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What are we learning? Why are we learning this?
content, procedures, skills
Tier II: High frequency words used across content areas. Key to understanding directions, understanding relationships, and for making inferences.
Tier III: Low frequency, domain specific terms
Building on what we already know
What vocabulary & concepts were learned in earlier grades?
Make connections to prior lessons from this year.
This is where we start building from.
Here we see the glow of Cherenkov radiation as a nuclear fission reactor starts up.
In principle there are many ways that we can generate nuclear power
1. nuclear fission of uranium
The largest metal atoms are not stable. They spontaneously break apart (“fission”) into smaller pieces. But the fascinating thing is that when you add up the mass of the smaller parts, they almost – but don’t quite – equal the mass of the parent atom!
Where did the massing mass go? We think mass could never “just disappear” – that violates the law of conservation of mass. Isn’t that a “law of nature”?”
Turns out that there is no law of conservation of mass. Sure, mass is usually conserved in everyday life, but it isn’t always conserved. So what’s the real deal?
Any missing mass has been converted into photons (particles of light) with high energy.
Under very specific conditions, mass can turn into energy, and vice-versa. So there’s no absolute ‘law of conservation of mass’ or ‘law of conservation of energy’. Rather, these are just two aspects of a higher order law of nature: ‘the law of conservation of mass & energy.’
Scientists have discovered how to use isotopes of uranium to create large amounts of power, which we use to create electricity.
2. nuclear fission of thorium
The general idea here is the same as for uranium. Nuclear fission of a radioactive metal to produce power. Thorium is far more abundant, easier to process, and much safer to use. It doesn’t sustain the kind of reactions that occur in an atomic or nuclear bomb. Thorium reactors can’t blow up. It makes very little radioactive waste, and the little that it makes degrades safely, in a shorter period of time. And it’s waste can’t be used to make nuclear weapons, so there is no fear of nuclear weapons proliferation. It has always been recognized as safer, cheaper, and better all around. So why aren’t we using it?
… research into the mechanization of nuclear reactions was initially driven not by the desire to make energy, but by the desire to make [atomic] bombs. The $2 billion Manhattan Project that produced the atomic bomb sparked a worldwide surge in nuclear research, most of it funded by governments embroiled in the Cold War. And here we come to it: Thorium reactors do not produce plutonium, which is what you need to make a nuke. How ironic. The fact that thorium reactors could not produce fuel for nuclear weapons meant the better reactor fuel got short shrift, yet today we would love to be able to clearly differentiate a country’s nuclear reactors from its weapons program.
… Thorium’s advantages start from the moment it is mined and purified, in that all but a trace of naturally occurring thorium is Th232, the isotope useful in nuclear reactors. That’s a heck of a lot better than the 3% to 5% of uranium that comes in the form we need.
Then there’s the safety side of thorium reactions. Unlike U235, thorium is not fissile. That means no matter how many thorium nuclei you pack together, they will not on their own start splitting apart and exploding. If you want to make thorium nuclei split apart, though, it’s easy: you simply start throwing neutrons at them. Then, when you need the reaction to stop, simply turn off the source of neutrons and the whole process shuts down, simple as pie….
… There are at least seven types of reactors that can use thorium as a nuclear fuel, five of which have entered into operation at some point. Several were abandoned not for technical reasons but because of a lack of interest or research funding (blame the Cold War again). So proven designs for thorium-based reactors exist and need but for some support.
– The Thing About Thorium: Why The Better Nuclear Fuel May Not Get A Chance, by Marin Katusa , Forbes, 2/16/2012
Here we see the difference between a uranium fission and a thorium fission nuclear power plant.
3. nuclear fusion (several types)
in the sun
Inside a star, gravity pulls billions of tons of matter towards the center. Atoms are pushed very close together. So close that sometimes two atoms will fuse into one, heavier atom.
The mass of this new atom is slightly less than the mass of the pieces that it was made of in the first place? Where the did missing go? It effectively becomes energy – which we see as photons, or as the heat/motion energy of other particles.
