Is there such a thing as a gamma radiation mirror?

Submitted by AlarmingAffect0 t3_yheipf in askscience

Is there any material capable of forming a surface that is not just opaque or translucent to gamma radiation, but capable of specular reflection, even of perpendicular radiation? How high can the reflectivity get?

EDIT: Can't find reflection per se, but I found something about refraction. It looks like in 2012 someone at the Max Planck Institute succeeded in building gold lenses?

> Scientists at Ludwig-Maximilians-Universität in Munich and the Max Planck Institute of Quantum Optics in Garching have opened up a new chapter in optics: in experiments with gamma rays at the Institut Laue-Langevin (ILL) in Grenoble they have proven that these extremely high-energy electromagnetic waves can be focused by lenses like conventional light — the researchers have thus refuted a fundamental assumption of theoretical physics that had been valid for decades. Their discovery will make a great many new applications possible in medicine and materials research, for example.
> Optical instruments like telescopes and microscopes are based on the refraction of light: in a medium such as glass the electromagnetic waves propagate more slowly than in air or in a vacuum, and are therefore diffracted — for example, onto the focal plane of a photo camera. The refractive index, which depends on the lens material and the frequency of the waves, describes how large this effect is: the more it deviates from 1, the stronger the diffraction of the light beams.
> Until now, physicists had assumed that electromagnetic radiation with far greater energy than that in the visible spectrum could not be diffracted with lenses. They had calculated that the refractive index in this region of the spectrum is almost precisely 1 for all materials. However, back in the mid-1990s it turned out that X-rays are also diffracted by beryllium or carbon lenses, and thus that X-ray optics were possible.
> When Dietrich Habs, professor at Ludwig-Maximilians-Universität in Munich and Fellow of the Max Planck Institute of Quantum Optics in Garching, and his team were making their measurements at the ILL they discovered that this also applies to the even higher energy gamma-rays — after X-ray optics, the era of gamma optics is now beginning.

TIL X-Ray Optics appear to have been a thing for a while, including mirrors.

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sault18 t1_iudkchm wrote

No, but x rays can be reflected off of smooth metallic surfaces if they hit at a shallow angle:

https://en.m.wikipedia.org/wiki/X-ray_optics

But yeah, gamma rays are little juggernauts. Once they get going, nothings gonna stop them...until they plow into lead, water, concrete or something substantial like that.

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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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Geminii27 t1_iudmn4w wrote

Replying to Busterwasmycat (#345,213)

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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AlarmingAffect0 OP t1_iudo3jg wrote

Replying to Busterwasmycat (#345,213)

> 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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Lance_E_T_Compte t1_iudydnf wrote

Replying to Busterwasmycat (#345,213)

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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ehj t1_iue8jvz wrote

Having done research in the field of high energy radiation, I have not seen that this should be possible in practice. However if you can create a dense enough charged plasma, you can in principle reflect gamma rays. We are just not anywhere near being able to produce a plasma with a higher density than solid materials. Perhaps in some astrophysical extreme circumstances you can find something like this.

Edit: See e.g. this on the frequency below which reflection happens https://en.wikipedia.org/wiki/Critical_frequency

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Anacoenosis t1_iuea1mh wrote

Replying to AlarmingAffect0 (#345,966)

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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Ragidandy t1_iuej4j2 wrote

Replying to Busterwasmycat (#345,213)

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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edjumication t1_iuemldg wrote

Replying to Busterwasmycat (#345,213)

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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_AlreadyTaken_ t1_iuetwgx wrote

Replying to AlarmingAffect0 (#345,966)

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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kftrendy t1_iuevq1s wrote

Replying to Lance_E_T_Compte (#348,228)

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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rootofallworlds t1_iuf5gqk wrote

The NuSTAR telescope has mirrors that reflect photons up to 79 keV, although only at glancing incidence (photon travelling close to parallel to the mirror surface). Astronomers typically regard energies below 100 keV as X-rays, but physicists regard photons emitted by atomic nuclei as gamma rays regardless of energy and some are in the range observed by NuSTAR, for example gamma rays emitted by decay of Titanium-44 in supernova remnants.

I don't know what the record is for photon energy reflected.

Edit: By contrast, the higher energy instrument on the Fermi gamma ray space telescope observes gamma rays from 20 MeV to 300 GeV, so at the high end that's over 3 million times as energetic as what NuSTAR observes. It does not use mirrors or lenses. Instead incoming gamma rays create electron-positron pairs and the telescope has a stack of detector layers that track their direction allowing the gamma ray direction to be determined fairly precisely, described in extreme detail by https://arxiv.org/abs/0902.1089 (scroll to end for the pictures)

INTEGRAL, working at lower energies from around 15 keV to 10 MeV, uses another approach, coded aperture masks. This is essentially the same idea as a pinhole camera, but with multiple pinholes and using computer process to unscramble the overlapping images.

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Baschoen23 t1_iufft47 wrote

Replying to rootofallworlds (#357,103)

Our understanding of scientific principles has come so far. I'm still impressed with the basic geometric engineering of the Ancient Egyptians and we can measure electronvolts from celestially distant energy emitting bodies. Unbelievable.

