I think nearly all of us are aware of the urgent need to reduce carbon emissions and ideally create a carbon-neutral society. There’s a major focus on renewable energy such as wind, tidal, hydroelectric, solar and geothermal. I’m making my own small contribution through solar panels on my house. However, when it comes to talking about reducing carbon emissions, there’s an elephant in the room. A source of electricity that is not renewable but can generate large amounts of electricity with negligible carbon emissions: nuclear power.

There are obvious and understandable reasons why discussions on reducing emissions tend to ignore the nuclear option. Windscale, Three Mile Island, Chernobyl and Fukushima are four of them. The management of nuclear waste which may remain radioactive for hundreds of thousands of years is another; as is the safe decommissioning of reactors at the end of their working life. But it didn’t have to be this way.

In the late 1940s, when research was going on into the potential use of nuclear energy for generating electricity, two possible fuels were investigated: thorium and uranium. When bombarded with neutrons, thorium is converted into uranium-232, which will then undergo nuclear fission, releasing heat. This can then be used to create high pressure steam to drive turbines. The other fuel, uranium-235, also undergoes nuclear fission to release heat.

It was clear from the beginning that thorium had some very significant advantages over uranium as a fuel. Firstly, thorium is much more abundant than uranium, and it is a lot easier and safer to mine and process. In fact, massive amounts of thorium are created as a waste product from mining other metals. In addition, nearly all thorium is ‘fertile’ – meaning it can be used as fuel. Uranium, by contrast, is mostly the non-fertile isotope uranium-238; only 0.7% is uranium-235, which can undergo nuclear fission. This means that thorium does not require expensive fuel enrichment processes.

Another benefit is that a thorium reactor produces much less radioactive waste than a uranium reactor; up to 1000 times less, in fact. In addition, those small amounts of waste products remain radioactive for between 1 and 100 years; by contrast, the waste products from uranium remain radioactive for tens or even hundreds of thousand years. The decommissioning of thorium plants is also safer and easier.

Thorium reactors are much, much safer than uranium reactors. In fact, they are literally melt-down proof. The reason for this is that they use a liquid fuel – molten thorium fluoride. In the bottom of a thorium reactor is a plug which will melt if the temperature of the fuel exceeds a set limit. The fuel will then be drained into a tank for safe storage. Since thorium must be bombarded with neutrons to undergo nuclear fission, once removed from the reactor, nuclear fission ceases and the fuel is safe.

By contrast, uranium reactors use a solid fuel and rely on control rods which can be lowered into the reactor to absorb neutrons and slow down or stop nuclear fission. In addition, any failure in the cooling system can lead to a meltdown. If the cooling system of a thorium reactor fails, the plug described in the previous paragraph will melt and the fuel will drain from the reactor.

Thorium reactors are also highly efficient. It is estimated that one ton of thorium can generate the same amount of electricity as 200 tons of uranium or 3,500,500 tons of coal.

There are some disadvantages. One is the cost of processing thorium ore into thorium fluoride fuel; however, uranium also requires extensive processing and enrichment before it can be used in a reactor. another disadvantage is that the molten thorium fluoride fuel is highly corrosive. However, it would be perfectly feasible to develop corrosion-resistant materials that could be used to line the reactor. There are a few other potential problems which I won’t go into as the science is quite complex; all of these can be solved if there is sufficient investment into thorium technology.

Between 1965 and 1969, an experimental thorium reactor was successfully developed and tested at the Oak Ridge National Laboratory in the USA. Nevertheless, in 1973 the US government made the decision to abandon thorium technology in favour of uranium. Other governments such as the UK and France had already made the decision in favour of uranium.

So, why did governments abandon a cheap, clean and safe fuel in favour of one that is more dangerous and generates more waste? The official reason was that uranium reactors are supposedly more efficient. The true answer lies in what is either thorium’s biggest advantage or its biggest disadvantage, depending on your point of view. Quite simply, a thorium reactor does not produce plutonium, which is needed to create nuclear weapons. In the climate of the Cold War, governments made the choice to go with the fuel that produced the plutonium they needed for their nuclear weapons programmes. In the late 1960s and early 70s, Alvin Weinberg, the director of Oak Ridge, argued passionately for the adoption of thorium as the fuel for nuclear power. His refusal to abandon what he considered to be a safer, cleaner option in favour of one with weapons applications eventually cost him his job.

So, what is the future? Many countries, including the USA and UK, are reluctant to provide the funding that is needed to develop thorium technology into a viable method of generating electricity. A notable exception is India, which has abundant supplies of thorium and is aiming to generate 30% of its electricity from thorium by 2050. In addition, despite the ending of the Cold War, many countries including the UK continue to maintain a nuclear deterrent. This means that the demand for plutonium is unlikely to end any time soon.

