Scientific watchmakers have created a prototype of a nuclear clock, hinting at future possibilities for using atomic nuclei to make precise time measurements and make new tests of fundamental theories of physics.

While the definition of “watch” is scientifically nebulous, the prototype has yet to be used to measure time. So it should technically be called the “frequency standard,” says physicist Jun Ye. But the work brings scientists closer to a nuclear clock than ever before. “For the first time, all the essential ingredients for a working nuclear clock are contained in this work,” says Ye, of JILA in Boulder, Colo.

While atomic clocks measure time based on electrons bouncing between energy levels in atoms, nuclear clocks measure time based on the energy levels of atomic nuclei. A certain frequency of laser light is needed for an atom or an atomic nucleus to make such a jump. The electromagnetic wave motion of that light can be used to tell time.

Nuclear clocks would keep time using a variety of the element thorium, called thorium-229. Most atomic nuclei make energy jumps that are too large to be triggered by a tabletop laser. But thorium-229 has two energy levels that are close enough to each other that the transition between these two levels can serve as a clock.

Now, researchers have pinpointed the frequency of light needed to initiate that jump. It’s 2,020,407,384,335 kilohertz, Ye and colleagues report on Sept. 5. Nature.

Most importantly, measurement has an uncertainty of 2 kilohertz. This is more than a million times the accuracy of the previous best measurement. And it’s more than a billion times the accuracy with which this frequency was known just over a year ago, highlighting multiple successive developments.

The enhancement depends on a component called a frequency comb (SN: 10/5/18). An essential component of many atomic clocks, a frequency comb creates a series of discrete frequencies of light. The use of a thorium-229 frequency comb has been a major research goal for some scientists (SN: 6/4/21). In the new work, Ye and colleagues compared the ticking of the nuclear clock with that of an atomic clock of a known frequency.

“This is something that will be important as a scientific application for tests of fundamental physics,” says physicist Ekkehard Peik of the National Institute of Metrology in Braunschweig, Germany, who was not involved in the new research.

In the future, such comparisons can be used to search for strange physical effects, such as shifting values ​​of fundamental constants (SN: 11/2/16). These are numbers that – as the name implies – are believed to be eternally fixed.

Quantum entanglement has made its way to the top.

Scientists have measured the strange quantum phenomenon of entanglement in top quarks, the heaviest fundamental subatomic particles known. It is the first detection of entanglement between pairs of quarks – a class of subatomic particles that make up larger particles, including protons and neutrons.

Particles that are entangled have properties that are linked or correlated with each other, causing the two to behave as a unit even when separated by large distances (SN: 15.6.17). Entanglement is usually studied in relatively small laboratory experiments using light particles or photons. In contrast, the new measurement required the world’s most powerful particle accelerator, the Large Hadron Collider at CERN, near Geneva. It is the highest energy detection of entanglement ever.

Using data from proton collisions, scientists with the ATLAS experiment, a particle detector at the Large Hadron Collider, studied the collisions that formed a top quark and its antimatter counterpart, a top antiquark. The two particles become entangled through their spin, a quantum property similar to spin motion. This means that the spins of the two particles are coupled, so measuring one spin will immediately tell you the other.

To detect the entanglement, scientists observed the particles into which the top quark and antiquark decayed. The angles at which those particles were emitted revealed the entanglement, researchers from the ATLAS collaboration report Sept. 18 in Nature. (CMS, another experiment at the Large Hadron Collider, also found evidence of top quark entanglement this year, in a study that has yet to be peer-reviewed.)

As quarks go, top quarks are special. In general, quarks don’t like to be alone, so when they break apart in high-speed collisions, pairs of quarks and antiquarks quickly materialize, morphing together into larger particles. This process, known as hadronization, removes any entanglement. But top quarks and antiquarks decay so fast that hadronization cannot occur, so the particles they decay into can carry the signature of their entanglement.

That is, for the demonstration of entanglement, the top quarks have the upper hand.

