Alpha particles

Here's a photograph of a little demonstration cloud chamber:

To the right in the chamber, diagonally across the picture, there's a tungsten welding rod. These rods work better if traces of other substances are added to them and this one has a small amount of thorium oxide. Thorium is a naturally occurring radioactive substance so these welding rods are very slightly radioactive, not enough to endanger the lives of welders - obviously! - but enough to be interesting in the cloud chamber.

Thorium is chemical element number 90. It has chemical symbol Th. The isotope we find in nature is ²³²Th, "thorium-232". From webelements.com we find that its half-life is 14 billion years - it stays radioactive for a long, long time, but at a low level.

Look at the two misty streaks heading left from the welding rod. Each of these is the path of a single alpha particle, a nucleus of the element helium, ejected forcibly from a thorium nucleus when it spontaneously decays. As it travels through the air in the chamber the fast-moving alpha particle knocks electrons out of atoms, leaving a trail of ions behind it. The chamber, cooled well below room temperature, contains alcohol vapour as well as air. Each ion becomes the centre for the formation of a little droplet of liquid alcohol and the path of the alpha particle becomes visible as a string of liquid droplets. The cloud chamber, Nobel-prize winning invention of the Scot CTR Wilson, doesn't quite show us individual electrons and ions but it does let us see where they go and how they move.

Let's do some sums. Alpha-particles emitted in radioactive decay all have more or less the same energy, depending only on which radioactive nucleus we started from. There's a table at this link, telling us that an alpha particle emitted by ²³²Th has an energy of 3.8111 MeV.

The eV - "electron-volt" - is the convenient unit of energy in the subatomic world. We need 14.5 eV of energy to completely liberate an electron from a nitrogen atom and make it into an ion - ionise it; 13.2 eV for an oxygen atom. The average energy of a photon of sunlight is about 2 eV. "M" stands for "mega": one million. So just one of these ²³²Th alpha's will ionise hundreds of thousands of atoms.

(Yes, we call them "alpha's" in a familiar way. Maybe even α's, using the Greek symbol. They're our friends.)

As an α travels away from the nucleus that spawned it, through the air of the laboratory, it loses energy by knocking electrons out of atoms. Each ion created robs the α of roughly 30 eV. How far can it go in air?

The answers to such questions are well known, even available online. From the NIST ASTAR program, available online, we learn that a 4 MeV α stops in a column density of 0.003 grams per square centimetre of air. We need to think about how much material the α meets, and this is best expressed as the amount of material in a cylinder of 1 cm² area. This hypothetical cylinder should include 0.003 grams. If it's very tenuous, like the air we might meet in the stratosphere, the cylinder has to be very long. At sea level where the air is much denser, it will be shorter. But it needs to include 0.003 grams. Air at sea level has a density of just over 0.001 grams per cubic centimetre, so the α will travel (0.003 grams per cm²)÷(0.001 grams per cm³) = 3 cm - slightly over an inch, just as we see in the picture.

In solar flares, ions sometimes get accelerated to energies of MeV and beyond, by strong electric fields, not in radioactive decay. The same ideas apply. How far will they go? How much will they heat up the solar atmosphere in the process? In the cloud chamber we can see much of the relevant physics, even for this remote and exotic application.

Celtic Connections

Celtic Connections is Glasgow's annual, winter festival of "roots music", Scottish and Celtic certainly but also genres like Country and Western that have some kinship, and indigenous musics from across the globe. Most music that still retains some element of "authenticity", according to some criterion or other, can turn up there. I don't enjoy only "clattery, atonal music" so there are always many more appealing gigs than I have time or money for.

My wife and I looked through the 2017 programme together. It's always a pleasure to find musical common ground. Both of us laughed out loud, involuntarily when we saw Olivia Newton-John's name among the headliners. Ms Newton-John started in country music, she's had a huge, starry career in popular music, she'll sell out at Celtic Connections and her audience will be ecstatic. So why did we laugh? Perhaps even the organisers expected some people to laugh when they wrote: "It might seem a startlingly long way from Sandy in Grease to Celtic Connections." Or perhaps the alternative version, "Olivia Neutron-Bomb", hybrid of 1980s headlines, popped up unbidden in both our minds. Pesky neutrons, there's so much to say about them, even before thinking of Ronald Reagan and the French nuclear weapons programme.

