Russia has an idea that could change the trip to Mars. Last week, their national nuclear corporation Rosatom announced it is building a nuclear engine that will reach Mars in a month and a half—with fuel to burn for the trip home. Russia might not achieve its goal of launching a prototype by 2025. But that has more to do with the country’s financial situation, which is really not great, than the technical challenges of a nuclear engine. Actually, Soviet scientists solved many of those challenges by 1967, when they started launching fission-powered satellites. Americans had their own program, called SNAP-10A, which launched in in 1965. Ah, the Cold War.
Both countries prematurely quashed their nuclear thermal propulsion programs (Though the Soviets’ lasted into the 1980s). “Prematurely” because those fission systems were made for relatively lightweight orbital satellites—not high-thrust, interplanetary vessels fattened with life support for human riders. Nonetheless, “A nuclear contraption should not be too far off, not too complicated,” says Nikolai Sokov, senior fellow at the James Martin Center for Nonproliferation Studies in Monterey, CA. “The really expensive thing will be designing a ship around these things.”
Nuclear thermal is but one flavor of nuclear propulsion. Rosatom did not respond to questions about their system’s specs, but its announcement hints at some sort of thermal fission. Which is to say, the engine would generate heat by splitting atoms and use that heat to burn hydrogen or some other chemical. Burning stuff goes one direction, spaceship goes the other.
The principle isn’t too far from chemical propulsion. The fastest chemical rockets produce thrust by igniting one type of chemical (the oxidizer) to burn another (the propellant), creating thrust. Chemical or otherwise, rocket scientists rate propulsion methods based on a metric called Specific Impulse, “Which means, if I have a pound of fuel, for how many seconds will that pound of fuel create a pound of thrust,” says Robert Kennedy, a systems engineer for Tetra Tech in Oak Ridge, TN, and former congressional fellow for the US House of Representatives’s space subcommittee. For instance, one pound of the chemical mixture powering the Space Launch System—NASA’s in utero rocket for the agency’s planned mission to Mars—produces about 269 seconds of thrust in a vacuum.
But the outcomes of those two methods are radically different, because chemical rocketry has a catch-22. The faster or farther you want to go, the more fuel you need to pack. The more fuel you pack, the heavier your rocket. And the heavier your rocket, the more fuel you need to bring…
Eventually, the equation balancing thrust to weight plateaus, which is why a year and a half is around the lower time limit for sending a chemically propelled, crewed mission to Mars. (Until Elon Musk’s spiritual descendants build asteroid-mined interplanetary fuel stations.) And that’s not even considering the incredible cost of launching fuel—about $3,000 a pound. Expensive, but the politics surrounding nuclear make it a harder sell in America, so NASA is stuck with the Space Launch System (and its thirsty fuel tanks) for now.
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Saturday, March 5, 2016
Friday, March 4, 2016
Atomic Bombs actually did something good
From 1945 to 1963, the United States and the Soviet Union detonated over 400 nuclear bombs aboveground in a very bad, no good, uh, weapons-measuring contest that the world never wants to happen again. Atolls were destroyed, steppes contaminated, and fallout spread around the world. But what if some good came out of those nuclear detonations?
No, seriously.
When all those nukes were detonated, they spit out neutrons that set off a chain of events to create carbon-14, an exceedingly rare isotope of carbon. The amount of carbon-14 in the atmosphere spiked. That carbon-14 reacted with oxygen to make carbon dioxide. Plants breathed it in, animals ate the plants, and humans ate the animals and plants. “Everyone alive has been labeled with it,” says Bruce Buchholz, a scientist at Lawrence Livermore National Laboratory. “The entire planet has been labeled.”
Unlike the short-lived radioactive particles that come out of nuclear detonations, carbon-14 is not dangerous to humans—but it is very useful, because levels of the isotope have been slowly falling off since the 1950s spike. By measuring the amount of carbon-14 in a sample, scientists can pinpoint its age within just a year or two. They can use the method to find the age of an unidentified body using tooth enamel, or study how often human fat cells are born and die, or discover how old trafficked ivory is. It works with literally anything that has carbon.
So every Monday afternoon, Buchholz and his colleagues at Lawrence Livermore fire up the accelerated mass spectrometer, the machine that measures carbon-14. They get samples from a hundred different scientists, law enforcement groups, and government agencies. That adds up to about 100 to 150 samples per week. The machine runs continuously through Thursday, day and night. They’re racing to do research that will soon be impossible.