As an example, here we see deuterium fusing with tritium. The resulting product has less mass than the parts going in to the collision. That missing mass we see becomes 3.5 mega electron-volts of energy,
For more details see Stars are powered by nuclear fusion.
How can we possibly replicate the energy of stars here on Earth? For the last 70 years people have been steadily working on creating and sustaining nuclear fission in the laboratory, and the process actually works! Not surprisingly it has been extremely challenging to do this.
In this device, called a torus, engineers have designed extremely powerful electromagnets. These create a super-powerful magnetic field, strong enough to contain the hot plasma. We see the plasma contained inside as a glowing blue gas.
At the present time we can not use nuclear fusion as a practical way to produce energy, but research is continuing at a steady rate.
In practice we are only using nuclear fission of uranium. Research on thorium fission reactors is slowly proceeding, and we expect to see such reactors operating within the next 20 years. (We could do it much sooner if governments sustainably funded more reserach.) Research on fusion reactors is slowly proceeding, but we don’t expect to see such reactors operating soon. It is unclear at the moment when such reactors will be practical.
How does nuclear fission power work?
What are the benefits of nuclear power?
What are the risks of nuclear power?
What about the nuclear power plant disasters?
What about the radiation release from not using nuclear power?
“At an archaeological dig, a piece of wooden tool is unearthed – and the archaeologist finds it to be 5,000 years old. A child mummy is found high in the Andes – and the archaeologist says the child lived more than 2,000 years ago. How do scientists know how old an object or human remains are? What methods do they use and how do these methods work?
Carbon-14 dating is a way of determining the age of archaeological artifacts of a biological origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.”
- How Stuff Works, How Carbon-14 Dating Works, Marshall Brain
“The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists. Libby received the Nobel Prize in Chemistry for his work in 1960. ” – Wikipedia
How does it work?
Radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen.
The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide.
That is incorporated into plants by photosynthesis.
Animals then acquire 14 C by eating the plants.
When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14 C it contains begins to decrease, as the 14
C undergoes radioactive decay.
Measuring the amount of 14 C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died.
The older a sample is, the less 14 C there is to be detected, and because the half-life of 14 C (the period of time after which half of a given sample will have decayed) is about 5,730 years.
The oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.
– Carbon Dating, Wikipedia
As years go by, how much C14 is left?
C12 does not decay and remains constant in a sample, whereas C14 decays at an even, constant rate.
By measuring the ratio of C12 to C14, we can understand how long a sample has been around for.
The half life of C 14 is around 5,730 years. As seen by the second graph, this means that if a sample has half of the C14 it should usually have, it has been around for 5,730 years. A quarter of the amount, double that time, one eight of the original amount, more still.
Carbon dating is only as accurate as the consistency of it’s decay rate, which is unchanging and extremely uniform.
It is almost exclusively used for organic material as all life on earth is carbon based.
There is a misconception that carbon dating is used to date the age of the earth. For longer time scales, other elements are used, based on the same principles.
Graphs from a video by Scientific American that explains carbon dating. Watch the full video here How Does Radiocarbon Dating Work? – Instant Egghead #28: Scientific American
- text from http://blunt-science.tumblr.com/post/109954909373/a-representation-of-the-age-span-carbon-dating-is
Is radiocarbon dating reliable?
Excerpted from National Center for Science Education, by Christopher Gregory Weber:
Radiocarbon dating can easily establish that humans have been on the earth for over twenty thousand years …. it is one of the most reliable of all the radiometric dating methods.
Question: How does carbon-14 dating work?
Cosmic rays in the upper atmosphere are constantly converting the isotope nitrogen-14 (N-14) into carbon-14 (C-14 or radiocarbon).
Living organisms are constantly incorporating this C-14 into their bodies along with other carbon isotopes.
When the organisms die, they stop incorporating new C-14
The old C-14 starts to decay back into N-14 by emitting beta particles.
The older an organism’s remains are, the less beta radiation it emits because its C-14 is steadily dwindling at a predictable rate.
