Gamma-ray laser

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A gamma-ray laser, or graser, is a hypothetical device that would produce coherent gamma rays, just as an ordinary laser produces coherent rays of visible light. [1] Potential applications for gamma-ray lasers include medical imaging, spacecraft propulsion, and cancer treatment. [2]

Contents

In his 2003 Nobel lecture, Vitaly Ginzburg cited the gamma-ray laser as one of the 30 most important problems in physics. [3]

The effort to construct a practical gamma-ray laser is interdisciplinary, encompassing quantum mechanics, nuclear and optical spectroscopy, chemistry, solid-state physics, and metallurgy—as well as the generation, moderation, and interaction of neutrons—and involves specialized knowledge and research in all these fields. The subject involves both basic science and engineering technology. [4]

Research

The problem of obtaining a sufficient concentration of resonant excited (isomeric) nuclear states for collective stimulated emission to occur turns on the broadening of the gamma-ray spectral line. [5] Of the two forms of broadening, homogeneous broadening is the result of the lifetime of the isomeric state: the shorter the lifetime, the more broadened the line. [6] [7] [8] [9] Inhomogeneous broadening comprises all mechanisms by which the homogeneously broadened line is spread over the spectrum. [10]

The most familiar inhomogeneous broadening is Doppler recoil broadening from thermal motion of molecules in the solid containing the excited isomer and recoil from gamma-ray emission, in which the emission spectrum is both shifted and broadened. Isomers in solids can emit a sharp component superimposed on the Doppler-broadened background; this is called the Mössbauer effect. [11] This recoilless radiation exhibits a sharp line on top of the Doppler-broadened background that is only slightly shifted from the center of the background. [12] [13] [14] [15] [16]

With the inhomogeneous background removed, and a sharp line, it would seem that we have the conditions for gain. [17] [18] [19] But other difficulties that would degrade gain are unexcited states that would resonantly absorb the radiation, opaque impurities, and loss in propagation through the crystal in which the active nuclei are embedded. [20] Much of the latter can be overcome by clever matrix crystal alignment [21] to exploit the transparency provided by the Borrmann effect. [22] [23] [24]

Another difficulty, the graser dilemma, is that properties that should enable gain and those that would permit sufficient nuclear inversion density seem incompatible. [25] [26] The time required to activate, separate, concentrate, and crystallize an appreciable number of excited nuclei by conventional radiochemistry is at least a few seconds. To ensure the inversion persists, the lifetime of the excited state must be considerably longer. Furthermore, the heating that would result from neutron-pumping the inversion in situ seems incompatible with maintaining the Mössbauer effect, although there are still avenues to explore.[ citation needed ]

Heating may be reduced by two-stage neutron-gamma pumping, [27] in which neutron capture occurs in a parent-doped converter, where it generates Mössbauer radiation that is then absorbed by ground-state nuclei in the graser. [28] Two-stage pumping of multiple levels offers multiple advantages. [29] [30] [ clarification needed ]

Another approach is to use nuclear transitions driven by collective electron oscillations. [31] [32] The scheme would employ a triad of isomeric states: a long-lived storage state, in addition to an upper and lower lasing state. The storage state would be energetically close to the short-lived upper lasing state but separated by a forbidden transition involving one quantum unit of spin angular momentum. The graser would be enabled by a very intense optical laser to slosh the electron cloud back and forth and saturate the forbidden transition in the near field of the cloud. The population of the storage state would then be quickly equalized with the upper lasing state whose transition to the lower lasing state would be both spontaneous and stimulated by resonant gamma radiation. A "complete" chart of nuclides likely contains a very large number of isomeric states, and the existence of such a triad seems likely, but it has yet to be found. [21] [33]

Nonlinearities can result in both spatial and temporal harmonics in the near field at the nucleus, [34] [35] opening the range of possibilities for rapid transfer from the storage state to the upper lasing state using other kinds of triads involving transition energies at multiples of the optical laser quantum energy and at higher multipolarities.