A Modest Proposal, Part I
Back in the ‘90s, it was Buchholz who pioneered the idea of using carbon-14 to date biological samples. He, a nuclear engineer, met a neuroscientist at a chemistry conference, and they began one of those beautiful multidisciplinary collaborations to study the age of plaques found in the brains of Alzheimer’s patients. The carbon-14 work, however, really took off when Jonas Frisén, a stem cell biologist at the Karolinska Institute, read Buchholz’s papers. Frisén studies whether adults can grow new brain cells. Neuroscience had long held as dogma that humans are born with all the neurons they will ever have. But studies in mice and rats were beginning to upend that idea. Friesen looked at Buchholz’s papers and saw a way to measure the age of neurons. If you could find 20-year-old neurons in the brain of a 70-year-old, then you have proof of that brain cells generate throughout an animal’s lifetime.
In a few years, some of this research will be impossible.
But no one knew yet if carbon-14 worked for dating brain tissue, and that task fell on Kirsty Spalding, then a postdoc in Frisén’s lab. Starting with human brains was no go, so they started with horses. Horses, like humans, live for decades. Spaulding would drive up to a slaughterhouse an hour out of Stockholm and collect horse heads. “It was not my most fun project,” she says. “Especially terrible as a vegetarian going to the slaughterhouse.” But the method worked. Inside the brains of a horse six years old and another 19 years old, they found measurable differences in the amount of carbon-14.
The work moved to humans. And Spalding found that a region of the brain called the hippocampus, involved in memory, indeed generated new neurons in adulthood. Frisen has since done similar work in heart cells, also thought to rarely—if never—regenerate. Spalding how has her own lab studying fat cells. Carbon-14 dating is a key method for understanding how tissues grow and re-grow in the body.
But carbon-14 in the atmosphere is still falling—by now, it is only 4 or 5 percent above pre-atomic age levels. In a few years, some of this research will be impossible. “That’s something we emphasize in grant applications,” says Frisén. “We need the money now.”
A Modest Proposal, Part II
So what if the someone, you know, detonated another bomb? For the sake of science! (And only science.)
“We’re talking to North Koreans about what they can do,” jokes Frisén. But more seriously, he says, “I would prefer that not happening. You would need dozens. It’s not anything we’re counting on.” Indeed, dozens, if not hundreds, of bombs are necessary to produce a big enough spike in carbon-14 to be useful for dating. And powerful ones too—the ones detonated over Hiroshima and Nagasaki are too small. Accidental radioactive leaks, like Chernobyl or Fukushima, make no difference, because it’s the detonation that produces the neutrons necessary for carbon-14.
But what if—if!—you could detonate a few dozen nuclear bombs? Could you safely do it somewhere remote? Well, not likely.
The United States’ atmospheric testing in the Nevada desert likely contributed to a 10 percent increase in thyroid cancers in exposed people. In the Marshall Islands, the testing caused an additional 1 percent increase in cancer. “No matter how remote, the contamination will reach people somewhere,” says Steve Simon, a radiation epidemiologist at the National Cancer Institute, who led the Marshall Islands Nationwide Radiological Study.
Detonating a nuclear bomb high in the atmosphere—in space, essentially—would reduce radioactive fallout and contamination. The US actually did several high-altitude tests back in the 1950s and 60s. But nukes in space? Think of the satellites! The high-altitude test Starfish Prime knocked out several satellites in 1962, and that’s not something to repeat (on purpose).
So the window on carbon-14 dating is slowly closing. But that it was ever open in the first place was an odd, unintentional consequence of the atomic age.
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No, seriously.
When all those nukes were detonated, they spit out neutrons that set off a chain of events to create carbon-14, an exceedingly rare isotope of carbon. The amount of carbon-14 in the atmosphere spiked. That carbon-14 reacted with oxygen to make carbon dioxide. Plants breathed it in, animals ate the plants, and humans ate the animals and plants. “Everyone alive has been labeled with it,” says Bruce Buchholz, a scientist at Lawrence Livermore National Laboratory. “The entire planet has been labeled.”
Unlike the short-lived radioactive particles that come out of nuclear detonations, carbon-14 is not dangerous to humans—but it is very useful, because levels of the isotope have been slowly falling off since the 1950s spike. By measuring the amount of carbon-14 in a sample, scientists can pinpoint its age within just a year or two. They can use the method to find the age of an unidentified body using tooth enamel, or study how often human fat cells are born and die, or discover how old trafficked ivory is. It works with literally anything that has carbon.
So every Monday afternoon, Buchholz and his colleagues at Lawrence Livermore fire up the accelerated mass spectrometer, the machine that measures carbon-14. They get samples from a hundred different scientists, law enforcement groups, and government agencies. That adds up to about 100 to 150 samples per week. The machine runs continuously through Thursday, day and night. They’re racing to do research that will soon be impossible.