A final note. Two of the most influential scientists in the development of nuclear power were Irene and Frederic Joliot-Curie, subjects of one of my previous posts. They oversaw the development of France’s first nuclear power station. Both died prematurely from radiation-related illnesses; Irene in 1956 and Frederic in 1958, when the nuclear program was in its infancy. As ardent pacifists, it is possible, even likely, that they would have championed the development of thorium as a nuclear fuel. Had they lived longer, would we now have a safe source of low-carbon nuclear energy?

Hi all, it’s been a while but I am back in action. When I started this blog the intention was for it to be a science blog that looked at aspects of science that are overlooked, quirky, controversial etc. With the pandemic it rapidly morphed into more of a COVID-19 blog. Now that things have (hopefully) settled down a bit, I am going to try and return to the original intention. I will still post about COVID but it won’t dominate the way it has in the past.

Watch this space,

Sarah

Haber’s life was the tragedy of the German Jew – the tragedy of unrequited love – Albert Einstein

Almost exactly 106 years ago, on the afternoon of April 22^nd 1915, things were fairly quiet on the Northern edge of the Ypres Salient between Gravenstafel and Langemark.  Possibly too quiet, as subsequent events would demonstrate.  But for the French Territorial and Colonial troops in the trenches, there was nothing to indicate the horror that was about to be unleashed.

As the afternoon drew on, a slight breeze began to blow from the direction of the German lines.  At approximately 5pm, a strange greenish-grey mist was observed moving towards the Allied lines from the German trenches.  It was chlorine gas, and when it reached the French trenches, all hell broke loose.  Men died in agony as the chlorine reacted with moisture in the linings of their airways to form corrosive hydrochloric acid.  The French troops broke and ran, leaving 4 miles of the front line completely undefended.  The Germans could have broken through to Ypres and on to the Channel Ports; however, two things saved the day for the Allies. 

The first was that the effectiveness of the gas took even the Germans by surprise, and they simply did not have enough troops to exploit the breakthrough.  The second was the almost unbelievable courage of the Canadian troops on the Southern flank of the breakthrough. They moved into the trenches the French had abandoned and fought off multiple gas attacks. In two days, the Allies lost about 5000 killed and 15000 wounded.  It was the first large-scale use of a lethal, asphyxiating gas in warfare, and set the scene for 3 years of horror as both sides raced to develop ever more effective chemical weapons.

The man behind it all was a quiet, bespectacled, middle-aged German army lieutenant named Fritz Haber, who would become one of the most controversial scientists of the 20th century.

Before the War, Haber had been a Professor of chemistry at the University of Karlsruhe, and in 1911 had become the first director of the new Kaiser Wilhelm Institute in Berlin.  His most important work, however, was carried out while he was at Karlsruhe.

Look at a graph of world population, like the one shown below, and you will see that until about 1800 ACE, population growth was very slow.  From 1800 on, the world’s population began to grow with increasing rapidity, as improvements in food production, medical care and living conditions began to reduce mortality rates.  As the end of the 19^th century approached, the world’s population was heading towards unsustainable levels.  Quite simply, the human population was about to exceed the Earth’s capacity to produce food.

The problem was a shortage of nitrogen.  This element is essential for plant growth, and without plants and their ability to photosynthesise, there is no food.  But nitrogen is one of the most abundant elements on Earth, so how could there be a shortage?  The answer is that the bulk of the Earth’s nitrogen is in the atmosphere, where it cannot directly be used by plants.  Plants require water-soluble nitrates, which can be taken up from the soil by their roots.  

In the ordinary way of things, this is taken care of by Mother Nature.  Bacteria in the soil and in the root nodules of leguminous plants ‘fix’ nitrogen into ammonia, and a small amount of atmospheric nitrogen is also ‘fixed’ by lightning. Other bacteria and fungi convert nitrogen from dead plant and animal matter into ammonia; a third group of bacteria then convert the ammonia into nitrates.  This is known as the nitrogen cycle. By the late 19^th century, these natural nitrogen-fixing processes could no longer produce enough nitrates to meet the increasing need for food crops.  A cull of the world’s population by means of a catastrophic world-wide famine was imminent, unless a way could be found of artificially fixing atmospheric nitrogen. 

Enter Fritz Haber and his assistant, Robert Le Rossignol, who in the summer of 1909 succesfully produced ammonia by reacting hydrogen and nitrogen gases at high temperature and pressure, using an iron catalyst. Once you have ammonia, it is then relatively straightforward to convert it into nitrates for fertilisers.