Bhavin Shastri still gets excited when he sees a laser pointer and has been fascinated by them since he was about 10 years old. “I was amazed that a beam of light could retain its brightness, concentrated in a small spot even after traveling a great distance,” says Shastri. “A laser pointer in my hand felt like a lightsaber Star Wars.

Now a physicist and engineer at Queen’s University in Kingston, Canada, Shastri wants to create light- or photonic-based computers. And he wants them to mimic the human brain.

Standard computers rely on electricity, using wires to transmit data via electrical currents. Photonic computers rely on light in the form of laser beams. Filters along the way change the intensity of the light to perform the calculations.

Although researchers have used light to transmit, store and process data in the laboratory, photonic computing is still in its infancy. Shastri has begun to push those boundaries. Its photonic computer chips are packaged together and connect photonic components that behave like brain neurons, creating a physical neural network on a chip. “Physics mimics biology,” says Shastri.

These types of chips are more powerful for certain applications and can be a big help for AI.

Modeling computers as brains

Shastri’s interest in light began young. He recalls an experiment he saw as a child: A plastic water bottle was punctured near its base so that a steady stream of water flowed out and down under the force of gravity. A laser shone through the hole in the bottle and, to Shastri’s surprise, it did not continue on a horizontal path. Instead, the beam bent down with the flow of water. “I was completely blown away by this experiment,” he says.

Since then, Shastri has been thinking about how light can be manipulated, while also exploring other research interests. In college, he worked with a professor who was researching machine learning and artificial intelligence, which sparked a new passion. Later, as a postdoc at Princeton University, Shastri met optical physicist Paul Prucnal, who would serve as Shastri’s advisor.

Prucnal told Shastri about his research creating “a laser that behaves like a biological neuron,” Shastri says, and how the team was looking to use such a laser to compute with light. This idea caught Shastri’s attention.

Shastri was “the first to connect the dots,” Prucnal says, when he realized that photonics could overcome some serious limitations of electronics.

Standard computers are “reaching their fundamental limits,” says Shastri. When most modern computers do computations, they cannot access much of their memory, and when they retrieve information from memory, they cannot compute. This makes computers slow and difficult for AI, image processing and other processing-intensive calculations. Training and running today’s AI algorithms consumes a huge amount of energy — collectively, it’s predicted to require as much as Japan’s total electricity consumption by 2026. Computers with brain-mimicking architectures, or neuromorphic computers , promise to be faster and use less energy.

“We want to build machines that will be much more energy efficient and much faster than other computers,” says Shastri.

But packing enough wires onto a chip to form a brain-like network of connections for use in an electronic computer is not easy. Electrical currents in close proximity will exert unwanted magnetic forces on each other, resulting in overheating and erratic performance. Light, however, usually does not interact with other light. Thus, countless light rays of different wavelengths can pass through the same path at the same time without any problem.

Prucnal notes that Shastri was the first to successfully create neuromorphic photonic computers on a chip. “Bhavin pioneered a way of thinking,” he says.

The study of light

A self-described “strong experimentalist,” Shastri designs, engineers, builds, and conducts experiments on chip-sized photonic devices. His team began by studying simpler devices similar to a single neuron, analyzing how they could mimic the function of a biological neuron. Years later, in as-yet-unpublished work, researchers have tentatively demonstrated that a chip with 100,000 neuron-like components can perform 120 billion operations per second, Shastri says—about 40 times faster than an average electronic computer.

Daniel Brunner, a machine learning and computing researcher at the FEMTO-ST Institute in France, who met Shastri when they were both postdocs, praised Shastri’s groundbreaking work. “I can’t even count the publications where he laid the groundwork” for using photonics to create physical neural networks, Brunner says.

And Shastri’s brilliance goes beyond his “incredible energy” and “incredible ability,” says Prucnal: Shastri is able to bring people together. “It’s not just about being likable, it’s about having a vision of how to do it [unite] these different fields”, he adds.