A Modest Proposal, Part I
Back in the ‘90s, it was Buchholz who pioneered the idea of using carbon-14 to date biological samples. He, a nuclear engineer, met a neuroscientist at a chemistry conference, and they began one of those beautiful multidisciplinary collaborations to study the age of plaques found in the brains of Alzheimer’s patients. The carbon-14 work, however, really took off when Jonas Frisén, a stem cell biologist at the Karolinska Institute, read Buchholz’s papers. Frisén studies whether adults can grow new brain cells. Neuroscience had long held as dogma that humans are born with all the neurons they will ever have. But studies in mice and rats were beginning to upend that idea. Friesen looked at Buchholz’s papers and saw a way to measure the age of neurons. If you could find 20-year-old neurons in the brain of a 70-year-old, then you have proof of that brain cells generate throughout an animal’s lifetime.
In a few years, some of this research will be impossible.
But no one knew yet if carbon-14 worked for dating brain tissue, and that task fell on Kirsty Spalding, then a postdoc in Frisén’s lab. Starting with human brains was no go, so they started with horses. Horses, like humans, live for decades. Spaulding would drive up to a slaughterhouse an hour out of Stockholm and collect horse heads. “It was not my most fun project,” she says. “Especially terrible as a vegetarian going to the slaughterhouse.” But the method worked. Inside the brains of a horse six years old and another 19 years old, they found measurable differences in the amount of carbon-14.
The work moved to humans. And Spalding found that a region of the brain called the hippocampus, involved in memory, indeed generated new neurons in adulthood. Frisen has since done similar work in heart cells, also thought to rarely—if never—regenerate. Spalding how has her own lab studying fat cells. Carbon-14 dating is a key method for understanding how tissues grow and re-grow in the body.
But carbon-14 in the atmosphere is still falling—by now, it is only 4 or 5 percent above pre-atomic age levels. In a few years, some of this research will be impossible. “That’s something we emphasize in grant applications,” says Frisén. “We need the money now.”
A Modest Proposal, Part II
So what if the someone, you know, detonated another bomb? For the sake of science! (And only science.)
“We’re talking to North Koreans about what they can do,” jokes Frisén. But more seriously, he says, “I would prefer that not happening. You would need dozens. It’s not anything we’re counting on.” Indeed, dozens, if not hundreds, of bombs are necessary to produce a big enough spike in carbon-14 to be useful for dating. And powerful ones too—the ones detonated over Hiroshima and Nagasaki are too small. Accidental radioactive leaks, like Chernobyl or Fukushima, make no difference, because it’s the detonation that produces the neutrons necessary for carbon-14.
But what if—if!—you could detonate a few dozen nuclear bombs? Could you safely do it somewhere remote? Well, not likely.
The United States’ atmospheric testing in the Nevada desert likely contributed to a 10 percent increase in thyroid cancers in exposed people. In the Marshall Islands, the testing caused an additional 1 percent increase in cancer. “No matter how remote, the contamination will reach people somewhere,” says Steve Simon, a radiation epidemiologist at the National Cancer Institute, who led the Marshall Islands Nationwide Radiological Study.
Detonating a nuclear bomb high in the atmosphere—in space, essentially—would reduce radioactive fallout and contamination. The US actually did several high-altitude tests back in the 1950s and 60s. But nukes in space? Think of the satellites! The high-altitude test Starfish Prime knocked out several satellites in 1962, and that’s not something to repeat (on purpose).
So the window on carbon-14 dating is slowly closing. But that it was ever open in the first place was an odd, unintentional consequence of the atomic age.
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Saturday, February 27, 2016
The F.B.I. just did the impossible
Tech companies aren't exactly known for playing nice with one another. Apple and Microsoft were once the fiercest rivals of personal computing. These days, Apple is up against Google in smartphones, while Google and Microsoft battle it out over business software. Amazon is fighting Apple when it comes to devices and media, and Microsoft when it comes to cloud hosting services (among other markets). Facebook is crushing Twitter in terms of social media users, and now Facebook and Google are vying for more mobile Internet eyeballs and ad dollars.
It's a rare day when all six of these companies can agree on something, but that day seems to have arrived, thanks to the U.S. Federal Bureau of Investigation.
It's a rare day when all six of these companies can agree on something, but that day seems to have arrived, thanks to the U.S. Federal Bureau of Investigation.
Last week, a judge ordered Apple to comply with an FBI request that Apple help circumvent security features on an iPhone used by a San Bernardino shooting suspect. Today, Apple filed a motion to dismiss the order to help unlock the iPhone for the FBI, and now Microsoft, Google, Facebook, Amazon, and Twitter all appear to be uniting behind Apple's move.
