep that stuff out in the shed or car park, far from the house.

Tuna tins are made of steel, right?
They have some sort of coating, (surely not tin any more), and some sort of plastic coating inside.
I never quite got it about "tin can". Tin is about as toxic as they come.

The can is magnetic. I would not have thought lead could do anything much to it, except stick to it like solder if it saw some flux. I know lead can never stick to aluminium.

Basically, I was trying to skip the pouring stage by having a disposable melt container.
Heat it all up, the lead melts into it.
Let it cool.
Trash the container.

 

[graham-xrf]

LTSpice can do Energy Integrations.

You can perform an integration of a waveform using the "idt" integration function.
You use an arbitrary voltage generator, making that voltage the analogue of the integration quantity.
You have to change the Absolute Current tolerance to 1e-012, and Voltage tolerance to 1e-009
Unfortunately, these are not remembered between program invocations.

There are instructions in the ZIP attached.
You plot the current from Iph1, a square wave in green, 4nA for 4uS
You probe the integrator output at B1.
You should see this..
Check out the correct answer 16fV on the left.

Of course, it does not have to be a square wave. I just used that to make the numbers easy.

Not so easy to use this on a Packet Geiger circuit. It operates with everything offset way up, to fit between 0V and 9V rails.
The integrator just integrates it all, including the big voltage shifts.

 

[homebrewed]

Update on trimming my aluminum "focus ring": there's still a substantial aluminum peak. Relatively speaking, the iron peak is higher so I know I've improved things _some_, but not enough to suit me.

Who made me make that ring out of aluminum, anyway? Oh, wait. It was me

The photo in message #1371 shows a spectrum acquired with the exact same settings, but with the focus ring intact.

I'm currently acquiring a no-sample background spectrum. The count rate is far lower so it's gonna take awhile.

 

[WobblyHand]

Tuna tins are made of steel, right?
They have some sort of coating, (surely not tin any more), and some sort of plastic coating inside.
I never quite got it about "tin can". Tin is about as toxic as they come.

The can is magnetic. I would not have thought lead could do anything much to it, except stick to it like solder if it saw some flux. I know lead can never stick to aluminium.

Basically, I was trying to skip the pouring stage by having a disposable melt container.
Heat it all up, the lead melts into it.
Let it cool.
Trash the container.

Use a tin can. Steel can. You can melt the lead in the can and after it cools, peel away the steel.

An aluminum beer can is really thin, like 0.004" thin. I don't think you could safely heat it up to lead melting point safely, certainly not over a flame. Maybe in an oven. Of course you could make a mold out of aluminum, if you drafted it, the lead should come right out after cooling.

For the cheap method, use a tuna tin. That's a nice chunk of lead if full.

 

[homebrewed]

I do agree, and it's not too hard to have that happen. Just changing the gain distribution, and using the available gain opportunity on the signal conditioning board gets you there.

I cannot think we have to deal with input currents for a arrival pulse of less than 40pA, and the circuit can see to values less than that. It can use a 100pA input to max out 2.4V at the other end. It also preserves the risetime.

I don't know yet, but I am thinking that if the pulse duration you are trying to sample moves across and back, depending on when it's rise happened to cross a fixed trigger, there is potential for all sorts of jitter. If the ADC was sampling at a constant, unrelenting, fixed rate, regardless, sometimes seeing invalid OTT pulses, or spending too long with ton of pulses all keeping coming on to pf one another, that's OK.

Once a trigger pulse is seen, the ring buffer is addressed at a point some samples down the line pre-trigger, tested for being low enough to be a good place to start, and then counting from there, one pulse duration's worth of samples is taken off. There is a test for the last sample being below some threshold, near zero, or that is evidence another pulse overlapped. We don't let the trigger event mess with our count. Count a whole pulse.

I know this sounds simplistic, and I may end up using all the stuff you have found out one has to do, because you have the actual thing powered, and have experience with it. Right now, what I have are my calculations, simulations, the part finished lead shield design with the need to melt the stuff next to me, and the KiCad circuit, incorporating all the best stuff I can gather. I also have a never-ending list of boring other home stuff that won't go away!

I will send you one of my boards, but I think, in a different physical form, you already have everything.

In terms of the trigger point relative to the pulse, we know that there's a fairly large noise component in the signal so that is going to be moving the trigger point back & forth relative to a hypothetical pure pulse waveform. So, yes, my code is looking "backwards" in time to find the start of the pulse. Actually a bit further back than that, on the assumption that uncorrelated noise will be averaged out to a large extent. And I'm doing the same thing on the tail end of the pulse.

Regarding your board, I agree with you. At this point we should have some kit that's pretty similar. It will be very interesting to see what results you get when you start digitizing some XRF pulses. If we're 'way different, well, there's an opportunity to learn more about the subject.

 

[graham-xrf]

Update on trimming my aluminum "focus ring": there's still a substantial aluminum peak. Relatively speaking, the iron peak is higher so I know I've improved things _some_, but not enough to suit me.

Who made me make that ring out of aluminum, anyway? Oh, wait. It was me

The photo in message #1371 shows a spectrum acquired with the exact same settings, but with the focus ring intact.

I'm currently acquiring a no-sample background spectrum. The count rate is far lower so it's gonna take awhile.

View attachment 435435

In general, you always have two clusters of energy. This happens regardless you take out the aluminium.
You are thinking this is because your ring is made out of aluminium, and you could be right!
You have been thinking it may help if it was made out of plastic.
Again, you could be right, but here, I think there might be surprises.

I think, at some stage, you should try to make it quit. Cut a small square of lead, and stick it over the photodiode. Do we get low or zero counts at all energies?

Take the shield away, and have it stare straight at a (bigger) sheet of lead. You might get peaks at 10.5KeV and 12.6KeV, or only one peak if resolution is low, perhaps from not enough bits.
There might also be seen, a whole lot of peaks. This might be from aluminium, or plastic, or depleted photons re-emerging.
Might the group to the right be a pile of leftover photons having expended initial energy making the group to the left? This is just mad speculation!

I would be quite interested in seeing what happens when it is shown a direct view of a Am241 source put right up against the photodiode. One would want something to happen way to the right, where 60KeV would be.

The count rate seems really slow. We have to wait a long time to get results.
I have been thinking about this. It involves figuring out where all the available decays went to.
I do get it that we can only use a limited solid angle from the source for practical reasons, but we make it as wide as possible consistent with only energizing the sample region. Your scheme that does not bury the sources way down in a lead pot, is, I think, the right approach, and I have modified the design of the lump I intend to put together to have it this way. (Still at the tin can + burner stage)!

I am actually considering a 16 smoke detector sources thingy. (The first try will be with 8)
This has to start to make sense, or I be thinking we got short-changed by Ali Express with feeble smoke detectors!

You are right in that our designs are converging into very similar schemes. The saying is "wheels are round"!
I do expect that when I power up, I will initially be looking at an incomprehensible racket, and I will have to work back from the ADC, making it become predictable. I will get there!

 

[WobblyHand]

Good thoughts on checking the detector. Back to first principles, block the radiation with lead, what is the background. Then 1 source only. Think I'll make a square aperture in lead, shielding the detector board as well.

A thought - won't we also be seeing the source carrier? That speck of Americium is sitting on some material, what is it? Won't we always see it's signature? It's getting bombarded. I'd expect that material spectrum would be present with source only.

Of course I'd be happy to see any pulses at all! Still a ways from that.