Amusement passed and attention moved on. I blogged about the famous photo of the 1927 Solvay Conference. I did not expect Olivia to pop up again so soon but she did. My mind is still slightly blown by the discovery that she is the granddaughter of Max Born, one of the founders of quantum mechanics. Love song pop music bumps up randomly against the fundamental nature of reality.

Here's the Solvay Conference picture again. Born is second from right in the second row, with Niels Bohr on his left-hand side at the end of the row. The Scot CTR Wilson is just to his left in the front row.

Born recognised that matrix algebra lay at the heart of Heisenberg's weird new view of inside the atom. Born was the man who saw how to use the wave in Schrödinger's wave equation to calculate the probability of finding the particle. No more little billiard ball particles ever again, but an elusive cloud of possibility. His contributions were recognised in the 1954 Nobel Prize for Physics.

I've been scouring - well, glancing at - Olivia Newton-John's discography. Can we find traces of fundamental physics? I'm afraid I struggled. Those country songs about home towns and true love, Banks of the Ohio, Take Me Home Country Roads, If You Love Me Met Me Know, there's not much traction there. But here she is singing, Let Me Be There: an impossible request. When the listener carries out that experiment that reveals exactly where Olivia is, there is no way of telling where she will be found. There is a most likely position, and a region around that where she has, say, a 90% chance of being found but we can never say exactly where she will be. "Let me be there" is a plea that might be satisfied, by chance, but there is no agency that can see to it for her; no hidden variables that can be manipulated to her advantage.

"This is nonsense," you say. "If Olivia wants to be in Ohio, or Carradale, or in her lover's arms, of course she either will or won't be." In practical terms this is true. Quantum effects play no role in predicting positions on the scale of everyday life. But if Planck's constant were bigger, we would have to think about these possibilities and they are an essential part of understanding the subatomic world.

I doubt I'll be be there myself - sorry, too far from my musical comfort zone - and I don't expect any of this will trouble very many others in Olivia Newton-John's Celtic Connections audience. But really, if she sings Let me be there, feel free to ask her what her grandfather would think.

From Bern to Solvay

I spent last week at the International Space Science Institute (ISSI), Bern, Switzerland. I was there with a team of scientists aiming to understand better the role of energetic ions in solar flares.

Our team went really well, excellent discussions, progress on our key questions, but by Friday afternoon everybody else had left. I worked for a little bit on the team website before skiving off to become a tourist for a few hours. (Complete aside: let me mention how surprised I was by the etymology of skive. As one of those few thousand words we all had in common in school, and a very important one, I always assumed it was a Scots word; not according to the Oxford English Dictionary).

Albert Einstein lived in Bern for a few years at the very start of the 20th century, famously working as a patent clerk at the same time as puzzling over questions like, "how would the world look to somebody travelling with a beam of light?" A scientific paper he wrote in 1905 earned him the Nobel Prize in Physics and it probably isn't even the most important paper he published that year. The time he spent in Bern represents an extremely important episode in the history of science and it's no surprise that the apartment he lived in is now a tiny museum, the Einsteinhaus.

On Friday afternoon I visited the Einsteinhaus. There are nice displays on his family life, his career, his fame. Among them my eye was caught by a mounted print of the photo at left, showing attendees at the 1927 Solvay conference. It's a very famous photo, showing many of the biggest names in 20th century physics all together at the same meeting. Like most physicists I've seen it often, in various places, and noted for example CTR Wilson, our great Scottish genius of experimental physics, second from right at the front.

In the Einsteinhaus I took some minutes to look again at this picture. It's amusing to see the faces that go with those famous names. Who looks confident, bold, who shy and diffident? At the far left-hand side I was slightly surprised to spot two gentlemen almost side by side whose names are often met together in the textbooks, Messrs Peter Debye and Irving Langmuir. Langmuir is right at the left end of the front row, with a rather natty cane. The moustachioed Debye is peering over Langmuir's right shoulder.

