Cauldrons in the Cosmos
Department of Physics
University of York
With thanks to Brian Fulton, York and Marialuisa Aliotta, Edinburgh
In search of the building blocks of the Universe
There is a saying that we are all stardust because all the elements that make up the known matter in the Universe, including us, originated from stars, but how are there so many considering that most stars are initially just hydrogen and helium.
Ancient Greek philosophers believed there were only four elements
Their ideas did nothing to advance the understanding of the nature of matter. We have to wait until 1661 when Robert Boyle defined an element as “a substance that cannot be broken down into a simpler substance by a chemical reaction”. This simple definition served for three centuries and lasted until the discovery of subatomic particles. During this time more and more elements were identified.
Robert Boyle, FRS, (25 January 1627 – 31 December 1691) was an Irish 17th-century natural philosopher, chemist, physicist, and inventor.
In 1817, Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1828, he found that he could form some of the elements into groups of three, with the members each of group having related properties. He termed these groups triads.
Johann Wolfgang Döbereiner (13 December 1780 – 24 March 1849) was a German chemist who is best known for work that foreshadowed the periodic law for the chemical elements.
Alexandre-Emile Béguyer de Chancourtois, a French geologist, was the first person to notice the periodicity of the elements — similar elements occurring at regular intervals when they are ordered by their atomic weights. He devised an early form of periodic table, which he named Vis tellurique (the ‘telluric helix’), after the heaviest element in his diagram, tellurium.
Alexandre-Émile Béguyer de Chancourtois (20 January 1820 – 14 November 1886) was a French geologist and mineralogist who was the first to arrange the chemical elements in order of atomic weights, doing so in 1862.
In 1865, the English chemist John Newlands classified the fifty-six known elements into eleven groups, based on their physical properties.
John Alexander Reina Newlands (26 November 1837 – 29 July 1898) was an English chemist who worked on the development of the periodic table.
The Russian chemist Dmitri Mendeleev was the first scientist to make a periodic table similar to the one used today. Mendeleev arranged the elements by atomic mass, corresponding to relative molar mass.
Dmitri Ivanovich Mendeleev; 8 February 1834 – 2 February 1907 O.S. 27 January 1834 – 20 January 1907) was a Russian chemist and inventor.
Mendeleev’s table allowed him to predict the discovery of new elements and he was able to leave spaces for those elements not yet discovered. It also allowed him to correct some of the atomic masses of elements. There were shortcomings however in that the table was not able to predict the existence of the noble gases. However, when this entire family of elements was discovered, Sir William Ramsay was able to add them to the table as Group 0, without the basic concept of the periodic table being disturbed.
Sir William Ramsay KCB FRS FRSE (1852–1916) was a 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”.
Another shortcoming of Mendeleev’s table was that a single position could not be assigned to hydrogen. It could be placed in either the alkali metals group or in the halogens group (and in some versions of the periodic table it sits on its own).
In 1914, a year before he was killed in action at Gallipoli, the English physicist Henry Moseley found a relationship between the X-ray wavelength of an element and its atomic number. He was then able to resequence the periodic table by nuclear charge, rather than by atomic weight. Before this discovery, atomic numbers were sequential numbers based on an element’s atomic weight. Moseley’s discovery showed that atomic numbers were in fact based upon experimental measurements.
Henry Gwyn Jeffreys Moseley (23 November 1887 – 10 August 1915) was an English physicist.
During his Manhattan Project research in 1943, Glenn T. Seaborg experienced unexpected difficulties in isolating the elements americium and curium. Seaborg wondered if these elements belonged to a different series, which would explain why their chemical properties were different from what was expected. In 1945, against the advice of colleagues, he proposed a significant change to Mendeleev’s table: the actinide series.
Glenn Theodore Seaborg (April 19, 1912 – February 25, 1999) was an American scientist whose involvement in the synthesis, discovery and investigation of ten transuranium elements earned him a share of the 1951 Nobel Prize in Chemistry.
The link below is an interactive periodic table
At present there are 118 elements but only the first 98 exist in nature so how, where and when were they made?
Why are some elements so much more abundant than others?