So, if we measure the rate of beta decay in an organic sample, we can calculate how old the sample is. C-14 decays with a half-life of 5,730 years.
Question: Kieth and Anderson radiocarbon-dated the shell of a living freshwater mussel and obtained an age of over two thousand years. ICR creationists claim that this discredits C-14 dating. How do you reply?
Answer: It does discredit the C-14 dating of freshwater mussels, but that’s about all. Kieth and Anderson show considerable evidence that the mussels acquired much of their carbon from the limestone of the waters they lived in and from some very old humus as well.
Carbon from these sources is very low in C-14 because these sources are so old and have not been mixed with fresh carbon from the air. Thus, a freshly killed mussel has far less C-14 than a freshly killed something else, which is why the C-14 dating method makes freshwater mussels seem older than they really are.
When dating wood there is no such problem because wood gets its carbon straight from the air, complete with a full dose of C-14.
Question: A sample that is more than fifty thousand years old shouldn’t have any measurable C-14. Coal, oil, and natural gas are supposed to be millions of years old; yet creationists say that some of them contain measurable amounts of C-14, enough to give them C-14 ages in the tens of thousands of years. How do you explain this?
Answer: Very simply. Radiocarbon dating doesn’t work well on objects much older than twenty thousand years, because such objects have so little C-14 left that their beta radiation is swamped out by the background radiation of cosmic rays and potassium-40 (K-40) decay.
Younger objects can easily be dated, because they still emit plenty of beta radiation, enough to be measured after the background radiation has been subtracted out of the total beta radiation. However, in either case, the background beta radiation has to be compensated for, and, in the older objects, the amount of C-14 they have left is less than the margin of error in measuring background radiation. As Hurley points out:
Without rather special developmental work, it is not generally practicable to measure ages in excess of about twenty thousand years, because the radioactivity of the carbon becomes so slight that it is difficult to get an accurate measurement above background radiation. (p. 108)
Cosmic rays form beta radiation all the time; this is the radiation that turns N-14 to C-14 in the first place. K-40 decay also forms plenty of beta radiation. Stearns, Carroll, and Clark point out that “. . . this isotope [K-40] accounts for a large part of the normal background radiation that can be detected on the earth’s surface” (p. 84).
This radiation cannot be totally eliminated from the laboratory, so one could probably get a “radiocarbon” date of fifty thousand years from a pure carbon-free piece of tin. However, you now know why this fact doesn’t at all invalidate radiocarbon dates of objects younger than twenty thousand years and is certainly no evidence for the notion that coals and oils might be no older than fifty thousand years.
Question: Creationists such as Cook (1966) claim that cosmic radiation is now forming C-14 in the atmosphere about one and one-third times faster than it is decaying. If we extrapolate backwards in time with the proper equations, we find that the earlier the historical period, the less C-14 the atmosphere had.
If we extrapolate as far back as ten thousand years ago, we find the atmosphere would not have had any C-14 in it at all. If they are right, this means all C-14 ages greater than two or three thousand years need to be lowered drastically and that the earth can be no older than ten thousand years. How do you reply?
Answer: Yes, Cook is right that C-14 is forming today faster than it’s decaying. However, the amount of C-14 has not been rising steadily as Cook maintains; instead, it has fluctuated up and down over the past ten thousand years. How do we know this? From radiocarbon dates taken from bristlecone pines. There are two ways of dating wood from bristlecone pines: one can count rings or one can radiocarbon-date the wood.
Since the tree ring counts have reliably dated some specimens of wood all the way back to 6200 BC, one can check out the C-14 dates against the tree-ring-count dates. Admittedly, this old wood comes from trees that have been dead for hundreds of years, but you don’t have to have an 8,200-year-old bristlecone pine tree alive today to validly determine that sort of date. It is easy to correlate the inner rings of a younger living tree with the outer rings of an older dead tree. The correlation is possible because, in the Southwest region of the United States, the widths of tree rings vary from year to year with the rainfall, and trees all over the Southwest have the same pattern of variations.
