Wednesday, 9 July 2014

On Microbial Antagonism, Antibiotics and Antibiotic Resistance

I am giving a course on Great Scottish Scientists at Strathclyde University and just started my talk on Alexander Fleming - who discovered penicillin in 1928.

The history of infectious diseases is fascinating.  Look closely at how life operates in nature and one can't help but marvel at the complex way different lifeforms interact. The delicate balance among species in nature must not be disturbed; something mankind is doing without regard to consequences. Come to think of it - we humans do a lot of things which can only be called irresponsible - but that is another story.

All life forms in nature operate on the same principle; it is the fight for survival.  Two essentials for survival are nutrients and space and this is what they all compete for.  From humans to microbes - it is the same struggle. Compete to survive!  Sometimes clever associations are formed for mutual benefits - ecosystems operate that way.  You break the chain by removing one species and part of the system collapses.

Historically, humans have suffered various forms of diseases caused by bacteria and viruses (microbes).  At times 50% of the population in Europe died because of rampant infections.  Louis Pasteur confirmed that such infectious diseases are caused by microbes whose sole aim appears to wish to increase their numbers and if humans could help them, then so be it.  Edward Jenner successfully developed vaccinations against smallpox and vaccination has proved to be very effective in controlling some diseases. Joseph Lister made surgery so much safer by using antispetics like phenol and alcohol.

But that is only a limited success.  Harmful bacteria lurk everywhere - from rose bushes to rusted nails.  Even human bodies harbour harmful bacteria which attack when the system is in a weakened state.

Let us not get it wrong - bacteria and viruses do not only attack and harm humans or big life forms.  They are fighting with each other with equal intensity.  Bacteria grow rapidly and need the resources - other microbes which come in their way have to watch out.  The best way to deal with the situation is by chemical means - produce chemicals that are toxic to invading bacteria.  This has been happening throughout the nature.  Plants produce such chemicals to fight microbial attacks, fungii do it, bacteria do it and we humans do it as well.
In 1922, Alexander Fleming discovered Lysozyme in human mucas, tears; in egg white and in all sort of places.  Lysozyme, as the name suggests, is an enzyme that lyses (dissolves) bacteria; but it only effects a few of them.

But what about using the chemicals that microbes produce to fight other microbes.  If we can find the right chemical that kills the infection-causing bacteria then we can use it to control the infection. Bacterial antagonism can really be put to good use.   Of course, the chemical must be tolerated by the human body and not be toxic so as to harm us as well. Gramicidin discovered in 1936 by Rene Dubos was one such chemical - good to kill bacteria but also toxic to humans - so no use to us.
Alexander Fleming discovered penicillin in 1928.  It is produced by the fungus penicillin notatum and the best source was found to be a cantaloupe in Illinois, USA!  Penicillin was found to be effective against gram positive bacteria (these are bacteria that have a particular type of membrane wall structure) and was effective in killing lot of infection causing microbes - pneumonia, meningitis and a whole lot more.  Penicillin is also tolerated by human body very well and this was to become an ideal weapon for fighting infections.
We call this class of chemicals antibiotics.
Streptomycin is another anitbiotic that was discovered by Selman Waksman in 1943 and it was very effective in fighting tuberculosis.

1940s and 50s were really the golden age of antibiotics.  Many more were discovered or synthesized, mainly derivatives of penicillin.  Penicillin alone saved millions of lives.

The thing about life is that there is never a final chapter.  Bacteria don't like getting killed this way and we soon started to see resistant strain of bacteria showing up.  The resistant strain are not affected by the antibiotic any more and we go back to either finding a new antibiotic that is effective in killing the bacteria or have the problem of reverting back to pre-antibiotic age when infections were a real problem.
Bacteria are great in producing resistant strains.  They have survived billions of years because they can quickly and efficiently adapt to changing environments. They multiply fast - so population of resistant bacteria builds up rather quickly. Bacteria mutate frequently and then they have at their disposal clever schemes for defeating the antibiotic attacks.  Bacteria can produce enzymes that breakdown the antibiotic molecules making them ineffective or they can cover the region where antibiotic would bind to the cell.  They also exchange resistant genes with other bacteria in the vicinity and spread the resistant genes very efficiently.