Gold is extracted at a rate of 300 tonnes per year
Iron extracted at a rate of 1500 million tonnes per year
The Sun is a pretty typical star whose composition is known from spectroscopy. The composition of the Sun in atomic abundance is shown below. Silicon is used as a basis for comparison because it allows convenient comparison of solar and planetary element abundances.
Note that the abundance scale is logarithmic
There is an overwhelming abundance of light elements with a strong preference for even-numbered elements. There is a peak in abundance at iron, followed by a steady decrease with elements 3-5, Lithium, Beryllium and Boron, at very low in abundance.
These patterns have to do with nucleosynthesis (element formation) in the stars.
So how did we get the atoms to form the elements in the first place?
The Big Bang
13.7 billion years ago:
Big bang nucleosynthesis occurred 1 second after the big bang when temperatures became cool enough for protons and neutrons to form.
When the temperature cooled further protons and neutrons fused to produce helium.
After 3 minutes the temperature reduced to a point where no more fusion occurred.
Only the 3 lightest elements, hydrogen, helium and lithium were created in the Big Bang.
Where did the heavier elements come from?
What are the ingredients?
A 2m human is made up of cells.
Cells are about 10 mm. Inside the nucleus of a cell is DNA which is about 2nm and the atoms that make up DNA contain a nucleus which is 10^-14m across.
Our knowledge of what makes up an atom is fairly recent but the idea that matter is made up of discrete units is a very old one, appearing in many ancient cultures such as Greece and India. The word “atom”, in fact, was coined by ancient Greek philosophers but their views on what atoms look like and how they behave was very incorrect. It wasn’t until the 19th century that the idea was embraced and refined by scientists, when the blossoming science of chemistry produced discoveries that only the concept of atoms could explain.
In the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers (the law of multiple proportions).
John Dalton FRS (6 September 1766 – 27 July 1844) was an English chemist, meteorologist and physicist.
Jean Perrin experimentally determined the mass and dimensions of atoms, thereby conclusively verifying Dalton’s atomic theory.
Jean Baptiste Perrin (30 September 1870 – 17 April 1942) was a French physicist.
The physicist J. J. Thomson, through his work on cathode rays in 1897, discovered the electron, and concluded that they were a component of every atom. Thus he overturned the belief that atoms are the indivisible, ultimate particles of matter. Thomson postulated that the low mass, negatively charged electrons were distributed throughout the atom in a uniform sea of positive charge. This became known as the plum pudding model.
Sir Joseph John “J. J.” Thomson, OM, FRS (18 December 1856 – 30 August 1940) was an English physicist.
A schematic presentation of the plum pudding model of the atom
In Thomson’s mathematical model the “corpuscles” (or modern electrons) were arranged non-randomly, in rotating rings
In 1909, Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, bombarded a metal foil with alpha particles to observe how they scattered. Going by Thomson’s plum pudding model, all the alpha particles should have passed straight through the foil with little deflection, because the positive charge of its atoms should have been too dilute to affect them much. They instead observed a small fraction of alpha particles being deflected by angles greater than 90°. To explain this, Rutherford proposed that each atom has a nucleus where the positive charge and most of the mass are concentrated, and these were what were deflecting those alpha particles so strongly.
Ernest Rutherford, 1st Baron Rutherford of Nelson, OM FRS (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist who became known as the father of nuclear physics. He was so surprised by the results of the scattering experiment that he said “It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you.”
He also famously said “In science there is only physics; all the rest is stamp collecting” and he is absolutely right (Helen Hare).
In 1913, physicist Niels Bohr suggested that the electrons were confined into clearly defined, quantized orbits, and could jump between these, but could not freely spiral inward or outward in intermediate states like satellites orbiting a planet.
The images below show the Bohr model of the atom, with an electron making instantaneous “quantum leaps” from one orbit to another. This model is now obsolete.
Niels Henrik David Bohr (7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory.
Also in 1913 Henry Moseley provided additional experimental evidence in favour of Niels Bohr’s theory. These results refined Rutherford’s model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today.
In 1920, Ernest Rutherford conceived the possible existence of the neutron. In particular, Rutherford considered that the disparity found between the atomic number of an atom and its atomic mass could be explained by the existence of a neutrally charged particle within the atomic nucleus. He considered the neutron to be a neutral double consisting of an electron orbiting a proton.