Google first showed tepid support for Apple in this fight last week, when CEO Sundar Pichai tweeted that "forcing companies to enable hacking could compromise users’ privacy."
Then it seemed like Microsoft might be siding with the FBI, when co-founder and former CEO Bill Gates gave an interview to the The Financial Times earlier this week saying that the FBI was only looking for Apple's help in this specific case. Apple has repeatedly contended that what the FBI is asking for — a way to bypass the auto-deletion feature on an iPhone 5C when a password is guessed incorrectly too many times — could be used to compromise other iPhones, including the hundreds of millions used by Apple's customers around the world.
But Gates, who is now just an "advisor" at Microsoft, later walked back those remarks, and today Microsoft's president and chief legal officer Brad Sims testified before Congress that his company "wholeheartedly" supports Apple and will be filing an amicus brief in the court case to that effect (amicus briefs are legal documents filed by parties who aren't directly involved in the case, but who have a strong interest in the outcome and may be affected by it.)
As it turns out, Microsoft isn't the only one about to do this: now Google, Facebook, and Twitter, are all coming together to file a joint amicus brief in support of Apple, according to USA Today. Amazon is also said to be working on "amicus brief options," according to a spokesperson who spoke to Buzzfeed.
Other smaller tech companies and digital advocacy groups including the Electronic Frontier Foundation have also said they plan to support Apple by filing such amicus briefs as the case moves forward.
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Friday, February 26, 2016
The Next B-2...Looks exactly like the B-2
Three days ago, the U.S. Air Force released the first image of its B-21, the supplement to the tiny B-2 fleet already in service. Formerly known as the Long Range Strike Bomber, or LRS-B, the new, Northrop Grumman designed plane is now the B-21. If that sounds at all familiar, it’s because America’s last brand-new shiny Northrop Grumman designed bomber was the B-2 Spirit. With the shroud lifted off the new bomber, we can see that the B-21 looks...almost exactly like its predecessor.
B-21 B-2
As I mentioned before, the B-2 fleet is tiny. Alas, the B-2 Spirit was a victim of its time: a highly advanced bomber that entered service right as the Cold War ended. As American security concerns switched from fears of Russian attack to worries about the side effects of Russian economic implosion, a top-of-the-line stealth bomber became the easiest fat to cut off the Pentagon’s budget. After just 21 planes were delivered, the program ended, leaving America with a super-fancy flying machine to show off at parades. Oh well. So, the B-21 will pick up where the B-2 left off, making it the B-2 the "iPhone 5S of bombers" (if Apple only came out with a new iPhone every 25 years). According to the USAF press desk, "designation B-21 recognizes the LRS-B as the first bomber of the 21st century," and is not a reference to the just 21 B-2s that were made. Again, it will supplement the tiny B-2 fleet, and replace the ancient B-52s still used by the Air Force today, as well as the older B-1 bombers. People have speculated a lot on the kind of tech the bomber will have, as well as whether it will be unmanned or not. In late 2014, Popular Science spoke with a senior defense official at the Pentagon involved in the program, who insisted that, when carrying a nuclear weapon, the bomber will have a human crew on board. The B-21’s Ace Combat 2-style concept art seems to confirm that, with windows visible on the plane. This matches the ad Northrop Grumman aired during the Super Bowl this year, which put cockpits for human pilots on their future fighters.
In a previous post I talked about the future of America's air force and had a paragraph on the SR-72. I want to make sure that people do not confuse the two, as the B-21 will not be capable of the speeds the SR-72 will be flying at.
417
B-21 B-2
As I mentioned before, the B-2 fleet is tiny. Alas, the B-2 Spirit was a victim of its time: a highly advanced bomber that entered service right as the Cold War ended. As American security concerns switched from fears of Russian attack to worries about the side effects of Russian economic implosion, a top-of-the-line stealth bomber became the easiest fat to cut off the Pentagon’s budget. After just 21 planes were delivered, the program ended, leaving America with a super-fancy flying machine to show off at parades. Oh well. So, the B-21 will pick up where the B-2 left off, making it the B-2 the "iPhone 5S of bombers" (if Apple only came out with a new iPhone every 25 years). According to the USAF press desk, "designation B-21 recognizes the LRS-B as the first bomber of the 21st century," and is not a reference to the just 21 B-2s that were made. Again, it will supplement the tiny B-2 fleet, and replace the ancient B-52s still used by the Air Force today, as well as the older B-1 bombers. People have speculated a lot on the kind of tech the bomber will have, as well as whether it will be unmanned or not. In late 2014, Popular Science spoke with a senior defense official at the Pentagon involved in the program, who insisted that, when carrying a nuclear weapon, the bomber will have a human crew on board. The B-21’s Ace Combat 2-style concept art seems to confirm that, with windows visible on the plane. This matches the ad Northrop Grumman aired during the Super Bowl this year, which put cockpits for human pilots on their future fighters.
