Moon has a water-rich interior

A new study of satellite data finds that numerous volcanic deposits distributed across the surface of the Moon contain unusually high amounts of trapped water compared with surrounding terrains. The finding of water in these ancient deposits, which are believed to consist of glass beads formed by the explosive eruption of magma coming from the deep lunar interior, bolsters the idea that the lunar mantle is surprisingly water-rich.

Scientists had assumed for years that the interior of the Moon had been largely depleted of water and other volatile compounds. That began to change in 2008, when a research team including Brown University geologist Alberto Saal detected trace amounts of water in some of the volcanic glass beads brought back to Earth from the Apollo 15 and 17 missions to the Moon. In 2011, further study of tiny crystalline formations within those beads revealed that they actually contain similar amounts of water as some basalts on Earth. That suggests that the Moon's mantle - parts of it, at least - contain as much water as Earth's.

"The key question is whether those Apollo samples represent the bulk conditions of the lunar interior or instead represent unusual or perhaps anomalous water-rich regions within an otherwise 'dry' mantle," said Ralph Milliken, lead author of the new research and an associate professor in Brown's Department of Earth, Environmental and Planetary Sciences. "By looking at the orbital data, we can examine the large pyroclastic deposits on the Moon that were never sampled by the Apollo or Luna missions. The fact that nearly all of them exhibit signatures of water suggests that the Apollo samples are not anomalous, so it may be that the bulk interior of the Moon is wet."

Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. By Gregory H. Revera (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

The research, which Milliken co-authored with Shuai Li, a postdoctoral researcher at the University of Hawaii and a recent Brown Ph.D. graduate, is published in Nature Geoscience.

Detecting the water content of lunar volcanic deposits using orbital instruments is no easy task. Scientists use orbital spectrometers to measure the light that bounces off a planetary surface. By looking at which wavelengths of light are absorbed or reflected by the surface, scientists can get an idea of which minerals and other compounds are present.

The problem is that the lunar surface heats up over the course of a day, especially at the latitudes where these pyroclastic deposits are located. That means that in addition to the light reflected from the surface, the spectrometer also ends up measuring heat.

"That thermally emitted radiation happens at the same wavelengths that we need to use to look for water," Milliken said. "So in order to say with any confidence that water is present, we first need to account for and remove the thermally emitted component."

To do that, Li and Milliken used laboratory-based measurements of samples returned from the Apollo missions, combined with a detailed temperature profile of the areas of interest on the Moon's surface. Using the new thermal correction, the researchers looked at data from the Moon Mineralogy Mapper, an imaging spectrometer that flew aboard India's Chandrayaan-1 lunar orbiter.

The researchers found evidence of water in nearly all of the large pyroclastic deposits that had been previously mapped across the Moon's surface, including deposits near the Apollo 15 and 17 landing sites where the water-bearing glass bead samples were collected.

"The distribution of these water-rich deposits is the key thing," Milliken said. "They're spread across the surface, which tells us that the water found in the Apollo samples isn't a one-off. Lunar pyroclastics seem to be universally water-rich, which suggests the same may be true of the mantle."

The idea that the interior of the Moon is water-rich raises interesting questions about the Moon's formation. Scientists think the Moon formed from debris left behind after an object about the size of Mars slammed into the Earth very early in solar system history. One of the reasons scientists had assumed the Moon's interior should be dry is that it seems unlikely that any of the hydrogen needed to form water could have survived the heat of that impact.

"The growing evidence for water inside the Moon suggest that water did somehow survive, or that it was brought in shortly after the impact by asteroids or comets before the Moon had completely solidified," Li said. "The exact origin of water in the lunar interior is still a big question."

In addition to shedding light on the water story in the early solar system, the research could also have implications for future lunar exploration. The volcanic beads don't contain a lot of water - about .05 percent by weight, the researchers say - but the deposits are large, and the water could potentially be extracted.

"Other studies have suggested the presence of water ice in shadowed regions at the lunar poles, but the pyroclastic deposits are at locations that may be easier to access," Li said. "Anything that helps save future lunar explorers from having to bring lots of water from home is a big step forward, and our results suggest a new alternative."

The research was funded by the NASA Lunar Advanced Science and Exploration Research Program (NNX12AO63G).

For more information visit:-

https://www.sciencedaily.com/releases/2017/07/170724114125.htm

https://en.wikipedia.org/wiki/Moon

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On this day in science history: the Hindenburg Zeppelin arrived at Lakehurst, New Jersey, USA

In 1936, the Hindenburg Zeppelin arrived at Lakehurst, New Jersey, USA, from Germany marking the beginning of a regular transatlantic passenger service. The flight, carrying 51 passengers and 56 crew, took 61 hours.