Through the 1920s, physicists had generally accepted an (incorrect) model of the atomic nucleus as composed of protons and electrons. It was known that atomic nuclei usually had about half as many positive charges than if they were composed completely of protons, and in existing models this was often explained by proposing that nuclei also contained some “nuclear electrons” to neutralize the excess charge. Thus, the nitrogen-14 nucleus would be composed of 14 protons and 7 electrons to give it a charge of +7 but a mass of 14 atomic mass units.
The new quantum mechanics implied that a particle as light as the electron could not be contained in a region as small as the nucleus with any reasonable energy. In 1930 Viktor Ambartsumian and Dmitri Ivanenko in the USSR found that, contrary to the prevailing opinion of the time, the nucleus cannot consist of protons and electrons. They proved that some neutral particles must be present besides the protons.
In 1932 Irène Joliot-Curie and Frédéric Joliot in Paris showed that if the unknown radiation, produced when alpha particles fell on light elements, fell on paraffin, or any other hydrogen-containing compound, it ejected protons of very high energy. This was not in itself inconsistent with the assumed gamma ray nature of the new radiation, but detailed quantitative analysis of the data became increasingly difficult to reconcile with such a hypothesis.
In 1932, James Chadwick performed a series of experiments at the University of Cambridge, showing that the gamma ray hypothesis was wrong. He suggested that the new radiation consisted of uncharged particles of approximately the mass of the proton, and he performed a series of experiments verifying his suggestion. These uncharged particles were called neutrons, apparently from the Latin root for neutral and the Greek ending -on (by imitation of electron and proton).
Sir James Chadwick CH FRS (20 October 1891 – 24 July 1974) was an English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932.
The most modern view of an atom is a central nucleus surrounded by a cloud of electrons.
Elements and Isotopes
Chemical elements have a different chemistry.
We use names for them but it is just a shorthand for counting the number of protons.
Some elements come with different masses. These forms are called isotopes.
Isotopes have the same number of protons but different numbers of neutrons. The chemistry doesn’t really change but they are very different in terms of nuclear physics.
Can we make any old nucleus by choosing different numbers of neutrons and protons?
No! – Because some are more stable than others.
The “Terra incognita” region show where some isotopes should exist, but can’t be produced (unless, perhaps, there is a supernova about)
The proton:neutron ratio and the evenness or oddness of the atomic number Z, neutron number N and, consequently, of their sum, the mass number A are factors affecting the nuclear stability of an atom. Oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei, generally, less stable. Even numbers make it easier to add neutrons.
The alchemist tried to turn base metals into gold using techniques which we would now call “Chemistry”.
It never worked…
Nuclei have a positive charge from the protons in them and so repel
To fuse nuclei together we need high energies (temperature and densities)
The life cycle of a star
All stars are born from gravitational collapsing clouds of gas and dust, often called nebulae or molecular clouds. In regions of higher density, the primordial H and He begin to gravitationally attract.
As the giant molecular cloud collapses it breaks into smaller and smaller pieces. In each of these fragments, the collapsing gas releases gravitational potential energy as heat. As its temperature and pressure increase, a fragment condenses into a rotating sphere of superhot gas known as a protostar. Eventually the temperature at the centre gets so high that nuclear reactions start.
Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star.
A new star is born
At the start of a star’s life it will release energy from proton fusion to produce helium from hydrogen
The proton–proton chain reaction dominates in stars the size of the Sun or smaller.
Net effect is 4 H atoms create 1 He atom, releasing 1.6×10^-13 J
Tiny energy release……
….but there is LOTS of H in a star
Our sun consumes 100,000,000 tonnes of H per second!
Idea: We could produce Carbon-12 by fusing three Helium-4 nuclei together
The problem: Berylllium-8 has a half-life of 10^-15 s
This process should be extremely slow… We could not produce carbon in any quantity
The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon
Because the triple-alpha process is unlikely, it needs a long time to produce much carbon. One consequence of this is that no significant amount of carbon was produced in the Big Bang because within minutes after the Big Bang, the temperature fell below that necessary for nuclear fusion.
