Living in an era that is highly dependent on smartphones, are you somewhat "mobile phone charging anxiety"? For people with battery anxiety, they simply dare not go out without a charger. The 100% in the upper right corner of the mobile phone screen is the source of their sense of security. And when the battery is about to run out, that must be the most crazy time: it would be great if you could have a battery that doesn't need to be recharged at this time!
The super battery that can enable electric cars and spacecrafts to last indefinitely is a basic configuration of science fiction works and a goal that scientists are committed to research and achieve. What characteristics should a perfect battery have? We expect it to have huge energy (the more energy it can store per unit mass, the better), long-term energy storage (it will not fail even after being left for many years), stable properties, safe and reliable.
Creating such a battery is not a far-fetched dream, because nature has provided the corresponding material form - nuclide in a long-lived homonuclear energy state. However, humans have not yet been able to harness this energy and still need to overcome many difficulties to find ways to utilize it flexibly.
With the treasure mountain ahead, can we return home with a full load?
Figure Isonuclear energy states are expected to be used in the research and development of new generation high energy density nuclear batteries and other products | Guo Song
NO.1
Beauty is like a flower across the clouds
Just like people have joys and sorrows, the moon has waxing and waning, the tiny nucleus will also be in many different states: among them, the lowest energy is called ground state , and the others are called excited state . For excited states with longer lifetimes (generally greater than 10 nanoseconds), scientists call them homonuclear and isoenergetic states . Since Otto Hahn and Lise Meitner discovered the homonuclear anisotropic state in 1921, after a hundred years of exploration, more than 2,500 homonuclear anisotropic states have been discovered.
Picture Hahn and Meitner Picture source | wikipedia
The excitation energy of some homonuclear energy states can reach millions of electron volts. If a homonuclear energy-state material the size of an ordinary power bank is used as a battery, its power can last for thousands of years for a current mobile phone.
Some homonuclear energy states of atomic nuclei have particularly long lifespans. For example, there is a homonuclear energy state in tantalum-180 with a lifespan of more than seven quadrillion years; and some homonuclear energy states also have high excitation energy and long lifetimes, such as the second isonuclear energy state in hafnium-178, which has an excitation energy of 2.5 million electron volts and a half-life of 31 years. In addition, the homonuclear heteroenergetic state is almost unaffected by chemical processes and has excellent stability.
However, in the natural state, if a certain isonuclear energy state has a lifespan of tens of thousands of years, its energy will be slowly released over tens of thousands of years. If you cannot find a shortcut for to release energy, it can only be used in very limited scenarios. For now, a perfect nuclear battery looks like an ethereal beauty, just out of reach.
NO.2
Heavy door and deep lock with no trace
So, what method can be used to quickly release the energy stored in the homonuclear energy state? At present, the generally accepted approach is to induce deexcitation through : excite the homonuclear isoenergetic state to its adjacent short-lived energy level, and then deexcite from the short-lived energy level to the ground state, in the process causing it to release all energy of.
Scientists hope to find a very efficient and controllable way to achieve the purpose of nuclear excitation - to use a smaller energy to trigger the excitation process and release a large amount of energy.
It was once thought that induced hyposensitivity was about to be put into use. In 1999, American scientist Collins used X-ray to bombard the homonuclear energy state of hafnium-178m2 with a half-life of 31 years and found that its deexcitation speed increased by about 4%. This discovery quickly attracted the attention of the U.S. military, and they quickly formulated plans to develop gamma bombs.If successful, using X-ray triggering, the gamma bomb can instantly produce destructive power equivalent to that of a nuclear bomb. However, follow-up research showed that the excitation efficiency of X-rays was far from meeting application requirements, and the plan was ultimately aborted.
picture In Marvel comics, the gamma bomb is a nuclear weapon designed by Dr. Banner, which can output super strong gamma ray energy.
Scientists have discovered that by bombarding atomic nuclei with charged ions, X or γ photons, the nuclei can be excited through Coulomb excitation and light absorption. However, so far, experimentally measured excitation probabilities have been quite low. This may indicate that the idea of stimulating atomic nuclei by direct means is not feasible. After all, the size of the atomic nucleus is pitifully small, accounting for only one hundred billionth of the volume of the entire atom . When people bombard matter with ions or photons, the chance of reaching an atomic nucleus is inherently low.
NO.3
But I doubt that spring is in the neighborhood
When it seems that the end of the road is over, scientists think of the good neighbor of the nucleus - electrons .
Atom is a quantum system composed of atomic nucleus and extranuclear electrons. The electrons bound within the atom are distributed in a series of electron orbits. If a foreign electron occupies an orbit, or if an electron switches between different orbits, energy is released (usually in the form of X-rays). If the energy released happens to be equivalent to the energy required for nuclear excitation, it may trigger the resonance process - exciting the nucleus without emitting photons .
