A military court jails leaders fighting for independence for the English-speaking part of Cameroon.
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Monday, August 19, 2019
Physicists design an experiment to pin down the origin of the elements
Nearly all of the oxygen in our universe is forged in the bellies of massive stars like our sun. As these stars contract and burn, they set off thermonuclear reactions within their cores, where nuclei of carbon and helium can collide and fuse in a rare though essential nuclear reaction that generates much of the oxygen in the universe.
The rate of this oxygen-generating reaction has been incredibly tricky to pin down. But if researchers can get a good enough estimate of what’s known as the “radiative capture reaction rate,” they can begin to work out the answers to fundamental questions, such as the ratio of carbon to oxygen in the universe. An accurate rate might also help them determine whether an exploding star will settle into the form of a black hole or a neutron star.
Now physicists at MIT’s Laboratory for Nuclear Science (LNS) have come up with an experimental design that could help to nail down the rate of this oxygen-generating reaction. The approach requires a type of particle accelerator that is still under construction, in several locations around the world. Once up and running, such “multimegawatt” linear accelerators may provide just the right conditions to run the oxgen-generating reaction in reverse, as if turning back the clock of star formation.
The researchers say such an “inverse reaction” should give them an estimate of the reaction rate that actually occurs in stars, with higher accuracy than has previously been achieved.
“The job description of a physicist is to understand the world, and right now, we don’t quite understand where the oxygen in the universe comes from, and, how oxygen and carbon are made,” says Richard Milner, professor of physics at MIT. “If we’re right, this measurement will help us answer some of these important questions in nuclear physics regarding the origin of the elements.”
Milner is a co-author of a paper appearing today in the journal Physical Review C, along with lead author and MIT-LNS postdoc Ivica Friščić and MIT Center for Theoretical Physics Senior Research Scientist T. William Donnelly.
A precipitous drop
The radiative capture reaction rate refers to the reaction between a carbon-12 nucleus and a helium nucleus, also known as an alpha particle, that takes place within a star. When these two nuclei collide, the carbon nucleus effectively “captures” the alpha particle, and in the process, is excited and radiates energy in the form of a photon. What’s left behind is an oxygen-16 nucleus, which ultimately decays to a stable form of oxygen that exists in our atmosphere.
But the chances of this reaction occurring naturally in a star are incredibly slim, due to the fact that both an alpha particle and a carbon-12 nucleus are highly positively charged. If they do come in close contact, they are naturally inclined to repel, in what’s known as a Coulomb’s force. To fuse to form oxygen, the pair would have to collide at sufficiently high energies to overcome Coulomb’s force — a rare occurrence. Such an exceedingly low reaction rate would be impossible to detect at the energy levels that exist within stars.
For the past five decades, scientists have attempted to simulate the radiative capture reaction rate, in small yet powerful particle accelerators. They do so by colliding beams of helium and carbon in hopes of fusing nuclei from both beams to produce oxygen. They have been able to measure such reactions and calculate the associated reaction rates. However, the energies at which such accelerators collide particles are far higher than what occurs in a star, so much so that the current estimates of the oxygen-generating reaction rate are difficult to extrapolate to what actually occurs within stars.
“This reaction is rather well-known at higher energies, but it drops off precipitously as you go down in energy, toward the interesting astrophysical region,” Friščić says.
Time, in reverse
In the new study, the team decided to resurrect a previous notion, to produce the inverse of the oxygen-generating reaction. The aim, essentially, is to start from oxygen gas and split its nucleus into its starting ingredients: an alpha particle and a carbon-12 nucleus. The team reasoned that the probability of the reaction happening in reverse should be greater, and therefore more easily measured, than the same reaction run forward. The inverse reaction should also be possible at energies nearer to the energy range within actual stars.
In order to split oxygen, they would need a high-intensity beam, with a super-high concentration of electrons. (The more electrons that bombard a cloud of oxygen atoms, the more chance there is that one electron among billions will have just the right energy and momentum to collide with and split an oxygen nucleus.)
The idea originated with fellow MIT Research Scientist Genya Tsentalovich, who led a proposed experiment at the MIT-Bates South Hall electron storage ring in 2000. Although the experiment was never carried out at the Bates accelerator, which ceased operation in 2005, Donnelly and Milner felt the idea merited to be studed in detail. With the initiation of construction of next-generation linear accelerators in Germany and at Cornell University, having the capability to produce electron beams of high enough intensity, or current, to potentially trigger the inverse reaction, and the arrival of Friščić at MIT in 2016, the study got underway.
“The possibility of these new, high-intensity electron machines, with tens of milliamps of current, reawakened our interest in this [inverse reaction] idea,” Milner says.
The team proposed an experiment to produce the inverse reaction by shooting a beam of electrons at a cold, ultradense cloud of oxygen. If an electron successfully collided with and split an oxygen atom, it should scatter away with a certain amount of energy, which physicists have previously predicted. The researchers would isolate the collisions involving electrons within this given energy range, and from these, they would isolate the alpha particles produced in the aftermath.
Alpha particles are produced when O-16 atoms split. The splitting of other oxygen isotopes can also result in alpha particles, but these would scatter away slightly faster — about 10 nanoseconds faster — than alpha particles produced from the splitting of O-16 atoms. So, the team reasoned they would isolate those alpha particles that were slightly slower, with a slightly shorter “time of flight.”