The triple alpha process is highly dependent on carbon-12 and beryllium-8 having resonances (A resonance in this context means a nuclear energy level at just the right place) with the same energy as helium-4, and before 1952, no such energy levels were known. The astrophysicist Fred Hoyle used the fact that carbon-12 is abundant in the universe as evidence for the existence of a carbon-12 resonance. This could be considered to be an example of the application of the anthropic principle: we are here, and we are made of carbon, thus the carbon must have been produced somehow. The only physically conceivable way is through a triple alpha process that requires the existence of a resonance in a given very specific location in the spectra of carbon-12 nuclei.
Sir Fred Hoyle FRS (24 June 1915 – 20 August 2001) was an English astronomer noted primarily for the theory of stellar nucleosynthesis. He predicted in 1953 that there must be a resonance that makes the three helium nuclei fuse much more rapidly.
In a sense, things are “just right” like the Three Little Bears’ porridge Move the carbon energy level only a little and you can stop production of carbon in stars or accelerate it so that stars die much faster
But if they weren’t just right would be here to see it?!?
Would you not say to yourself, “Some super-calculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule.” Of course you would . . . A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question. —Fred Hoyle, “The Universe: Past and Present Reflections.” Engineering and Science, November, 1981. pp. 8–12
A plaque at Bingley Grammar School commemorating him
How do we reproduce the nuclear reactions involved in stars on earth?
The Gran Sasso National Laboratory (LNGS) is one of four INFN national laboratories.
It is the largest underground laboratory in the world for experiments in particle physics, particle astrophysics and nuclear astrophysics. It is used as a worldwide facility by scientists, presently over 900 in number, from 29 different countries, working at about 15 experiments in their different phases.
The mission of the Laboratory is to host experiments that require a low background environment in the field of astroparticle physics, nuclear astrophysics and other disciplines.
Main research topics of the present programme are: neutrino physics using neutrinos naturally produced in the Sun and in Supernova explosions, neutrino oscillations with a beam from CERN (CNGS program), search for neutrino mass in neutrino-less double beta decay, dark matter search and nuclear reactions of astrophysical interest.
Nuclear reactions that generate energy and synthesize elements take place inside the stars in a relatively narrow energy window. In this region, which is in most cases below 100 keV, the reaction cross-section drops almost exponentially with decreasing energy. It’s extremely low value has always prevented its measurement in a laboratory at the Earth’s surface, where the signal to background ratio would be too small because of cosmic ray interactions.
Instead, the observed energy dependence of the cross section at high energies is extrapolated to the low energy region, leading to substantial uncertainties.
In order to explore this new domain of nuclear astrophysics they have installed two electrostatic accelerators underground in LNGS: a 50 kV accelerator that took data until 2001 and a 400 kV one that was installed in 2000 (LUNAII in the image below).
LUNA has shown that, by going underground and by using the typical techniques of low background physics, it is possible to measure nuclear cross sections down to the energy of the nucleo-synthesis inside stars.
What about heavier elements?
Further stages of collapse and burning of a star can occur, building up heavier and heavier elements
“Onion skin” structure of a late, main sequence star
The build-up stops at Iron – the most tightly bound nucleus
When a star dies it expels these new elements into space.
All elements heavier than iron are generated in Supernova explosions and scattered into space.
Modelling the explosions
Nuclear physics provides one of the inputs – nuclear reaction rates
But which nuclear reactions are important?
Which nuclear reactions are involved?
The r-process is a nucleosynthesis process, that occurs in core-collapse supernovae, and is responsible for the creation of approximately half of the neutron-rich atomic nuclei heavier than iron.
Evolution of the Table of Isotopes
The existence of isotopes was first suggested in 1913 by the radiochemist Frederick Soddy, based on studies of radioactive decay chains that indicated about 40 different species described as radioelements (i.e. radioactive elements) between uranium and lead, although the periodic table only allowed for 11 elements from uranium to lead.
Frederick Soddy FRS (2 September 1877 – 22 September 1956) was an English radiochemist who explained, with Ernest Rutherford, that radioactivity is due to the transmutation of elements, now known to involve nuclear reactions. He also proved the existence of isotopes of certain radioactive elements.
