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Understanding Small-Angle X-Ray Scattering



Small angle X-ray scattering, or SAXS, is an experimental method where the intensity of the scattered X-rays is measured as a function of the scattering angle. The information obtained in a SAXS experiment can be used to recover information about the bulk microstructure within a sample and is commonly used to study condensed matter systems that are only partially ordered.

Image Credit: Juergen Faelchle/

One of the advantages of SAXS for the analysis of nanomaterials is that it can be used to analyze samples on a variety of length scales. In a typical SAXS experiment, the length scales measured can vary from the nanoscale to the mesoscale.


While for nanomaterial studies, some of the unique phenomena exhibited at the smallest length scales, such as enhanced thermal properties, are of primary interest, for many materials applications, the behavior across all length scales can be crucial for ensuring proper device performance.

SAXS Technique

In an X-ray scattering experiment, a sample is illuminated with an incident X-ray beam. Due to the interaction between the X-ray photons and atoms in the sample, some of the incident radiation will be scattered at different angles. Elastic scattering occurs when no energy exchange occurs between the incident X-ray photon and sample, so the scattered radiation is equal in energy to the incident radiation.

Some X-ray photons will be deflected or scattered at different angles to the incident X-ray radiation. By measuring the scattering angle and intensity of the X-ray radiation, information on the structural features of the sample can be recovered, such as particle sizes and distributions or the degree of disorder.

SAXS refers specifically to measuring the elastically scattered X-rays at small (~0 – 10°) angles. There is a related technique, wide-angle X-ray scattering (WAXS), that also measures elastically scattered radiation but at much wider scattering angles (> 10°).

Often, SAXS and WAXS experiments are performed together as changing the relative distance between the detector and the sample is sufficient to switch between a collection of wide or small-angle scattered radiation.

Many SAXS experiments are performed at advanced light source facilities such as synchrotrons as the weak nature of the scattering signal means that a high incident photon intensity is beneficial for improved signal-to-noise and reduced acquisition times in the measurement. However, there are a number of laboratory-based SAXS instruments as well, though acquisition times are typically very long.

Applications of SAXS

SAXS has several applications, including in the analysis of biological materials and nanomaterials. For nanoparticle analysis, SAXS is now often used as an in situ technique to monitor nanoparticle growth and formation. Understanding growth processes is an important part of developing synthesis strategies to grow nanoparticles in a controlled fashion and the structure of the nanoparticles determines their overall properties.

Nanoparticle sizing is a common application of SAXS due to the excellent spatial resolution of the technique that is achievable even in a laboratory environment. SAXS can also be used to extract concentration information from such samples.

SAXS is well-suited to in situ measurements of processes such as nanoparticle growth or materials synthesis as it requires minimal sample preparation and is compatible with a variety of sample types, including disordered solids and colloidal dispersions. In situ measurements require relatively short acquisition times to capture multiple images of the process as it occurs to see its evolution.

Biological applications account for a large number of SAXS studies, as SAXS can be used to determine the protein, nucleic acid and biopolymer structures and sizes.

As many biological systems undergo continual structural changes even at room temperature, one of the advantages of SAXS for biological imaging is that time-resolved variants of the technique can be used to capture processes such as protein folding in action. This makes SAXS an invaluable tool for not just understanding single structures in structural biology but the full landscape of how different conformers and structures are interconnected.


As SAXS experiments use 2D detectors, a large amount of data is generated with each image recorded. Finding ways to reduce data sizes, speed up data processing and automate large parts of the analysis procedure has been very important in turning SAXS into a routine analytical tool. It is necessary to use some fitting and reconstruction procedures to convert from the recorded 2D image data to structural information such as particle sizes or distances.

Many of the algorithms for such procedures are available as relatively easy-to-use software packages for simple cases.

Brighter synchrotron sources, more efficient and sensitive detectors and greater degrees of automation of the experimental acquisition and data analysis will all help improve the throughput of SAXS measurements. With advances in nanoscale fabrication methods such as focused ion beams, there will continue to be a great demand for techniques such as SAXS that can characterize materials on the nanoscale reliably.

