Shattered crocodile. Formally, Confractosuchus. It was found in Australia when a bulldozer clearing a boulder broke a stone into items. Uncovered parts of the broken-up rock made clear that fossils had been inside, however there was no instant signal that this discovery would later reveal an unprecedented snapshot of life from the Cretaceous Interval.
Paleontologist Matt White of the College of New England in Armidale, Australia, and colleagues organized to have the fossil-laden rock scanned with X-ray computed tomography. Like a medical CT scan, the strategy takes a number of pictures of an object that may be assembled right into a 3-D map of the inside. The crew hoped to make use of the scans as guides to isolate particular person bones within the fossil with out eradicating them, then manipulate the 3-D pictures to just about put the shattered croc again collectively.
However one part of the fossil puzzle gave them bother. Iron-rich stone surrounding the bones made it troublesome to get good X-ray pictures. So the researchers determined to strive one other method.
They despatched the thriller chunk to chemist Joseph Bevitt of the Australian Centre for Neutron Scattering in Sydney, who makes a speciality of utilizing subatomic neutron particles to picture historic objects. Together with the anticipated croc bones, Bevitt found one which appeared like a dinosaur leg bone. It was within the portion of rock the place the crocodile’s abdomen cavity would have been.
“After I noticed the neutron consequence and the little dino femur, I used to be shaking with shock,” Bevitt says, “each in awe and doubt with what we had seen.”
Years of study plus extra X-ray and neutron scanning ultimately confirmed that the stays of a beforehand unknown species of dinosaur, bitten into chunks and scored with tooth marks, had been within the croc’s stomach. The discovering earned the shattered crocodile the second half of its title: sauroktonos, for lizard killer. White, Bevitt and colleagues printed their discovery of each the newly recognized species of crocodile and the never-before-seen dinosaur inside final yr in Gondwana Analysis (SN: 3/26/22, p. 5).
It’s a shocking discovery: Confractosuchus sauroktonos, the shattered crocodile lizard killer, and the stays of its final meal, its dinosaur sufferer, frozen in stone 100 million years in the past. It’s a vignette that will by no means have come to gentle if not for neutron tomography. Though neutrons have been used for imaging in industrial and army purposes since shortly after the neutron was found in 1932, it’s solely in the previous couple of a long time that these subatomic particles have begun to supply scientists with unprecedented views inside fossils and antiquities.
Look, don’t contact
There was a time when learning fossils and artifacts typically meant damaging or destroying them. Mummified stays had been dissected. Sealed containers had been cracked open. Fossils had been pried unfastened from rock. In some circumstances, fossil-containing samples had been floor down, layer by layer, to create pictures of sequential parts in slices that exposed the fossilized buildings inside.
Happily, X-rays supply nondestructive insights. As a high-energy type of electromagnetic radiation, or gentle, X-rays work together with the electrical and magnetic fields related to electrically charged particles. In a health care provider’s workplace, when a technician shines a beam of X-rays at a damaged leg, the sunshine will get scattered or absorbed by the fields of the electrons round atoms within the leg. The denser a fabric is, the extra electrons are packed in it, and the much less successfully X-rays can cross via. That’s why higher-density parts of the physique — like bones — stand out in X-ray pictures greater than lower-density parts. Pores and skin, muscle and different comfortable tissues are basically invisible as a result of X-rays cross straight via.
X-rays have supplied views into the hidden interiors of artifacts for the reason that radiation was found in 1895. However after computationally intensive X-ray CT was developed within the Nineteen Seventies, it turned the usual method to learning objects in paleontology and archaeology (SN: 12/18/21 & 1/1/22, p. 44). X-ray CT scanning is now the modern-day various to the grinding that nineteenth century scientists typically relied on. Current examples embrace scans of mummified animals from historic Egypt (SN: 9/12/20, p. 17); newly uncovered inscriptions on the 2,000-year-old Antikythera mechanism, an historic Greek astronomical calculator used to foretell eclipses and different celestial occasions (SN: 12/2/06, p. 357); and a examine of the mind cavity in a 20-million-year-old monkey cranium (SN: 9/14/19, p. 11). Many giant museums and analysis establishments have their very own X-ray CT scanners available which might be basically the identical techniques that docs use.
For all that X-ray imaging has revealed concerning the previous, although, it nonetheless has some drawbacks. X-rays can’t penetrate a very dense materials, like lead or thick layers of different metals, to see an object hidden inside. On the flip aspect, an object manufactured from low-density materials, similar to comfortable tissue, can be invisible to X-rays.
Neutrons can fill within the image.