It is thus an ongoing war.  We have to keep inventing/discovering new antibiotics - stronger and stronger ones to fight the resistant strains. Something, we have not done very well for the past 40 years or so.  Drug companies did not see much money in this pursuit and governments also got complacent.  But now the problem of resistant bacteria is such that people are waking up to the reality - Alexander Fleming warned about this in 1945 and we all could see this coming but not much was done in the interim.

Even more complicated situation has arrived in the form that many bacterial strains are resistant to several antibiotics with some now resistant to all known antibiotics.  We soon will come full circle here.

In the highly developed societies with good hygiene and clean environment, people do not normally suffer many minor infections.  This also means that they do not develop immunities the same way as societies in the past, who were exposed to many more microbes as routine, did. We also live in much more crowded cities and we travel more. All this can spread infections quickly and efficiently.  When an infection strikes, we shall be less well prepared and the death rates will be correspondingly higher.

The prognosis is not good.

Sunday, 6 July 2014

Scottish Nobel Prize Winners

Scotland is a small country but its contributions in sciences and other fields have been disproportionately large.  This is evidenced by the number of Nobel Prizes awarded to people of Scottish origin or who have done their main work while in Scotland. In the following, I have collected brief biographies of the Scottish Nobel Laureates.   
Science for All  is a programme to promote science awareness in the community through talks on a variety of science related topics.  I started the programme in 2006 at the time of my retirement from Glasgow University. I continue to be associated with GU as an honorary fellow.  Further information about the past activity of the programme is available at
About Nobel Prizes
Alfred Nobel (1833 - 1896), a Swedish industrialist, amassed a fortune during his lifetime, with most of his wealth from his 355 inventions, of which dynamite  is the most famous.   An article in a French newspaper published an obituary of Alfred Nobel (instead of his brother's)  disconcerted Nobel and made him apprehensive about how he would be remembered.
Nobel's will specified that his fortune be used to create a series of prizes for those who confer the "greatest benefit on mankind“ in physics, chemistry, peace, physiology or medicine, and literature.
Nobel bequeathed 94% of his total assets, US$186 million to establish the five Nobel Prizes.  Economic Sciences was added in 1968.  
Nobel stated that the Nobel Prizes in Physics should be given "to the person who shall have made the most important 'discovery' or 'invention' within the field of physics.”

2016 Nobel Laureates in Chemistry:
Sir Fraser Stoddart was born in 1942 in Edinburgh and currently works in Northwestern University in Illinois.  He shared the Nobel with Professor Jean-Pierre Sauvage (University of Strasbourg) and Professor Bernard Feringa (University of Groningen).
The Nobel was awarded for their work of creating microscopic controllable machines that are more than 1000 times smaller than the width of a human hair.  Yet, they operate much-like large scale machinery with rings spinning round axles, components moving back and forth along tracks, platforms that rise and fall.

2016 Nobel Laureates in Physics:
David Thouless was born in 1934 in Bearsden. He is an emeritus professor at the University of Washington.
Michael Kosterlitz was born in 1942 in Aberdeen. He is currently affiliated to Brown University.
   Both David and Michael won "this year's Nobel for their theoretical work that discovered a set of totally unexpected regularities in the behaviour of matter, which can be described in terms of an established mathematical concept - namely, that of topology."This has paved the way for designing new materials with novel properties and there is great hope that this will be important for many future technologies."
Sir James W Black Uddingston, Lanarkshire (1924 – 2010)
Scottish doctor and pharmacologist.  He spent his career both as researcher and as an academic at several universities. Black established the physiology department at the University of Glasgow, where he became interested in the effects of adrenaline on the human heart. He went to work for ICI Pharmaceuticals in 1958 and, while there, developed propranolol, a beta blocker used for the treatment of heart disease. Black was also responsible for the development of cimetidine, an H2 receptor antagonist, a drug used in a similar manner to treat stomach ulcers. He was awarded the Nobel Prize for Medicine in 1988 for work leading to the development of propranolol and cimetidine.
Sir John Boyd Orr  1st Baron Boyd-Orr;  Kilmaurs, Kilmarnock (1880 - 1971)
a Scottish teacher, doctor, biologist and politician; studied at University of Glasgow. Received the 1949 Nobel Peace Prize for his scientific research into nutrition and his work as the first Director-General of the United Nations Food and Agriculture Organization (FAO). He was the co-founder and the first President (1960–1971) of the World Academy of Art and Science (WAAS)
Sir Alexander Fleming Darvel, East Ayrshire (1881 – 1955)
Discoverer of Penicillin  Nobel Prize 1945
Full Biography available here