Splitting the atom
Ernest Rutherford is widely credited with first “splitting the atom” in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered (and named) the proton. He became Director of the Cavendish Laboratory at Cambridge University in 1919 and under his leadership the neutron was discovered by James Chadwick in 1932 and in the same year the first experiment to split the nucleus in a fully controlled manner, performed by students working under his direction, John Cockcroft and Ernest Walton occurred.
Sir John Douglas Cockcroft OM KCB CBE FRS (27 May 1897 – 18 September 1967) was a British physicist. He shared the Nobel Prize in Physics for splitting the atomic nucleus with Ernest Walton, and was instrumental in the development of nuclear power.
Ernest Thomas Sinton Walton (6 October 1903 – 25 June 1995) was an Irish physicist and Nobel laureate for his work with John Cockcroft with “atom-smashing” experiments done at Cambridge University in the early 1930s, and so became the first person in history to artificially split the atom, thus ushering the nuclear age.
The image below left shows the Cockcroft–Walton voltage multiplier. It was part of one of the early particle accelerators responsible for development of the atomic bomb. Built in 1937 by Philips of Eindhoven it is now in the Science Museum.
On 14 April 1932 Walton set up the tube and bombarded lithium with high energy protons. He then crawled into the little observation cabin set up under the apparatus and immediately saw scintillations of the fluorescent screen. The reaction was giving off alpha-particles.
Walton had seen alpha-particles. Cockcroft and Rutherford were informed at once. Rutherford was ‘manoeuvred with some difficulty into the cabin’ shouting out instructions to Walton: ‘Switch off the proton current! Increase the accelerating voltage!.’ Eventually he came out, sat on a stool and said: ‘Those scintillations look mighty like alpha-particle ones. I should know an alpha-particle when I see one for I was in at the birth of the alpha-particle and I have been observing them ever since’!
Cockcroft was later alleged to have gone skipping down King’s Parade (the road past the front of King’s College) shouting ‘We’ve split the atom! We’ve split the atom!’ though in fact Rutherford swore the two men to secrecy for the next few days, allowing them to analyse their results without interruption. On 16 April they wrote a paper at Rutherford’s house, and the on 30 April their results were published in Nature.
Cockcroft and Walton had used an accelerator to split atoms of lithium. This was the first nuclear disintegration that was entirely under human control. The reaction they had observed was:
Li + H = He + He + 17 MeV (2.72 x 10^-12J)
The combined mass of the resulting helium nuclei is actually slightly less than the combined mass of the original lithium and hydrogen nuclei. The very small change in mass becomes energy, its amount calculated using Einstein’s famous equation E = mc². Cockcroft and Walton measured the speed of the two helium nuclei and found that the loss could be accounted for by this mass difference, so their experiment was the first verification of Einstein’s law, E = mc².
Amusingly Rutherford thought that as so little energy was produced during nuclear fission it would never be a viable source of energy.
Radioactive ion production
Production of radioactive isotopes beams by means of an in-flight separation scheme provides opportunities to study reactions and properties of very unstable nuclei.
The most important advantage of the in-flight separation scheme is that it can be applied to the production of all kinds of unstable nuclei independent of their chemical nature.
A simple method for producing radioactive nuclei consists in fragmenting stable nuclei into several pieces. This is the technique used in the GANIL facility.
In practice, a large quantity of atoms of a given chemical element are prepared, and transformed into ions by tearing off several of their electrons. This is the role of an ion source.
Since ions are charged particles, they may be accelerated by means of particle accelerators, and fired onto a piece of matter which itself contains atoms. From time to time, the nucleus of an accelerated ion strikes the nucleus of an atom in the target and breaks up into several fragments: this will produce ions having either a stable or a radioactive nucleus, according to their composition.
All that remains to be done is to select the radioactive ions of interest: this sorting operation is performed by instruments called spectrometers, which control the ions according to their electric and magnetic fields.
GSI operates a worldwide unique large-scale accelerator facility for heavy ions and currently employs about 1.100 people. In addition approximately 1.000 researchers from universities and other research institutes around the world use the facility for their experiments.