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<span class="mw-page-title-main">Laser</span> Device which emits light via optical amplification

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation. The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories, based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow.

<span class="mw-page-title-main">Maser</span> Device for producing coherent EM waves in the sub-visible spectrum

A maser is a device that produces coherent electromagnetic waves (microwaves), through amplification by stimulated emission. The term is an acronym for microwave amplification by stimulated emission of radiation. The first maser was built by Charles H. Townes, James P. Gordon, and Herbert J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are also used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep-space spacecraft communication ground stations.

<span class="mw-page-title-main">Neutron</span> Subatomic particle with no charge

The neutron is a subatomic particle, symbol
n
 or
n0
, which has a neutral charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one dalton, they are both referred to as nucleons. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks.

<span class="mw-page-title-main">Nuclear physics</span> Field of physics that studies atomic nuclei

Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.

<span class="mw-page-title-main">Spectroscopy</span> Study involving matter and electromagnetic radiation

Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. In simpler terms, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.

The Mössbauer effect, or recoilless nuclear resonance fluorescence, is a physical phenomenon discovered by Rudolf Mössbauer in 1958. It involves the resonant and recoil-free emission and absorption of gamma radiation by atomic nuclei bound in a solid. Its main application is in Mössbauer spectroscopy.

<span class="mw-page-title-main">Nuclear isomer</span> Metastable excited state of a nuclide

A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels. "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). The term "metastable" is usually restricted to isomers with half-lives of 10−9 seconds or longer. Some references recommend 5 × 10−9 seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life. Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the 180m
73Ta
 nuclear isomer survives so long (at least 1015 years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by 180m
73Ta
 as well as 192m2
77Ir
, 210m
83Bi
, 242m
95Am
 and multiple holmium isomers.

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Natural tantalum (73Ta) consists of two stable isotopes: 181Ta (99.988%) and 180m
Ta
 (0.012%).

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<span class="mw-page-title-main">Mössbauer spectroscopy</span> Spectroscopic technique

Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer in 1958, consists of the nearly recoil-free emission and absorption of nuclear gamma rays in solids. The consequent nuclear spectroscopy method is exquisitely sensitive to small changes in the chemical environment of certain nuclei.

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<span class="mw-page-title-main">Gamma ray</span> Energetic electromagnetic radiation arising from radioactive decay of atomic nuclei

