Needing more than a spark test?

[WobblyHand]

8 Am241 sources showed up in today's mail. Have no way of knowing if they are fake or not. Hope to find out after building all this XRF stuff up!

My original smoke detector claims 1uC, these AliExpress ones are labeled < 29.6 KBq < 0.8uC, for what it is worth. They are, however, seemingly matching the original picture in the listing, so I cannot complain about it. Have to find a place to put them, don't really want them right next to me for extended periods of time. Once they are in a proper setup, it will be fine.

 

[homebrewed]

Jumpers are both good and bad. In a way, I like 0 ohm resistors better. You can use them to bridge tracks, and they offer a lower profile. They are easy to place and remove (relatively) if at least 0603 and larger. Jumpers are somewhat more convenient, but are not good for trying to cram a board into a tight place.

That's a good idea. It would serve a dual purpose, too -- instead of using zero ohm resistors, make 'em the damping resistors.

 

[graham-xrf]

Well I went with the "cadillac" model. I found some bare-bones versions for about half that

Fleshing out the "revision list", I'm open to any/all suggestions. My current thoughts:

1. Completely separate DGND and OGND planes.
2. Separate +5 input for OVDD LDO, with a jumper to permit using the Teensy's 3.3V supply
3. Series damping resistors for all the ADC's control lines.
Question: what about the data output lines? It would be best to have damping resistors on the receiving end but that would require modding the Teensy. Possible but probably not easy for the average hobbyist to accomplish.
4. Test points to ease debugging with a DVM and oscilloscope.
5. Change the physical connections so the ADC can be plugged into the Teensy. This will greatly shorten the signal lines, which should help regarding signal integrity.

Regarding #5, the data pins will have to be different if plugging into a T4.0 vs. a T4.1. I don't like jumpers but they may be the most expedient way to customize the ADC board. The other option: don't design it to accommodate a 4.0. A 4.1 isn't much more expensive; and the ADC driver code is a lot cleaner.

Anything else?

Pretty much agreed on most of it. I will admit there is something else going on right now, (water supply fail called), so my concentration is limited.

1. DGND is also analog GND, and consists of letting pins 20, 30 join in under the ADC onto GND. Yes indeed, if OGND has it's own ground plane, with the 100nF and the 10uF located close to the ADC, that works.

2. Separate 5V supply to drive the LDO, so you can make a 3.3V for OVDD (pin 18) is OK. Once the 5V analog supply, and it's GND are separate, if the Teemnsy has a 3.3V supply, I would think it could be used without a special . Similar to the Raspberry Pi. That said, a supply not carrying the burden of a computer clocking on it, is better.

3. Series damping resistors on ADC control lines. These are digital interface lines, and use the OVDD supply. Kirchoff's Law over these small distances make it OK to put the series resistance somewhere in the line. If the data line were a transmission line, the series resistance goes at the send end, and the parallel termination goes at the receive end. I would guess that 20Ω to 100Ω anywhere in the line would damp most ringing. That would be stuff for experiment. What such resistors do, (in a big way), is limit the amount of noise in the 0V (digital) return.
These are inputs. They do not take a whole load of current.

The biggest current jolts happen when a count rolls over to put a 1 in the next bit, and all the rest go from 1 to 0, all at once. In the way data is offered from a ADC, I don't think this the major contributor.

All the data output lines are taking power from OVDD. They are trying to assert their rise times and fall times on a line to a Teensy. If a Teensy input can be higher impedance, and likes that ringing is damped, resistance in these lines definitely does limit the currents in the OGND plane.
Resistors here may be more effective than in the control lines. Again, values can be low ohms.

4. Yes please. Test points. If one is using scope, or DVM, then they can have 1K or so in series. Possibly, the test point tracking should not include the input to the TIA.

5. In my initial test setup, I put the ADC on a "Pi hat" over the GPIO, so separated from any amplifier. I never did get that together, being less than successful at transforming a Pocket Geiger. By the time the gain has been applied, the measure signal is low impedance, and can easily survive going through a twisted pair, or a coax, up to the ADC. Tricky though, because I was concerned not expose the ADC input to too much stuff on the way to it. I put the ADC driver right up next to it.

Over the distances we are talking about, and the frequencies components that might be present, jumpers should be perfectly OK. This is a relatively low frequency amplifier. For me, anything below 50MHz is "almost audio"! Wavelengths are huge compared to any jumper.

Regarding #5. I think you should go with T4.1, and lose the difficulties of accommodating incompatible data links.

Looking at the isolated USB power dodge, it occurs to me that a ex-phone wall wart charger might be cheaper.

 

[graham-xrf]

8 Am241 sources showed up in today's mail. Have no way of knowing if they are fake or not. Hope to find out after building all this XRF stuff up!

My original smoke detector claims 1uC, these AliExpress ones are labeled < 29.6 KBq < 0.8uC, for what it is worth. They are, however, seemingly matching the original picture in the listing, so I cannot complain about it. Have to find a place to put them, don't really want them right next to me for extended periods of time. Once they are in a proper setup, it will be fine.

View attachment 436616

They are OK, and look exactly like mine. They are also safe, so long as you don't extract the sources, and eat them. You could probably tuck the whole lot into your underpants, without any worries. I think the 59.5KeV photons go right through you and out the other side.