It operates one of the most powerful accelerators facilities of the world. It is the only facility that allows the acceleration of ions – ions are charged atoms – of all chemical elements occurring on Earth. The so-called ion sources are the devices where the ions are generated. Ions are charged atoms. The positively charged ions used at GSI are gained by stripping electrons off the shell of the atom. GSI is able to produce ions of many different kinds of elements, more than any other laboratory in the world. Depending on the element different types of ion sources are used.
The best-known results are the discovery of six new chemical elements and the development of a new type of tumour therapy using ion beams.
NSCL is a world-leading laboratory for rare isotope research and nuclear science education. With support from the U.S. National Science Foundation, the laboratory operates as a national user facility that serves more than 700 researchers from 100 institutions in 35 countries.
Scientists at NSCL work at the forefront of the research into these rare nuclei. Using superconducting cyclotrons, they accelerate stable isotopes to half the speed of light before smashing them into other nuclei in order to make and study the rare isotopes that cannot be found on Earth.
The RI Beam Factory (RIBF) is an accelerator complex which consists of an old facility (since 1986) and a new facility which has been completed recently.
The aim of this facility is to expand our nuclear world on the nuclear chart into terra incognita.
The international research facility FAIR is a new, unique international accelerator facility for the research with antiprotons and ions. It will be constructed to explore the nature of matter and the evolution of the universe.
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is various. The largest variety is used in research (e.g. in chemistry where atoms of “marker” nuclide are used to figure out reaction mechanisms).
The on-line isotope mass separator ISOLDE is a facility dedicated to the production of a large variety of radioactive ion beams for many different experiments in the fields of nuclear and atomic physics, solid-state physics, materials science and life sciences. It is a unique source of low-energy beams of radioactive nuclides, those with too many or too few neutrons to be stable. The facility fulfils in fact the old alchemical dream of changing one element into another. It permits the study of the vast territory of atomic nuclei, including the most exotic species.
The facility is located at the Proton-Synchrotron Booster (PSB) at CERN, the European Organization for Nuclear Research. It is operated by the ISOLDE collaboration, whose present members are Belgium, CERN, Denmark, Finland, France, Germany, Greece, India, Ireland, Italy, Norway, Romania, Spain, Sweden and the United Kingdom. The relation between CERN and the ISOLDE collaboration is specified in a Memorandum of Understanding from 2012 (following those in 1993 and 2007).
The installation of the REX-ISOLDE post-accelerator has opened up new fields of research with radioactive ion beams of higher energies. REX-ISOLDE can provide post-accelerated nuclei covering the whole mass range from Helium to Uranium for reaction studies and Coulomb excitation with energies up to 3 MeV/u.
Added Value of ISOLDE includes: It covers several Physics Domains; A possibility of high-precision nuclear experiments; Complementary to particle physics; A place for many potential new users; Easier for small countries
Common Interest with Other CERN Experiments such as: Detector and Instrumentation; Computing techniques; N-To F, Antiprotons….
ISOLDE targets: Radioactive beam is provided by ISOL technique: 1.4-GeV protons hit thick target material; Low-energy beam; Singly-charged ions; Isotopically pure beam; Mixture of isobars
MINIBALL @ REX-ISOLDE
It was specially designed for low multiplicity experiments with low-intensity radioactive ion beams (RIB).
GANIL, Grand Accélérateur National d’Ions Lourds (National Large Heavy Ion Accelerator), in Caen, Basse-Normandie, France provides heavy ion beams for nuclear and atomic physics, astrophysics, material science and radiobiology. GANIL-SPIRAL is the largest accelerator complex in France and one of the two largest facilities for heavy ions in EUROPE along with GSI in Darmstadt (Germany). The installation was jointly created and constructed by two research organizations, CEA/DSM and CNRS/IN2P3. It is jointly operated as a Economic Interest Group (GIE).
The ISOL method with SPIRAL is for the production and acceleration of radioactive ions. The stable heavy ion beams of GANIL are sent into a target and source assembly. The radioactive atoms produced through nuclear reactions are released from the target, kept at high temperature, into an ECR source. After ionization and extraction from the source (extraction voltage < 34kV), the multi-charged radioactive ions can be used at the low-energy facility or accelerated up to a maximum energy of 25MeV/A by the compact cyclotron. They are then delivered to nuclear physics experiments.