Hindenburg at Lakehurst, by U.S. Department of the Navy. Bureau of Aeronautics. Naval Aircraft Factory, Philadelphia, Pennsylvania (USA). [Public domain], via Wikimedia Commons

The Hindenburg was a large German commercial passenger-carrying rigid airship, the lead ship of the Hindenburg class, the longest class of flying machine and the largest airship by envelope volume. It was designed and built by the Zeppelin Company (Luftschiffbau Zeppelin GmbH) on the shores of Lake Constance in Friedrichshafen and was operated by the German Zeppelin Airline Company (Deutsche Zeppelin-Reederei). The Hindenburg had a duralumin structure, incorporating 15 Ferris wheel-like bulkheads along its length, with 16 cotton gas bags fitted between them. The bulkheads were braced to each other by longitudinal girders placed around their circumferences. The airship's outer skin was of cotton doped with a mixture of reflective materials intended to protect the gas bags within from radiation, both ultraviolet (which would damage them) and infrared (which might cause them to overheat). The gas cells were made by a new method pioneered by Goodyear using multiple layers of gelatinized latex rather than the previous goldbeater's skins. In 1931 the Zeppelin Company purchased 5,000 kg (11,000 lb) of duralumin salvaged from the wreckage of the October 1930 crash of the British airship R101, which might have been re-cast and used in the construction of the Hindenburg.

The interior furnishings of the Hindenburg were designed by Fritz August Breuhaus, whose design experience included Pullman coaches, ocean liners, and warships of the German Navy. The upper "A" Deck contained small passenger quarters in the middle flanked by large public rooms: a dining room to port and a lounge and writing room to starboard. Paintings on the dining room walls portrayed the Graf Zeppelin's trips to South America. A stylized world map covered the wall of the lounge. Long slanted windows ran the length of both decks. The passengers were expected to spend most of their time in the public areas, rather than their cramped cabins.

The lower "B" Deck contained washrooms, a mess hall for the crew, and a smoking lounge. Harold G. Dick, an American representative from the Goodyear Zeppelin Company, recalled "The only entrance to the smoking room, which was pressurized to prevent the admission of any leaking hydrogen, was via the bar, which had a swiveling air lock door, and all departing passengers were scrutinized by the bar steward to make sure they were not carrying out a lit cigarette or pipe."

Helium was initially selected for the Hindenburg’s lifting gas because it was the safest to use in airships, as it is not flammable. One proposed measure to save helium was to make double-gas cells for 14 of the 16 gas cells; an inner hydrogen cell would be protected by an outer cell filled with helium, with vertical ducting to the dorsal area of the envelope to permit separate filling and venting of the inner hydrogen cells. At the time, however, helium was also relatively rare and extremely expensive as the gas was only available in industrial quantities from distillation plants at certain oil fields in the United States. Hydrogen, by comparison, could be cheaply produced by any industrialized nation and being lighter than helium also provided more lift. Because of its expense and rarity, American rigid airships using helium were forced to conserve the gas at all costs and this hampered their operation.

Despite a U.S. ban on the export of helium under the Helium Control Act of 1927, the Germans designed the airship to use the far safer gas in the belief that they could convince the US government to license its export. When the designers learned that the National Munitions Control Board would refuse to lift the export ban, they were forced to re-engineer the Hindenburg to use hydrogen for lift. Despite the danger of using flammable hydrogen, no alternative lighter-than-air gases could provide sufficient lift. One beneficial side effect of employing hydrogen was that more passenger cabins could be added. The Germans' long history of flying hydrogen-filled passenger airships without a single injury or fatality engendered a widely held belief they had mastered the safe use of hydrogen. The Hindenburg's first season performance appeared to demonstrate this, however the airship was destroyed by fire 14 months later on May 6, 1937, at the end of the first North American transatlantic journey of its second season of service. Thirty-six people died in the accident, which occurred while landing at Lakehurst. This was the last of the great airship disasters; it was preceded by the crashes of the British R38 in 1921 (44 dead), the US airship Roma in 1922 (34 dead), the French Dixmude in 1923 (52 dead), the British R101 in 1930 (48 dead), and the US Akron in 1933 (73 dead).

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On this day in science history: polyethylene was discovered

Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long –CH2– chains and termed it polymethylene.