Arthur Henderson   Glasgow (1863 - 1935)
A British iron moulder and Labour politician. He was the first Labour cabinet minister, the 1934 Nobel Peace Prize Laureate and served three terms as the Leader of the Labour Party. He was popular among his colleagues, who called him "Uncle Arthur" in acknowledgement of his integrity, devotion to the cause and imperturbability. He was a transition figure whose policies were closer to the Liberal Party for the trades unions rejected his emphasis on arbitration and conciliation and thwarted his goal of unifying the Labour Party and the trades unions.
Sir Peter W Higgs   Newcastle upon Tyne  (1929 - ... )
British theoretical physicist2013 Nobel Prize laureate and emeritus professor at the University of Edinburgh where he has stayed since 1954. He is best known for his 1960s proposal of broken symmetry in electroweak theory, explaining the origin of mass of elementary particles in general and of the W and Z bosons in particular. This so-called Higgs mechanism, predicts the existence of a new particle, the Higgs boson (which was often described as "the most sought-after particle in modern physics". CERN announced on 4 July 2012 that they had experimentally established the existence of a Higgs-like boson, but further work is needed to analyse its properties and see if it has the properties expected from the Standard Model Higgs boson. On 14 March 2013, the newly discovered particle was tentatively confirmed to be + parity and zero spin
John J R MacLeod   Clunie, Dunkeld  (1876 - 1935)
Scottish biochemist & physiologist. Studied at University of Aberdeen.  Chief interest in carbohydrate metabolism.
He is noted for his role in the discovery and isolation of insulin during his tenure as a lecturer at the University of Toronto, for which he and Frederick Banting received the 1923 Nobel Prize in Physiology or Medicine
Sir James Alexander Mirrlees   Kirkcudbrightshire  (1936 - ...)
Scottish economist and winner of the 1996 Nobel Memorial Prize in Economic Sciences. Mirrlees was educated at the University of Edinburgh (Mathematics and Natural Philosophy in 1957) & Cambridge (Mathematical Tripos) and PhD in 1964 with thesis title Optimum planning for a dynamic economy). Mirrlees and Vickrey shared the 1996 Nobel Prize for Economics "for their fundamental contributions to the economic theory of incentives under asymmetric information“. His students have included eminent academics and policy makers. 
Sir William Ramsay   Glasgow (1852 - 1916)
Scottish chemist who discovered the noble gases and received the Nobel Prize in Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements in air" (along with his collaborator, Lord Rayleigh, who received the Nobel Prize in Physics that same year for their discovery of argon). After the two men identified argon, Ramsay investigated other atmospheric gases. His work in isolating argon, helium, neon, krypton and xenon led to the development of a new section of the periodic table.  Named the gas, which is inert, with the Greek word for "lazy", "argon"
In the following years, he discovered neon, krypton, and xenon.  He also isolated helium which had been observed in the spectrum of the sun but had not been found on earth. In 1910 he also made and characterized radon.
Ronald Ross ??  Almora, India (1857 - 1932)  (Not sure about) 
Indian-born British medical doctor who received the 1902 Nobel Prize for Physiology or Medicine for his work on malaria. His discovery of the malarial parasite in the gastrointestinal tract of mosquito led to the realisation that malaria was transmitted by mosquitoes, and laid the foundation for combating the disease. He worked in the Indian Medical Service for 25 years. It was during his service that he made the groundbreaking medical discovery. In 1926 he became Director-in-Chief of the Ross Institute and Hospital for Tropical Diseases, which was established in honour of his works. 
Sir Alexander R Todd  Baron Todd of Trumpington, Glasgow 
(1907 - 1997)
British biochemist whose research on the structure and synthesis of nucleotides,  nucleosides, and nucleotide coenzymes gained him the 1957 Nobel Prize for Chemistry.
BSc from Glasgow University in 1928In 1955, he elucidated the structure of vitamin B12, later working on the structure and synthesis of vitamin B1 and vitamin E, the anthocyanins (the pigments of flowers and fruits) from insects (aphids, beetles) and studied alkaloids found in hashish and marijuana. He served as chairman of the Government of the United Kingdom's advisory committee on scientific policy from 1952 to 1964. 
Charles T R Wilson   Glencorse, Midlothian;  (1869 - 1959)
Scottish physicist and meteorologist who received the 1927 Nobel Prize in Physics for his invention of the cloud chamber.  In 1893 he began to study clouds and their properties. He worked for some time at the observatory on Ben Nevis, where he made observations of cloud formation. He then tried to reproduce this effect on a smaller scale in the laboratory in Cambridge, expanding humid air within a sealed container. He later experimented with the creation of cloud trails in his chamber caused by ions and radiation. For the invention of the cloud chamber he received the Nobel Prize in 1927.

