Third Thursday Telecons

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DanZ
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Re: Third Thursday Telecons

Post by DanZ » Mon Aug 20, 2018 4:24 pm

Ah, now I get that last part Augusto - what a wonderful, fun story - I love it! :P

BTW, as my passed down middle name indicates, I come from a long line of Grants, so perhaps that's why you tolerate me??? :lol:

Back to John now, below is the verbatim answer I received from Zack on your question regarding gamma ray microscopes - which I enjoyed immensely. I hope it satisfies you as well!

Dan
Ooh! What a fun question. :-)

It is such a good idea that Werner Heisenberg himself did a thought experiment using a gamma-ray microscope in order to derive an early version of the Heisenberg uncertainty principle.

So, can we build it? Well the short answer is yes and here it is: http://www.spring8.or.jp/wkg/BL31LEP/in ... mmary_view

And we also have a gamma ray telescope: https://fermi.gsfc.nasa.gov

Just to make sure definitions are clear, when we say gamma rays, we usually mean photons that were emitted by atomic nuclei as a result of nuclear processes. The reason the electromagnetic spectrum has a region called “Gamma Rays” is because most of the natural radiation that occurs in that portion of the spectrum is caused by radioactive decay emission. However, many gamma rays have energies that occur all the way down into the X-ray band. However, the point is clear, why can’t we just use *really* high energy (short wavelength) photons in order to get resolutions small enough to see atoms?

While it is true that as you go to smaller wavelengths the theoretical resolution of the microscope gets better and better, at some point other engineering considerations become dominant. Just from an engineering point of view, gamma rays penetrate matter easily and so designing a mirror system to focus them can be a bit tricky.

Now, if you use an electron instead of a photon, then you can get an electron to have wavelengths much smaller than an atom quite easily. In fact, it only takes a few thousand volts to do that. The electron microscopes I use are using electrons between 80,000 and 300,000 V. At 300,000 V, the wavelength of the electron is about 2 picometers — already much smaller than a hydrogen atom (which is small for atoms). For electron microscopes, the best resolution we’ve seen is about 50 picometers, and the limit is not caused by the wavelength of the electrons but other factors influencing how well you can focus the beam and so on. As it turns out, our very own microscopy facility here in Berkeley is on the cutting edge of high-resolution electron microscopes with a number of record firsts. For example, see this: https://physicstoday.scitation.org/do/1 ... 0691/full/

Cheers,

Zack

jsmaje
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Re: Third Thursday Telecons

Post by jsmaje » Tue Aug 21, 2018 2:06 pm

Oh Augusto, you are such fun!

I've found a Wikipedia picture of an ancient carving, supposedly of the original Angus: Óengus mac Fergusso ("Angus son of Fergus"), who was king of the Picts in Scotland until he died in 761 AD, his kingdom (like others throughout England) soon to be disrupted by those pesky Vikings.

It's rather blurry, but I hereby challenge you to find the best match you can within any single SD@H frame!
Image


And thanks Zack for your info on gamma-ray microscopy and astronomy. I'd got a little mixed up between EM radiation and electrons, but aren't they a bit mixed up themseves at quantum level anyway? That "The laser-electron photon (LEP) beam is a polarized GeV gamma-ray beam which is produced by backward Compton scattering of injected ultraviolet (or deep ultraviolet) laser photon off circulating 8-GeV electrons" clearly explains all(?) So thanks for that!

John

DanZ
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Re: Third Thursday Telecons

Post by DanZ » Thu Aug 23, 2018 1:28 pm

Hi John,

Zack was kind enough to follow up on your additional inquiry.

Enjoy!

Dan
Since electrons and photons can be converted into each other (E=mc^2 is often quoted here) there is sometimes a bit of confusion about them being “the same thing,” but that’s a bit like saying that iron and my car are the same thing because they can be converted into one another. In some sense the statement is true — and actually quite useful when you are in the business of recycling — but it does ignore the conversion process which is substantial! Indeed, most people will yell “lemon!” if you sell them a car and give them a pile of iron instead.

When electrons get shaken up they can produce photons. The way that electrons and light particles interact at the quantum level is luckily pretty different, which is why we sometimes want to use an electron microscope instead of a light microscope, or vice versa. This is a good thing because it gives us more ways to see samples we want to study. Maybe this also highlights why it is important to have many different kinds of microscopes — they are useful for complimentary studies.

Cheers,

Zack

McAngus
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Re: Third Thursday Telecons

Post by McAngus » Fri Aug 24, 2018 8:57 am

The challenge is accepted.
The prize: a beer, of course!

Did you know that the Scots say the word beer as we Italians (birra)?

Augusto
Image
ad augusta per angusta

jsmaje
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Re: Third Thursday Telecons

Post by jsmaje » Fri Aug 24, 2018 12:10 pm

McAngus wrote:
Fri Aug 24, 2018 8:57 am
The challenge is accepted.
The prize: a beer, of course!
Did you know that the Scots say the word beer as we Italians (birra)?
Augusto
Great, Augusto! I look forward to seeing what you come up with.

Yes, the Scots do like to roll their "R"s (be careful how you pronounce that!)
How might I send you the birra? Perhaps via the yet-to-be-invented transference process that my local pub once advertised: "Meals ordered by email will be gratefully received".

And thanks again to Zack for yet more photons of enlightenment to shine on the darkness of my understanding.

John

caprarom
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Re: Third Thursday Telecons

Post by caprarom » Fri Aug 24, 2018 4:07 pm

Great exchange, Guys, thanks! At the moment there are six people logged in to this forum (me and five "guests"). How long has it been since we've had that much action?
Yay 42, Augusto!
Mike

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