X-ray fluorescence detects elements based on their characteristic electromagnetic spectrum when irradiated with x-rays.
Not very much like a mass-spectrometer which creates a characteristic pattern of masses resulting from the test material as it is manipulated by the electron ionization or chemical ionization process. Where ions are detected across the atomic mass range of the particular spectrometer, forming a characteristic pattern or "spectrum" across that range.
Actually more jewelers and gold dealers than ever are using the x-ray guns professionally for bulk assay on an everyday basis. There are some handhelds which may be sensitive enough for trace analysis in food, but that requires a whole nother level of dedication beyond identification of metal objects, not just in technique and training but "laboratory" preparation as well.
The first obstacle would be convincing an owner of an instrument having capable specs, to embrace usage for things other than gold and silver assay. Then seriously pursue mastery of the instrument more so than ever to accomplish decent detection of low levels of lead and other metals like chromium, mercury, cadmium, etc.
[1] https://pubmed.ncbi.nlm.nih.gov/25214856/ ("Contaminated turmeric is a potential source of lead exposure for children in rural Bangladesh" / "Results: Lead concentrations in many turmeric samples were elevated, with lead concentrations as high as 483 ppm")
The higher it is, the less likely for challenges in detection, and/or interference from background.
>lead concentrations as high as 483 ppm
SSDD.
Shouldn't be that hard to detect at that level which is way above ppb. There are a number of reliable methods.
However if the Minimum Detectable Level for a particular test procedure was only 500 ppm or above, one of these samples would report just as clean as a sample having no lead whatsoever; < 500.
MDL's like this which vary among different test methods do need to be carefully compared to the toxicity levels being screened for.
That's another one of the confounding aspects to be aware of.
Depending on circumstances, I may or may not prefer a different calibration session for each of these two levels, even though they are both within the same order of magnitude.
Either way ideally I would be preparing NIST-traceable reference materials at the proper levels for comparison & confirmation. Not much differently than I would do for the benchtop models and the forklift models of x-ray units. And to really get down into the ppb levels that's when the ICP/mass-spec comes in handy, that's a benchtop unit itself, too big to fit on a regular desk though. However you don't really get the most out of the ICP without a huge cryogenic tank of liquid argon out back so you can "consume mass quantities" ;)
With a handheld x-ray unit, if you are only assaying gold & silver it may be fine to send it back for calibration once a year, if the pawn shops even do that. For food testing I would want more of a laboratory-style analytical procedure and calibration which is concurrent with materials being tested.
I agree that hand-held XRF guns should be able to detect such lead levels, and I believe that was in fact what the police used when they did the publicity stunt in the Bangladesh market. At any rate, it sounds like you know a lot more about the question than I do. I was only disputing pfdietz's comment, "The concentrations of lead being discussed here are as much as 1000 ppm or even higher."
Good call because results should be expectd to be all over the ball park, and I think even higher numbers could be found. But no amount of lead is supposed to be acceptable.
>sounds like you know a lot more about the question
SSDD says it all without explanation, but here's a little.
Until you've spent lots of time at the bench, it's not easy to understand why a 1000 and a 483 might just be the same sample tested in different labs.
Or even the same lab on different days.
If so that would look even more embarrassing when my arbitrary reporting convention < 500 is applied.
But it's actually not unheard of to get a positive and a negative on the same sample even with some of the most sophisticated equipment
Explaining the rest of the story could fill textbooks, but the operators wouldn't be reading them anyway :\
So that's the most important thing to know, besides the actual spectrums which are table stakes.
Back in graduate school, I TA'd an electrostatics course. We were going through the details of the basic parallel-plate capacitor, and so Prof. Peter Hagelstein (of the project you listed above) used the example of how much energy was stored in a football-field sized set of parallel-plate capacitors with oil as a high-breakdown dielectric.
The students were dutifully copying the lecture while I was sitting there with my mouth agape realizing that he was working through a simplified example of what energy storage was required for the X-ray laser. IIRC Those guys had their own substation, and would charge the capacitors. The switch would get thrown and the sublasers would shoot at the molybdenum target, which would laze in the X-ray spectrum (and the molybdenum would vaporize, I think.)
