‘Nothing in life should be feared, everything should be understood’ Marie Curie told her daughters. This phrase expresses all the passion that fuelled this exceptional scientist and female research pioneer. Today, at the heart of the polemic surrounding nuclear power, and at a time when the tsunami-damaged reactors in Fukushima contaminate all North-Eastern Japan, we can ask ourselves if the Curie and Joliot Curie couples suspected the consequences of their discoveries.
The Fukushima effect: an influence on opinions ?
‘Stamps of Marie Curie?’ said the post office clerk ‘People rarely ask me for them at the moment’. I raised my eyes in astonishment to look at her. Has the reputation of this exceptional scientist and feminist icon been tarnished by the consequences of recent nuclear accidents?
The Curie family, also known as the family of ‘five Nobel prizes’, was a family passionate about science. They gave their health for physics, chemistry, mathematics and medicine. Eve Curie rightly said of her mother that she did scientific research simply ‘...because she loved it’. But, as the Curies remained enclosed in the dark room for many hours manipulating dangerous products, did they suspect the future consequences of their discoveries? The opinions brought to bear on science often change across eras according to the changing state of knowledge, but also to history. Nevertheless, the speeches made during Pierre Curie’s Nobel Prize conference in 1903, then during that of Irène Joliot-Curie and Frédéric Joliot in 1935 are significant in that they display the degree of anticipation at the time regarding opinions about radioactivity and nuclear technology.
From radioactivity to nuclear power ?
Between dependence and fear, our relationship with nuclear power is ambiguous. Here we want to retrace, as objectively as possible, the history and discovery of radioactivity and nuclear. To this end, we will present the various actors of this nuclear narrative, touching upon their intuitions and the implications of their discoveries
A history of the atom exploration
The history of the radioactivity cannot be dissociated from that of the exploration of the structure of the atom. At the time when the Curies began their studies on uranium rays, the scientific description of the atom was of an abstract, indivisible and full object. Thanks in large part to Niels Bohr’s work on the atom (1913), we later learnt that it was composed of a hard core (protons and neutrons) as well as electrons gravitating very quickly around this core. We also learnt that the atom was mostly composed of a lot of emptiness.
In our time, the model of the atom used originates from quantum mechanics in which electrons no longer circle around the core in orbits, but where electrons are distributed according to probability (the well known ‘electron cloud’).
Created principally at the centre of stars, the atomic core is composed of nucleons: protons (with a positive charge) and neutrons (with no charge). The latters have masses approximately 2000 times that of an electron. Following a number of discoveries it became clear that not all cores were stable. In this context, natural radioactivity encompasses all radiations spontaneously emitted by materials composed of unstable atoms.
It is very interesting to sift through speeches given at the Pierre Curie Nobel Prize conference in 1903 and the Irène and Frédéric Joliot-Curie Nobel prize conference of 1935. In these speeches, it appears that everything, or almost everything, regarding radioactivity was either understood or had been calculated*1. In Pierre Curie’s speech we should also note the introduction of the term ‘radioactivity’ as being an ‘atomic’ property of uranium and thorium.
The diverse effects of emitted radiation can be attributed to an emission of energy, already classified into three categories. Over these years, Rutherford was responsible for understanding the composition of the core as well as the radiations referred to as ‘radioactive’. It was he who named the three classes of radiation: alpha, béta and gamma. Finally, between Pierre Curie’s speech and those of Irène and Frédéric Joliot-Curie, the hypotheses relating to the nature of the three classes of radiation were confirmed and validated, and the existence of a corpuscle (the electron) had been predicted. Frédéric Joliot’s description of these phenomena is surprisingly similar to that used today, with only neutrinos (non-charged particles with almost zero mass, emitted during radioactive emissions) and the properties introduced by quantum mechanics, being absent.
