For those of you have been following the progress of the Dungeness C story - Anthony Dunning has written an explanation about nuclear power and where it comes from which dispels the myths and missconceptions.

Atoms

There are 92 naturally occurring chemical elements. An atom is the smallest unit of an element. So there are 92 different chemical atoms. The simplest atom is the hydrogen atom and the most complicated naturally occurring is the uranium atom. In what follows, we shall drop the epithet “naturally occurring” and it will be assumed we are talking about naturally occurring atoms, unless we specify otherwise. The elements can be arranged in the so-called periodic table devised by the Russian chemist, Dmitry Mendeleev in the 1860s

All of the wonderful things we see around us in the natural and man-made world are made up of these 92 varieties; the sky, the stars, mountain ranges, the seas, the plants, the animals and your favourite woman or man are made of these Lego pieces. Wonderful, innit!

But, remarkably, it gets much simpler. Nature, or was it God? – I leave you to choose – found a way to construct the 92 atomic varieties out of just three ingredients, and added a fourth, a bit more mysterious, so that the three could interact and “talk” to each other.

These three basic ingredients, with which all the recipes to delight can be made, are called the proton, the neutron and the electron. The fourth one is the photon. Let there be light!

Atomic and nuclear size

All isolated atoms are electrically neutral and about 10^-10m across, so about 10 billion of them fit into a metre. We may consider they are roughly spherical. The proton carries one unit of positive electric charge and the neutron carries no residual electric charge; both are about 10^-13m in size, 1 trillionth of a metre. The electron carries one unit of negative electric charge and appears to be a point particle – no extensive size.

In every atom, its component protons and neutrons are ring-fenced in the nucleus, which therefore has as many units of positive charge as there are protons in it. The neutrons contribute no electrical charge. Protons and nucleons are collectively called nucleons. The electrons flutter around like butterflies outside the nucleus; there is the same number of them as the number of protons in the nucleus, which is why an isolated atom is electrically neutral – equal numbers of oppositely charged protons and electrons.

We haven’t mentioned mass yet. Bizarrely, the electron’s mass is approximately one two thousandth that of the proton or neutron, which have similar though not identical masses. Being so light, we may think of them as fluttering like butterflies. By the way, when we say mass, we mean rest mass, the one that appears in E = mc².We don’t really know yet why the disparity in mass of the basic ingredients exists, but it is felicitous, for the world as we know it would be very different or even inexistent if this were not the case. We wouldn’t be here to observe it.

An essential concept is the indistinguishability of all protons, and of all neutrons and of all electrons. This is true and fundamental for the development of physical theory. All protons are identical; there aren’t fat ones and thin ones, blondes and brunettes. This is serious equality and no diversity. Boring it may sound, but look at the glories of the world that can be created from such conformity. The same goes for neutrons and electrons, though not photons.

Elements

Which element a given atom belongs to is determined purely by its number of electrons fluttering around the nucleus, or, what amounts to the same thing, the number of protons in its nucleus. We noted above that these two numbers are the same so that the isolated atom is electrically neutral.

Thus hydrogen, the simplest atom, has one proton in its nucleus and one electron fluttering close by outside. As a matter of fact, that’s all there is to an atom of “ordinary” hydrogen. But we haven’t said much about the neutrons. One might imagine that there could be as many neutrons as one liked in the nucleus as they do not affect the overall electrical neutrality of the atom. This turns out to be not true, although nuclei of the same element may have variable numbers of neutrons within certain limits.

Atoms with different numbers of neutrons for a fixed number of protons (and electrons) are called isotopes. To complete the picture, atoms with different numbers of protons (and electrons) for a fixed number of neutrons in their nuclei are called isotones. Radioactive isotopes have many valuable applications in medicine, notably in cancer treatments, and diagnostic engineering

Returning briefly to hydrogen, there are three isotopes: ordinary ₁H¹ (1 p, 0n), deuterium ₁H² (1 p, 1n), and tritium ₁H³ (1p, 2n). Here p means proton, n means neutron, the superscript represents the atomic mass number = sum of the nucleons and the subscript represents the atomic number = number of protons and characterized by its chemical symbol.