In very hot gases, like those met in the outer layers of the Sun, collisions between atoms are sufficiently violent that they completely remove electrons; ionise the atoms. The constituents of the gas are electrically charged. We call the gas a plasma - a term first used by Langmuir, apparently. Plasma behaves in all sorts of new and interesting ways compared to the ordinary, neutral gas we're surrounded by here at sea level on Earth.

The Debye length is the greatest distance over which an electric field can persist in a plasma - because its constituents are electrically charged, if we try to impose an electric field the charges will just move to short it out. Langmuir waves are something like sound waves but with electric fields playing a central role. Their natural frequency, the plasma frequency, is one of the basic numbers that describe a plasma. The Debye length is another. In the first few pages of any book on plasma physics we meet the names of Langmuir and Debye so it tickled me to find the two of them side by side in the 1927 Solvay Conference picture.

Both were Nobel Prize winners, for Chemistry rather than Physics. Langmuir later became rather notorious for attempts at rain-making. The great German scientist Arnold Sommerfeld was once asked what was his greatest discovery. "Debye," he replied.

A maths problem

A very rare sort of alfalfa sprout is highly valued in the health food shops of the world. We discover that it grows wild on a remote, uninhabited Scottish island and set out to make lots of money. On our first visit we harvest one tonne. However the sprout population does not completely recover from harvesting and we soon discover that each harvest yields only 96% of the mass of the previous one, so that the second harvest gives us 0.96 tonnes, the third one 0.96² = 0.9216 tonnes, etc. Supposing we could go on indefinitely, what is the maximum total amount of sprout we could ever harvest from this island?

I look up

A smartphone makes it so easy to look at email. No dismal slow boot process; I can get straight to the latest spam, grumble, exciting research news. It's so easy to just deal with simple emails over the morning coffee, maybe also glance at news, Twitter, etc. All of a sudden it's time to rush out.

Last Thursday went exactly like this. Noticing the clock I rushed around, pulled on my bike gear, shot out to the garage where my bike is; helmet, bike lock, backpack pulled on, lock the garage again, time to zoom off to work.

The weather here has been cloudy and grey for a couple of weeks. Last Thursday was different. As I turned from locking the garage door a seagull caught my eye, brilliant white drifting leisurely across a featureless blue sky. Higher up two swallows darted about. It struck me that they'd probably been here since April or May without catching my eye until now, at the start of July. I wondered why I don't pause and look up more often.

Consume Red

As a young fellow I formed a rather definite view of university. One went there to learn from people who had worked over many years at understanding their chosen subjects, at developing their own sophisticated understanding and, in most cases, going beyond the books to contribute new ideas and knowledge. Often these people were strong, distinctive characters with broad interests. They WERE the university - not the buildings or the history - and one learnt so much from them, not just about their subjects but about being a person.

The original conception of this blog involved several authors, colleagues in the old DACE. Our several disciplines would bump up against each other and all sorts of conversations would take place, a virtual mirror of those that happened spontaneously in the corridors, or especially in some of the day schools when we took pleasure in mixing up different academic disciplines. That hasn't worked out so instead you get just me. If you're looking for a blog purely on astronomy, adult education, politics or whatever, you'll be disappointed. What's here is my own, personal jumble of interests. "How to build your blog" websites will tell you this is not how to build an audience. Sorry. Me is what's here.

There's been Astronomy, adult education and universities but the promised "clattery atonal music" has been gravely lacking. I've let the reader down badly - no Henry Cow, Derek Bailey, John Zorn. So here in seriously belated recompense is a link to Ground Zero's Consume Red. It starts with the shrill, piercing sound of the Korean hojok, played by Kim Suk Chul, 82nd valuable intangible cultural asset of the Republic of Korea; "brilliant music sacred enough to blow away any puny ideas about copyright." Over the next minutes the musicians of Ground Zero start to join in, scratchy, electric improvisation over the keening cry of the hojok, getting more coherent and louder until a huge, monolithic noise develops over a brutal, thumping rhythm section. It's intense, claustrophobic but fantastically invigorating; I know of few other recordings quite so crushing. I love it!