The researchers could then calculate the rate of the inverse reaction, given how often slower alpha particles — and by proxy, the splitting of O-16 atoms — occurred. They then developed a model to relate the inverse reaction to the direct, forward reaction of oxygen production that naturally occurs in stars.
“We’re essentially doing the time-reverse reaction,” Milner says. “If you measure that at the precision we’re talking about, you should be able to directly extract the reaction rate, by factors of up to 20 beyond what anybody has done in this region.”
Currently, a multimegawatt linear accerator, MESA, is under construction in Germany. Friščić and Milner are collaborating with physicists there to design the experiment, in hopes that, once up and running, they can put their experiment into action to truly pin down the rate at which stars churn oxygen out into the universe.
“If we’re right, and we make this measurement, it will allow us to answer how much carbon and oxygen is formed in stars, which is the largest uncertainty that we have in our understanding of how stars evolve,” Milner says.
This research was carried out at MIT’s Laboratory for Nuclear Science and was supported, in part, by the U.S. Department of Energy Office of Nuclear Physics.
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WATCH: The must-see message for Black America about Byron Allen’s billion dollar lawsuit
The Supreme Court showdown between Black media mogul Byron Allen and Comcast is arguably the biggest civil rights case in the country right now.
Allen, CEO of Entertainment Studios, is suing Comcast and Charter Communications for $20 billion dollars over racial discrimination, claiming that the companies wouldn’t carry his networks or even meet with him, because Entertainment Studios is a minority-owned company.
Allen alleges the networks were specifically in violation of the Civil Rights Act of 1866, which prohibits racial discrimination in contracting.
The Supreme Court has agreed to hear the case, and if Allen wins it would be a major victory for Black-owned companies and Black media.
So why aren’t more people talking about what’s at stake?
Lawyer and political commentator Antonio Moore, dropped a must-see message about the case that’s started to go viral, for the way it exposes how political interests are keeping people quiet and scared to challenge the powers that be.
“We need to have the discussion,” states Moore. “This is one of the biggest lawsuits in Black history and nobody is talking about it.”
“We’re here for ownership. We’re here to demand that we get access. We need the tools that allow us to actually make claims. There is no Black business, because they’re not doing business with us.”
Last week the Department of Justice filed an amicus brief saying Allen needed to prove race was the singular motivating factor in his claims against Comcast and Charter. The demand creates yet another legal hurdle for Allen to clear in order to hold the cable giants accountable.
“This is historic,” says Allen. “Donald Trump’s DOJ and Comcast are working together to destroy a civil rights statute in the U.S. Supreme Court.”
“You have one of the biggest media companies in the world, which has been beating up Donald Trump for racism, and now they are saying we will work together to maintain institutionalized racism in America, in this Amicus Brief they delivered last Thursday.”
Watch the full video below and hit us up in the comments with your thoughts. Why are people being silent? And what will it take to motivate people to action?
theGrio is owned by Entertainment Studios.
The post WATCH: The must-see message for Black America about Byron Allen’s billion dollar lawsuit appeared first on theGrio.
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Boosting computing power for the future of particle physics
A new machine learning technology tested by an international team of scientists including MIT Assistant Professor Philip Harris and postdoc Dylan Rankin, both of the Laboratory for Nuclear Science, can spot specific particle signatures among an ocean of Large Hadron Collider (LHC) data in the blink of an eye.
Sophisticated and swift, the new system provides a glimpse into the game-changing role machine learning will play in future discoveries in particle physics as data sets get bigger and more complex.
The LHC creates some 40 million collisions every second. With such vast amounts of data to sift through, it takes powerful computers to identify those collisions that may be of interests to scientists, whether, perhaps, a hint of dark matter or a Higgs particle.
Now, scientists at Fermilab, CERN, MIT, the University of Washington, and elsewhere have tested a machine-learning system that speeds processing by 30 to 175 times compared to existing methods.
Such methods currently process less than one image per second. In contrast, the new machine-learning system can review up to 600 images per second. During its training period, the system learned to pick out one specific type of postcollision particle pattern.
“The collision patterns we are identifying, top quarks, are one of the fundamental particles we probe at the Large Hadron Collider,” says Harris, who is a member of the MIT Department of Physics. “It’s very important we analyze as much data as possible. Every piece of data carries interesting information about how particles interact.”
Those data will be pouring in as never before after the current LHC upgrades are complete; by 2026, the 17-mile particle accelerator is expected to produce 20 times as much data as it does currently. To make matters even more pressing, future images will also be taken at higher resolutions than they are now. In all, scientists and engineers estimate the LHC will need more than 10 times the computing power it currently has.
“The challenge of future running,” says Harris, “becomes ever harder as our calculations become more accurate and we probe ever-more-precise effects.”
Researchers on the project trained their new system to identify images of top quarks, the most massive type of elementary particle, some 180 times heavier than a proton. “With the machine-learning architectures available to us, we are able to get high-grade scientific-quality results, comparable to the best top-quark identification algorithms in the world,” Harris explains. “Implementing core algorithms at high speed gives us the flexibility to enhance LHC computing in the critical moments where it is most needed.”
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