Tuesday, 4 March 2014

Laws of Nature, Common Sense and Religion (Part 2)

In Part 1 we had discussed why common sense is fundamentally incapable of explaining and making sense of the world we live in.  Simply, it is a matter of scale.  The world operates at the atomic/molecular level (~0.000001 mm or a nano meter) where particles move near the speed of light (300,000 km/sec) while common sense is built up over centuries from observations made by our senses operating at distances typically greater than 0.1 mm and speeds less than 0.1 km/sec.  Additionally, time scales for understanding fundamental chemical and biological processes are less than a billionth of a second, more than a million times faster than our reaction time.

To understand the working of the natural world using common sense is like trying to understand the geography of the UK by standing at a corner in George Square in Glasgow! An impossible task.

We had built up a whole series of laws by extrapolating what we could observe with our senses - that is until about 500 years ago when technological advances started to extend the limits of our observations. The rest is history; now in the 21st Century, we are truly appreciating the intricacies of the natural world and I believe, correctly formulating the laws governing it - the laws of nature. Theories of Relativity and Quantum Mechanics have made possible the development of new technologies - digital, nano-, bio-, medicine and many others.  Life without these is unimaginable. To somebody living in the 19th Century, the technology today will be science fiction.

Humans like to make sense of things.  With extremely limited empirical information, acquired through our senses, for our ancestors it would have been impossible to explain much of what was happening around us. Natural phenomena like rain, thunder, lightening, tides, storms, earthquakes, motion of heavenly bodies, infectious/mental and other diseases etc. are mediated by causes well outside the range of human perception.  Theories and explanations would be put forward – of course different in different societies – to make sense of such events.  This can give rise to beliefs, customs, rituals, superstitions etc.
Who controls the clockwork-like motion of heavenly bodies; what causes earthquakes and storms? There has to be some almighty, omniscient being looking over the working of nature, controlling everything happening on the Earth.   
Reproduction and death were mysteries.  What happens after death would be a great puzzle.  Losing a loved one for ever is difficult and it would be natural to assume that he/she comes back to life again at some other place and time. Alternately, after death the person would go to some other unknown world where he/she will have access to all the comforts and good life, may be not available when alive.  
A mind full of a large number of unanswerable questions is very receptive to any suggestion that can even partially reduce the bewilderment.  

In distant past humans, with nomadic lifestyle, did not have a great deal of interaction with others.  They were preoccupied with the problems of survival - finding food and shelter was more important than worrying about the philosophical questions of how and why of things.  As humans started to settle in communities - particularly after discovering agriculture - they started to face a whole set of new problems.  In a community, one has to live in close proximity with the neighbours, there is more time to reflect on the natural phenomena around you and people would be living longer so there would be more continuity between generations.  Some sort of tradition will begun to be defined.  

Having evolved from the apes and with the history of struggle to survive, human nature would have the tendency to be selfish - hoarding of food and providing comfort to the family must have been of utmost importance. Physical strength would help to grab more land for growing food and to ensure security.  How does a community survive when everybody is fighting for a bigger share of whatever is available?  There is no point if the mightiest kills all the neighbours; then we are back to nomadic lifestyle. One needs a system of government and rules of conduct and, of course, punishment.      