Don’t expect a photonic neuromorphic computer in your home anytime soon, though. These computers are best suited for specific research or industry applications. In addition to AI, Shastri and his colleagues are working on applications involving old problems in radio signal optimization and image processing.

Shastri may be committed to transforming computers, but his work is motivated by a decades-long fascination with light and its properties. “I’ve been very lucky to be able to do something,” he says, “it’s always been my childhood dream.”

At the age of 12, Tracy Slatyer felt sorry for a book. She read a newspaper article about how many people were buying A brief history of time by Stephen Hawking. “But then … nobody was reading it,” she says. “People were just leaving it on their coffee tables.”

Determined to right this wrong, Slayer picked up a copy and diligently read every page. The famous physicist’s popular text revealed to her “that mathematics was in a sense an expressive language for describing how things really work,” she says. “That, to me, was exciting.”

These days, Slatyer, a theoretical physicist at MIT, uses her math skills to dream up new ideas about dark matter. The mysterious substance makes up about 85 percent of the matter in the universe. However, it has repeatedly eluded scientists’ attempts to find it. Slatyer tries to understand where dark matter might be created, how it might interact with itself or with something else, and, most importantly, the consequences of those interactions.

Physicists know that dark matter exists because they can see its gravitational influence on galaxies, galaxy clusters, and the overall evolution of the universe. Beyond that, there is little data to work with. Slatyer has helped imagine the myriad ways that dark matter could leave subtle signatures on the fabric of reality that would show up in observations.

Among scientists doing such work, “I don’t think there’s been one that’s had more impact,” says Dan Hooper, a physicist at the University of Chicago. “She’s as big a deal as I can make her be.”

Discovery of Fermi bubbles

Born in the Solomon Islands, Slatyer grew up in Canberra, Australia. After her encounter with Hawking’s book, she knew she wanted to study physics. While in graduate school at Harvard University in the 2000s, she met physicist Douglas Finkbeiner, who was investigating mysterious signals at the center of the Milky Way.

A research satellite had noticed strange excesses of positrons, electron antiparticles and high-energy photons called gamma rays that could not be explained by conventional theories. Together, Slatyer and Finkbeiner began looking deeper into a type of self-destructing dark matter that might address the mystery. In their particular model, this dark matter would leave behind electrons and positrons, which would interact with starlight to create gamma rays.

In 2008, NASA launched the Fermi Gamma-ray Space Telescope, which provided unprecedented views of high-energy photons emanating from the galactic jet. If dark matter was truly self-annihilating, it would show up in Fermi’s observations. The following year, Slatyer and Finkbeiner used Fermi’s public data to find out.

“We analyzed the data and saw this big fuzzy glow north and south of the galactic center,” Slatyer recalls. “So we’re like, ‘Victory!’

But the more they and another Finkbeiner student, Meng Su, looked at the signals, the more they realized it wasn’t dark matter. Fermi’s images revealed a giant hourglass figure stretching 25,000 light-years above and below the plane of the Milky Way. Dark matter is thought to be present in a diffuse halo around our galaxy, but this structure had very sharp edges.

Supermassive black holes that feed on gas and dust at the centers of other galaxies have been known to eject material in hourglass shapes. Finally, Slatyer and her colleagues realized that this might be something similar. These Fermi bubbles, as they became known, have been the subject of numerous subsequent studies, leading to a long-running debate over the mechanisms driving bubble creation (SN: 11/9/10; SN: 4/20/23).

Slatyer hadn’t found dark matter, but, she says, “I try not to complain when nature gives me exciting new things, whether or not they were what I was looking for in the first place.”

Dark matter in the early universe

Much of her work since then has focused on various dark matter scenarios. For example, some of her research has looked at how the mysterious substance might have annihilated or decayed in the early universe, leaving behind fundamental particles that would cause small changes in the expected temperature of the overall cosmos. Such an effect can be seen in the cosmic microwave background, or CMB, a remnant light left over from when the universe was only 380,000 years old.