The distinction is within the scattering
Neutrons, as their title implies, are impartial. These subatomic particles don’t have any electrical cost, so neutron beams don’t discover the electrons in orbit round atoms. As an alternative, neutrons cross proper by electrons and hit nuclei filled with protons and neutrons on the facilities of atoms. Incoming neutrons can bounce off an atom’s nucleus or be absorbed into the atom. The interactions are extra sophisticated than with X-rays and rely on how briskly the neutrons are transferring and on advanced quantum mechanical interactions.
Neutrons appropriate for tomography are produced with comparatively large particle accelerators or as by-products from nuclear reactors. The neutrons are comparatively sluggish transferring, with energies one-hundred-millionth these of X-rays in CT scanners. These sluggish neutrons work together strongly with some low-density supplies that X-rays cross via blithely, together with lithium, boron and hydrogen.
“Water to neutrons is like lead for X-rays,” due to the hydrogen atoms, Bevitt says. An excessive amount of hydrogen-rich materials can conceal particulars from neutron beams. However in the identical approach {that a} steel hip joint stands out in a medical X-ray, hydrogen may also make some options seen in neutron pictures. Lead, iron and copper, alternatively, are basically clear to low-energy neutrons.
Physicist Jacob LaManna of the Nationwide Institute of Requirements and Expertise in Gaithersburg, Md., likes to display the comparative capabilities of neutron and X-ray imaging with a CT “nonetheless life” of Asiatic lilies tucked inside a hole cask with thick lead partitions. “The neutrons can go proper via the lead, after which you may see mainly all of the water [in the] vascular construction of the flowers,” LaManna says. An X-ray scan would present nothing however the opaque outer floor of the cask.
The flexibility to glide via dense supplies that block X-rays has made neutron imaging an vital know-how for industrial testing of cars and planes. The particles can reveal the stream of hydrogen-rich oil inside engine blocks or expose flaws in steel castings. Because the Nineteen Seventies, U.S. nationwide laboratories have relied on neutron imaging to develop and preserve the nation’s nuclear weapons stockpiles; the neutrons are highly effective quality-control instruments for mapping out the insides of dense bomb components and for learning hydrogen-rich fusion explosives inside warhead elements.
At NIST, LaManna leads the Neutron and X-ray Tomography, or NeXT, facility, which may concurrently run X-ray and neutron imaging. The twin views present distinct but complementary details about issues that comprise combos of supplies — like hydrogen gasoline cells, constructing supplies and soil samples — that will be troublesome to check with just one or the opposite imaging method.
During the last couple a long time, as phrase has unfold concerning the capabilities, a rising variety of paleontologists, archaeologists and anthropologists have added neutron imaging to their analytical toolboxes. Regardless of neutron imaging being round for some time, “we’re actually the brand new youngsters on the block,” Bevitt says.
Along with revealing a number of dinosaur bones within the stomach of a shattered crocodile, together with the femur that originally caught Bevitt’s eye, neutron computed tomography has allowed researchers to check the material swaddling cat mummies with out unwrapping them, discover indicators of lately utilized glues holding collectively fraudulently assembled artifacts, and uncover probably the most historic vertebrate coronary heart ever discovered, in a 380-million-year-old fish.
Rewards and dangers
Paleontologist James Clark locations a pair of fossilized crocodile skulls on the desk in his basement lab at George Washington College in Washington, D.C. The 165-million-year-old fossils are dwarfed by a close-by trendy alligator cranium. Whereas the alligator cranium is about so long as my forearm, the fossilized croc skulls are solely barely larger than my thumb tip.
The delicate skulls, which Clark collected in Mexico 4 a long time in the past, are embedded in hardened blobs of sediment with only a few bones and tooth peeking via. At first look, the specimens resemble wads of chewed gum, however manufactured from gritty, iron-rich mudstone. “If you happen to attempt to X-ray that, you mainly find yourself with … these brilliant sparkles from all of the iron,” Clark says. The result’s blurring and streaking that conceal the skeletal buildings.
Clark may have employed preparers to wash away the sediment surrounding the fragile bones. But it surely’s a sluggish and costly course of that may find yourself damaging the specimen, he says.
It wasn’t till 2019 that he lastly acquired a great take a look at the hidden bones. After a seminar the place he met Bevitt, Clark realized that neutron scanning could possibly be the reply. The occasion led to an introduction to LaManna and the NIST facility 25 kilometers up the street in Maryland.
As a result of iron is basically clear to neutrons, LaManna says, “it’s a lot simpler to mainly isolate simply the fossil portion of the thing.” Photos from the NIST neutron CT scans revealed the intricate particulars of the tiny bones. “You may then begin enjoying digital jigsaw puzzles with the bone fragments to attempt to reconstruct the actual creature.”
Whereas the fabric round a fossil or object might current an issue for X-rays, generally it’s the thing itself that’s the problem. Tissues, fibers, wooden and different low-density supplies could be troublesome to resolve with X-rays, and metals inside an object can block different options from view. Each challenges plague researchers learning antiquities like the three,000-year-old dagger-axes that I noticed on show within the Smithsonian’s Freer Gallery of Artwork in Washington, D.C.