Afterwards, I asked him how on earth the energy was transferred from the caps to the sublasers: He just smiled and said "very carefully".
He spoke at MIT (early 90s?) and I remember him talking about making fun of PacBell colleagues in his comic: They would recognize themselves, ask him to autograph the comic for them, and then go away happy (thus making fun of them a second time.)
Not if you know the reputation of John Baez: Anyone familiar with him or his writings would know without hesitation that he understands black-body and E&M radiation, so his choice of title is clearly meant to be provocative.
It says to the reader "I wonder what he means?" To this reader, I'll also say that he delivered a terrific blog post.
Perhaps, but "Mathematical Physicists HATE when authors make THIS ONE ASSUMPTION!!1!" would be more click baity. I took it more as Baez writing for his physics audience.
Purely out of pedantic interest: is that a meaningful distinction, or is it just the same thing for a different audience? I'm reminded of chess youtubers who give similarly "click baity" titles to their videos which are only click bait to people who watch chess videos. Isn't it the same?
All the power to them by the way. It's the crushing power of the algorithm. No hard feelings, just something I've been wondering.
Well, you got me thinking about "What exactly is clickbait?"
So full disclosure: I've directly interacted with John Carlos Baez only in social media, with the topics as disparate as music and observational astronomy. My own QFT & GR background is grad course level but with little actual usage in my career. (I've done more solid-state + high-speed electronics work, with a bunch of programming as well.) With that background, and turning the pedantry dial up to 11:
To me, one distinguishing element of clickbait is that the post is ultimately disappointing. The usual M.O. for clickbait is that the website needs eyeballs for advertising, so they beef up a headline of an uninteresting article with the expectation of getting extra monetization compared to an honest headline.
I would venture a guess that he doesn't actually care about monetization, or really even extra clicks, with this post. The screenshot with the big red X through the popsci article sets the expectation pretty quickly, and the tone of the rest of the post is really a rant that mediocre science made it into PRL and then into the popular science literature. He explicitly calls out the popsci journalists for laziness, but in a clever (I'm pretty sure Mark Twain would approve of his name being taken in vain) and erudite (correct use of the subjunctive) way.
Would I have clicked on the title without seeing the authorship johncarlosbaez.wordpress.com? Maybe but I doubt it. There is so much bad popsci physics out there that I'm pretty trained to ignore obviously inadequate headlines. So on a scale of 1-10, I'd rate the click-baityness of the headline no more than a 3. He got me to click, but only because I knew it was his post.
As for others, the set of people who understand that Hawking radiation exists has nearly 100% overlap with those who know that black bodies and spinning magnets radiate, so for those folks who are in the set who are also unfamiliar with the author, perhaps it's more clickbaity.
[edit: And I can't believe you got me to write that many words on the clickbait philosophy. Have I been baited? :) ]
> I took it more as Baez writing for his physics audience.
I have a degree in Physics with an emphasis in Astronomy, and my thought on reading the title was "that's absurd". Even if you somehow infer that "radiate" specifically means "emit hawking radiation" which I don't know how you would without more context, "dead stars" generally is considered to include black holes, which do emit hawking radiation.
> As for others, the set of people who understand that Hawking radiation exists has nearly 100% overlap with those who know that black bodies and spinning magnets radiate, so for those folks who are in the set who are also unfamiliar with the author, perhaps it's more clickbaity.
So according to my theory, you must in the set that understands Hawking radiation + black bodies + E&M, but not in the set familiar with Baez.
I worked hard on my theory, please don't let me down and be a counterexample. :)
I vaguely remember an episode of some thriller series when I was too young to be watching it, perhaps Twilight Zone (or similar) where someone was hearing screaming, they went out a d saw trees being cut.
The only shortcoming is that they currently use opacity even if there is only one author. In that case, it would seem natural to render the text as-is.
> So far, I've not been able to devise any way to improve such recall
The only way I've found is not intuitive: Extreme health consciousness, both in diet and exercise. I pretty much had to give up alcohol as well, just a couple of glasses of wine and I would experience these weird name/word outages.