Polythylene balls, by Lluis tgn (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

The first industrially practical polyethylene synthesis (diazomethane is a notoriously unstable substance that is generally avoided in industrial application) was discovered in 1933 by Eric Fawcett and Reginald Gibson, again by accident, at the Imperial Chemical Industries (ICI) works in Northwich, England.  Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde they again produced a white, waxy material. Because the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was, at first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939. Because polyethylene was found to have very low-loss properties at very high frequency radio waves, commercial distribution in Britain was suspended on the outbreak of World War II, secrecy imposed, and the new process was used to produce insulation for UHF and SHF coaxial cables of radar sets. During World War II, further research was done on the ICI process and in 1944 Bakelite Corporation at Sabine, Texas, and Du Pont at Charleston, West Virginia, began large-scale commercial production under license from ICI.

The breakthrough landmark in the commercial production of polyethylene began with the development of catalyst that promote the polymerization at mild temperatures and pressures. The first of these was a chromium trioxide–based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are heavily used industrially. By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for HDPE production. In the 1970s, the Ziegler system was improved by the incorporation of magnesium chloride. Catalytic systems based on soluble catalysts, the metallocenes, were reported in 1976 by Walter Kaminsky and Hansjörg Sinn. The Ziegler- and metallocene-based catalysts families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low density polyethylene and linear low-density polyethylene. Such resins, in the form of UHMWPE fibers, have (as of 2005) begun to replace aramids in many high-strength applications.

One of the main problems of polyethylene is that without special treatment it's not readily biodegradable, and thus accumulates. In Japan, getting rid of plastics in an environmentally friendly way was the major problem discussed until the Fukushima disaster in 2011. It was listed as a $90 billion market for solutions. Since 2008, Japan has rapidly increased the recycling of plastics, but still has a large amount of plastic wrapping which goes to waste.

In May 2008, Daniel Burd, a 16-year-old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Pseudomonas fluorescens, with the help of Sphingomonas, can degrade over 40% of the weight of plastic bags in less than three months.

The thermophilic bacterium Brevibacillus borstelensis (strain 707) was isolated from a soil sample and found to use low-density polyethylene as a sole carbon source when incubated together at 50°C. Biodegradation increased with time exposed to ultraviolet radiation.

In 2010, a Japanese researcher, Akinori Ito, released the prototype of a machine which creates oil from polyethylene using a small, self-contained vapor distillation process.

In 2014, a Chinese researcher discovered that Indian mealmoth larvae could metabolize polyethylene from observing that plastic bags at his home had small holes in them. Deducing that the hungry larvae must have digested the plastic somehow, he and his team analyzed their gut bacteria and found a few that could use plastic as their only carbon source. Not only could the bacteria from the guts of the Plodia interpunctella moth larvae metabolize polyethylene, they degraded it significantly, dropping its tensile strength by 50%, its mass by 10% and the molecular weights of its polymeric chains by 13%.

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On this day in science history: the first X-rays were observed

In 1895, Wilhelm Röntgen first observed X-rays during an experiment at Würzburg University. After further investigation, on 1 Jan 1896, he notified other scientists of his discovery of this new radiation that would become known as X-rays. He sent copies of his manuscript and some of his X-ray photographs to several renowned physicists and friends, including Lord Kelvin in Glasgow and in Paris. On 5 Jan 1896, Die Presse published the news in a front-page article which described his investigations and suggested new methods of medical diagnoses might be made with this new kind of radiation.

Wilhelm Röntgen, by Nobel foundation [Public domain or Public domain], via Wikimedia Commons

So, what are the properties of X-Rays? 

X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a short period of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.

Hard X-rays can traverse relatively thick objects without being much absorbed or scattered. For this reason, X-rays are widely used to image the inside of visually opaque objects. The most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry (e.g. industrial radiography and industrial CT scanning) and research (e.g. small animal CT). The penetration depth varies with several orders of magnitude over the X-ray spectrum. This allows the photon energy to be adjusted for the application so as to give sufficient transmission through the object and at the same time good contrast in the image.

X-rays have much shorter wavelength than visible light, which makes it possible to probe structures much smaller than what can be seen using a normal microscope. This can be used in X-ray microscopy to acquire high resolution images, but also in X-ray crystallography to determine the positions of atoms in crystals.

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On this day in history - the Bikini H-Bomb test took place

In 1954, at Bikini, in the Pacific Ocean, the blast of the U.S. hydrogen bomb code-named Bravo was the most powerful of all U.S. thermonuclear bomb tests in the area.

The 15 megaton nuclear explosion far exceeded the expected yield of 4 to 8 megatons (6Mt predicted), and was about 1,000 times more powerful than each of the atomic bombs dropped on Hiroshima and Nagasaki during World War II. The scientists and military authorities were shocked by the size of the explosion and many of the instruments they had put in place to evaluate the effectiveness of the device were destroyed.