If the discovery of radioactivity is attributed to Pierre and Marie Curie, the discovery of artificial radioactivity is the fruit of the labour of their successors: Irène Joliot-Curie and Frédéric Joliot who received the Nobel Prize for Chemistry in 1935. By bombarding different atom cores with alpha radiation, they proved that they could make the material radioactive. This is due to the fact that the bombarded core can, in turn, emit radiation said to be radioactive: the alpha radiation corresponds to the radiation of the helium atom, the beta radiation corresponds to the emission of electrons and positrons, and gamma radiation corresponds to the emission of photons. They quickly understood that a part of the core is torn off during these emissions. The core thus changes composition and the material undergoes a transmutation, forming a material with a smaller core. This phenomenon is fundamental as it shows that radioactivity is a property of all material, that it is in a state of permanent change and that, thanks to artificial radiation, humans can reproduce lost radioactive substances through the decomposition of their cores.
Atoms can be classified in a table called ‘the valley of stability’.At the bottom of the valley, stable elements can be found that are lighter than the others. The elements to the left carry an excess of neutrons, whilst those to the right carry an excess of protons. When bombarded by alpha radiation, neutrons can be transformed into protons and back again. The (heavier) elements at both extremities can then travel down in a cascade until the stable and lightest element. Understanding this complex phenomenon is not easy, and requires an introduction to concepts of quantum mechanics as well as the use of fundamental elements that compose protons and neutrons, called quarks. It is these elements that, during transmutation, change identity and modify the composition of the core. Electrons and neutrinos can also be emitted alongside this transmutation. This is the artificial radioactivity!
Les « suites » de la découverte de la radioactivité
Hiroshima, Nagasaki, Tchernobyl, Three Mile Island, Fukushima, all names fatally associated with radioactivity, or more accurately, nuclear power. As the question of whether to roll back nuclear power is being posed today, so the legitimacy of scientific knowledge is also called into question. In the 21st century, our relationship with radioactivity thus reflects our ambivalent relationship with science. Somewhere between dependence and fear, we remain fascinated by phenomena that have surpassed the wildest of imaginations. Over 80% of energy produced in France by the company EDF is produced using nuclear technology. Many medical techniques are linked to radioactivity, notably curietherapy (Brachytherapy), still used today.
The transmutation phenomena allow material to be modified*2. By comparing materials before and after transmutation, much information regarding the origin and formation of the material can be ascertained. Thus the discovery of artificial radioactivity had consequences in all domains of knowledge including geology, chemistry, biology and so on.
The first applications of radioactivity were developed in medicine. Radioactive elements were used at the beginning of the 20th century to place energy into direct contact with target tissue to cure cancer. Soon afterwards, a new medicine called ‘curietherapy’ appeared. In 1923, Georg von Hevesy discovered the indicator method, but it was principally the discovery of artificial radioactivity in 1934 by Irène and Frédéric Joliot-Curie that put a vast range of short-life radioactive isotopes at the disposition of doctors and biologists. Iodine 131, obtained by the fission of uranium 235, is one example of these. The new short-life elements were quickly used as radioactive tracers in the human body. After injecting radioactive iodine into the body, following the biological progression of internal organs became possible, as did the capacity to trace injected substances. Maximum doses must be respected so as not to negatively affect the patient’s health. The iodine is then naturally eliminated. This heralded the start of a new discipline: nuclear medicine with diagnostic applications (scintigraphy, MRI, etc) and therapies (chemotherapy, radiation therapy, etc.)
Irène et Frédéric Joliot-Curie, precursors of the French Atomic Agency (CEA)
Frédéric Joliot proved to be prescient. He and Irène realised immediately that artificial radioactivity would have applications not only in the fields of medicine, biology, and astrophysics but in many other domains as well. In December 1935, he would conclude his Nobel speech with these words:
[…] we are right to think that researchers constructing or breaking elements at will would be able to create explosive transmutations, veritable chemical chain reactions. If such transmutation starts to propagate in material, one can imagine the freeing of an enormous amount of utilisable energy that will occur.Irène Joliot-Curie and Frédéric Joliot, Nobel speech, 1935"
The idea of chain reactions (on which nuclear power relies) was floated, though the reactions themselves were only produced in 1939. Four years previously, Frédéric Joliot had already imagined an explosion that could free a colossal amount of energy, and finished his speech by expressing his hope that researchers would take ‘...all precautions necessary to contain it’.