Carl Bosch of the BASF company scaled-up the process to industrial level, with the first operational ammonia plant opening in 1913 at Oppau.  Now known as the Haber-Bosch process, this was one of the biggest breakthroughs industrial chemistry has ever seen, and paved the way for the large-scale manufacture of nitrate fertilisers, meaning that food production could continue to increase and meet the needs of the expanding population.

By a (not so?) happy coincidence, Haber and Bosch’s work also meant that if war broke out, Germany would be able to manufacture nitrates to make explosives. Prior to the invention of the Haber-Bosch process, the main source of nitrates for both fertilisers and explosives was guano. Yes, you did read that right, guano as in bird poo. Guano is a rich source of nitrates, and the best sources of guano in terms of both quality and quantity could be found in South America, particularly the Chincha Islands in Peru, where millions of seabirds create mountains of guano up to 150 feet high. In the 19th century, the importation of guano by sea was big business. In the event of a war, it was possible, even likely, that a Royal Navy blockade would be able to prevent Germany from importing guano. The Haber-Bosch process meant that in this event, Germany’s munitions factories could continue to churn out shells and bullets. Despite this, the invention of ammonia synthesis was, overall, something that benefited humankind. So how did Haber go from that to chemical warfare?

Fritz Haber was intensely patriotic.  Part of this was due to his having been born into a Jewish family. In the early 20th century, antisemitism in Germany was nowhere near as prevalent as it would become in the Nazi era. However, it was significant enough for Haber to feel that despite his having converted to Christianity, he needed to prove his patriotism and devotion to the Fatherland. Haber was enthusiastic about the war, and was one of 93 German intellectuals to sign a proclamation which enthusiastically endorsed the declaration of war.

In addition to his patriotism, Haber had two areas of expertise that made him the ideal person to lead Germany’s efforts to develop poisonous gas as a weapon. The first was in electrochemistry, which is crucial in the manufacture of chlorine gas. The second was in working with gases under pressure, which enabled him to develop equipment with which to deliver the gas, and meant that throughout the war, German equipment was superior to anything used by the allies.

For the duration of the War, Haber led the German efforts to develop both chemical weapons and defences such as gas masks. The result was that Germany was always one step ahead of the allies in both. It is estimated that there were about 1.3 million casualties as a result of gas, with approximately 90,000 fatalities – relatively trivial in relation to the overall numbers of casualties. But gas was, first and foremost, a weapon of terror; its aim was to disrupt, damage morale and consume resources treating the wounded. During the first gas attack at Second Ypres, many of the troops who broke and ran did so out of sheer terror, having seen the effects of the gas on others. Mustard gas in particular was designed to maim and terrorise rather than kill.

Haber’s involvement in chemical warfare was to cost him dearly. On 2nd May 1915, his wife Clara committed suicide, shooting herself through the heart with Haber’s own army revolver while her husband was celebrating his promotion to captain. A dedicated pacifist and a talented chemist in her own right, her husband’s involvement in the war is thought to have been a major factor in Clara’s suicide.

After the war, Haber came in for a great deal of criticism from the scientific community. He was awarded the 1918 Nobel Prize for Chemistry for his work on ammonia synthesis, and this was controversial to put it mildly. Many eminent scientists boycotted the award ceremony in 1919, and it is said that Sir Ernest Rutherford refused to shake Haber’s hand.

In the post-war years, Haber continued as Director of the Kaiser Wilhelm Institute, where he led Germany’s secret efforts to develop new chemical weapons, in direct contravention of the Treaty of Versailles. But dark clouds were gathering on the horizon. When Hitler became Chancellor in 1933, he immediately began to target Jewish scientists. Haber was personally targeted, with Hitler claiming that his appointment as director of the Institute was a result of his being the nephew of a Jewish profiteer (which he wasn’t). This came as a shock to Haber, who had thought that his service in WW1 and his conversion to Christianity would be enough to protect him. Although Haber could not legally be dismissed, the Nazis made his position untenable and he resigned in October 1933. He left Germany and after a brief spell in England, in January 1934 he set out to take up a new job in Palestine. But he never reached his destination. Events had taken a severe toll on Haber’s health and on 29th January 1934 he died of heart failure while breaking his journey in Switzerland.

There is a final hideous twist to the story of Fritz Haber, the scientist hounded out of Nazi Germany because of his Jewish roots. Between the wars, the research Haber was overseeing at the Kaiser Wilhelm Institute included the development of new pesticides and fumigants. This included the development of a highly effective class of fumigants which consisted of hydrogen cyanide gas adsorbed onto diatomaceous earths. When exposed to air, the lethal gas was released. These agents were given the name ‘Zyklons’ and included Zyklon B, which would be used in the murder of 1.1 million people in the Holocaust. Among those who would perish in the gas chambers were several members of Fritz Haber’s own extended family.