Satellites measuring this light have found that it shows the cosmos was almost exactly the same temperature no matter which direction they look, with deviations of just one part in 100,000. Slatyer and her colleagues calculated that, if dark matter annihilation had occurred, it could have generated an even subtler temperature signature, down to one part per million. Her team reported in 2023 how the presence of self-annihilating dark matter would distort the CMB—a signal for future instruments to look for.

In a study published in May 2024, she and colleagues looked at other possible effects of excess heat in the early universe from dark matter. In some scenarios, this higher temperature may have generated excess free electrons. Those free electrons could have acted as catalysts for chemical reactions that would have favored star formation, possibly leading to the creation of large numbers of stars very early.

Other teams have suggested that the excess heat would have pushed gas and dust around more easily, a move that may have reduced star formation. In that case, larger clumps of material may have collapsed into massive black holes, which could have become the seeds around which the first galaxies coalesced.

Such ideas may help explain what the James Webb Space Telescope has seen as it looks into cosmic history. The telescope appears to have found black holes and unexpectedly large galaxies in the early universe (SN: 3/4/24). Slatyer and her colleagues are suggesting that dark matter may be the culprit behind these surprisingly massive cosmic objects.

By taking her theories to their logical conclusions, Slatyer has made herself invaluable to the community of theoretical and observational physicists searching for dark matter. “She’s one of these people who is kind of ubiquitous,” Finkbeiner says. “She shows up at every meeting. She has her finger in every pie. She is on every panel to understand what the field needs to do for the next 10 years.”

Given how little researchers know about dark matter, Slatyer thinks it’s important to imagine a wide range of possible possibilities and then come up with experiments to test those options. “We try to … make sure we don’t miss anything glaringly obvious,” she says.

Imagine Victorian London, but its skies are filled with airplanes. Steam robots crowd the streets, mingling with people in hats and cloaks. This kind of retrofuturistic mash-up is the fantasy realm of steampunk, a genre of literature, film, and other creative media. Theoretical physicist Nicole Yunger Halpern sees her specialty, the field of quantum thermodynamics, as the real-life version of steampunk.

In steampunk, “there’s a strange juxtaposition of old environment and futuristic technology,” says Yunger Halpern. “That’s what we do in quantum thermodynamics.”

Thermodynamics, developed in the 1800s in the context of the Industrial Revolution, describes the physics concepts of heat, work, and energy (SN: 6/12/24). The field arose out of scientific efforts to understand steam engines. Unlike the clatter and clatter of industrial machines, quantum physics describes phenomena at the scale of atoms, electrons, and the like, and has fueled the development of modern technologies such as quantum computers (SN: 28/6/23).

In the past, some physicists didn’t think the idea of ​​quantum thermodynamics made sense. “They saw it as an oxymoron,” says Yunger Halpern.

Now, however, the two concepts collide in quantum engines and other miniature devices. Quantum thermodynamics researchers aim to develop the tools to describe heat, work, cooling, and efficiency in quantum systems and to determine the performance limits of quantum devices. Yunger Halpern, a National Institute of Standards and Technology physicist based at the Joint Center for Quantum Information and Computer Science in College Park, Md., is at the forefront of these efforts.

“She has a vision and follows it,” says quantum physicist Aram Harrow of MIT. “She’s also good at recruiting other people to her vision.”

One of Yunger Halpern’s major contributions has been exploring what the quantum concept behind Heisenberg’s uncertainty principle might mean for thermodynamics.

Imagine a hot cup of tea. Thermodynamics describes how energy moves from the tea to the surrounding air, or how evaporating water molecules escape. Both of these quantities—energy and water molecules—are conserved in this scenario, meaning they can move from one place to another, but the total amount is fixed. The problem of explaining how conserved quantities are exchanged occurs repeatedly in thermodynamics.