It was during his time as director of the French National Centre for Scientific Research (CNRS) under the government of Général de Gaulle, that Frédéric Joliot was named high commissioner of the French Atomic Agency. In 1948 he opened the first French nuclear reactor, named Zoé. At the same time he was active in the International peace movement. Through the World Peace Council, he made the famous ‘Stockholm appeal’ (appel de Stockholm) on 9 March 1950, calling for the atomic bomb to be banned :
"We demand the absolute ban of the atomic weapon, a weapon of terror and mass extermination of populations. We demand the establishment of rigorous international controls to ensure the application of this ban. We consider that the government that first uses the atomic weapon against any other country is committing a crime against humanity and would be treated as a war criminal. We call upon all men of good will in this world to sign this appeal. Stockholm appeal, 1950"
His position taking, at the time of the Cold War, caused him to lose his position at the head of the French Atomic Agency. Here the extent of self-interrogation entered into by those who had conceived of these different discoveries is clear.
And if Pierre Curie spoke to us of nuclear power?
Renaud Huynh, director of the Curie Museum (1 Rue Pierre et Marie Curie) reminds us that ‘Pierre Curie was a dreamer, but he was also a thinker’. At a time when nuclear power did not yet exist, and no energy had been extracted from radioactive materials, it is remarkable to look over the final paragraph of Pierre Curie’s speech to the Nobel academy in 1903. Though imprecise, it gives a sense of the dangers of the discovery of radioactivity :
We can also imagine that radium could be very dangerous in the hands of criminals, and here we can ask ourselves if it is to humanity’s advantage to learn the secrets of nature, and whether humanity is sufficiently mature to benefit from it or whether this knowledge will be harmful to it. The example of Nobel’s discoveries is instructive; powerful explosives have allowed man to do admirable work. They are also a means of terrible destruction in the hands of criminals who lead peoples to war. I am of those who, like Nobel, think that humanity will draw more good than bad from new discoveries.Pierre Curie, Nobel Speech, 1903."
The controversies that question mass use of nuclear power as a source of energy to power our cities and our industries will not be discussed here. Nor will the health risks associated with it. The aim of this article has simply been to recollect the history of radioactivity by reintroducing the principal actors of the initial discoveries as well as the basics of the atom structure. As the history of radioactivity underlies all modern scientific disciplines, this article will allow us to return later to terms and concepts discussed.
The few phrases cited here of Pierre Curie and Frédéric Joliot are fairly representative of one section of the state of society’s contemplation faced with the new phenomenon of radioactivity. Above all, these phrases are representative of society’s suspicions concerning the phenomenal quantities of energy that could be freed as well as concerning its use; as much to humanity’s benefit as to its detriment.
*1 These scientific advances are not all due to the Curie family members and the Curies were obliged to associate each new concept with the names of those at the origin of each advance.
*2 This method allowed each material to be probeduntil the day when, in 1932, Ernest Lawrence built the first particle accelerator at Berkeley – precursor to the modern accelerators at CERN.
(c) Metin Tolun; tiero; uwimages - Fotolia.com Photos du Musée Curie
We thank the Curie Museum for receiving us on their premises. The museum is provisionally closed for a redevelopment of the premises until the second semester of 2011. All the work will be financed by a bequest from Madame Eve Curie-Labouisse, youngest daughter of Pierre and Marie Curie. She passed away in 2007. Always very close to the Curie Institute, she wanted the Curie Museum to undergo renovation in her mother’s memory.
1) A site directed towards the general public, written by researchers and/or teacher-physicians of IN2P3/CNRS (in French). It presents diverse aspects of radioactivity and all its applications in collaboration with other multimedia researchers. http://www.laradioactivite.com/