These ceremonial weapons from China’s Shang dynasty are suspended in a vertical glass case, the place I may get my nostril only a few centimeters from the jade blades and turquoise-encrusted bronze handles. I discovered it was greatest to lean up shut in order that I may respect the intricate blue-green patterns of gem stones sunk into the steel.
Smithsonian artwork conservator Ariel O’Connor would like to understand how the dagger-axes had been put collectively. X-ray CT doesn’t work on the mixture of stone, steel, fibers and different supplies that could be inside. Neutron imaging may assist, however it comes with a danger. Neutron beams make issues radioactive. It’s not all the time clear prematurely how radioactive a pattern will turn out to be, however supplies typically exceed the extent of radioactivity that’s secure for people to deal with, and even view in a museum, for days to weeks after publicity to neutron beams.
“We may truly do calculations and decide what’s going to be the problematic aspect and the way lengthy wouldn’t it be radioactive and the way a lot,” LaManna says. “[But,] within the case of the jade, the place it’s materials mainly simply utterly dug up from the bottom, it may possibly have all types of stuff in it that you just may not essentially count on.” That makes residual radioactivity troublesome to foretell.
So, O’Connor determined to do a take a look at. She and colleagues made a crude reproduction of an historic dagger-ax. They used jade from Wyoming in lieu of the traditional Chinese language jade, stacks of brass from a repurposed door kickplate to simulate the bronze deal with, and a few silk thread much like the sort that holds some Shang dynasty dagger-axes collectively. Then LaManna scanned the dagger with X-rays and neutrons at NIST.
As anticipated, the brass was totally opaque to the X-rays, hiding options of the reproduction’s development. However the neutron beam revealed key particulars, together with a view of the jade inserted contained in the brass deal with and even particular person silk threads.
As for residual radioactivity, the reproduction confirmed none of any significance 9 days later. Usually, Bevitt says, residual radiation dies down rapidly. One fossil he studied remained radioactive for 3 months, as a result of presence of radium, however most samples are secure to ship again to labs and museums inside just a few weeks or much less.
Nonetheless, with that uncertainty and questions on how chemically related the reproduction is to the actual dagger-axes, O’Connor will not be but able to danger scanning the artifacts.
“As a conservator, I’m entrusted with the preservation and security of those exceptional 3,000-year-old objects to make sure they continue to be for future generations. If an analytical method similar to neutron imaging would possibly reply our analysis questions however would alter the objects and stop them from being accessible” attributable to induced radioactivity, O’Connor says, “we are going to search for different choices.”
Opening a brand new window to the previous
Regardless of the rising reputation of neutron tomography for learning fossils and antiquities, X-ray CT stays the go-to imaging selection for many researchers. Within the Nineteen Nineties, just a few dozen scholarly papers on utilizing neutrons to check the previous had been printed yearly; lately, it’s been a whole bunch per yr. Publications associated to imaging fossils and artifacts with X-ray CT, although, quantity within the hundreds yearly.
More often than not, X-rays suffice, and the benefits are clear. They provide excessive decision to uncover small particulars with no lingering radioactivity. X-ray CT machines are additionally broadly accessible as a result of they’ve been utilized in medical settings for over 50 years, they usually’re sufficiently small to slot in most labs and museum analysis areas.
In the mean time, there are just a few dozen neutron tomography amenities on the planet. The particle accelerators and nuclear reactors that produce appropriate neutrons are giant, costly and closely regulated. Solely a handful of the amenities worldwide can be found to investigate fossils and antiquities, based on Burkhard Schillinger, a physicist on the Technical College Munich who runs the neutron imaging beamline there. He ticks off just a few amenities in the US, a half dozen in Europe and one in Australia.
Nonetheless, LaManna says the shortage of entry doesn’t appear to be the bottleneck in widespread adoption of the method. Together with the issues over lingering radioactivity, the novelty of the know-how and normal lack of knowledge might stand in the way in which.
“I attempt to recruit as broad a spread of customers as I can” to submit fossils and antiquities for imaging at NIST, LaManna says. “It’s not like they’re getting pushed out of the way in which” to create space for extra standard neutron research. “It’s simply extra of getting the right individuals to then write proposals, come to us [and] work with us to get beam time.”
Within the final decade, Australia-based Bevitt has unfold the phrase on neutron tomography via lectures and outreach around the globe. Many of the consultants contacted for this story hint their preliminary curiosity in neutron imaging to Bevitt’s affect. Many researchers in his house nation have already embraced the know-how.
“Principally, in Australia, when a brand new dinosaur is found,” Bevitt says, “the very first thing that occurs is it involves our lab.”