Now, what if the tea wasn’t a whole cup, but a packet of just a few atoms? Yunger Halpern wants to know how the exchange would change. In quantum physics, conserved quantities can be mutually exclusive. This means that they cannot be measured simultaneously. Heisenberg’s uncertainty principle, which states that the better you know the position of a quantum object, the worse you know its momentum and vice versa., give a famous example (SN: 1/12/22).

“For many decades, almost nobody thought about what happens when you have a system and environment that exchange quantities that are incompatible,” says Yunger Halpern. It turns out that incompatibility can have a real impact on how the system behaves, she and colleagues noted in a survey of the topic published in 2023 in Nature Reviews Physics. For example, incompatibility can reduce the amount of entropy, or disorder, that is produced in such exchanges. Because the total entropy of an isolated system tends to increase with time, some scientists think that entropy is closely related to an “arrow of time” that distinguishes the future from the past.SN: 7/10/15). In a sense, says Yunger Halpern, this means that incompatible quantities can hinder a system’s ability to experience that arrow of time.

Quantum thermodynamics has led to some neat laboratory demonstrations. For example, a single atom can be turned into a quantum engine that converts heat into work (SN: 14.4.16). Now, Yunger Halpern aims to put quantum thermodynamics to practical use through autonomous quantum machines.

Typical quantum devices, such as single-atom engines, atomic clocks, or the quantum parts that make up quantum computers, require constant prodding by experimenters to operate. Autonomous devices will operate automatically.

Yunger Halpern joined colleagues to bring this idea to reality. The result was an autonomous quantum refrigerator that can automatically cool a quantum particle, the team reported in May 2023 on arXiv.org.

And in a July 2023 arXiv article, she and colleagues laid out the criteria that must be met to create an autonomous quantum machine. For example, these machines must have structural integrity and sufficiently pure quantum states. In addition, their output must be worth the input required to execute them. This means that a quantum motor cannot take in more energy to control it than it puts out. Quantum physicist Marcus Huber worked with Yunger Halpern in developing these criteria. “I found it brilliant, but also mega intense and focused,” says Huber, from TU Wien in Vienna. “She will bombard you with relevant and good questions.”

It’s not just her science that’s in the spotlight—her writing is, too. Yunger Halpern’s book 2022, Quantum Steampunk: Yesterday’s Tomorrow’s Physicsattracted the attention of the public in the field. She is also a science blogger at the website Quantum Frontiers. Writing, Yunger Halpern says, allows him to explore new ideas without the constraints of scientific publishing (fantasy speculations and “out there” ideas aren’t likely to pass peer review). “Thinking really big and wild and so creatively that you feel like thinking on a certain day of the month is helpful for keeping creativity in physics.”

And just as her work juxtaposes old and new, Yunger Halpern often illustrates contrasts, says Shayan Majidy of the University of Waterloo in Canada and soon to join Harvard University, who recently completed his Ph.D. advised by Yunger Halpern. She holds her students to high standards, but is warm and caring as a counselor. Majidy says that when he got married, Yunger Halpern somehow figured out his favorite local ice cream brand — Kawartha Dairy — and sent him a gift card.

Her hobbies tend towards quiet and slow-paced activities: walks, museum visits. Yet she injects intense passion into her work. “She has very old-fashioned interests and tastes,” Majidy says, “but she’s this very young, energetic researcher of rising stars.”

An asteroid heading toward Earth can be deflected without ever touching a spacecraft.

The trick is to use X-rays to deflect the space rock, researchers report Sept. 23 Nature Physics. In laboratory experiments, scientists heated the surfaces of free-falling artificial asteroids with X-ray radiation, producing steam plumes that blew the objects away. Later computer simulations showed that X-rays emitted from a distant nuclear explosion could deflect several asteroids that are roughly as wide as the National Center in Washington, DC, is tall.

“There is only one method that has been proposed that has enough energy to deflect the most threatening asteroids, the largest asteroids, or in some cases even smaller asteroids where the warning time is short, maybe a year or less.” , says physicist Nathan. Moore of Sandia National Laboratories in Albuquerque. “The consensus in the planetary defense community is that X-rays from a nuclear device would be the only option in those scenarios.”

