Proposed gamma-ray laser could emit 'nuclear light'

( -- Building a nuclear gamma-ray laser has been a challenge for scientists for a long time, but a new proposal for such a device has overcome some of the most difficult problems. In the new study, Eugene Tkalya from the Institute of Nuclear Physics at Moscow State University has theoretically proven how the stimulated gamma emission of thorium nuclei can emit coherent visible light. Although the nuclear gamma-ray laser emits light based on stimulated emission, it operates a bit differently than a normal laser.

“Photons in a normal are emitted by atoms, by ions, and so on,” Tkalya told “In the nuclear gamma-ray laser, the photons are emitted by atomic .”

In the study, which is published in a recent issue of , Tkalya explains that a nuclear gamma-ray laser has to overcome at least two basic problems: accumulating a large amount of isomeric nuclei (nuclei in a long-lived excited state) and narrowing down the gamma-ray emission line. The new proposal fulfills these requirements by taking advantage of thorium’s unique nuclear structure, which enables some of the photons from an external laser to interact directly with thorium’s nuclei rather than its electrons.

Tkalya’s proposal uses a lithium-calcium-aluminum-fluoride (LiCaAlF6) compound, in which some of the calcium is replaced with thorium. After a sufficient amount of isomeric thorium nuclei have been excited by an external laser, the nuclei can interact with a surrounding electric or magnetic field to create a population inversion, so that the system contains more excited nuclei than unexcited nuclei. (In a regular laser, a population inversion usually involves getting more electrons in a higher energy level than a lower energy level.) Then, Tkalya showed that the nuclei can emit or absorb photons without recoil, allowing them to produce light without losing energy.

“The nuclear gamma-ray laser considered in my article can emit ‘visible’ (vacuum ultraviolet [VUV]) light (or of the optical range) only,” Tkalya said.

As Tkalya explained, a nuclear gamma-ray laser could open up several interesting applications, although he has not thoroughly investigated them yet. One possibility is that the gamma-ray emission of the excited nuclei is in the optical range called “nuclear light.”

“In my opinion, it is interesting to see a ‘nuclear light,’” he said. “An application of nuclear light is the nuclear metrological standard of frequency, or the ‘nuclear clock.’”

In addition, the device could be used to test many fundamental properties of nature, such as the exponentiality of the decay law and the effect of the variation of the fine structure constant.

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More information: E.V. Tkalya. “Proposal for a Nuclear Gamma-Ray Laser of Optical Range.” Physical Review Letters 106, 162501. DOI:10.1103/PhysRevLett.106.162501

A possibility of the amplification of the 7.6 eV γ radiation by the stimulated γ emission of the ensemble of the 229mTh isomeric nuclei in a host dielectric crystal is proved theoretically. This amplification is a result of (1) the excitation of a large number of 229mTh isomers by laser radiation, (2) the creation of the inverse population of nuclear levels in a cooled sample owing to the interaction of thorium nuclei with the crystal electric field or with an external magnetic field, (3) the emission or absorption of the optical photons by thorium nuclei in the crystal without recoil, and (4) the nuclear spin relaxation through the conduction electrons of the metallic covering.

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May 02, 2011
Yet another PhysOrg piece of ambiguous reporting. For 30 yrs, laser scientists have tried & failed to invent a GRASER (gamma ray laser), in which stimulated emission of gamma rays occurs. Nothing has changed, altho this article purports such via lousy science writing. Indeed, the stimulated emission from this laser consists of Optical photons, in the electron-volt range. A GRASER would emit a coherent beam of gamma ray photons which are Hundreds of Thousands of times more energetic, ~0.1 Mev.

May 02, 2011
True, but remember lasers began as masers...

May 02, 2011
So this laser outputs photons of energy 7.6 eV?

Sorry, that's not gamma. That's not even xray. That's just high end visible light.

0.12-12 keV = soft xray
12-120 keV = hard xray
>120 keV = gamma

So why are they calling this a gamma ray laser when it clearly is not?

Nevertheless, I do think that stimulated emission from an atomic nucleus is quite an achievement, even in theory.

May 02, 2011
Not to mention the inability to reflect gamma rays...

May 02, 2011
Gamma vs X-ray can mean energy range, or it can refer to the source: X-ray from electron transitions, Gamma from nuclear transitions. They're using Gamma in this latter sense, but this is really the point anyway: they're describing stimulated emission from a nuclear transition. If this can be done in practice for this system, this has the potential to lead to high energy Gamma rays (Gamma rays in the first sense), since typical nuclear transitions are in the 100keV - MeV range.

May 02, 2011
It seems like it would be very difficult to do a high energy gamma laser... The requirement for a recoilless emission is that the energy be less than the quantized lattice vibrational energy. This can be done with Cobalt 57 for example, which has a 14.4 keV transition, but it's hard to imagine doing it with any higher energy. Moreover, the 14.4 keV recoilless emission is already something like 20% efficient at most, so amplifying it would be very difficult.

Plus, as far as I know there is no way to reflect a gamma ray in a chamber like you do in a normal laser. So how would it be amplified, if you can't bounce it around several times?

I dunno. I don't see this going anywhere. It seems physically impossible.

May 02, 2011
Gamma photons can be produced by LINAC, CPA, Anti-Matter/Matter Annihilation according to Advanced Plasma Industries Inc.

May 03, 2011
Tkayla is using nucleii here and not the whole atoms, molecules, etc. This is new, like the 'MASER' was back in the early sixties of the last century. At that time, efficiencies were very poor, modern powers were considered science fiction, and the weaponization of them so unimagined that serious consideration by a scientific professional could cost him/her a career. Serious development of this idea will come and soon enough we will have our 'big honkin' space gun' from the Stargate SG1 series in real life....or our ideal small scale fusion ignition device for power sources for VASIMR drives in single stage to orbit space shuttles. We ARE accumulating the enabling tech to go to space, bit by bit.

May 03, 2011
So this could be used to find Nuclear weapons?

May 05, 2011
Can you send a traveling wave down one of these beams? And if you can, could you use it to line up atoms to create chains and/or lattices?

May 08, 2011
I think what is more interesting is that they seem to be able to absorb energy in the nuclei store it for a time and later release it.

It would be interesting if this technology could be the basis of a nuclear battery.

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