Time-resolved studies with SAXS are also likely to play an important role with the increasing availability of X-ray free-electron laser sources. Achieving very short (< 100 fs) time resolutions with high photon flux at synchrotrons can be very challenging.

Free-electron lasers, with their high peak brightnesses, also offer the ability to perform SAXS measurements on materials under extreme conditions to understand phenomena such as plasma formation and propagation in materials.

References and Further Reading

Giannini, C., Ladisa, M., Altamura, D., Siliqi, D., Sibillano, T., & Caro, L. De. (2016) X-ray Diffraction : A Powerful Technique for the Multiple-Length-Scale Structural Analysis of Nanomaterials. Crystals, 6, p. 87.

Shi, S., & Russell, T. P. (2018). Nanoparticle Assembly at Liquid – Liquid Interfaces : From the Nanoscale to Mesoscale. Advanced Materials, 30, p. 1800714.

Li, T., Senesi, A. J., & Lee, B. (2016). Small Angle X‑ray Scattering for Nanoparticle Research. Chemical Reviews, 116, pp. 11128–11180.

Garcia, P. R. A. F., Prymak, O., Grasmik, V., Pappert, K., Wlysses, W., Otubo, L., Epple, M., & Oliveira, C. L. P. (2020). SAXS investigation of the formation of silver nanoparticles and bimetallic silver – gold nanoparticles in controlled wet-chemical reduction synthesis. Nanoscale Advances, 2, pp. 225–238.

Pauw, B. R., Ka, C., & Thunemann, A. F. (2017). Nanoparticle size distribution quantification : results of a small-angle X-ray scattering inter-laboratory comparison research papers. Journal of Applied Crystallography, 50, pp. 1280–1288.

Brosey, C. A., & Tainer, J. A. (2019). Evolving SAXS versatility : solution X-ray scattering for macromolecular architecture , functional landscapes , and integrative structural biology. Current Opinion in Structural Biology, 58, pp. 197–213.

Kluge, T., Rödel, M., Metzkes-ng, J., Pelka, A., Garcia, A. L., Prencipe, I., Rehwald, M., Nakatsutsumi, M., Mcbride, E. E., Schönherr, T., Garten, M., Hartley, N. J., Zacharias, M., Grenzer, J., Erbe, A., Georgiev, Y. M., Galtier, E., Nam, I., Lee, H. J., … Landstraße, B. (2018). Observation of Ultrafast Solid-Density Plasma Dynamics Using Femtosecond X-Ray Pulses from a Free-Electron Laser. Physical Review X, 8(3), p. 31068.

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Asteroid 2023 BU just passed a few thousand kilometres from Earth. Here’s why that’s exciting – The Tribune India



Perth (Australia), January 28

There are hundreds of millions of asteroids in our Solar System, which means new asteroids are discovered quite frequently. It also means close encounters between asteroids and Earth are fairly common.

Some of these close encounters end up with the asteroid impacting Earth, occasionally with severe consequences.


A recently discovered asteroid, named 2023 BU, has made the news because today it passed very close to Earth.

Discovered on January 21 by amateur astronomer Gennadiy Borisov in Crimea, 2023 BU passed only about 3,600 km from the surface of Earth (near the southern tip of South America) six days later on January 27.

That distance is just slightly farther than the distance between Perth and Sydney and is only about 1 per cent the distance between Earth and our Moon.

The asteroid also passed through the region of space that contains a significant proportion of the human-made satellites orbiting Earth.

All this makes 2023 BU the fourth-closest known asteroid encounter with Earth, ignoring those that have impacted the planet or our atmosphere.

How does 2023 BU rate as an asteroid and a threat?

2023 BU is unremarkable, other than that it passed so close to Earth. The diameter of the asteroid is estimated to be just 4–8 metres, which is on the small end of the range of asteroid sizes.

There are likely hundreds of millions of such objects in our Solar System, and it is possible 2023 BU has come close to Earth many times before over the millennia. Until now, we have been oblivious to the fact.

In context, on average a 4-metre-diameter asteroid will impact Earth every year and an 8-metre-diameter asteroid every five years or so                  

Asteroids of this size pose little risk to life on Earth when they hit because they largely break up in the atmosphere. They produce spectacular fireballs, and some of the asteroids may make it to the ground as meteorites.