Holifield Radioactive Ion Beam Facility ceased operations April 15, 2012. It was involved in producing high quality beams of short-lived, radioactive nuclei for studies of exotic nuclei and astrophysics research.
The TRIUMF Isotope Separator and Accelerator (ISAC) facility uses the isotope separation on-line (ISOL) technique to produce rare-isotope beams (RIB). The ISOL system consists of a primary production beam, a target/ion source, a mass separator, and beam transport system. The rare isotopes produced during the interaction of the proton beam with the target nucleus are stopped in the bulk of the target material. They diffuse inside the target material matrix to the surface of the grain and then effuse to the ion source where they are ionized to form an ion beam that can be separated by mass and then guided to the experimental facilities.
With support approved by independent peer-review processes, scientists can use detectors and facilities at TRIUMF to analyse beams at ISAC or they can bring their own. The full suite of experimental facilities presently available for use at TRIUMF is impressive. The ISAC Science Forum is a regular meeting where experiments are discussed.
Status of our understanding
Well understand (we think):
The reaction rates for standard fusion reactions in stars
The broad properties of reaction networks for explosive scenarios
Verifying that extrapolations to low energies are valid for all cases e.g. carbon burning
Understanding in detail the nuclear reactions involved in supernovae
The reactions that trigger runaway explosions
The cycle of life & our cosmic inheritance
There is a connection between the very big and the very small
(EXPERIMENTAL) NUCLEAR ASTROPHYSICS
To study energy generation processes in stars
To study nucleosynthesis of the elements
MACRO-COSMOS intimately related to MICRO-COSMOS
NUCLEAR PHYSICS is the key to understand Universe at large
Answers to questions
Elements with mass numbers greater than iron that are naturally found originated from supernovae
A supernova is a stellar explosion that briefly outshines an entire galaxy, radiating as much energy as the Sun is expected to emit over its entire life span, before fading from view over several weeks or months.
Supernovae can be triggered in one of two ways: by the sudden reignition of nuclear fusion in a degenerate star; or by the gravitational collapse of the core of a massive star. In the first case, a degenerate white dwarf may accumulate sufficient material from a companion, either through accretion or via a merger, to raise its core temperature, ignite carbon fusion, and trigger runaway nuclear fusion, completely disrupting the star. In the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy that can create a supernova explosion.
They play a significant role in enriching the interstellar medium with higher mass elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.
In main sequence stars neutron capture is slow
but rapid in supernovae.
Most neutron-rich isotopes of elements heavier than nickel are produced, either exclusively or in part, by the beta decay of very radioactive matter created during the r-process by rapid absorption, one after another, of free neutrons created during the explosions. The creation of free neutrons by electron capture during the rapid collapse to high density of the supernova core along with assembly of some neutron-rich seed nuclei makes the r-process a primary process.
Supernova nucleosynthesis is the production of new chemical elements inside supernovae, a picture due to Fred Hoyle. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning. Those fusion reactions create the elements silicon, sulphur, chlorine, argon, sodium, potassium, calcium, scandium, titanium and iron peak elements: vanadium, chromium, manganese, iron, cobalt, and nickel. These are called “primary elements”, in that they can be fused from pure hydrogen and helium in massive stars. As a result of their ejection from supernovae, their abundances increase within the interstellar medium. Elements heavier than nickel are created primarily by a rapid capture of neutrons in a process called the r-process. However, these are much less abundant than the primary chemical elements. Other processes thought to be responsible for some of the nucleosynthesis of underabundant heavy elements, notably a proton capture process known as the rp-process and a photodisintegration process known as the gamma (or p) process. The latter synthesizes the lightest, most neutron-poor, isotopes of the heavy elements.
Once the core fails to produce enough energy to support the outer envelope of gases the star explodes as a supernova producing the bulk of elements beyond iron. Production of elements from iron to uranium occurs within seconds in a supernova explosion. Due to the large amounts of energy released, much higher temperatures and densities are reached than at normal stellar temperatures. These conditions allow for an environment where transuranium elements might be formed.
In models of supernovae there is some missing physics. The models don’t show the explosion.
Periodic table showing the origin of elements, including supernova nucleosynthesis