If I am an intelligent person then I could exploit the situation by solving all the problems in one stroke.  I would attribute all the natural phenomena to an almighty who is benevolent by giving us rain for growing food, wood for making our huts, cows for milk etc. but will punish our collective bad behaviour by bringing storms, earthquakes, diseases and other natural calamities.  Someone who will nourish us but also punish us. He will also tell us how to behave in the community.  This code of conduct will be given to the community through a medium - somebody who can communicate with the almighty being.  Humans are too ignorant and too frail to question what the almighty decides - they must accept without question what is being decided for them.  They must have faith - blind faith is better as this makes the implementation of rules easier ensuring stability of the society. 

We have religion with an almighty God who we must try our best to please.  We have to have a prophet who can bring the message and the priests who can interpret the word of God for the common man.

Let us face it, most of the humans are not that clever.  They are already confused with what is happening around them in nature and about their safety and well-being.  A good lazy way for them will be to follow the code of conduct - it comes with the additional promise of good life after death. To keep reminding the community about the rules of conduct, we have to have beliefs, rituals and superstitions  - if faith is strong then all these make good sense - the main thing is not to question, just follow.

Of course, different regions will have their own unique way of describing God and the rules of conduct, rituals etc.  It does not really matter as nobody is there to question?  If one falls out of line - faith is shaken - then the community can take care of that by removing the unfaithful altogether. The good of the community is paramount and the chief priest can always decide what God wants - he has a direct line to Him.

One can have one God or several Gods looking after different issues. You can have unwritten code of conduct, everything is verbal (easier to modify) or you can have one book or several describing the will of God.  One does not even have to have a God - it could be just an energy field or an abstract being - who is somehow passionately concerned about the earthlings and their welfare.  As long there is unquestioning faith, the system can and has worked.  And it has worked for several millenia.

The question is how do the laws of nature (derived from the empirical evidence) and religion (needed historically to make sense of things) live side by side.  Things will be straightforward but for the idiosyncrasies of the human mind.  We shall leave this for the next installment (Part 3).

Saturday, 1 March 2014

The Curie Family - A remarkable Story (Part 2: Irene and Frederic Joliot-Curie)

Marie and Pierre Curie started the new discipline of radioactivity. Attempts to understand this strange and puzzling phenomenon and the source of energy in radioactive decays engendered the field of Nuclear Physics. Marie Curie and other pioneers like Ernest Rutherford worked and studied naturally occurring radioactivity but nobody was thinking about producing new radioactive nuclides not found in nature - producing artificial radioactive elements.  This would really be a "Holy Grail".  Already natural radioisotopes had shown their effectiveness in medicine, chemistry and research.  Artificially produced radioisotopes would be a game changer.

This is exactly what Irene and Frederic Joliot-Curies achieved and were immediately recognized by the award of the 1935 Nobel Prize in chemistry. Their journey to stardom was not without setbacks and they missed two certain opportunities of being the first to make groundbreaking discoveries which earned Chadwick (discovery of the neutron) and Anderson (discovery of the positron) the 1935 and 1936 Nobel awards respectively.

Irene and Frederic were two very different personalities.  Irene grew in the shadow of her mother Marie Curie.  She developed an intuitive feeling about radioactivity, went to Stockholm in 1911 for the Nobel award ceremony, accompanied Marie Curie during her American trip  where they received a charmed welcome.  Irene had helped Marie during the first world war with X-ray work saving lives of thousands of soldiers and joining the Radium Institute to work on her doctorate to study the radiation from polonium-210. Irene was cut-out for achieving great things - she was intelligent, head strong and very hard working.
Frederic, three years younger than Irene, came from an engineering background and in December 1924 when he was hired by Marie Curie, Fred was doing national service, had no serious physics qualifications. Frederic was a gregarious and outgoing young man who found Irene somewhat enigmatic.
They soon started to like each other and despite Marie Curie's serious reservations, got married in October 1926 and adopted the name Joliot-Curie.
Irene and Frederic made a great team.  They were immensely helped by having strong alpha particle fluxes from the polonium source that Marie curie had collected at the Radium Institute. Frederic also turned out to be very good with instruments and had sensitive detectors like ionisation chambers and cloud chambers for detecting particles.