I don't think it should be freely available on YouTube like this but you wouldn't get to hear it if it wasn't. I bought a legit copy from ReR Megacorp - it's only £5.00 at the moment.

If you meet me in Glasgow University it may be in the hope of learning something about Maths, Physics or Astronomy. Perhaps there will be some illustration or remark based on a book, a film, music I've enjoyed; maybe less overwhelming than Consume Red but I hope they add to the experience anyway.

Tycho Brahe, Great Britain, internationalism

Last week we marked the end of this year's Access programme in the normal way, with a "presentation evening". We invite everybody who's completed Access to come along, with pals, parents, partners, children if they wish. There is a little ceremony in which they are each presented with a certificate testifying to their completion of Access and the grades they achieved - one of this year's students has shared a photo of his certificate on Instagram. At the end I made just a few concluding comments, leading to the most important points: "well done, and good luck for whatever comes next!"

To fill out the concluding comments I drew on some tales of Tycho Brahe, the 16th century Danish astronomer. These tales are not in short supply. Tycho must be the prototype of the gothic horror movie philosopher wizard in his castle, surrounded by an array of lurid courtiers. The real castle was called Uraniborg, designed according to thoroughly thought-out philosophical principles and constructed on the island of Hven, in the Øresund between Denmark and Sweden. It no longer exists but woodcuts and prints from the time show a most amazing building. He maintained a substantial household there, assistants and visiting students, as well as cooks, servants, estate workers, a lutenist and indeed a dwarf jester called Jeppe. Some more of the more lurid Tycho tales are recounted here.

The Brahes were one of the ruling families of Denmark and Tycho was born to power and influence. Most Brahes became soldiers or statesmen; the Church would have been a more normal route for an intellectually inclined child. Clearly Tycho was a strong character who forged his own path, but his high birth meant that no path was closed off to him. Now many, many more people are able to work at studying, understanding and advancing knowledge.

In 1590 the histories of Scotland and of Astronomy collided briefly when King James VI sailed across the North Sea to collect his new bride, Anne of Denmark. During his stay in Denmark he visited Uraniborg, "the spot to which the eyes of all the learned men of Europe were directed", and took great delight in the intellectual discussion he enjoyed there. Tycho corresponded regularly with other learned men across the continent, exchanging and developing ideas, and his name was widely known (and yes, they were "men" - sorry, that's the way it was). Scots visitors to Uraniborg were not so terribly unusual and Tycho knew people in Scotland. Before he left Denmark King James granted Tycho a 30 year copyright on his works in Scotland, and presented him with two large guard dogs.

I wanted to use this story to illustrate the international character of academic research, and in particular to emphasise that this has been the case for hundreds of years. I wanted also to make a further point about the value of meeting people from other countries and cultures, as one will in higher education, and the importance of making them welcome, irrespective of one's voting preference in the EU referendum. I was happy that everybody in the room, as far as I could see, wanted to applaud at this point.

King James VI, of course, also became James I of England shortly, although it took a further century for the Parliaments to follow where simple heredity had first led. With the integrity of the United Kingdom once again up for discussion, this incident from four centuries ago seems to resonate in several respects with the worrying modern world.

Scotland

"....Scotland as a damp, brooding place in which man's nobler instincts are invariably forced to confront a recurring cycle of evil brought on by politics and financial gain. Even the Christian institution of marriage is portrayed as a breeding ground for insanity and death,....." I edited out the word "medieval" at the beginning. Didn't seem necessary, really. Naughty me. These words are from http://www.mondo-digital.com/tess.html, by the way.

Neutrons

One can never read too many books about neutrons so I'm tackling Neutrons, Nuclei and Matter by James Byrne. Neutrons do everything: weak, strong, electromagnetic, and of course gravity. Everybody who remembers high school chemistry knows that the nucleus of the atom is made up of protons and neutrons. Hit a nucleus hard enough, with a proton for instance, and neutrons may be liberated. A neutron on its own is radioactive: unleash a cloud of neutrons and half of them will have disintegrated into other things inside about 10 minutes. Neutrons can penetrate deeply into substances that are opaque even to X-rays and are so useful as probes that the UK government has spent 100s of millions of pounds building the ISIS neutron source (I know - an unfortunate name nowadays).