I have a bunch of thorium oxide gas lamp mantles, not yet fired into becoming the fragile things they end up as. These are harder to control in ending up as powder in the environment. They happen to be stuffed into the same plastic bag as the AM241 sources. Now was this not the same recipe one infamous David Hahn used to "breed" radioactive stuff in his car trunk that had cleanup crews in protective suits trying to lower the radiation count in the street where he lived?

Here is where we may need @RJSakowski to let us know what happens if we (Ok then - me) stores 10 Thorium mantles in the same packet as 10.8uCi of Am241? After my AliExpress shipment arrives, it would become 21.6uCi of Am241.

 

[WobblyHand]

You could probably tuck the whole lot into your underpants, without any worries.

No need for that! Not going to happen either.

Prolonged exposure just isn't a good thing. No matter what we think now. It seems that most exposure limits are reduced as we learn more. Not keeping the material in a living area, until or unless it is necessary. Prudence. Exposure to microwaves was thought to be harmless as well, until many people developed cataracts at elevated rates. Now we try to reduce exposure to elevated microwave field strengths.

Caution is advised, but not paranoia.

You can do what you please, including throwing thorium mantles in the air, but I won't join your thorium throwing soiree
As for your "mini-reactor", I'd separate those things, if possible, but that's a gut sense, which could be wrong, and the caution flag is waving at me. That caution flag has saved my skin before, so I tend to pay attention to it rather than ignore it. Part of my life experience, I suppose.

 

[graham-xrf]

No need for that! Not going to happen either.

Prolonged exposure just isn't a good thing. No matter what we think now. It seems that most exposure limits are reduced as we learn more. Not keeping the material in a living area, until or unless it is necessary. Prudence. Exposure to microwaves was thought to be harmless as well, until many people developed cataracts at elevated rates. Now we try to reduce exposure to elevated microwave field strengths.

Caution is advised, but not paranoia.

You can do what you please, including throwing thorium mantles in the air, but I won't join your thorium throwing soiree
As for your "mini-reactor", I'd separate those things, if possible, but that's a gut sense, which could be wrong, and the caution flag is waving at me. That caution flag has saved my skin before, so I tend to pay attention to it rather than ignore it. Part of my life experience, I suppose.

I am now getting a bit of "can't wait" for my glittering vibrating nuclear radiation detection thingy to arrive. I have had the email that "it's in the country". OK - it started from outside, but not sure where from. Originally China, that I know.

I really want to point it at the "radioactives" plastic storage box. Especially, I want to show it a single smoke detector source.

Who would guess that a flight from New York to LA is worth two chest X-rays?

 

[WobblyHand]

I am now getting a bit of "cant wait" for my glittering vibrating nuclear radiation detection thingy to arrive. I have had the email that "it's in the country". OK - it started from outside, but not sure where from. Originally China, that I know.

I really want to point it at the "radioactives" plastic storage box. Especially, I want to point show it a single smoke detector source.

Who would guess that a flight from New York to LA is worth two chest X-rays?

View attachment 436628

I've seen that airplane related exposure posted before. It gave me a little pause when I was traveling a lot. Didn't change my behavior, because it wasn't an option for me. Seems we can eat a lot of bananas before we get to just a normal day's exposure... Quite the chart with the increasing dose levels.

 

[homebrewed]

Looking at the isolated USB power dodge, it occurs to me that a ex-phone wall wart charger might be cheaper.

It totally depends on what role the teensy is asked to play. If it's going to be the front end of a PC-based analysis system, it has to communicate to the PC. If it's standalone, maybe using its own display, then any external supply will do.

 

[homebrewed]

They are OK, and look exactly like mine. They are also safe, so long as you don't extract the sources, and eat them. You could probably tuck the whole lot into your underpants, without any worries. I think the 59.5KeV photons go right through you and out the other side.

I have a bunch of thorium oxide gas lamp mantles, not yet fired into becoming the fragile things they end up as. These are harder to control in ending up as powder in the environment. They happen to be stuffed into the same plastic bag as the AM241 sources. Now was this not the same recipe one infamous David Hahn used to "breed" radioactive stuff in his car trunk that had cleanup crews in protective suits trying to lower the radiation count in the street where he lived?

Here is where we may need @RJSakowski to let us know what happens if we (Ok then - me) stores 10 Thorium mantles in the same packet as 10.8uCi of Am241? After my AliExpress shipment arrives, it would become 21.6uCi of Am241.

The critical mass for an Am241 sphere is 87kg so I wouldn't worry about the boom factor. It predominantly is an alpha emitter so it also won't neutron-activate anything that is near it. There IS a nuclear process by which Beryllium emits neutrons when bombarded by alpha particles so you do want to keep your beryllium spheres away from Am241 .

 

[WobblyHand]

There's no beryllium here that I know of. But I suppose there could be beryllium in those springy copper strips, that I don't know about...

Not particularly worried about this, just an abundance of caution, and truthfully, simply too much clutter for this room. So I moved it elsewhere until I need it. Wikipedia claims the critical mass of Am241 is between 57.6–75.6 kg. So don't collect too much of it