Now that 2023 BU has been discovered, its orbit around the Sun can be estimated and future visits to Earth predicted. It is estimated there is a 1 in 10,000 chance  2023 BU will impact Earth sometime between 2077 and 2123.

So, we have little to fear from 2023 BU or any of the many millions of similar objects in the Solar System.

Asteroids need to be greater than 25 metres in diameter to pose any significant risk to life in a collision with Earth; to challenge the existence of civilisation, they’d need to be at least a kilometre in diameter.

It is estimated there are fewer than 1,000 such asteroids in the Solar System and could impact Earth every 5,00,000 years. We know about more than 95 per cent of these objects.

Will there be more close asteroid passes?

2023 BU was the fourth closest pass by an asteroid ever recorded. The three closer passes were by very small asteroids discovered in 2020 and 2021 (2021 UA, 2020 QG and 2020 VT).

Asteroid 2023 BU and countless other asteroids have passed very close to Earth during the nearly five billion years of the Solar System’s existence, and this situation will continue into the future.

What has changed in recent years is our ability to detect asteroids of this size, such that any threats can be characterised. That an object roughly five metres in size can be detected many thousands of kilometres away by a very dedicated amateur astronomer shows that the technology for making significant astronomical discoveries is within reach of the general public. This is very exciting.

Amateurs and professionals can together continue to discover and categorise objects, so threat analyses can be done. Another very exciting recent development came last year, by the Double Asteroid Redirection Test (DART) mission, which successfully collided a spacecraft into an asteroid and changed its direction.

DART makes plausible the concept of redirecting an asteroid away from a collision course with Earth if a threat analysis identifies a serious risk with enough warning. (The Conversation)

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An SUV-sized asteroid zoom by Earth in close shave flyby in this time-lapse video



Asteroid 2023 BU zipped past Earth Thursday night (Jan. 26) to the delight of amateur astronomers worldwide. For skywatchers without access to a telescope or those who had their view hampered by bad weather, luckily the Italy-based Virtual Telescope Project was there to observe the event and livestream the whole thing for free.

The Virtual Telescope is a robotic telescope operated by Italian amateur astronomer Gianluca Masi near Rome, Italy. As 2023 BU hurtled toward Earth, the telescope was able to track the rock through a gap in the clouds when it was about 13,670 miles (22,000 kilometers) from the closest point on Earth’s surface (about the altitude of the GPS navigation satellite constellation) and 22,990 miles (37,000 km) from the Virtual Telescope.

Masi, who shared an hour-long webcast of the observations on the Virtual Telescope website, wasn’t able to capture the closest approach as clouds rolled in, however. Nonetheless, the Virtual Telescope Project was able to get a good look at the car-sized rock, seen in time-lapse above.



The Italy-based Virtual Telescope captured asteroid 2023 BU shortly before its closest approach to Earth. (Image credit: The Virtual Telescope Project)

The rock, discovered less than a week ago on Saturday (Jan. 21), passed above the southern tip of South America at 7:27 p.m. EST on Thursday Jan. 26 (0027 GMT on Jan. 27), at a distance of only 2,240 miles (3,600 km) at its closest point to Earth’s surface.

This close approach makes 2023 BU the fourth nearest asteroid ever observed from Earth, with the exception of five space rocks that were detected before diving into Earth’s atmosphere.

Only 11.5 to 28 feet wide (3.5 to 8.5 meters), 2023 BU posed no danger to the planet. If the trajectories of the two bodies had intersected, the asteroid would mostly have burned up in the atmosphere with only small fragments possibly falling to the ground as meteorites.

In the videos and images shared by Masi, the asteroid is seen as a small bright dot in the center of the frame, while the longer, brighter lines are the surrounding stars. In reality, of course, it was the asteroid that was moving with respect to Earth, traveling at a speed of 21,000 mph (33,800 km/h) with respect to Earth. As Masi’s computerized telescope tracked its positionthe rock appeared stationary in the images while rendering the stars as these moving streaks.