Such explosions would, in theory, occur at safe distances from Earth.

Two years ago, NASA deliberately rammed a spacecraft into the asteroid Dimorphos, changing the space rock’s orbit around a larger asteroid (SN: 26.9.22; SN: 10/11/22). It was a watershed moment for the planetary defense community. But such impacts only work if the asteroid is small and has enough time to change its trajectory, Moore says. So he and colleagues set out to test the defective X-ray noise.

The experiment began in a vacuum chamber that held a cranberry-sized model asteroid made of quartz — a mineral composed of the common asteroid component silica. Using the world’s most powerful X-ray generator, the team blasted the chamber in 6.6 nanoseconds. The pulse vaporized the lamellar supports that suspend the quartz, releasing the mineral in free fall. It also heated and vaporized the surface of the falling ore, generating a gas plume.

The expanding plume propelled the quartz like the discharge of a rocket, Moore says, pushing the mineral away from the X-ray source at approximately 250 kilometers per hour. Tests with fused silica gave similar results.

Assessing the viability of the planetary protection scheme requires incorporating experimental results into computer simulations. X-rays from a nuclear explosion several kilometers away can deflect an asteroid of similar composition that is up to 4 kilometers across, the team found.

The researchers hope to perform similar experiments with iron and other asteroid components. “Asteroids come in many flavors, made up of different types of minerals,” he says. “This is just a starting point.”

Above the cloud tops, storms blow with a complex and frenetic light show of high-energy radiation.

A view from a refurbished spy plane flying 20 kilometers up revealed storms glowing and flickering in gamma rays, high-energy light invisible to the eye. Ten flybys of the aircraft, NASA’s ER-2 aircraft, captured the flickering of gamma-ray bursts on a variety of time scales and intensities, suggesting that the emissions are more complex and common than previously thought. And the study revealed a whole new type of gamma-ray burst that the researchers called a quivering gamma-ray flash.

“I’m absolutely amazed,” says physicist David Smith, of the University of California, Santa Cruz, who was not involved in the research. It’s the most important new data in the field in more than a decade, he says.

Scientists knew of two main types of gamma-ray emissions from the storm. Short, intense bursts, called terrestrial gamma-ray flares, are so bright they can be seen from space and last only fractions of a millisecond (SN: 1/10/23). Then there are longer, fainter emissions called gamma-ray bursts. Scientists saw both during the flights.

The flashes, the scientists found, were unexpectedly continuous and widespread. They persisted for hours, covered thousands of square kilometers and were seen on nine out of 10 aircraft flights, physicist Nikolai Østgaard and colleagues report on Oct. 3. Nature.

“It’s surprising,” says physicist Ningyu Liu of the University of New Hampshire in Durham, who was not involved in the work.

Moreover, the gamma-ray flashes were not static, as previously thought, but were constantly simmering, repeatedly brightening and darkening on time scales of seconds. “Big storms are blowing. It’s like a boiling pot,” says Østgaard, from the University of Bergen in Norway.

Loaded with sensors to detect gamma rays, radio waves, visible light and more, the plane flew over storms in the Caribbean and Central America. Cruising at an altitude about twice that of commercial flights, the plane had a front-row seat for the fireworks. And because the plane was rigged to send data back to the ground in real time, the researchers could direct the plane’s pilot back to regions bouncing with gamma rays.

The flights also found ground-based gamma-ray flares, including ones too faint to be seen by satellites in space, the team reported Sept. 7 in Geophysical Research Letters. This suggests that previous satellite observations missed many ground-based gamma-ray flares, making them more common than previously thought.

Thunderstorms produce gamma rays when electrons are accelerated in strong electric fields that are created within clouds (SN: 15.3.19). These electrons produce more electrons, and so on. When the electrons in this avalanche collide with air molecules, gamma rays result. But even though this process is well understood, scientists don’t understand the details behind the different types of gamma-ray bursts, or how they are related.