In view of what he [Moseley] still have accomplished … his death might well have been the most costly single death of the War to mankind generally – Isaac Asimov

The First World War was one of the most deadly and wasteful conflicts in human history. An entire generation torn apart, and many brilliant minds lost. Who knows what Wilfred Owen might have gone on to achieve, had he not been killed in action almost exactly a week before the armistice? And he was just one among many. But while most people have heard of Wilfred Owen, many of you reading this may never have heard of Henry Gwyn Jeffreys Moseley.

Henry Moseley, known to his friends as Harry, was born in 1887. His father was a professor of anatomy and physiology at the University of Oxford, and his mother, herself the daughter of an eminent biologist, went on to become the British women’s chess champion in 1913. So it’s hardly surprising that Harry excelled at science, winning the physics and chemistry prizes at Eton where he had been awarded a King’s scholarship. What is perhaps more surprising is that Harry did not follow the family tradition and go into biology – his interests lay in chemistry and physics, and particularly in the structure of the atom.

After graduating from Trinity College, Oxford, Harry Moseley went to Manchester to work under Sir Ernest Rutherford, one of the most eminent scientists of the time, who was studying radioactivity. In 1913 Rutherford offered Harry a fellowship, which he declined, preferring to return to Oxford where he could work on his own independent research. In particular he wanted to work on solving the problem of how to measure atomic number.

The periodic table of the elements is one of the most powerful tools known to science, and one which we now take for granted. Russian chemist Dmitry Mendeleev created the first true periodic table by putting the elements in order of mass. He noticed that this resulted in certain pairs of elements (for example, iodine and tellurium) being ‘back-to-front’ based on their properties, and incorrectly assumed that this was due to errors in calculating their atomic masses.

Mendeleev assigned each element an atomic number based on its position in the periodic table; however, in cases such as iodine and tellurium, this was semi-arbitrary (science-speak for ‘educated guess’) and based on chemical properties. Moseley would be the one to prove that these elements were placed correctly, based on atomic structure. He would also be the first to find experimental evidence to support the existence of atomic numbers – a concept that until then had been theoretical only.

Moseley’s speciality was X-rays. Not medical X-rays, but the study of how X-rays relate to atomic structure. I won’t go into too much technical detail, but basically what he did was to shine a beam of high energy electrons onto different metals in a vacuum. As you can see on the left, this causes the metal to emit X-rays at an angle to the electron beam. This is called diffraction.

By using a detector, Moseley could measure the angles at which the X-rays were emitted. By applying Bragg’s Law (a mathematical formula relating angle and wavelength), he could then calculate the wavelengths of X-rays given off by each metal. So far, so what? The important breakthrough came when Moseley compared wavelengths to the position of each metal in the periodic table, and found that there was a direct mathematical relationship – now known as Moseley’s Law. Finally, atomic number could be proved experimentally. Amongst other things, Moseley was able to show that Mendeleev’s positioning of problematic elements such as iodine and tellurium was correct. He was also able to solve the problem of where to put the lanthanides – in the periodic table, that is – which had been occupying chemists for years (we don’t get out much…).

In August 1914, Harry Moseley’s work was rudely interrupted by the outbreak of the First World War. In the rush of patriotism following the declaration of war, young men flocked in their thousands to enlist. Despite the efforts of his family and friends to dissuade him, Moseley felt it his patriotic duty to join them, and enlisted in the Royal Engineers. In April 1915 he was sent to Gallipoli where he served as a communications officer. On 10th August 1915, at the age of 27, one of the most brilliant young scientists of his generation was killed in action – shot by a Turkish sniper whilst relaying an order over the telephone.

The consequences to science of the loss of Moseley were significant, and his death provoked an outcry within the scientific community. Robert Millikan, who would go on to win the Nobel Prize for Physics in 1923, wrote that,

“Had the European War had no other result than the snuffing out of this young life, that alone would make it one of the most hideous and most irreparable crimes in history.”

Many scientists, including Sir Ernest Rutherford, speculated that had he lived, Moseley would certainly have been awarded a Nobel Prize for his work on atomic structure. Moseley did leave one important legacy though. His death in the First World War was a significant factor in ensuring that in the Second World War, scientific research would be designated as a reserved occupation, ensuring that scientists who would otherwise be eligible for military service were unable to enlist. Just one of many scientists whose life may well have been saved by this was Alan Turing, who made crucial discoveries in the field of computer science and played a key role in cracking the Enigma code.