A random selection of the elements

Radioactivity

Radioactivity is a natural phenomenon. It emanates from certain types of rocks containing, notably, uranium or thorium salts in many countries of the world, and has no doubt played a role in the evolution of all living things on planet earth over the last 3.5 billion years.

Henri Becquerel discovered radioactivity in his Paris laboratory on 1 March 1896. The press with their usual perspicacity in scientific matters didn’t notice. He was investigating the effect of uranium salts on photographic plates. In 1903 he was awarded the Nobel Prize for physics jointly with the Curies (Marie and Pierre).

It turns out that some nuclei, bubbling as they are with protons and neutrons, are stable and therefore do not emit radiation or particles, or indeed disintegrate, and others are unstable and do. It’s all a question of energy, especially potential energy, that may be converted into kinetic energy (motion) but we don’t need to delve into the technicalities here. Suffice it to say that, in the hustle and bustle inside an unstable nucleus, occasionally a particle finds its way out, or gets thrown out – a bit like people leaving or being ejected from a rowdy cocktail party.

The naturally occurring radioactive isotopes, with their half-lives and percentage natural abundances are set out in the following table. The symbol in the “Isotope” column, e.g. ₁₉K⁴⁰ means potassium (i.e. kalium), 19 protons (all potassium atoms have 19 protons), and 40 nucleons = mass number; there must of course be 40 – 19 =21 neutrons in the nucleus of all atoms of this isotope of potassium. Under “Emissions” Mev = 1 million electron –volts, a unit of energy. 1ev is the energy an electron gains when it “falls” through a potential of 1 volt. The half life of an assemblage of atoms of a radioactive isotope is the time it takes for half of the atoms to decay. 238g of uranium238 contains about 6.022×10²³ atoms; so after 4.51 billion years (see table) there will be about 3×10²³ of them left. A free neutron outside the nucleus has a half life of 12m. So, if we have a million neutrons, after 1h there will be ½x½x½x½x½x1,000,000 or 31250 left. It’s classical exponential decay. The first example looks as though nothing much has happened in 4.51 billion years, but the second on a much more human timescale shows that quite a lot has happened in 1 hour.

From the table, we note that these naturally occurring radioactive species have extremely long half lives, billions of years, for obvious reasons; if they didn’t, they wouldn’t still be around. The majority of radioactive atoms, however, have extremely short half lives of the order of seconds to days, some so short that it is difficult to measure them, for example £ 10^-21s (less than one zeptosecond)!

Many artificially radioactive isotopes are created in nuclear reactors. Many of them provide essential application, especially in medicine and diagnostic engineering. Others are waste products, some of them with half lives of months, years or centuries, which means they have to be rendered harmless or disposed of. Let us remember though that the dangers should not be exaggerated. The half life is not the only parameter; the energy of the particles or radiation emitted and their absorption coefficients in air, water and readily available containment materials are also significant for mitigating the problem.

Remember also that when a radioactive atom emits its radiation to reach a more favourable lower energy state, that’s it; it doesn’t keep doing it, although if the new atom created by the first emission is itself radioactive, then the process continues with a different radiation until a non-radioactive atom is created at the end of the chain.

So, what are the ways in which an atomic nucleus loses energy by emission? In simple terms there are five ways:

1. α-emission: the nucleus emits an α particle which is a helium nucleus, consisting of 2 protons and 2 neutrons. It carries an electric charge of +2 units. So the atomic nucleus becomes that of an element in the periodic table with 2 fewer protons. Energy and momentum are conserved; the nucleus recoils, and the α moves off in the opposite direction to that of the recoil with a certain amount of kinetic energy which it gives up to the surrounding atoms.

2. β-emission: the nucleus emits a β-particle with either -1 unit of electric charge (an electron) or +1 unit of electric charge (a positron). The particle is emitted by the nucleus; if it is an electron, it is not one of the electrons fluttering outside the nucleus. Since both the electron and the positron carry electric charge the atomic nucleus changes its charge and therefore becomes one of a different element. Energy and momentum are conserved. As noted earlier, the electron (positron) is much lighter than a nucleon, and since they share the energy, it moves quite fast The energy spectrum is continuous from almost zero up to a maximum, so, in order to conserve energy in the process (conservation of energy being a fundamental law of physics,), there must be some invisible other particle to balance the books. It is the neutrino.