The newly discovered gamma-ray flares may be a missing link between terrestrial gamma-ray flares and gamma-ray flares, as their brightness and duration fell between those of the other two classes. Like high-energy strobe lights, these bursts consisted of short pulses of gamma rays that repeated over tens to hundreds of milliseconds, the team reported in a second paper in Nature.

Additionally, many of the gamma-ray bursts were followed by a type of burst called a narrow bipolar event, which was then followed by lightning. This could mean that gamma-ray bursts help initiate lightning, a process that is not yet understood (SN: 10/21/11).

Gamma rays may also be involved in limiting how strong electric fields can get into thunderstorms, says co-author Steven Cummer, an electrical engineer at Duke University. This means that “this whole process of generating gamma rays that was interesting and unusual before now seems to be quite central to all atmospheric electricity.”

Cancer-destroying particle beams have been caught red-handed.

Particle beams can deliver a burst of destructive energy directly to tumors – assuming the beam is in the right place. Now, using a radioactive beam, scientists have determined the location of the beam while treating tumors in mice. It is the first successful treatment of tumors with a radioactive beam, the scientists report in a paper submitted Sept. 23 to arXiv.org.

The technique could eventually allow scientists to treat human patients with millimeter precision — especially important when a tumor is located near a sensitive organ such as the spinal cord or brain stem.

Different types of radiation can treat cancer. The most common is X-rays, high-energy light that can destroy the DNA in tumor cells. But X-rays deposit their energy along the beam path, resulting in possible collateral damage to other parts of the body. More precise tumor targeting is possible with particles such as protons or ions – electrically charged atoms – which throw most of their energy into a single spot.

Ionic treatment is currently performed in more than a dozen centers around the world. These treatments use stable, non-radioactive ions – usually carbon-12, a variety of carbon with six protons and six neutrons in its nucleus. Electrons are removed from the particles in the beam, giving them a positive charge.

The tumor is targeted based on calculations of how deep a beam will penetrate, along with previous images of the patient, for example, a CT scan (SN: 12/10/21). But bodies are not rigid, and organs can move between imaging and treatment. Ideally, the position of the beam would be confirmed in real time. This is exactly what the new technique allows.

“If you use a radioactive ion, you can simultaneously kill the tumor and see the beam,” says physicist Marco Durante of the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany.

Durante and colleagues used carbon-11 ions, which have one less neutron in their atomic nuclei than carbon-12 ions, making them radioactive. When carbon-11 decays, it emits a positron—a positively charged antimatter partner of an electron. Scientists can detect that the positron annihilates with an electron in the body through positron emission tomography, or PET (SN: 2/13/14). This identifies where the beam throws its particles.

In the study, scientists used carbon-11 ions to treat mice with tumors near the spine. The scientists were able to check the beam’s position during treatment and confirm that it was in place. Sure enough, the treatment shrank the tumors.

Scientists had already tried to use PET to measure the location of a stable ion beam. Stable ions do not emit positrons, but some of the stable atomic nuclei split as they pass through the material. Those fragments can make radioactive ions that emit positrons in their decay. But the technique is difficult since the number of such particles is small.

With radioactive ion beams, many more positrons are emitted. “This allows [you] to get a very clear and beautiful image of where the particle stops,” says radiation physicist Mitra Safavi-Naeini of the Australian Nuclear Science and Technology Organization in Sydney, who was not involved in the research.

The technique can also help scientists understand how radioactive material moves through the body after an ion treatment, says Safavi-Naeini. Radioactive particles are washed out of the bull’s eye of the beam by the blood flowing through the body. This propagates the positron signal over time. The amount of this washout can help scientists understand whether the blood vessels are being destroyed by the treatment, thereby cutting off the tumor’s energy supply. This could help scientists figure out how best to use the particle beam to make cancer disappear.