Discovery of the neutron:

Chadwick concluded that Bothe-Becker radiation consisted not of gamma rays but of neutral particles of the same mass as the proton, i.e., neutrons.  Joliot-Curies had done the right experiment but their interpretation robbed them of being the first to discover the neutron.

Discovery of the Positron:
Joliot Curies had a very sensitive cloud chamber.  During their studies of cosmic rays, they observed positron tracks in their films.  They interpreted the positron tracks as due to negative electrons which had been scatterd in the backward direction.
This is a picture of one of the first positron tracks observed by Anderson in 1933. It was taken in a cloud chamber in the presence of a magnetic field of 2.4 Tesla pointing into the paper (so the particle paths are curved to the left). The cloud chamber (17x17x3 cm) contained a gas supersaturated with water vapour. In the presence of a charged particle (such as a positron), the water vapour condenses into droplets - these droplets mark out the path of the particle. 
The band across the middle is a lead plate, 6 mm thick, which slows down the particles. The radius of curvature of the track above the plate is smaller than that below. This means that the particle is travelling more slowly (23 MeV) above the plate than below it (63 MeV), and hence it must be travelling upwards. From the direction in which the path curves one can deduce that the particle is positively charged. That it is a positron and not a proton can be deduced from the long range of the upper track - a proton would have come to rest in a much shorter distance (~5 mm) 
Carl Anderson won the 1936 Nobel Prize for Physics for this discovery.  
Picture taken from C.D. Anderson, Physical Review 43, 491 (1933).

Production of Artificial Radioactive Elements:
"With the neutron, we were too late; with the positron, we were too late; now we are in time"  ... Frederic Joliot Curie, Jan 1934

Discovery of Nuclear Fission  
Yet again Irene and Frederic missed the opportunity to get credit for their pioneering experiments in the observation of the fission of uranium.

Irene and Frederic had strong views about atomic weapons, peace, women's rights and had overt communist leanings.  Their views lost them favour with the politicians and to some extent with the scientific establishment, particularly in France.
Frederic was a true patriot. Pretending to be busy with his research in nuclear physics, he risked his life by using his lab to manufacture explosives and radio equipment for the Resistance. After the liberation of France, he was appointed director of the National Center for Scientific esearch. He was elected to the French Academy of Sciences.  Soon thereafter he became head
of the French Atomic Energy Commission. His task was to make France a world leader in the nuclear industry. Irène became not only a commissioner but also the director of the Radium Institute. 
 But the Joliot-Curies' political activities led to their downfall. In spring 1942 Fred had secretly joined the French Communist party, at that time a leading anti-Nazi force. Although Irène never became a member, she sympathized with many movements in which French Communists took a lead, including support of equal rights for French women.
At the height of the Cold War, Fred was dismissed from his position at the French Atomic Energy Commission. A few months later Irène also lost her post as commissioner.

Wednesday, 19 February 2014

Alexander Graham Bell Family Tree

A remarkable inventor and teacher, Alexander Graham Bell is known as the person who gave the world the telephone.  Bell actually never stopped inventing and improving devices right until his last days.  Above all Bell was a teacher of deaf and dumb and in his own words he ranks his work with the deaf above the invention of the telephone.

Below is the picture of Bell's Family Tree:

Tuesday, 11 February 2014

James Clerk Maxwell Family Tree

James Clerk Maxwell is considered the most influential scientist of the 19th Century.  He is ranked third after Newton and Einstein for his work on Electromagnetism and on the Molecular Theory of Gases.  A man of many talents, paradoxically, Maxwell is not well known outside the physics community.  This is partly because he died young (age 48) soon after publishing his seminal papers.

I shall be talking about James Maxwell in my talks on Great Scottish Inventors for Strathclyde Centre for LifeLong Learning and for my Science for All programme in East Kilbride.  The talks will take place in July/August 2014.