3. γ-emission: the nucleus emits γ rays. These are very energetic versions of ordinary light. They are plain vanilla electromagnetic waves, but of a much higher frequency, i.e. shorter wavelength, and travel at the speed of light. This type of emission doesn’t change the chemical nature of the atom; it remains the same.

4. neutron emission: the nucleus emits one or more neutrons. Unlike α and β emission here again the nucleus remains that of the same chemical element.

5. Fission: this is not so much the emission of particles or radiation but involves the splitting of the atomic nucleus into two more or less equal parts, and is usually accompanied by the emission of other particles (α or β or neutrons) or radiation. The amount of energy released per nuclear fission is impressive (~5Mev).

It is of course this fission process that is, literally, at the core of nuclear power. There are incontrovertible physical reasons why the energy density in atomic nuclei is vastly greater than that contained in molecules like those in coal, oil and natural gas, which in turn is far greater than that available in wind and wave power. Having laid down some foundations in this article, maybe we can consider this issue, together with the physics of nuclear power stations and radiation safety issues in subsequent articles. We might even go into the force fields involved: the electromagnetic field, the weak nuclear force field and the strong nuclear force field.

There article will be followed up soon. . .

Local interest groups and a small number of residents attended the ‘Eco –Tourism summit’ at the RSPB visitors centre on March 3.

Although only 24 people attended, the meeting was generally thought to be a success with important issues addressed and discussed.

Representatives from the wildlife organisations on the Marsh, the Romney Hythe and Dymchurch Railway, Angling Associations, Shepway Cycle Forum and several Conservative Councillors were among those present.

Many speakers were strongly in favour of the initiative, although sometimes the meeting was a fractious as attendees disagreed on several issues.

Concerns were raised that residents did not want extra tourists visiting the area and the current infrastructure, especially the lack of public toilets, would not be able to cope with an increase in numbers.

Chris Kirkham of Discover Folkestone cautioned against Dungeness becoming ‘tawdry and tacky’ if initiatives were not well managed.

The need to create jobs was repeatedly stressed and caused some of the sharpest exchanges.

Malcom Dyer of Romney Marsh regeneration Partnership said, ‘we have to provide something that will improve the economic wellbeing of the area.’ Conservative Councillor Russell Tillson echoed this point and cautioned that any plan would likely need a ’15 to 20 year timeframe.’

Resident Brian Godfrey raised the strongest concerns that the project would fail. Mr Godfrey criticised the speakers, saying ‘not one of you has talked directly about job creation.’

Lambasting Marsh-based organisations and councils for the lack of communication, Mr Godfrey also raised concerns that charitable organisations were taking over vast swathes of the Marsh and were stifling development and improvement of infrastructure.

Conservative Councillor Carole Waters criticised Cllr Beaumont for ‘sounding naive.’

Speaking after the meeting, Cllr Beaumont admitted that the number of attendees was not as high as hoped, saying several organisations had expressed interest but were unable to send a representative.

Cllr Beaumont accepted the concerns raised but emphasised that an alternative plan was needed for the Marsh given that Dungeness C will not go ahead.

Cllr Tillson, who had previously called plans ‘cloud cuckoo land thinking’ said ‘I fully support any initiative to promote the Marsh,’ and added that he was pleased Ms Beaumont had been alerted to some of the difficulties faced by such projects.

The issue of the Marsh has become a major political issue in the area, and the Eco-tourism summit has so far been a key point in the Liberal Democrat’s green message.

Since the government decision not to consider Dungeness C as a site for new nuclear power station, Conservatives continue to fight for Dungeness C. This divide seems to be gaining in importance and could have a great effect on the national election this year and the District elections in 2011.

From Tom Weatherleys Blog: http://fromunderthestone.blogspot.com/2010/03/mixed-messages-at-lib-dem-eco-tourism.html

Posted by Tom Weatherley http://fromunderthestone.blogspot.com/

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