In solar flares, individual ions are accelerated to high energies. They collide with other ions and produce all sorts of by-products, including neutrons. Some of these escape from the Sun. If we detect them with spacecraft experiments they can tell us about the events of the flare. Even light takes eight minutes to get here from the Sun so the neutrons need to be pretty high speed if they're not going to decay long before they reach Earth. When they decay they glow faintly in X-rays; maybe we'll be able to detect this radiation.

Anyway the prompt for this posting was not so much the wee neutrons themselves as the Preface to Neutrons, Nuclei and Matter, which begins by discussing George Bernard Shaw, looks back into scientific history, references several poets and includes a quote from Shelley, who Byrne is sure "would have understood what many of our legislators and educators appear to have forgotten: that science is concerned first and foremost with revealing the secrets of nature, and scientists have more in common with artists than they have with accountants, politicians or lawyers." What a great start!

MD40

What a lovely girl Gwen was, bright, pretty, outgoing, popular with teachers and class mates alike. School work came easily to her. She was particularly good at languages. Everybody assumed she would go to university and follow some professional career, like most of the other bright kids in her well-off part of town. But she and a boy called Daniel had caught each others' eyes and this secure, sunny future evaporated when she got pregnant at 16. Only when little Jessica reached the age of 10 did Gwen's thoughts turn again to education. Daniel - still with her - was supportive, but was there any way for her to recover what had slipped away?

Kyle was always a laid-back kind of guy, easy going, never had to work at enjoying life. He was bright but nothing in school outside football held his interest. He had little thought of further or higher education and drifted into a job as a salesman. Despite himself he was a success, earning good money, smiled at by managers but he was watching his mates from school progress through university to become the sort of people who told him what to do. He began to feel both that he'd missed out on something, and maybe also that he had more to offer the world than an easy manner and the gift of the gab. But how to step sideways from a well-defined, if limited career path?

Later in life Tommy told people, "my school was like a battleground. Nobody should have been allowed to go to that school." He escaped as soon as he could and started as an apprentice in an engineering works. Promotion to Supervisor took only a few years and he moved to a nicer part of town with the wife and kids he'd acquired in the meantime. He enjoyed learning from the graduate engineers he worked beside but he also began to realise they weren't any brighter than him. One even seemed pretty dim, despite the letters after his name. Sadly the goodwill of your immediate bosses is no protection from the winds of globalisation and Tommy found himself out of a steady job before his 30th birthday. Although his skills and his contacts kept him in short-term contract work he began to wonder if this was the moment to go back to education. But how to get there?

These aren't real people but their stories are like those I meet on our part-time, mature student Access programme. I could have invented lots more: people whose schooling was disrupted by family break-up, women chased by teachers into Arts degrees even although they loved science, people who suffered from depression in late teens... I imagine most of us would agree there should be ways back into education for such folk, both so that they can grow and develop as people and so that the economy can benefit from the full employment of their abilities. Adult routes to university do exist: university Access programmes like ours; the Scottish Wider Access Programme Access courses and many other possibilities in the Further Education Colleges; the Open University. But current "widening participation" policy in Scotland focuses almost entirely on the Scottish Index of Multiple Deprivation (SIMD), and specifically on measures to encourage participation from the bottom 40% of postcodes as classified in the SIMD; so-called MD40. Are our institutions rewarded for helping Gwen? Only if she now lives in a MD40 postcode area. If she does, the fact that she went to a good school would be irrelevant. Tommy? He shouldn't have moved to a better part of town. Kyle? Depends where he lives.

Obviously our Access course still operates and we could be useful to all of these people. Some of the other possibilities might also work for them. The Part-Time Fee Grant is a great help to Scottish adults coming back to study and eligibility depends on income, not where they happen to live. But the lack of recognition in policy of the complexities of adult lives, and in particular the simple fact that adults don't have to stay where they were born, casts a shadow over this kind of work. If times get really tough, institutions will focus exclusively on the activities they're rewarded for. Of course we should start with identifiable, disadvantaged communities, but we need to think more broadly than MD40 if our answer to Gwen is not to become, "you went to a good school. You had your chance. Should have kept your knickers on."