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References

  1. ↑ Baldwin, G. C. (1979). "Bibliography of GRASER research". Los Alamos Scientific Laboratory Report LA-7783-MS. doi:10.2172/6165356. OSTI   6165356.
  2. ↑ Pittalwala, Iqbal (2019-12-05). "Gamma-ray laser moves a step closer to reality". University of California, Riverside. Retrieved 2022-11-27.
  3. ↑ Ginzburg, V. L. (2003). "On superconductivity and superfluidity". The Nobel Prize in Physics 2003: 96–127.
  4. ↑ Baldwin, G. C.; Solem, J. C.; Gol'danskii, V. I. (1981). "Approaches to the development of gamma-ray lasers". Reviews of Modern Physics. 53 (4): 687–744. Bibcode:1981RvMP...53..687B. doi:10.1103/revmodphys.53.687.
  5. ↑ Baldwin, G. C.; Solem, J. C. (1979). "On the direct pumping of gamma-ray lasers by neutron capture". Nuclear Science & Engineering. 72 (3): 290–292. doi:10.13182/NSE79-A20385.
  6. ↑ Vali, V.; Vali, W. (1963). "Induced gamma y-ray emission". Proceedings of the IEEE. 51 (1): 182–184. doi:10.1109/proc.1963.1677.
  7. ↑ Letokhov, V. S. (1973). "On the problem of the nuclear-transition gamma-laser". Journal of Experimental and Theoretical Physics. 37 (5): 787–793. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  8. ↑ Kamenov, P.; Bonchev, T. (1975). "On the possibility of realizing a gamma laser with long-living isomer nuclei". Bolgarskaia Akademiia Nauk, Doklady. 28 (9): 1175–1177. Bibcode:1975BlDok..28.1175K.
  9. ↑ Il'inskii, Yu. A.; Khokhlov, R. V. (1976). "Possibility of creating a gamma-laser". Radiophysics and Quantum Electronics. 19 (6): 561–567. Bibcode:1976R&QE...19..561I. doi:10.1007/bf01043541. S2CID   120340405.
  10. ↑ Baldwin, G. C. (1977). "On the Feasibility of Grasers". Laser Interaction and Related Plasma Phenomena. Vol. 4A. pp. 249–257. doi:10.1007/978-1-4684-8103-7_13. ISBN   978-1-4684-8105-1.
  11. ↑ Andreev, A. V.; Il'inskii, Yu. A.; Khokhlov, R. V. (1977). "Role of collective and induced processes in the generation of Mössbauer gamma radiation". Journal of Experimental and Theoretical Physics. 46 (4): 682–684. Bibcode:1977JETP...46..682A. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  12. ↑ Hien, P. Z. (1970). "Spontaneous emission of gamma quanta by a system containing identical nuclei". Journal of Experimental and Theoretical Physics. 31 (1): 83–86. Bibcode:1970JETP...31...83Z. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  13. ↑ Gol'danskii, V. I.; Kagan, Yu. M. (1973). "Feasibility of the nuclear-transition gamma laser (Graser)". Soviet Physics Uspekhi. 16 (4): 563–565. doi:10.1070/pu1974v016n04abeh005305.
  14. ↑ Namiot, V. A. (1973). "Stimulated line narrowing and the Mössbauer effect for long-lived isomers". JETP Letters. 18 (6): 369–373. Archived from the original on 2019-02-07. Retrieved 2016-02-24.
  15. ↑ Andreev, A. V.; Il'inskii, Yu. A.; Khokhlov, R. V. (1974). "Narrowing of gamma resonance lines in crystals by continuous radio-frequency fields". Journal of Experimental and Theoretical Physics. 40 (5): 819–820. Bibcode:1975JETP...40..819A. Archived from the original on 2016-09-27. Retrieved 2016-02-24.
  16. ↑ Baldwin, G. C. (1979). "Time-domain spectroscopy of recoilless gamma rays". Nuclear Instruments and Methods. 159 (2–3): 309–330. Bibcode:1979NucIM.159..309B. doi:10.1016/0029-554x(79)90656-6.
  17. ↑ Terhune, I. H.; Baldwin, G. C. (1965). "Nuclear superradiance in solids". Physical Review Letters. 14 (15): 589–591. Bibcode:1965PhRvL..14..589T. doi:10.1103/physrevlett.14.589.
  18. ↑ Baldwin, G. C. (1974). "Is There a High Frequency Limit to Laser Action?". Laser Interaction and Related Plasma Phenomena. Vol. 3B. pp. 875–888. doi:10.1007/978-1-4684-8416-8_23. ISBN   978-1-4684-8418-2.