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AlarmingAffect0 OP t1_iufnnci wrote

Replying to ehj (#350,407)

> a plasma with a higher density than solid materials

> Perhaps in some astrophysical extreme circumstances you can find something like this.

Does the iron vapor 'atmosphere' at the surface of neutron stars count?

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AlarmingAffect0 OP t1_iufoexp wrote

Replying to _AlreadyTaken_ (#354,623)

> 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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somneuronaut t1_iuftvlq wrote

Replying to AlarmingAffect0 (#362,301)

>Is there some sort of relativistic mass-energy equivalence stuff going on

indeed. the surface magnetic fields of magnetars are measured in tens of giga-Teslas. this results in an enormous energy density, which greatly exceeds regular matter, even with its large rest mass term.

edit: some quick napkin math reveals an energy density on the order of hundreds of yotta-joules per meter cubed. aka millions of billions of gigajoules per cubic meter.

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namnit t1_iufz12l wrote

Replying to Lance_E_T_Compte (#348,228)

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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ILikeDaWubbs t1_iughdmt wrote

I work as a Radiation control tech. I'm the one that tells you to move over or stand back so you don't get microwaved lol. (I also keep people from eating uranium lol, but that isn't the point here.)

I've seen containers with rad material in them, behind lead-brick shielding (walls but no "roof") and my instrument reads more than what should be present after traveling through the shielding. I've heard this called shine (eg "beta shine" or "gamma shine").

I don't know why or how this happens, all I know is that I've seen it. Any explanations would be cool!

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intervenroentgen t1_iugioo8 wrote

Replying to [deleted] (#361,494)

That’s not quite accurate. An electron beam is accelerated to high speeds towards the anode where photoelectric and bremmstrahlung interactions take place, resulting in energy released as an extreme amount of heat and some X-rays which are emitted isotropically. The X-rays that leave the tube do so through a radiolucent “window” forming the useful xray beam. The rest of the X-rays produced are absorbed by the tube housing.

The rotation of the anode is for heat dissipation. The electron beam can literally melt a hole through the tungsten target. Even with the high rotations, a lot of X-ray tubes tend to be replaced because of vaporization of the tungsten and it’s deposition on the tube walls creating an electrical short from the cathode to anode.

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Orgalorgg t1_iugwumz wrote

Replying to Anacoenosis (#350,676)

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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Quixeh t1_iuh3ahz wrote

Replying to ILikeDaWubbs (#369,228)

Gamma rays can scatter when they interact with some material; you're probably reading gamma rays which have travelled above the shielding and scattered towards you off the ceiling. The intensity of scattered radiation is significantly reduced however, and it's had to travel that much further to get to you so the inverse square law has some impact.

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Beer_in_an_esky t1_iuhedux wrote

Replying to somneuronaut (#362,885)

Yocto or yotta? Because a yocto joule is 10 to negative 24 J, which is not much at all.

Assuming you mean yotta though... That's terrifying. Amazing to think about, but utterly alien to any human-accessible frame of reference.

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phoboid t1_iuhljp5 wrote

If your angle of incidence is shallow enough, you can reflect almost anything. This is why gamma ray space observatories use grazing incidence mirrors to focus the incoming gamma rays. Similar designs are used at particle accelerators to harvest radiation for other use.

Now if you want something close to normal incidence, things become much more difficult and you need to use Bragg reflectors (i.e., multilayers of materials with alternating index of refraction that is tuned to the wavelength you want to reflect). These work as well (e.g., in semiconductor production machines), but you will be restricted to a narrow band of wavelengths and incidence angles, and you may be restricted by the available materials. Not every wavelength you want to reflect may have materials available that have the appropriate indices of refraction.

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Monguce t1_iuhqqcj wrote

Replying to intervenroentgen (#369,600)

I had always wondered why it had to rotate. That makes far more sense than I expected!

You know how something can be opaque, translucent or transparent?

Shouldn't the equivalent terms for radioactivity be something like radio-opaque, transradiant and... Urm... transparent?

Radiolucent means radio-light, which sort of sounds like nonsense. Translucent means light gets through. Shouldn't it be transradiant?

Just wondering.

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rootofallworlds t1_iuihm0d wrote

Replying to Aquatic-Vocation (#370,253)

More like a disintegration field. You know how atoms are round? Not in a magnetic field of 10^5 Tesla or more they aren't. The magnetic field is strong enough to distort the electron orbitals into narrow rods and ordinary molecules just fall apart. https://www.osti.gov/etdeweb/biblio/6961623 To borrow a phrase from Randall Munroe, "you would stop being biology and start being physics."

Oh, and the vacuum becomes birefringent - the speed of light depends on its polarisation.

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intervenroentgen t1_iuipl9x wrote

Replying to Monguce (#380,812)

-lucent as a suffix can have broad definitions. I work in the medical industry. I went to school for and worked as a radiologic technologist for years. Radiolucent and radiopaque were the standard terms used in radiology by both technologists and radiologists (ie: “the X-ray shows multiple radiolucent lesions”)

There may be more technically correct terms from a physician standpoint, but at this point it’s an established set of terms use in medicine. I’d be interested to see if it was terms used initially because of its time period and the definition of -lucent adapted to reflect that over time, or if it’s just terms used by tradition, which does happen.

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