When experts compare the tree-ring dates with the C-14 dates, they find that radiocarbon ages before 1000 BC are really too young—not too old as Cook maintains. For example, pieces of wood that date at about 6200 BC by tree-ring counts date at only 5400 BC by regular C-14 dating and 3900 BC by Cook’s creationist revision of C-14 dating (as we see in the article, “Dating, Relative and Absolute,” in the Encyclopaedia Britannica). So, despite claims, C-14 before three thousand years ago was decaying faster than it was being formed and C-14 dating errs on the side of making objects from before 1000 BC look too young, not too old.
Question: But don’t trees sometimes produce more than one growth ring per year? Wouldn’t that spoil the tree-ring count?
Answer: If anything, the tree-ring sequence suffers far more from missing rings than from double rings. This means that the tree-ring dates would be slightly too young, not too old.
Of course, some species of tree tend to produce two or more growth rings per year. But other species produce scarcely any extra rings. Most of the tree-ring sequence is based on the bristlecone pine. This tree rarely produces even a trace of an extra ring; on the contrary, a typical bristlecone pine has up to 5 percent of its rings missing. Concerning the sequence of rings derived from the bristlecone pine, Ferguson says:
In certain species of conifers, especially those at lower elevations or in southern latitudes, one season’s growth increment may be composed of two or more flushes of growth, each of which may strongly resemble an annual ring.
Such multiple growth rings are extremely rare in bristlecone pines, however, and they are especially infrequent at the elevation and latitude (37� 20′ N) of the sites being studied. In the growth-ring analyses of approximately one thousand trees in the White Mountains, we have, in fact, found no more than three or four occurrences of even incipient multiple growth layers. (p. 840)
In years of severe drought, a bristlecone pine may fail to grow a complete ring all the way around its perimeter; we may find the ring if we bore into the tree from one angle, but not from another. Hence at least some of the missing rings can be found. Even so, the missing rings are a far more serious problem than any double rings.
Other species of trees corroborate the work that Ferguson did with bristlecone pines. Before his work, the tree-ring sequence of the sequoias had been worked out back to 1250 BC. The archaeological ring sequence had been worked out back to 59 BC. The limber pine sequence had been worked out back to 25 BC.
The radiocarbon dates and tree-ring dates of these other trees agree with those Ferguson got from the bristlecone pine. But even if he had had no other trees with which to work except the bristlecone pines, that evidence alone would have allowed him to determine the tree-ring chronology back to 6200 BC. …
Question: Does outside archaeological evidence confirm the C-14 dating method?
Answer: Yes. When we know the age of a sample through archaeology or historical sources, the C-14 method (as corrected by bristlecone pines) agrees with the age within the known margin of error.
For instance, Egyptian artifacts can be dated both historically and by radiocarbon, and the results agree. At first, archaeologists used to complain that the C-14 method must be wrong, because it conflicted with well-established archaeological dates; but, as Renfrew has detailed, the archaeological dates were often based on false assumptions.
One such assumption was that the megalith builders of western Europe learned the idea of megaliths from the Near-Eastern civilizations. As a result, archaeologists believed that the Western megalith-building cultures had to be younger than the Near Eastern civilizations.
Many archaeologists were skeptical when Ferguson’s calibration with bristlecone pines was first published, because, according to his method, radiocarbon dates of the Western megaliths showed them to be much older than their Near-Eastern counterparts.
However, as Renfrew demonstrated, the similarities between these Eastern and Western cultures are so superficial that the megalith builders of western Europe invented the idea of megaliths independently of the Near East. So, in the end, external evidence reconciles with and often confirms even controversial C-14 dates.
One of the most striking examples of different dating methods confirming each other is Stonehenge. C-14 dates show that Stonehenge was gradually built over the period from 1900 BC to 1500 BC, long before the Druids, who claimed Stonehenge as their creation, came to England.