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The gravitational kick that 2023 BU received during its encounter with Earth will alter the shape of its orbit around the sun. Previously, the space rock followed a rather circular orbit, completing one lap around the sun in 359 days. From now on, BU 2023 will travel through the inner solar system on a more elliptical path, venturing half way toward Mars at the farthest point of its orbit. This alteration will add 66 days to BU 2023’s orbital period.

The asteroid was discovered by famed Crimea-based astronomer and astrophotographer Gennadiy Borisov, the same man who in 2018 found the first interstellar comet, which now bears his name, Borisov.


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Green comet zooming our way, last visited 50,000 years ago



This photo provided by Dan Bartlett shows comet C/2022 E3 (ZTF) on Dec. 19, 2022. It last visited during Neanderthal times, according to NASA. It is expected to come within 26 million miles (42 million kilometers) of Earth on Feb. 1, 2023, before speeding away again, unlikely to return for millions of years. Credit: Dan Bartlett via AP

A comet is streaking back our way after 50,000 years.

The dirty snowball last visited during Neanderthal times, according to NASA. It will come within 26 million miles (42 million kilometers) of Earth Wednesday before speeding away again, unlikely to return for millions of years.

So do look up, contrary to the title of the killer- movie “Don’t Look Up.”

Discovered less than a year ago, this harmless green comet already is visible in the northern night sky with binoculars and small telescopes, and possibly the naked eye in the darkest corners of the Northern Hemisphere. It’s expected to brighten as it draws closer and rises higher over the horizon through the end of January, best seen in the predawn hours. By Feb. 10, it will be near Mars, a good landmark.


Skygazers in the Southern Hemisphere will have to wait until next month for a glimpse.

While plenty of comets have graced the sky over the past year, “this one seems probably a little bit bigger and therefore a little bit brighter and it’s coming a little bit closer to the Earth’s orbit,” said NASA’s comet and asteroid-tracking guru, Paul Chodas.

Green from all the carbon in the gas cloud, or coma, surrounding the nucleus, this long-period comet was discovered last March by astronomers using the Zwicky Transient Facility, a wide field camera at Caltech’s Palomar Observatory. That explains its official, cumbersome name: comet C/2022 E3 (ZTF).

On Wednesday, it will hurtle between the orbits of Earth and Mars at a relative speed of 128,500 mph (207,000 kilometers). Its nucleus is thought to be about a mile (1.6 kilometers) across, with its tails extending millions of miles (kilometers).

The comet isn’t expected to be nearly as bright as Neowise in 2020, or Hale-Bopp and Hyakutake in the mid to late 1990s.

Green comet zooming our way, last visited 50,000 years ago
This photo provided by Dan Bartlett shows comet C/2022 E3 (ZTF) on Dec. 19, 2022. It last visited during Neanderthal times, according to NASA. It is expected to come within 26 million miles (42 million kilometers) of Earth on Feb. 1, 2023, before speeding away again, unlikely to return for millions of years. Credit: Dan Bartlett via AP

But “it will be bright by virtue of its close Earth passage … which allows scientists to do more experiments and the public to be able to see a beautiful comet,” University of Hawaii astronomer Karen Meech said in an email.

Scientists are confident in their orbital calculations putting the comet’s last swing through the ‘s planetary neighborhood at 50,000 years ago. But they don’t know how close it came to Earth or whether it was even visible to the Neanderthals, said Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California.

When it returns, though, is tougher to judge.

Every time the comet skirts the sun and planets, their gravitational tugs alter the iceball’s path ever so slightly, leading to major course changes over time. Another wild card: jets of dust and gas streaming off the comet as it heats up near the sun.

“We don’t really know exactly how much they are pushing this comet around,” Chodas said.

The comet—a time capsule from the emerging solar system 4.5 billion years ago—came from what’s known as the Oort Cloud well beyond Pluto. This deep-freeze haven for comets is believed to stretch more than one-quarter of the way to the next star.

While comet ZTF originated in our solar system, we can’t be sure it will stay there, Chodas said. If it gets booted out of the solar system, it will never return, he added.

Don’t fret if you miss it.

“In the comet business, you just wait for the next one because there are dozens of these,” Chodas said. “And the next one might be bigger, might be brighter, might be closer.”

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