Scientists thus proposed two excitation mechanisms: electronic transition excitation and electron capture excitation.
electronic transition excites , which uses the transition induced resonance process of electrons between different orbits to excite the atomic nucleus. Therefore, the energy released by the electronic transition is required to be very close to the energy required for nuclear excitation. This mechanism has been confirmed experimentally in the excitation of the gold-197 ground state. However, because this process has very stringent energy requirements for energy levels, no homonuclear heteroenergetic states that can meet the corresponding energy requirements have yet been found.
electron capture excites , which uses the energy released when foreign electrons occupy the orbit. Since the original kinetic energy of foreign electrons will also participate in the resonance process, precise control of the kinetic energy of electrons can accurately meet the resonance condition . Therefore, research on this mechanism has been favored by the academic community in recent years.
Figure Schematic diagram of electronic transition excitation and electron capture excitation. Figure | Guo Song
NO.4
The color of grass looks far away but there is no
In 2018, the research on using electron capture to stimulate homonuclear energy states ushered in an important breakthrough. American scientists reported in Nature magazine that they observed for the first time in experiments the electron capture-induced nuclear excitation of the homonuclear isoenergetic state of molybdenum-93 (molybdenum-93m), and extracted a considerable excitation probability (approximately equal to 1 %). Electron capture appears to be much more efficient than other known mechanisms.
However, shortly afterwards, some theorists estimated the excitation probability of molybdenum-93m under the experimental conditions and obtained a very low calculated value (about 0-11), which resulted in a huge gap of 9 orders of magnitude between theory and experiment. difference.
In order to understand the differences between theory and experiment, researchers from the Institute of Modern Physics, Chinese Academy of Sciences, carefully evaluated the experiment from an experimental perspective. In the case of nuclear excitation due to electron capture, rare photons of specific energy are generated in a short period of time. However, in this experiment, the primary reaction between the beam and the target will also produce a large number of photons, forming a thick and complex background. The light intensity of and is probably hundreds of millions to trillions of times that of the target photons.
Picture The GAMMASPHERE detection array at Argonne National Laboratory in the United States is used to capture and measure these rare photons.Image source | Researchers from the Institute of Modern Physics at Argonne National Laboratory in the United States found through demonstration that the background of this work was not properly deducted, which may lead to the contribution of the background being mistaken for nuclear excitation caused by electron capture. thus overestimating its excitation probability. In 2020, researchers from the Institute of Modern Physics published relevant comments in the "Matters Arising" column of "Nature" magazine, further triggering discussions in the academic community on the mechanism of nuclear excitation caused by electron capture.
NO.5
The light firefly flow in the cool night sand
Because the background of the spectrum is thick and complex, it is very difficult to find rare events in this environment. Just like looking for the flashing firefly in the sun, even if you know that it is a special green light, it is easily obscured by the strong light. Why not look for fireflies in the dark like every naughty child?
In order to get rid of the influence of heavy background, researchers and collaborators from the Institute of Modern Physics creatively used homonuclear heteroenergy state beams to study electron capture based on the radioactive beam line RIBLL1 of the Lanzhou Heavy Ion Accelerator Facility (HIRFL). Nuclear excitation phenomenon. Relevant research was published in " Physical Review Letters " on June 17, 2022.
researchers have proposed an improved experimental plan: using a radioactive beam line of about 35 meters to separate and transmit molybdenum-93m to a low background measurement area. This keeps the electron capture-induced nuclear excitation process away from the primary reaction, and the thick background will not affect experimental measurements.
Figure Using a radioactive beam line of about 35 meters to separate and transmit molybdenum-93m to a low background measurement area, the measurement accuracy of the experiment is significantly improved. Figure | Guo Song
The phenomenon of nuclear excitation caused by electron capture is expected to occur at the moment when molybdenum-93m ion is implanted at the detection end. Therefore, using the injection signal timing to search only for photons at that moment can further reduce the impact of irrelevant photons and improve detection accuracy.
Figure Experimental measurement end. Five high-purity germanium detectors are used to measure photons, and a plastic scintillator detector placed in an aluminum alloy box detects the injected ions.
In the experiment, about 130 million molybdenum-93m ions entered the detection area. However, the researchers ultimately did not observe the phenomenon of nuclear excitation caused by electron capture, and the upper limit of the experimental excitation probability extracted was only 2×0 -5. The reviewer believes: "Compared with previous reports, the results of this work are more reliable, and the measurement accuracy has also been significantly improved."
This study shows that homonuclear anisotropic ions are slowed down and blocked in solid materials. During the process, the probability of excitation is small, which is consistent with the expectations of multiple theoretical works. This work verifies the feasibility and necessity of using homonuclear heteroenergetic state beams to study nuclear excitations caused by electron capture, and points out the direction for subsequent research.
NO.6
Conclusion
Although new research shows that electron capture nucleation excitation will not be efficiently generated during the blocking process, it does not deny the possibility of its application. For such a resonance mechanism, experimental detection can only be carried out under low-probability conditions before it is fully studied. After the dominant factors are clarified, there is still hope to significantly improve the nuclear excitation efficiency through exquisite design.
As a rich gift from nature, the homonuclear energy state of the atomic nucleus has excellent energy storage potential. If it can be put into application, it will profoundly change human society. Even if its application prospects are still far away, sufficient basic research is still needed.
thanks the Chinese Nuclear Physics Society for its support.
Author | Guo Song Liu Fang
Paper link: https://doi.org/10.1103/PhysRevLett.128.242502
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