Bikini is a Pacific archipelago that is part of the Marshall Islands. In this test, one of the atolls was totally vaporized and disappeared in the over 100-mile wide mushroom cloud.

Fallout exceeded predictions. Earlier tests began in 1946 after the indigenous people were evacuated to an island believed to be a safe distance away. (They were moved again in 1949.)

Castle Bravo blast. By United States Department of Energy [Public domain], via Wikimedia Commons

The military authorities and scientists had promised the Bikini Atoll's native residents that they would be able to return home after the nuclear tests. A majority of the island's family heads agreed to leave the island, and most of the residents were moved to the Rongerik Atoll and later to Kili Island. Both locations proved unsuitable to sustaining life, resulting in starvation and requiring the residents to receive ongoing aid.

Despite the promises made by authorities, nuclear tests rendered Bikini unfit for habitation, contaminating the soil and water, making subsistence farming and fishing too dangerous. The United States later paid the islanders and their descendants $2 billion in compensation for damage caused by the nuclear testing program and their displacement from their home island.  

As of 2014, it may be technically possible for the former residents and their descendants to live on the atoll's islands, but virtually none of those alive today have ever lived on the atoll and very few want to move there.

For more information visit:

https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atoll

http://www.todayinsci.com/3/3_01.htm

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Carbon emissions 'postpone ice age'

The next ice age may have been delayed by over 50,000 years because of the greenhouse gases put in the atmosphere by humans, scientists in Germany say.

They analysed the trigger conditions for a glaciation, like the one that gripped Earth over 12,000 years ago.

The shape of the planet's orbit around the Sun would be conducive now, they find, but the amount of carbon dioxide currently in the air is far too high.

Earth is set for a prolonged warm phase, they tell the journal Nature.

"In theory, the next ice age could be even further into the future, but there is no real practical importance in discussing whether it starts in 50,000 or 100,000 years from now," Andrey Ganopolski from the Potsdam Institute for Climate Impact Research said.

"The important thing is that it is an illustration that we have a geological power now. We can change the natural sequence of events for tens of thousands of years," he told BBC News.

The Earth seen from space

Earth has been through a cycle of ice ages and warm periods over the past 2.5 million years, referred to as the Quaternary Period.

This has seen ice sheets come and go. At its maximum extent, the last glaciation witnessed a big freeze spread over much of North America, northern Europe, Russia and Asia.

In the south, a vast expanse of what are now Chile and Argentina were also iced up.

A fundamental parameter determining what dips Earth into an ice age is the changing nature of its orbit around the Sun.

The passage around the star is not a perfect circle and over time our planet's axis of rotation also rocks back and forth.

These movements alter the amount of solar radiation falling on the Earth's surface, and if a critical threshold is reached in mid latitudes in the Northern Hemisphere then a glaciation can be initiated.

Dr Ganopolski colleagues confirm this in their modelling but show also the role played by the concentration of greenhouse gases in the atmosphere.

And one of their findings is that Earth probably missed the inception by only a narrow margin a few hundred years ago, just before the industrial revolution took hold.

"We are now in a period when our (northern) summer is furthest from the Sun," the Potsdam researcher explained.

"Under normal circumstances, the interglacial would be terminated, and a new ice age would start. So, in principle, we are in the perfect conditions from an astronomical point of view. If we had a CO2 concentration of 240 parts per million (200 years ago) then an ice age could start, but luckily we had a concentration that was higher, 280ppm." Today, industrial society has taken that concentration to over 400ppm.

The team says that an interglacial climate would probably have been sustained anyway for at least 20,000 years, and, very probably, for 50,000 years, even if CO2 had stayed at its eighteenth century level.

But the almost 500 gigatonnes of carbon that has been released since the Industrial Revolution means we will likely miss the next best astronomical entry point into a glaciation, and with a further 500 gigatonnes of emissions the "probability of glacial inception during the next 100,000 years is notably reduced", the scientists say in their Nature paper.

Add a further 500 Gt C on top of that and the next ice age is virtually guaranteed to be delayed beyond the next 100,000 years.

Commenting on the study, Prof Eric Wolff from the University of Cambridge, UK, said: "There have been previous papers suggesting that the next ice age is many tens of thousands of years away, and that the combination of seasonal solar energy at the latitude where an ice sheet would form, plus CO2, is what determines the onset of an ice age. But this paper goes much further towards quantifying where the limits are.

"It represents a nice confirmation that there is a relatively simple way of estimating the combination of insolation and CO2 to start an ice age," he told the Science Media Centre.