In a previous post I talked about the future of America's air force and had a paragraph on the SR-72. I want to make sure that people do not confuse the two, as the B-21 will not be capable of the speeds the SR-72 will be flying at.
417
Thursday, February 25, 2016
The Mozart Effect and You should be playing an instrument!
You've heard of the Mozart effect, right? If not, here's a little background information for ya.
In the '90s, there was a study done by Rauscher, Shaw, and Ky that pointed to the theory that Mozart's music had an effect on spatial reasoning. Although the study only showed that it made temporary increases in spatial reasoning the findings were peddled to the masses through books and CDs under the false pretense that his music made your baby permanently smarter.
A report, published in the journal Pediatrics, said it was unclear whether the original study in 1993 has detected a "Mozart effect" or a potential benefit of music in general. But they said a previous study of adults with seizures found that compositions by Mozart, more so than other classical composers, appeared to lower seizure frequency. One team said it was possible that the proposed Mozart effect on the brain is related to the structure of his compositions, as Mozart's music tends to repeat the melodic line more frequently. In more condemning evidence, a team from Vienna University's Faculty of Psychology analyzed all studies since 1993 that have sought to reproduce the Mozart effect and found no proof of the phenomenon's existence. Overall, they looked at 3,000 individuals in 40 studies conducted around the world. It did not even need Bach to have the same effect: "Those who listened to music, Mozart or something else – Bach, Pearl Jam – had better results than the silent group. But we already knew people perform better if they have a stimulus," said Jakob Pietschnig, who led the study. "I recommend everyone listen to Mozart, but it's not going to improve cognitive abilities as some people hope," he added. In 1999, psychologist Christopher Chabris, now at Union College in Schenectady, N.Y., performed a meta-analysis on 16 studies related to the Mozart effect to survey its overall effectiveness. "The effect is only one and a half IQ points, and it's only confined to this paper-folding task," Chabris says. He notes that the improvement could simply be a result of the natural variability a person experiences between two test sittings. In almost every study done, there were little to no improvements on any level.
However, playing an instrument is a different ball game. Instead of listening to music passively, Rauscher advocates putting an instrument into the hands of a youngster to raise intelligence. She cites a 1997 University of California, Los Angeles, study that found, among 25,000 students, those who had spent time involved in a musical pursuit tested higher on SATs and reading proficiency exams than those with no instruction in music. Other effects of playing an instrument are learning how to listen, increased memory capacity, sharper concentration, growth of perseverance, improvement of non-verbal communication skills, an increased sense of responsibility, better coordination, stress relief, growth of creativity, better memory recall, organizational skills and time management, help with crowd anxiety, people skills, and growing of a social network within the people you play with. In other words, either learn how to play an instrument or have your children learn how to play an instrument.
https://en.wikipedia.org/wiki/Mozart_effect
http://www.bbc.com/future/story/20130107-can-mozart-boost-brainpower
http://www.telegraph.co.uk/news/health/children/11500314/Mozart-effect-can-classical-music-really-make-your-baby-smarter.html
http://www.scientificamerican.com/article/fact-or-fiction-babies-ex/
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In the '90s, there was a study done by Rauscher, Shaw, and Ky that pointed to the theory that Mozart's music had an effect on spatial reasoning. Although the study only showed that it made temporary increases in spatial reasoning the findings were peddled to the masses through books and CDs under the false pretense that his music made your baby permanently smarter.
A report, published in the journal Pediatrics, said it was unclear whether the original study in 1993 has detected a "Mozart effect" or a potential benefit of music in general. But they said a previous study of adults with seizures found that compositions by Mozart, more so than other classical composers, appeared to lower seizure frequency. One team said it was possible that the proposed Mozart effect on the brain is related to the structure of his compositions, as Mozart's music tends to repeat the melodic line more frequently. In more condemning evidence, a team from Vienna University's Faculty of Psychology analyzed all studies since 1993 that have sought to reproduce the Mozart effect and found no proof of the phenomenon's existence. Overall, they looked at 3,000 individuals in 40 studies conducted around the world. It did not even need Bach to have the same effect: "Those who listened to music, Mozart or something else – Bach, Pearl Jam – had better results than the silent group. But we already knew people perform better if they have a stimulus," said Jakob Pietschnig, who led the study. "I recommend everyone listen to Mozart, but it's not going to improve cognitive abilities as some people hope," he added. In 1999, psychologist Christopher Chabris, now at Union College in Schenectady, N.Y., performed a meta-analysis on 16 studies related to the Mozart effect to survey its overall effectiveness. "The effect is only one and a half IQ points, and it's only confined to this paper-folding task," Chabris says. He notes that the improvement could simply be a result of the natural variability a person experiences between two test sittings. In almost every study done, there were little to no improvements on any level.