Maxwell came from a family of high achievers - both from his father and mother side.  Two family trees are given for that reason

Click on the figures to enlarge the image

James Watt Family Tree

James Watt's improvement of the steam engine is credited for driving the Industrial Revolution.  Watt was a prolific inventor and is highly respected for the originality of his thinking.

James Watt's family tree is given below.  I shall have occasion to write much more about James Watt as I prepare his biography for my talks on Great Scottish Inventors for Strathclyde Centre for LifeLong Learning and for my Science for All programme in East Kilbride.  The talks will take place in July/August 2014.

Click on the figure to enlarge the image

The Curie's Family Tree...

The curies werewere an extraordinary family.

Study their family tree to learn more about them:
Click on the picture to see the enlarged view:

Secular Equilibrium - Radioactive decay Series

It  is interesting that heavy elements like uranium decay to lighter elements which themselves are radioactive and in turn decay to new lighter elements.  This sequence can go on for some time until a stable product is formed.

The sequence of decays defines a radioactive decay series.  In the series, the various intermediate elements are present in definite amounts such that the decay rate of the parent element (or the production rate of the daughter element) is equal to the decay rate of the daughter element.
The decay rates depend on the number of atoms present and the half life of the element (time required for half of the atoms to decay).

Thus all the elements in a radioactive series are present in definite amounts depending on their half lives.

This is explained in the slide below.
Click on the slide to see the full-scale figure with an example of U-238, Ra-226 and Po-210:

The way the graph in the figure is explained is that at the beginning if we start with pure parent element then in one second it will produce a number of daughter nuclii.  Since this number is very small, there are not many decay per second of the daughter element (activity of daughter is small).  This means that more daughters are produced than are decaying and their numbers increase.  As their nos. increase their decay rate increases also and after about 6 to 7 half-lives an equilibrium is reached when the production rate of daughter is equal to the decay rate of the daughter element.  This is Secular equilibrium.

Since Uranium has been in the earth's crust for billions of years, there has been enough time for secular equilibrium to have been reached and all parent-daughter pairs in the radioactive series are found in the correct proportions.

The Curie Family - A remarkable Story (Part 1: Marie and Pierre Curie)

Last month, I had the opportunity of giving a talk in Glasgow University on the remarkable achievements of the Curies. It will be fair to say that they were responsible for starting the new discipline of Radioactivity and Nuclear Physics.  For almost half a century the Curies dominated research in nuclear physics and amassed five Nobel Prizes.

Their story is one of brilliance aided by hard work and dedication.  They valiantly struggled against the prevailing forces of discrimination against women both in the male dominated scientific community and in the French media of the early 20th Century.  The harmful nature of X-rays and nuclear radiation was not understood and the Curies suffered serious health problems throughout their lives.

Marie Curie was born in Warsaw, Poland in 1867 during the time of Russian occupation.  Russian policy was to destroy Polish culture, language and education system to neutralise Polish identity.  Poles were not able to hold good jobs and Marie's family were financially not well off. Women were not allowed to go to universities in Poland.  Marie's education in science really started when she went to Sorbonne in Paris in 1891 - at age 24 years.  She got married in 1895 to Pierre Curie who was 8 years her senior and already well established as a scientist having discovered piezoelectric effect and for his fundamental studies in magnetic properties of elements - Curie Point and Curie Temperature are named after him.  Pierre Curie was a quiet and sensitive person who had dedicated his life to science.
Following Becquerel's discovery of radiation emitted by uranium in 1896, Marie Curie chose to look into this for her doctoral thesis. Soon she discovered that the only other known element to emit such radiation was thorium.

But the ore, pitchblende, from which uranium is extracted showed the surprising behaviour of being 4 times more radioactive than an equal mass of uranium.  Sensing that this indicated the presence of a minute quantity of some unknown element much more radioactive than uranium or thorium, Marie worked extremely hard in very poor working conditions to extract bismuth like Polonium and barium like Radium from several tons of pitchblende. Her lab was an old discarded hut in seriously bad repair with no heating and leaking roof.  The equipment she was allowed was primitive.  Pierre Curie, realising the potential of Marie's research had joined in her work.