And Prof Chris Rapley, from University College London, added: "This is an interesting result that provides further evidence that we have entered a new geological [Epoch] - 'The Anthropocene' - in which human actions are affecting the very metabolism of the planet."

For more information visit:

http://www.bbc.co.uk/news/science-environment-35307800

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How we know what lies at Earth’s core

Humans have been all over the Earth. We've conquered the lands, flown through the air and dived to the deepest trenches in the ocean. We've even been to the Moon. But we've never been to the planet's core.

We haven't even come close. The central point of the Earth is over 6,000km down, and even the outermost part of the core is nearly 3,000 km below our feet. The deepest hole we've ever created on the surface is the Kola Superdeep Borehole in Russia, and it only goes down a pitiful 12.3 km.

All the familiar events on Earth also happen close to the surface. The lava that spews from volcanoes first melts just a few hundred kilometres down. Even diamonds, which need extreme heat and pressure to form, originate in rocks less than 500km deep.

What's down below all that is shrouded in mystery. It seems unfathomable. And yet, we know a surprising amount about the core. We even have some idea about how it formed billions of years ago – all without a single physical sample. This is how the core was revealed.

One good way to start is to think about the mass of the Earth, says Simon Redfern of the University of Cambridge in the UK.

We can estimate Earth's mass by observing the effect of the planet's gravity on objects at the surface. It turns out that the mass of the Earth is 5.9 sextillion tonnes: that's 59 followed by 20 zeroes.

There's no sign of anything that massive at the surface.

"The density of the material at the Earth's surface is much lower than the 

average density of the whole Earth, so that tells us there's something much denser," says Redfern. "That's the first thing."

Essentially, most of the Earth's mass must be located towards the centre of the planet. The next step is to ask which heavy materials make up the core.

The answer here is that it's almost certainly made mostly of iron. The core is thought to be around 80% iron, though the exact figure is up for debate.

The main evidence for this is the huge amount of iron in the universe around us. It is one of the ten most common elements in our galaxy, and is frequently found in meteorites.

Given how much there is of it, iron is much less common at the surface of the Earth than we might expect. So the theory is that when Earth formed 4.5 billion years ago, a lot of iron worked its way down to the core.

That's where most of the mass is, and it's where most of the iron must be too. Iron is a relatively dense element under normal conditions, and under the extreme pressure at the Earth's core it would be crushed to an even higher density, so an iron core would account for all that missing mass.

But wait a minute. How did that iron get down there in the first place?

The iron must have somehow gravitated – literally – towards the centre of the Earth. But it's not immediately obvious how.

Most of the rest of the Earth is made up of rocks called silicates, and molten iron struggles to travel through them. Rather like how water on a greasy surface forms droplets, the iron clings to itself in little reservoirs, refusing to spread out and flow.

A possible solution was discovered in 2013 by Wendy Mao of Stanford University in California and her colleagues. They wondered what happened when the iron and silicate were both exposed to extreme pressure, as happens deep in the earth.

By pinching both substances extremely tightly using diamonds, they were able to force molten iron through silicate.

"The pressure actually changes the properties of how iron interacts with the silicate," says Mao. "At higher pressures a 'melt network' is formed."

This suggests the iron was gradually squeezed down through the rocks of the Earth over millions of years, until it reached the core.

At this point you might be wondering how we know the size of the core. What makes scientists think it begins 3000km down? There's a one-word answer: seismology.

When an earthquake happens, it sends shockwaves throughout the planet. Seismologists record these vibrations. It's as if we hit one side of the planet with a gigantic hammer, and listened on the other side for the noise.

"There was a Chilean earthquake in the 1960s that generated a huge amount of data," says Redfern. "All the seismic stations dotted all over the Earth recorded the arrival of the tremors from that earthquake."

Depending on the route those vibrations take, they pass through different bits of the Earth, and this affects how they "sound" at the other end.

Early in the history of seismology, it was realised that some vibrations were going missing. These "S-waves" were expected to show up on one side of the Earth after originating on the other, but there was no sign of them.

The reason for this was simple. S-waves can only reverberate through solid material, and can't make it through liquid.

They must have come up against something molten in the centre of the Earth. By mapping the S-waves' paths, it turned out that rocks became liquid around 3000km down.

That suggested the entire core was molten. But seismology had another surprise in store.

In the 1930s, a Danish seismologist named Inge Lehmann noticed that another kind of waves, called P-waves, unexpectedly travelled through the core and could be detected on the other side of the planet.

She came up with a surprising explanation: the core is divided into two layers. The "inner" core, which begins around 5,000km down, was actually solid. It was only the "outer" core above it that was molten.