However, playing an instrument is a different ball game. Instead of listening to music passively, Rauscher advocates putting an instrument into the hands of a youngster to raise intelligence. She cites a 1997 University of California, Los Angeles, study that found, among 25,000 students, those who had spent time involved in a musical pursuit tested higher on SATs and reading proficiency exams than those with no instruction in music. Other effects of playing an instrument are learning how to listen, increased memory capacity, sharper concentration, growth of perseverance, improvement of non-verbal communication skills, an increased sense of responsibility, better coordination, stress relief, growth of creativity, better memory recall, organizational skills and time management, help with crowd anxiety, people skills, and growing of a social network within the people you play with. In other words, either learn how to play an instrument or have your children learn how to play an instrument.
https://en.wikipedia.org/wiki/Mozart_effect
http://www.bbc.com/future/story/20130107-can-mozart-boost-brainpower
http://www.telegraph.co.uk/news/health/children/11500314/Mozart-effect-can-classical-music-really-make-your-baby-smarter.html
http://www.scientificamerican.com/article/fact-or-fiction-babies-ex/
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Saturday, February 20, 2016
Icecube: In the Antartic
The IceCube Neutrino Observatory is a massive neutrino detector in Antarctica that takes advantage of the fact that the south pole is covered in a medium through which charged particles can travel faster than light: ice. A kilometer down, the ice is beautifully clear, allowing bursts of Cherenkov radiation to propagate through it unhindered. The IceCube observatory itself consists of 5,160 digital optical modules, each about 25 centimeters in diameter, suspended on 86 individual strings lowered into boreholes in the ice. Each string sits between 1450m and 2450m below the surface, spaced 125m horizontally from neighboring strings, resulting in a neutrino detector that's a full cubic kilometer in size. What IceCube is looking for are the tiny flashes of blue light emitted by the electrons, muons, and tau particles flashing through the ice after a neutrino collides with a water molecule. These flashes are very dim, but there are no other sources of light that far down under the ice, and the photomultiplier tube inside each digital optical module can detect even just a handful of photons.
Depending on what kind of subatomic particle the neutrino turns into, IceCube will detect different Cherenkov radiation patterns. An electron neutrino will produce an electromagnetic shower (or cascade) of particles. The muon produced by a muon neutrino, on the other hand, can travel hundreds of meters, leaving a track that points back along the same trajectory as the muon neutrino that created it. A tau neutrino will produce a sort of combination of these two signatures. Maybe. I think. Tau neutrinos are difficult to detect, because tau particles themselves are extraordinarily massive and short lived: they're something like 3,500 times the mass of an electron (and 17 times the mass of a muon), with a lifetime of just 0.0000000000003 second, which means that they decay into other subatomic particles virtually instantaneously and are easily mistaken for electron neutrinos. IceCube has some ideas of what unique radiation signatures might suggest the detection of a tau (including the "double bang," the "inverted lollipop," and the "sugardaddy"), but they haven't found one yet.
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Depending on what kind of subatomic particle the neutrino turns into, IceCube will detect different Cherenkov radiation patterns. An electron neutrino will produce an electromagnetic shower (or cascade) of particles. The muon produced by a muon neutrino, on the other hand, can travel hundreds of meters, leaving a track that points back along the same trajectory as the muon neutrino that created it. A tau neutrino will produce a sort of combination of these two signatures. Maybe. I think. Tau neutrinos are difficult to detect, because tau particles themselves are extraordinarily massive and short lived: they're something like 3,500 times the mass of an electron (and 17 times the mass of a muon), with a lifetime of just 0.0000000000003 second, which means that they decay into other subatomic particles virtually instantaneously and are easily mistaken for electron neutrinos. IceCube has some ideas of what unique radiation signatures might suggest the detection of a tau (including the "double bang," the "inverted lollipop," and the "sugardaddy"), but they haven't found one yet.