Astronomer Gerald S. Hawkins calculated with a computer what the heavens were like back in the second millennium BC, accounting for the precession of the equinoxes, and found that Stonehenge had many significant alignments with various extreme positions of the sun and moon (for example, the hellstone marked the point where the sun rose on the first day of summer). Stonehenge fits the heavens as they were almost four thousand years ago, not as they are today, thereby cross-verifying the C-14 dates.
Relative Ages of Rocks: WIkiBooks
(WikiBooks: A project hosted by the Wikimedia Foundation for the creation of free content textbooks)
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012), from the National Research Council of the National Academies.
By the end of grade 12. Radioactive decay lifetimes and isotopic content in rocks provide a way of dating rock formations and thereby fixing the scale of geological time.
ES.3 Earth’s History: Relative and Absolute dating. Students understand that various dating methods — relative and absolute — have been used to determine the age of Earth.
Suggested Connections. Between Earth Science and Other Disciplines: Evidence of Common Ancestry and Divergence (LS.1.1); Living Systems and the Physical Environment (LS.3.1); Nuclear Chemistry (C.1.6); Nuclear Interactions and the Conservation of Mass–Energy (P.2.3)
Knowledge of radioactivity helps them understand how rocks can be dated, which helps them appreciate the scale of geologic time… Scientific evidence indicates that some rock layers are several billion years old. 4C/H6** (BSL)
For most people the biggest cancer risk from radiation hovers in the sky above us giving us all warmth and light. There is no cancer risk from Wi-Fi or microwaves.
Wear sunscreen, but use WiFi without fear. (Image: Spazturtle/SMS (CC))
What is radiation, and where does it come from? nuclear chemistry
What is cancer? How is caused? Cancer
Coal Ash Is More Radioactive Than Nuclear Waste
By burning away all the pesky carbon and other impurities, coal power plants produce heaps of radiation
By Mara Hvistendahl on December 13, 2007
The popular conception of nuclear power is straight out of The Simpsons: Springfield abounds with signs of radioactivity, from the strange glow surrounding Mr. Burn’s nuclear power plant workers to Homer’s low sperm count. Then there’s the local superhero, Radioactive Man, who fires beams of “nuclear heat” from his eyes. Nuclear power, many people think, is inseparable from a volatile, invariably lime-green, mutant-making radioactivity.
Coal, meanwhile, is believed responsible for a host of more quotidian problems, such as mining accidents, acid rain and greenhouse gas emissions. But it isn’t supposed to spawn three-eyed fish like Blinky.
Over the past few decades, however, a series of studies has called these stereotypes into question. Among the surprising conclusions: the waste produced by coal plants is actually more radioactive than that generated by their nuclear counterparts. In fact, the fly ash emitted by a power plant—a by-product from burning coal for electricity—carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy. * [See Editor’s Note at end of page 2]
At issue is coal’s content of uranium and thorium, both radioactive elements. They occur in such trace amounts in natural, or “whole,” coal that they aren’t a problem. But when coal is burned into fly ash, uranium and thorium are concentrated at up to 10 times their original levels.
Fly ash uranium sometimes leaches into the soil and water surrounding a coal plant, affecting cropland and, in turn, food. People living within a “stack shadow”—the area within a half- to one-mile (0.8- to 1.6-kilometer) radius of a coal plant’s smokestacks—might then ingest small amounts of radiation. Fly ash is also disposed of in landfills and abandoned mines and quarries, posing a potential risk to people living around those areas.
Nuclear Danger Still Dwarfed by Coal
By Christopher Wanjek, LiveScience, 4/26/11
One must accept a risk of radiation exposure when flying in and out of Narita International Airport, the busiest airport in Japan, just east of Tokyo, but perhaps not for the reason you are thinking.
Fukushima Daiichi, the tsunami-damaged nuclear reactor site about 150 miles (241 kilometers) to the north, as the foolish crow flies, continues to leak trace amounts of radiation. Radioactive iodine-131 made it into the water supply here last month. But most, as physics would have it, has since decayed into stable xenon.