Lehmann's idea was eventually confirmed in 1970, when more sensitive seismographs found that P-waves really were travelling through the core and, in some cases, being deflected off it at angles. Sure enough, they still ended up on the other side of the planet.

It's not just earthquakes that sent useful shockwaves through the Earth. In fact, seismology owes a lot of its success to the development of nuclear weapons.

A nuclear detonation also creates waves in the ground, so nations use seismology to listen out for weapons tests. During the Cold War this was seen as hugely important, so seismologists like Lehmann got a lot of encouragement.

Rival countries found out about each other's nuclear capabilities and along the way we learned more and more about the core of the Earth. Seismology is still used to detect nuclear detonations today.

We can now draw a rough picture of the Earth's structure. There is a molten outer core, which begins roughly halfway to the planet's centre, and within it is the solid inner core with a diameter of 1,220 km.

But there is a lot more to try and tease out, especially about the inner core. For starters, how hot is it?

This turns out to be quite tricky to determine, and baffled scientists until quite recently, says Lidunka Vočadlo of University College London in the UK. We can't put a thermometer down there, so the only solution is to create the correct crushing pressure in the lab.

In 2013 a team of French researchers produced the best estimate to date. They subjected pure iron to pressures a little over half that at the core, and extrapolated from there. They concluded that the melting point of pure iron at core temperatures is around 6,230 °C. The presence of other materials would bring the core's melting point down a bit, to around 6,000 °C. But that's still as hot as the surface of the Sun.

A bit like a toasty jacket potato, Earth's core has stayed warm thanks to heat retained from the formation of the planet. It also gets heat from friction as denser materials shift around, as well as from the decay of radioactive elements. Still, it is cooling by about 100 °C every billion years.

Knowing the temperature is useful, because it affects the speed at which vibrations travel through the core. That is handy, because there is something odd about the vibrations.

P-waves travel unexpectedly slowly as they go through the inner core – slower than they would if it was made of pure iron.

"Wave velocities that the seismologists measure in earthquakes and whatnot are significantly lower [than] anything that we measure in an experiment or calculate on a computer," says Vočadlo. "Nobody as yet knows why that is."

That suggests there is another material in the mix.

It could well be another metal, called nickel. But scientists have estimated how seismic waves would travel through an iron-nickel alloy, and it doesn't quite fit the readings either.

Vočadlo and her colleagues are now considering whether there might be other elements down there too, like sulphur and silicon. So far, no-one has been able to come up with a theory for the inner core's composition that satisfies everyone. It's a Cinderella problem: no shoe will quite fit.

Vočadlo is trying to simulate the materials of the inner core on a computer. She hopes to find a combination of materials, temperatures and pressures that would slow down the seismic waves by the right amount.

She says the secret might lie in the fact that the inner core is nearly at its melting point. As a result, the precise properties of the materials might be different from what they would be if they were safely solid.

That could explain why the seismic waves pass through more slowly than expected.

"If that's the real effect, we would be able to reconcile the mineral physics results with the seismological results," says Vocadlo. "People have not been able to do that yet."

There are plenty of riddles about the earth's core still to solve. But without ever digging to those impossible depths, scientists have figured out a great deal about what is happening thousands of kilometres beneath us.

Those hidden processes in the depths of the Earth are crucial to our daily lives, in a way many of us don't realise.

Earth has a powerful magnetic field, and that is all thanks to the partially molten core. The constant movement of molten iron creates an electrical current inside the planet, and that in turn generates a magnetic field that reaches far out into space.

The magnetic field helps to shield us from harmful solar radiation. If the core of the Earth wasn't the way it is, there would be no magnetic field, and we would have all sorts of problems to contend with.

None of us will ever set eyes on the core, but it's good to know it's there.

For more information visit:-

http://www.bbc.com/earth/story/20150814-what-is-at-the-centre-of-earth

https://www.prlabs.co.uk/lab-supplies.php?N=nickel-1000ppm-for-icp&Id=60172

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The Chernobyl Nuclear Plant Disaster

28 years ago in the early morning hours of April 26, 1986, the Chernobyl nuclear power plant in Ukraine (formerly part of the Soviet Union) exploded, creating what has been described as the worst nuclear disaster the world has ever seen.

 
Chernobyl is located about 81 miles (130 km) north of the city of Kiev in Ukraine, and about 12 miles (20 km) south of the border with Belarus.  The four reactors at the Chernobyl Nuclear Power Plant were designed and built during the 1970s and 1980s. A manmade reservoir, roughly 8.5 square miles (22 sq. km) in size and fed by the Pripyat River, was created to provide cooling water for the reactor.