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Friday, February 19, 2016
Detections of Cosmic Neutrinos
Neutrinos are elementary particles (like quarks, photons, and the Higgs boson) that have no charge and virtually no mass. Since they're small, fast, and charge-free, they aren't affected by nuisances like electromagnetic fields, meaning that they can pass unmolested through rather a lot of pretty much anything. Some 65 billion solar neutrinos just passed through every square centimeter of your body, and if you wait a second, 65 billion more of them will do it again. The only way to bring a neutrino to a halt is if it runs smack into an electron or the nucleus of an atom, but this is ridiculously improbable: you'd need a piece of lead about a light year long to be reasonably sure catching any one specific neutrino. Fortunately, the enormous number of neutrinos that are flying through everything all the time compensates for the low probability of collision, and that has allowed us to learn some things about these elusive particles.
We’re pretty sure that neutrinos come in three different (but equally tasty) flavors: electron, muon, and tau. Each flavor has a slightly different (but tiny) mass, on the order of a million times smaller than the mass of a single electron, and a neutrino can oscillate between these three flavors as it zips along. The original flavor that each neutrino takes depends on how it was created: most often, neutrinos are created through high energy nuclear processes like you'd find going on inside stars. To take one common example, protons and neutrons colliding with each other create pions, which are subatomic particles that decay into a mix of muon and electron neutrinos.
The most common source for the neutrinos that we see here on Earth is the sun, which produces an electron neutrino every time two protons fuse into deuterium. (This happens a lot.) What's much rarer to see are neutrinos that aren't produced close to home—neutrinos that come from outside of our solar system, and even outside of our galaxy. These are called cosmic neutrinos, or astrophysical neutrinos.
Cosmic Neutrinos
Cosmic neutrinos are born, we think, in the same sorts of ultra high energy events out in the universe that also generate gamma rays and cosmic rays. We're talking events like supernova remnant shocks, active galactic nuclei jets, and gamma-ray bursts, which can emit as much energy in a few seconds as our sun does over ten billion years. As you might expect, the resulting neutrinos have stupendously high energies themselves: a million billion electronvolts (1 petaelectronvolt) or so. That works out to be about a tenth of a millijoule, which is a lot for a particle that has an effective size of nearly zero, and it is about equivalent to the kinetic energy of a thousand flying mosquitoes, in case that horrific unit of measurement is of any help to you.
The reason that cosmic neutrinos are important is the same reason that neutrinos themselves are so frustrating to measure: they ignore almost everything. This allows them to carry valuable information across the entire universe. What sort of information can be carried by a particle that we can't even measure directly? Here are three examples:
Since neutrinos aren't affected all that much by even the densest matter, they can escape from the core of a supernova well before the shock wave from the inside of the collapsing star makes it to the outside and releases any photons. By detecting this initial neutrino burst, we can get a warning of as long as a few hours before a supernova would be visible from Earth.
Since neutrinos aren't affected at all by magnetic fields and therefore travel in straight lines, they can help us pinpoint the origin of ultra high energy cosmic rays, which are affected by magnetic fields and therefore can follow winding paths. We know that some cosmic rays come from supernovae, but many of them don't, and we're not sure where the rest of them originate. With energies over a million times greater than the Large Hadron Collider, it would be nice to know where they come from.
The ratio between different flavors of neutrinos may suggest how they were formed. For neutrinos produced by pion decay, we'd expect to see two electron neutrinos for every muon neutrino. If we see different ratios, it would suggest a different formation environment, and particularly weird ratios could even lead to new physics.
Detecting Neutrinos
Since neutrinos don't really interact with anything, there's no reliable way to detect them directly. Whether they're coming from the sun, the atmosphere, or somewhere more exotic, the best we can do is try and spot the aftermath of a very unlucky neutrino smashing headlong into something while we watch.
When a neutrino does smash into something, one of two different things can happen. If the neutrino isn't super energetic, it might just bounce off in a new direction, passing on some of its momentum and energy into whatever it hits (which recoils in response) and occasionally causing that thing to break into pieces. Some neutrino detectors are designed to watch for both of these effects. The other thing that can happen is that the neutrino obliterates itself, dissolving into a subatomic particle that depends on the neutrino's flavor-of-the-moment: an electron neutrino turns into an electron, a muon neutrino turns into a muon, and a tau neutrino turns into a tau particle, stripping electric charge off of whatever it hits as it does so. Some detectors look for this change in charge of the thing that the neutrino ran into (it's the only way of detecting neutrinos with energies less than 1 MeV), but the detector that we're interested in looks for traces of the ex-neutrino's subatomic particle itself.
Detecting particles moving at very high speeds is a (relatively) straightforward thing, at least conceptually. The key is what's called Cherenkov radiation, which is created by charged particles moving through a medium faster than the speed of light in that medium. It's sort of like the sonic boom created by an object travelling through air faster than the speed of sound, except with with light. Here's what the Cherenkov radiation created by a burst of beta particles from a nuclear reactor being pulsed looks like:
So now that we've got some lovely blue glowy-ness to look for, all we need a medium through which charged particles can travel faster than light, and some kind of detection system that can spot the resulting Cherenkov radiation.