A walk in the shadow of Chernobyl

I spent one of the last hours of 2015 walking in Whitelee Forest, on the Eaglesham Moor. I visit those forest tracks every now and again and they have already featured once in this blog. For the benefit of non-weegies, the Eaglesham Moor is a large area of high, rough moorland just south of Glasgow. After festive indulgence and indolence some cold breeze, rough ground and maybe a wee rain shower or two were called for.

Things are changing out there. Whitelee Windfarm continues to expand; or maybe other wind power developments are springing up on its edges. Anyway the road has been resurfaced, there is new fencing, access roads across what used to be solely farmland, fire rendezvous points. The picture at left looks down the road to the Myres Hill turbine test site, which was there before the big windfarm. It shows the rough, informal parking arrangements as they were in 2009 but improvements to road and fencing have left less space for cars. I first discovered these places just by following my nose on a bike run sometime around 1990. On nice days they're very popular with people looking for wee strolls somewhere close to the south edge of the city so it seems a shame that parking has been made harder.

Whitelee has civilised the wild, boggy, unfrequented Eaglesham Moor I first started to discover in the 1990s. I'm all for wind power, however, and you can still find boggy, unfrequented corners if you work at it a little. Walking about after dark helps!

I followed the sign across the field behind Carrot Farm and climbed up the track towards the Munzie Burn, aiming for a circular walk (made possible by a track established in the forest only in the last few years - something else that has changed). Eventually I came to an area where trees are being felled, shown at left. The light had faded a lot by then, hence the poor picture. Signs forbade me to proceed unless authorised. I'm seldom "authorised". Fortunately I didn't need to proceed and could turn right at this crossroads but I started to think about the fact of the felling.

Some years ago I was told about the origin of Whitelee Forest (where and by whom is a story, too. I'll save that for another time unless people tell me what follows is wrong). The rough, upland Eaglesham Moor used to be devoted to sheep farming. That ended after the explosive events of 26 April, 1986 at the Chernobyl nuclear power station in Ukraine. In the days that followed, radioactive fallout was deposited over most of Western Europe. ¹³⁷Cs (caesium-137) is a radioactive isotope of caesium that doesn't occur in nature, but was one of the most important sorts of waste carried across the continent following Chernobyl. Like all the best isotopes it has its own Wikipedia page. It accumulates in the bodies of animals that eat it. It has a half-life of 30 years, i.e. a fixed amount of it is half as radioactive after 30 years. So we have to be wary of eating animals that have been gobbling ¹³⁷Cs and it was almost 25 years before many upland farmers in the UK were allowed to sell the meat from their animals. Farmers can't survive indefinitely when they can't sell their animals and big bits of the Eaglesham Moor wound up sold for forestry.

Bits of Whitelee Forest have been getting cleared for a year or two now but coming across this area of felling, in the half-dark, got me thinking about this more than previously. I thought I remembered that a forest of conifers comes to maturity in about 30 years. I was wrong; it's more like 70 but selective felling might start from 20-25 years; just the right timing after all. The shadow of Chernobyl still hangs over Whitelee.

Chernobyl was a destructive incident whose wide-ranging consequences highlight the possible negative side of nuclear energy. There is no doubt that it has had an enduring effect on perceptions of nuclear energy, and must be one of the factors impeding its acceptance as part of a low-carbon future - just look at this article con, or this one pro. The phrase "low carbon" of course brings us back to Whitelee, second biggest windfarm in Europe.

Many of us head out onto various corners of the Eaglesham Moor to get away from complex, modern lives; to spend an hour or two away from machines and crowds. How strange to realise that the management of these places has for decades now been determined by aspects of one of the big technology debates of our time: how to keep heating and lighting and heating our homes, and powering our factories, without simultaneously driving catastrophic climate change. And how weird, particularly, to recall that the Whitelee Forest's existence and development stems from the few hours of the Chernobyl nuclear accident, 2300 km away, in 1986.

This won't stop me from enjoying the Moor and the Forest. If anything these realisations will add a certain piquancy and the quiet of the forest will be just the place to mull over these stories and their meaning.