On 26 April 1986, at 01:23, reactor four suffered a catastrophic power increase, leading to explosions in its core. This dispersed large quantities of radioactive fuel and core materials into the atmosphere and ignited the combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles, carried by the smoke, as the reactor had not been encased by any kind of hard containment vessel. The accident occurred during an experiment scheduled to test a potential safety emergency core cooling feature, which took place during a normal shutdown procedure.

In most nuclear reactors, where water is used as a coolant and to moderate the reactivity of the nuclear core, as the core heats up and produces more steam, the increase in steam bubbles or "voids" in the water reduces the reactivity in the nuclear core. This is an important safety feature found in most reactors built in the United States and other Western nations.

 

But not in the RBMK-1000, which used graphite to moderate the core's reactivity and to keep a continuous nuclear reaction occurring in the core. As the nuclear core heated and produced more steam bubbles, the core became more reactive, not less, creating a positive-feedback loop that engineers refer to as a "positive-void coefficient."

Basically, when extremely hot nuclear fuel rods were lowered into cooling water, an immense amount of steam was created, which — because of the RBMK reactors' design flaws — created more reactivity in the nuclear core of reactor number 4. The resultant power surge caused an immense explosion that detached the 1,000-ton plate covering the reactor core, releasing radiation into the atmosphere and cutting off the flow of coolant into the reactor.

A few seconds later, a second explosion of even greater power than the first blew the reactor building apart and spewed burning graphite and other parts of the reactor core around the plant, starting a number of intense fires around the damaged reactor and reactor number 3, which was still operating at the time of the explosions.

The explosions killed two plant workers, who were the first of several workers to die within hours of the accident. For the next several days, as emergency crews tried desperately to contain the fires and radiation leaks, the death toll climbed as plant workers succumbed to acute radiation sickness.

Most of the radiation released from the failed nuclear reactor was from iodine-131, cesium-134 and cesium-137. Iodine-131 has a relatively short half-life of eight days, according to UNSCEAR, but is rapidly ingested through the air and tends to localize in the thyroid gland. Cesium isotopes have longer half-lives (cesium-137 has a half-life of 30 years) and are a concern for years after their release into the environment. 

On April 27, the residents of Pripyat were evacuated — about 36 hours after the accident had occurred. By that time, many were already complaining about vomiting, headaches and other signs of radiation sickness. Officials eventually closed off an 18-mile (30 km) area around the plant; residents were told they would be able to return after a few days, so many left their personal belongings and valuables behind.

Abandoned Pripyat

During the construction of the sarcophagus, a scientific team re-entered the reactor as part of an investigation dubbed "Complex Expedition", to locate and contain nuclear fuel in a way that could not lead to another explosion. These scientists manually collected cold fuel rods, but great heat was still emanating from the core. Rates of radiation in different parts of the building were monitored by drilling holes into the reactor and inserting long metal detector tubes. The scientists were exposed to high levels of radiation and radioactive dust.

After six months of investigation, in December 1986, they discovered with the help of a remote camera an intensely radioactive mass in the basement of Unit Four, more than two metres wide and weighing hundreds of tons, which they called "the elephant's foot" for its wrinkled appearance. The mass was composed of sand, glass and a large amount of nuclear fuel that had escaped from the reactor. The concrete beneath the reactor was steaming hot, and was breached by solidified lava and spectacular unknown crystalline forms termed chernobylite. It was concluded that there was no further risk of explosion.

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions, much of it deposited on mountainous regions such as the Alps, the Welsh mountains and the Scottish Highlands, where adiabatic cooling caused radioactive rainfall.

For more information visit:-
http://en.wikipedia.org/wiki/Chernobyl_disaster
http://www.livescience.com/39961-chernobyl.html

 

Ionising Radiation-What's it all about?

Ionising Radiation

Sources of radiation dose to the UK population.
The total annual equivalent dose is 0.0026 Sv,
but individual doses vary enormously.

Introduction

 

The presence of natural background radiation is an inescapable fact of life. We are all exposed to it. We breathe small amounts of the radioactive gas 'radon'. The ground and buildings around us are slightly radioactive. Our bodies contain natural radioactivity from our food and drink, and cosmic rays fall on us all the time.
The subject of radiation receives a great deal of attention in our society partly because radiation is one cause, among many, of cancer. We cannot in general sense radiation and this no doubt adds to our anxiety. However radiation can also be used for our benefit, particularly in healthcare. Most of us are familiar with chest and dental X-rays, investigation of bone fractures or other diagnostic procedures.

 

The insides of a molecule

What is Radiation?