  19. ↑ Andreev, A V.; Il'inskii, Yu. A. (1975). "Amplification in a gamma laser when the Bragg condition is satisfied". Journal of Experimental and Theoretical Physics. 41 (3): 403–405. Bibcode:1975JETP...41..403A. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  20. ↑ Il'inskii, Yu. A.; Khokhlov, R. V. (1974). "On the possibility of observation of stimulated gamma radiation". Soviet Physics Uspekhi. 16 (4): 565–567. doi:10.1070/pu1974v016n04abeh005306.
  21. 1 2 Baldwin, G. C.; Solem, J. C. (1997). "Recoilless gamma-ray lasers". Reviews of Modern Physics. 69 (4): 1085–1117. Bibcode:1997RvMP...69.1085B. doi:10.1103/revmodphys.69.1085.
  22. ↑ Borrmann, G. (1941). "Über Extinktionsdiagramme der Röntgenstrahlen von Quarz". Physikalische Zeitschrift. 42: 157–162.
  23. ↑ Kagan, Yu. M. (1974). "Use of the anomalous passage effect to obtain stimulated emission of gamma quanta in a crystal". JETP Letters. 20 (1): 11–12. Archived from the original on 2016-09-06. Retrieved 2016-02-24.
  24. ↑ Andreev, A. V.; Il'inskii, Yu. A. (1976). "Possible use of the Borrmann effect in the gamma laser". Journal of Experimental and Theoretical Physics. 43 (5): 893–896. Bibcode:1976JETP...43..893A. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  25. ↑ Baldwin, G. C.; Solem, J. C. (1979). "Maximum density and capture rates of neutrons moderated from a pulsed source". Nuclear Science & Engineering. 72 (3): 281–289. Bibcode:1979NSE....72..281B. doi:10.13182/NSE79-A20384.
  26. ↑ Baldwin, G. C.; Solem, J. C. (1995). "Kinetics of neutron-burst pumped gamma-ray lasers". Laser Physics. 5 (2): 326–335.
  27. ↑ Gol'danskii, V. I.; Kagan, Yu.; Namiot, V. A. (1973). "Two-stage pumping of Mössbauer gamma-ray lasers". JETP Letters. 18 (1): 34–35. Archived from the original on 2016-03-06. Retrieved 2016-02-24.
  28. ↑ Gol'danskii, V. I.; Kagan, Yu. (1973). "The possibility of creating a nuclear gamma laser". Journal of Experimental and Theoretical Physics. 37 (1): 49. Bibcode:1973JETP...37...49G. Archived from the original on 2016-03-11. Retrieved 2016-02-24.
  29. ↑ Baldwin, G. C.; Solem, J. C. (1980). "Two-stage pumping of three-level Mössbauer gamma-ray lasers". Journal of Applied Physics. 51 (5): 2372–2380. Bibcode:1980JAP....51.2372B. doi:10.1063/1.328007.
  30. ↑ Baldwin, G. C. (1984). "Multistep Pumping Schemes for Short-Wave Lasers". Laser Interaction and Related Plasma Phenomena. Vol. 6. pp. 107–125. doi:10.1007/978-1-4615-7332-6_8. ISBN   978-1-4615-7334-0.
  31. ↑ Solem, J. C.; Biedenharn, L. C. (1987). "Primer on coupling collective electronic oscillations to nuclei" (PDF). Los Alamos National Laboratory Report LA-10878. Bibcode:1987pcce.rept.....S.
  32. ↑ Biedeharn, L. C.; Baldwin, G. C.; Boer, K. (1986). Nuclear excitation by laser driven coherent outer shell electron oscillations. Proceedings of the First International Laser Science Conference, Dallas, TX, November 18–22, 1985. Stwalley, W. C.; Lapp, M.; Eds. Vol. 146. pp. 52–53. Bibcode:1986AIPC..146...52B. doi:10.1063/1.35933.
  33. ↑ Solem, J. C.; Biedenharn, L. C.; Rinker, G. A. (1987). "Calculation of harmonic radiation from atoms subjected to strong laser fields and the possibility of nuclear excitation". Journal of the Optical Society of America A. 4: P53. Bibcode:1987JOSAA...4...53S.
  34. ↑ Solem, J. C.; Biedenharn, L. C. (1988). "Laser coupling to nuclei via collective electronic oscillations: A simple heuristic model study". Journal of Quantitative Spectroscopy and Radiative Transfer. 40 (6): 707–712. Bibcode:1988JQSRT..40..707S. doi:10.1016/0022-4073(88)90066-0.
  35. ↑ Solem, J. C. (1988). "Theorem relating spatial and temporal harmonics for nuclear interlevel transfer driven by collective electronic oscillation". Journal of Quantitative Spectroscopy and Radiative Transfer. 40 (6): 713–715. Bibcode:1988JQSRT..40..713S. doi:10.1016/0022-4073(88)90067-2.

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