Continued in next post...
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We’re pretty sure that neutrinos come in three different (but equally tasty) flavors: electron, muon, and tau. Each flavor has a slightly different (but tiny) mass, on the order of a million times smaller than the mass of a single electron, and a neutrino can oscillate between these three flavors as it zips along. The original flavor that each neutrino takes depends on how it was created: most often, neutrinos are created through high energy nuclear processes like you'd find going on inside stars. To take one common example, protons and neutrons colliding with each other create pions, which are subatomic particles that decay into a mix of muon and electron neutrinos.
The most common source for the neutrinos that we see here on Earth is the sun, which produces an electron neutrino every time two protons fuse into deuterium. (This happens a lot.) What's much rarer to see are neutrinos that aren't produced close to home—neutrinos that come from outside of our solar system, and even outside of our galaxy. These are called cosmic neutrinos, or astrophysical neutrinos.
Cosmic Neutrinos
Cosmic neutrinos are born, we think, in the same sorts of ultra high energy events out in the universe that also generate gamma rays and cosmic rays. We're talking events like supernova remnant shocks, active galactic nuclei jets, and gamma-ray bursts, which can emit as much energy in a few seconds as our sun does over ten billion years. As you might expect, the resulting neutrinos have stupendously high energies themselves: a million billion electronvolts (1 petaelectronvolt) or so. That works out to be about a tenth of a millijoule, which is a lot for a particle that has an effective size of nearly zero, and it is about equivalent to the kinetic energy of a thousand flying mosquitoes, in case that horrific unit of measurement is of any help to you.
The reason that cosmic neutrinos are important is the same reason that neutrinos themselves are so frustrating to measure: they ignore almost everything. This allows them to carry valuable information across the entire universe. What sort of information can be carried by a particle that we can't even measure directly? Here are three examples:
Since neutrinos aren't affected all that much by even the densest matter, they can escape from the core of a supernova well before the shock wave from the inside of the collapsing star makes it to the outside and releases any photons. By detecting this initial neutrino burst, we can get a warning of as long as a few hours before a supernova would be visible from Earth.
Since neutrinos aren't affected at all by magnetic fields and therefore travel in straight lines, they can help us pinpoint the origin of ultra high energy cosmic rays, which are affected by magnetic fields and therefore can follow winding paths. We know that some cosmic rays come from supernovae, but many of them don't, and we're not sure where the rest of them originate. With energies over a million times greater than the Large Hadron Collider, it would be nice to know where they come from.
The ratio between different flavors of neutrinos may suggest how they were formed. For neutrinos produced by pion decay, we'd expect to see two electron neutrinos for every muon neutrino. If we see different ratios, it would suggest a different formation environment, and particularly weird ratios could even lead to new physics.
Detecting Neutrinos
Since neutrinos don't really interact with anything, there's no reliable way to detect them directly. Whether they're coming from the sun, the atmosphere, or somewhere more exotic, the best we can do is try and spot the aftermath of a very unlucky neutrino smashing headlong into something while we watch.
When a neutrino does smash into something, one of two different things can happen. If the neutrino isn't super energetic, it might just bounce off in a new direction, passing on some of its momentum and energy into whatever it hits (which recoils in response) and occasionally causing that thing to break into pieces. Some neutrino detectors are designed to watch for both of these effects. The other thing that can happen is that the neutrino obliterates itself, dissolving into a subatomic particle that depends on the neutrino's flavor-of-the-moment: an electron neutrino turns into an electron, a muon neutrino turns into a muon, and a tau neutrino turns into a tau particle, stripping electric charge off of whatever it hits as it does so. Some detectors look for this change in charge of the thing that the neutrino ran into (it's the only way of detecting neutrinos with energies less than 1 MeV), but the detector that we're interested in looks for traces of the ex-neutrino's subatomic particle itself.
Detecting particles moving at very high speeds is a (relatively) straightforward thing, at least conceptually. The key is what's called Cherenkov radiation, which is created by charged particles moving through a medium faster than the speed of light in that medium. It's sort of like the sonic boom created by an object travelling through air faster than the speed of sound, except with with light. Here's what the Cherenkov radiation created by a burst of beta particles from a nuclear reactor being pulsed looks like:
So now that we've got some lovely blue glowy-ness to look for, all we need a medium through which charged particles can travel faster than light, and some kind of detection system that can spot the resulting Cherenkov radiation.
Continued in next post...
1081
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