Radiation is the energy carried by either electromagnetic waves or moving particles. Electromagnetic waves can vary in energy and wavelength.
Quantum mechanics predicts that very short wavelength electromagnetic waves behave as uncharged particles, called photons. Therefore the distinction between waves and particles at short wavelengths as with X-ray and gamma rays is blurred.
Ions are atoms with too few or too many electrons. Ionising radiation is radiation that has enough energy to kick electrons out of atoms and therefore produce ions. X-rays and gamma rays are forms of ionising radiation.
Ionisation can start chemical processes for example in an X-ray photographic image. On the other hand radiation induced chemical processes can in turn lead to biological effects such as the destruction of a cancer tumour.
Particles other than photons can also carry 'radiation' energy. Electrons, sometimes called beta particles, are small mass, negatively charged particles. Protons are larger mass positively charged particles. Neutrons have a similar mass to protons, but are uncharged. The particles described so far fit together to make atoms. Alpha particles are particularly stable groups of two protons and two neutrons. All types of atomic particles can carry energy.




The Electromagnetic Spectrum

Radiation Sources

Radiation sources can be split into two main types: naturally radioactive atoms and artificial sources using accelerated and/or decelerated charged particles.
Some nuclei naturally break up, because they are unstable. The process is called radioactive decay. Radioactive nuclei can be produced artificially. When the constituents of nuclei rearrange themselves to release energy and become stable they normally produce gamma rays and other particles.
Charged particles experience a force when placed in an electric field. Therefore charged particles can be accelerated to very high energy.
The sudden slowing down of charged particles produces X-rays e.g. in an X-ray set. X-rays can also be produced when atoms rearrange themselves to release energy. These are called characteristic X-rays.

Radiation Quantities and Units

Radiation is difficult to measure, we cannot detect it through any of our senses though we can measure it by indirect means. We can interpret the measurements we make in terms of the energy deposited by the radiation. The amount of energy deposited per unit mass in a material is called the 'absorbed dose'. The unit of absorbed dose is the gray (Gy), which is one joule per kilogram.
Ionising radiations differ in the way in which they interact with biological materials, so that equal absorbed doses do not always have equal biological effects. 'Equivalent dose' is the absorbed dose multiplied by a factor that takes account of the relative effectiveness in causing biological harm. The unit of equivalent dose is the sievert (Sv), which is one joule per kilogram.
For beta, gamma and X-rays, 1 Gy is the same as 1 Sv, but neutrons and alpha rays are more damaging and, for these, 1 Gy is worth between 5 Sv and 20 Sv.
The unit of radioactivity is the becquerel (Bq), this is equal to one nuclear disintegration per second.

Ranges of absorbed dose

 

Radiation Measuring Instruments

There are a wide variety of instruments used to measure different types of radiation, different energy ranges and different accuracies. Here are a few examples. In radiography such as a chest X-ray, the variation of the penetrating power of X-rays in bone and tissue gives rise to an image. It is natural to use an ion chamber to measure ionising radiation. An ionisation chamber collects the charge normally from ions in a gas. Since most of the energy absorbed by radiation eventually appears as heat, it is possible to measure the temperature rise due to radiation directly. These devices are called calorimeters. The primary standard for absorbed dose is a device of this type.
In order to characterise a radioactive material, two pieces of information are needed: the activity and the way in which the nuclei decay. The latter information depends solely on the particular radioactive nuclei present. The activity of radioactive material, however, is a measurement that needs to be made in each individual case.

Radiation Scale

	Equivalent Dose (Sv)
Dose required to sterilise medical products	25 000
Typical total radiotherapy dose to cancer tumour	60
50% survival probability, whole body dose	4
Legal worker dose limit (whole body)	0.02
Average annual dose from all sources in Cornwall	0.008
Average annual dose from natural radiation	0.002
Typical chest X-ray dose	0.000 02
Average dose from a flight from UK to Spain	0.000 01

A Brief History of Radiation

	1895	Röntgen discovered X-rays as the cause of fluorescence
	1898	Marie and Pierre Curie discover the radioactive elements Radium and Polonium
	1905	Einstein discovered the mass energy relation E = mc2
	1913	Bohr suggested the idea of a nuclear atom
	1910-1926	Balloon experiments in upper atmosphere confirm the presence of cosmic radiation
	1942	Fermi achieved the first self-sustaining chain reaction and thereby initiated the controlled release of nuclear energy in nuclear reactors
	1979	Nobel Prize awarded to Hounsfield and Cormack following invention of CT scanner

For a poster and more information, visit the Amazing NPL website below.

http://www.npl.co.uk/educate-explore/factsheets/ionising-radiation/