So, few in this Tokyo region have been exposed to radiation levels as high as someone just hopping off a plane. The international flyer receives a dose of about 0.10 millisievert, or the amount of ionizing radiation in two dental X-rays, from the sun’s radioactive cosmic rays. That means that folks who left Tokyo because of the threat at Fukushima likely received more radiation on the airplane flight than they would have if they had stayed at home. [Mysterious Radiation May Strike Airline Passengers]
Such is the irony of nuclear energy, so potentially dangerous yet so much remarkably safer than most other energy sources, namely coal and other fossil fuels.
Dirty, dirty coal
As bad as Japan’s nuclear emergency could have gotten, it would never be as bad as burning coal. Coal is fantastically dangerous, responsible for far more than 1 million deaths per year, according to the World Health Organization.
Start with the coal miners, thousands of whom die from mine collapses and thousands more from various lung diseases. Next, add the hundreds of thousands of deaths in the public from breathing coal’s gaseous and particulate pollution, mostly from respiratory and heart disease.
Next, add the untold deaths and disabilities resulting from mercury in coal entering into the food chain. Then add the millions of acres of land, river and lake destroyed by mining waste.
Some of China’s citizens worried about a radioactive wind blowing over from Japan, but coal-burning power plants from China are causing far more health problems for both China and Japan.
Coal even releases more radioactive material than nuclear energy — 100 times more per the same amount of energy produced, according to Dana Christensen of the U.S. Department of Energy (DOE), as reported in Scientific American in 2007.
According to WHO statistics, there are at least 4,025 deaths from coal for every single death from nuclear power. Switch to “clean” natural gas? That’s still 100 times deadlier than nuclear energy. Oil is 900 times deadlier.
Not many are expected to die from the Fukushima Daiichi accident.
The U.S. DOE predicts a yearly dose of about 2,000 millirems for some people living northwest of the nuclear facility within 19 miles (31 kilometers), which could slightly increase their cancer risk if they haven’t left the area. But Japanese health authorities were quick to warn the public not to eat certain local foods with harmful levels of radioactivity, namely milk and spinach; people living within 12 miles (19 km) of the nuclear facility have been evacuated as a precaution; more are expected to be evacuated; and radiation levels continue to fall daily.
Coal and Gas are Far More Harmful than Nuclear Power
By Pushker Kharecha and James Hansen — April 2013
NASA Science Briefs, Goddard Institute for Space Studies
In a recently published paper (ref. 1), we provide an objective, long-term, quantitative analysis of the effects of nuclear power on human health (mortality) and the environment (climate). Several previous scientific papers have quantified global-scale greenhouse gas (GHG) emissions avoided by nuclear power, but to our knowledge, ours is the first to quantify avoided human deaths as well as avoided GHG emissions on global, regional, and national scales.
The paper demonstrates that without nuclear power, it will be even harder to mitigate human-caused climate change and air pollution. This is fundamentally because historical energy production data reveal that if nuclear power never existed, the energy it supplied almost certainly would have been supplied by fossil fuels instead (overwhelmingly coal), which cause much higher air pollution-related mortality and GHG emissions per unit energy produced (ref. 2).
Using historical electricity production data and mortality and emission factors from the peer-reviewed scientific literature, we found that despite the three major nuclear accidents the world has experienced, nuclear power prevented an average of over 1.8 million net deaths worldwide between 1971-2009 (see Fig. 1). This amounts to at least hundreds and more likely thousands of times more deaths than it caused. An average of 76,000 deaths per year were avoided annually between 2000-2009 (see Fig. 2), with a range of 19,000-300,000 per year.
Likewise, we calculated that nuclear power prevented an average of 64 gigatonnes of CO2-equivalent (GtCO2-eq) net GHG emissions globally between 1971-2009 (see Fig. 3). This is about 15 times more emissions than it caused. It is equivalent to the past 35 years of CO2 emissions from coal burning in the U.S. or 17 years in China (ref. 3) — i.e., historical nuclear energy production has prevented the building of hundreds of large coal-fired power plants.