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Busterwasmycat t1_iudkr6w wrote

The general idea of wave behavior is that waves reflect when obstructions are repeated and have a gap range smaller than the wavelength (so the wave "sees" the series of objects as if they are a solid wall). When wavelengths get down into the range of the gap size, diffraction occurs. When gap sizes are way bigger than wavelength, nothing really happens to the waves. it is as though no such objects were even present.

So, for your question, you have to consider what the wavelength of the energy is, and for gamma rays it is on the order of picometers (the range is actually several orders of magnitude, but for discussion, 10^11 m is the big end and picometers is 10^-12 m).

The spacing between atoms in a typical crystal structure is longer than about 100 picometers, so gamma rays, except perhaps the very long end of the range, basically do not see crystalline solids as "solid" structures (the gaps are big enough that the waves pass through mostly unaffected, as if nothing were there at all). So, there are no crystalline solids which can reflect gamma rays. You would have to get into subatomic matter and such materials do not cluster in large enough masses to create an important obstruction.

Sort of like an island a few km offshore from land. The small waves do "see" the island and get blocked and reflected by it, but the overall pattern of waves is unaffected (only a small proportion of the waves are obstructed by the lone object and the rest move on unchanged). There are no substances we possess or can create which can produce the regular obstructions at the necessary tiny gap size needed to force gamma rays to reflect instead of basically ignore them.

There are things that can be done using energy fields though, but I don't know much about that at all. Not basic knowledge for a geologist (basic optics is, because of optical mineralogy and coloration of minerals-we geologists are jacks of all trades in science terms - we know something about a bit of everything).

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AlarmingAffect0 OP t1_iudo3jg wrote

> You would have to get into subatomic matter and such materials do not cluster in large enough masses to create an important obstruction.

I suppose Neutron Stars might reflect Gamma then? Though the point would be moot unless one could direct enough gamma towards the surface of one that the reflection would be appreciable compared to the vast amounts of energy it already radiates.

> basic optics is, because of optical mineralogy and coloration of minerals

Having done some optical mineralogy in Uni, I have nothing but respect for those who are actually comfortable with the study of crystalline structures and how we could guess them out using various frequencies of electromagnetic radiations. That sort of stuff was practically opaque to me, pun intended. I remember trying to read an explanation of why Calcite did its double refraction thingie and coming out more confused than when I came in.

On the other hand, historical geology is very intuitive to understand and it really feels amazing to be able to make rather reliable educated guesses as to why our world looks the way it does. It's truly wondrous stuff.

Anyway, Geologists, severely underrated, need more hype.

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Anacoenosis t1_iuea1mh wrote

On the geologists front, I wholeheartedly agree. My personal favorite is Nick Zentner of Central Washington University, whose lectures on YouTube are extremely lucid and clear about how geologists arrived at their conclusions and what's still up for debate.

Still mindblowing to me that plate tectonics were still "up for debate" as late as the early 1960s.

Anyway, my favorite lecture of his is Ancient Rivers of the Pacific Northwest.

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mglyptostroboides t1_iufolp0 wrote

I'm appreciating all the geologist love in this thread. I should go back to college and finish my degree...

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Orgalorgg t1_iugwumz wrote

Yes! I saw the Ancient Rivers of the PNW one as well and am close enough that I went out to eastern oregon to see the gigantic blobs of lava rock that still exist there. Very cool to see!!! Oddly terrifying even though it happened millions of years ago.

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HOLLANDSYTSE t1_iuh4xz2 wrote

Geography teacher here, thanks for this. Need to brush up in geology a bit!

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colonel_Schwejk t1_iuh7n0n wrote

he's bloody good!

i only regret he specializes into american geography, i'd like to listen to what he knows about every place on earth :)

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_AlreadyTaken_ t1_iuetwgx wrote

As far as I understand the surface of a neutron star is a very thin layer of normal nuclei and an extremely thin iron vapor "atmosphere". Gamma rays might end up interacting with the surface and having pair production (coverting to an electron snd positron) before reaching the neutron density layer.

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AlarmingAffect0 OP t1_iufoexp wrote

> Gamma rays might end up interacting with the surface and having pair production (coverting to an electron snd positron) before reaching the neutron density layer.

Is there a way of estimating how much of the gamma radiation would make it to the neutron density layer?

Also is that hot iron in the form of vapor rather than plasma?

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gravity_surf t1_iufc2ao wrote

you would enjoy the randall carlson podcast. earth history by way of geology and cosmology.

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Generically_Yours t1_iufqzls wrote

I love him. Whole new take on a planet we've been standing on our whole lives every time I listen to him.

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[deleted] t1_iudmllt wrote

[removed]

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Lance_E_T_Compte t1_iudydnf wrote

So that would be for perpendicular incidence. Yes?

If the waves are approaching almost parallel to the surface, wouldn't they "see" the atoms much closer together?

Maybe if you could only reflect for less than 1% incidence, but you could put ~180 of your mirrors?

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kftrendy t1_iuevq1s wrote

That’s a grading-incidence mirror, and it’s used for X-rays. The Chandra and NuSTAR space telescopes are good examples of their use. They’re very low efficiency and heavy, though, and that would get even worse for gamma rays, where the incidence angle would have to be even smaller.

In practice a gamma ray telescope uses collimators (basically blocking all light other than that which is coming from straight on) or coded-aperture masks, which are kind of like pinhole cameras. Neither of those involve reflecting gamma rays though.

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namnit t1_iufz12l wrote

There’s a group at NASA’s MSFC that develop X-ray optics and have done so for the Chandra and IXPE missions, among others. The grazing-incident mirrors are usually in a nested configuration inside cylindrical shells.

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Ragidandy t1_iuej4j2 wrote

But aren't you making the same assumption that the OP citation proved wrong? All the same arguments were made for diffraction, and now we see diffraction is possible. That doesn't mean reflection is possible, but it does negate or weaken this argument that it's impossible. Actually, if diffraction is possible, then a specific sequence of diffractors should be able to reflect, right?

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Geminii27 t1_iudmn4w wrote

It'd be interesting to be able to set up virtual energy fields where the packets effectively simulated atomic-scale masses at picometer spacings. I wonder if 'real' photons would see that as effectively matter, or just as other photons they could pass straight through.

Huh. That'd basically be projected matter. I wonder if someone could find a use for that.

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edjumication t1_iuemldg wrote

Geology is fascinating to me and we touch on it a bit in our industry (landscape construction). We actually worked on a geologists house once and it was a cool experience. He explained that some of the mossy boulders weren't actually true granite but mostly mica.

He also informed us we shouldn't be putting barrier fabric at the bottom of our weeper pit because it will create a biofilm and slow the water from seeping into the surrounding earth (we put fabric on the walls of the pit to keep the soil from intruding into the drainage stone)

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MyFacade t1_iudzc4e wrote

What if the object had an irregular structure, kind of like how an n95 mask is not uniform?

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Busterwasmycat t1_iuhdu99 wrote

Glass (non-crystalline solid=NCS) can be reflective but it is again a matter of wavelength and gap size. Does the object act like a solid zone of contact to the waves?

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tomdarch t1_iug2qdd wrote

Could some sort of ultra dense object like a dead star core act as a reflector for wavelengths this short?

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nighthawk_md t1_iug9tdk wrote

Hey, thanks! I've never heard a good explanation of why gamma rays pass through everything.

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Sea_Divide_3870 t1_iuekhn5 wrote

It’s great you know enough about a lot of things. That helps with system thinking .. keep it up!

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