Such was the excitement created by her research and its importance appreciated by the scientific community that even before the PhD thesis was completed, Marie had already earned the 1903 Nobel Prize in Physics.  The story behind the award of the 1903 Nobel Prize tells the sort of discriminatory environment that a women scientist faced.  The male scientific community nominated only Pierre Curie for the Nobel Prize stating that Marie's role was merely of a lab assistant and she did not deserve to be included in the award.  This was untrue as the lab notes clearly demonstrate the important and original contributions that Marie made in the discovery and subsequent study of the properties of Ra and Po.  Pierre refused to accept the prize unless Marie was also included.  In the end, the Nobel Prize committee had to bend a few rules so that the award can be made jointly to Marie and Pierre Curie.
Even after winning the Nobel Prize, Marie could not get a professorship in France or win funding to improve her basic lab facilities.  Marie and Pierre Curie had two daughters Irene (born 1897) and Eve (born 1904).  Pierre Curie's health was not good - having been affected by close contact with radiation from radium.  Pierre was tragically killed in a road accident in 1906 - age 47 years.  Heartbroken at losing her trusted companion, Marie continued her work in radioactivity while raising her two daughters.  After Pierre's death, Marie was appointed to his vacant professorship at Sorbonne University.

Marie Curie was awarded the 1911 Nobel Prize in Chemistry for her successful isolation of Polonium and Radium elements from the ore - something which was not possible until 1910.
To appreciate the difficult task that Marie had undertaken - one ton of pitchblende has less than 300 mg of radium and 0.075 mg of polonium.

The year 1911 was marred by controversies and rather aggressive/unreasonable behaviour by the French media.  Marie was accused of having an affair with Paul Langevin, a colleague and famous physicist.  Marie's house was put under siege by the newspapers, bricks were thrown at her house, windows broken and defamatory articles written.  In this atmosphere of hate, even the Nobel Committee asked Marie to refrain from attending the prize giving ceremony.  Marie refused this request firmly saying that her personal life has nothing to do with her scientific achievements for which the Nobel was being awarded and attended the ceremony.  French media gave little or no coverage about Marie's Nobel Prize.  For her personal safety, Marie left France for a year to live in England.

Even though Marie had won the 1903 Nobel Prize, and in 1906 she was appointed Professor at Sorbonne, the university did not provide her with proper lab facilities to continue her work effectively.  In 1908, University of Geneva, Switzerland offered Marie a professorship with much increased salary and excellent research facilities.  The offer was too tempting for Marie to refuse.  However, at this point, the French scientific community rallied and funding was obtained for The Radium Institute for Marie Curie.
The Institute was completed in 1914 with a wing for biological/medical research involving radioactivity.

As a woman, Marie Curie had not been treated fairly by the French media and authorities.  Even then Marie remained faithful to her adopted country. World War 1 broke out in 1914 and Marie did her best to help France. She used her Nobel Prize money to buy government bonds and gave all her time in developing mobile X-Ray radiography equipment and courses which helped to save a very large number of lives of injured soldiers.
Marie's daughter Irene Curie was with her mother all this time helping her efforts.

Marie Curie made two trips to the USA - helping to raise funds for purchasing radium.  Marie was an advocate for women's cause and actively promoted admission of women in scientific work.  In poor health, she continued her work till the very end - Marie died in 1934 of pernicious anemia, caused by long-term exposure to radiation. She did not live to learn about the Nobel Award to Irene and Frederic Joliot-Curie but did see the production of artificial radioactive elements in the Radium Institute.

Marie Curie, like Albert Einstein and Alexander Fleming, not only excelled as a scientist but also won the affection and admiration of the public and the politicians throughout the world.
Her life is seen as remarkable, notable for the many firsts:

First doctorate awarded to a woman in science in Europe
First woman to win a Nobel Prize
First woman to win two Nobel Prizes
First person to win two Nobel Prizes in different subjects
First Professor at a French University
First to use the term Radioactivity
First mother and daughter to win Nobel Prize

Marie chose Curie as the unit of radioactivity.
This is the quantity of a radioactive substance that undergoes 3.3 x 10^10 decays per second (Becquerel or Bq). 1 Bq = 1 decay per second
One gm of radium-226 has an activity of 1 Curie (Ci)