Another big community of researchers, including myself, is intrigued by investigating the structure of the nucleus. Indeed, nuclei come in lots of different shapes which arise from the delicate interplay of the nuclear strong force and Coulomb interactions. We often imagine the nucleus as a sphere, a homogeneous mix of protons and neutrons.
In fact the majority of nuclei are not spherical, but prolate deformed like a rugby ball in their lowest energy states, ie when they are coldest, in what is called the ground state see figure 1: Nuclear shapes. However, the specific structure of the nucleus can change depending on the amount of internal energy. For the same number of protons and neutrons the degree of excitation or heating of the nucleus affects the precise arrangement of proton and neutron orbits, which can lead to a variety of eccentric and intriguing shapes within the same nucleus.
An example for lead is shown in figure 1: Nuclear shapes. Figure 1: Nuclear shapes. Different nuclear shapes are possible. Three of the most common are shown here for the lead nucleus as the excitation energy increases -- spherical, oblate and prolate shapes from left to right. Figure from A. Andreyev et al.
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As can be seen from figure 2: Nuclear chart there are many different isotopes; nuclei of the same element ie with the same number of protons , but different numbers of neutrons. Figure 2: Nuclear chart.
The large yellow area shows the as yet unexplored region of isotopes. There are over isotopes predicted theoretically to exist but only about half of them have been successfully created in the laboratory to date. It is difficult to produce a lot of the nuclei since the majority of them are unstable. There are only about stable nuclei which are depicted in black in figure 2: Nuclear chart.
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The remaining, unstable nuclei decay via a range of different processes for example by beta decay, alpha decay or spontaneous fission, though other, more exotic decays are also possible. To answer this question we have to move further along the time-line of the universe. A few seconds after the big bang, primordial nucleosynthesis began and was responsible for the formation of most of the lightest elements we find, such as hydrogen and helium. Similar processes occur in stars like our Sun in which the fusion of protons and neutrons is taking place via a three-step process to synthesise alpha-particles helium-4 nuclei comprising 2 protons and 2 neutrons.
To produce heavier elements like carbon and oxygen, which are necessary for all life on Earth, alpha-particles need to fuse together. But there is a problem: when two alpha particles fuse together they form beryllium-8, which falls apart within 10 —16 seconds! This, together with the absence of a stable mass-five nucleus creates a bottleneck for production of heavier elements see figure 3: Bottleneck. In this helium shell, the pressures are lower and the mass is not supported by electron degeneracy.
Thus, as opposed to the center of the star, the shell is able to expand in response to increased thermal pressure in the helium shell. Expansion cools this layer and slows the reaction, causing the star to contract again.
Triple-alpha process - Wikipedia
This process continues cyclically, and stars undergoing this process will have periodically variable radius and power production. These stars will also lose material from their outer layers as they expand and contract. The triple alpha process is highly dependent on carbon and beryllium-8 having resonances with slightly more energy than helium-4 , and before , no such energy levels were known for carbon.
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The astrophysicist Fred Hoyle used the fact that carbon is abundant in the universe as evidence for the existence of a carbon resonance. The only way Hoyle could find that would produce an abundance of both carbon and oxygen is through a triple alpha process with a carbon resonance near 7.
Hoyle went to nuclear physicist William Alfred Fowler 's lab at Caltech and said that there had to be a resonance of 7. There had been reports of an excited state at about 7. Finally, a junior physicist, Ward Whaling , fresh from Rice University , who was looking for a project decided to look for the resonance. Fowler gave Whaling permission to use an old Van de Graaff generator that was not being used.
Hoyle was back in Cambridge when his prediction was verified a few months later.
The Triple Alpha Process
The nuclear physicists put Hoyle as first author on a paper delivered by Whaling at the Summer meeting of the American Physical Society. A long and fruitful collaboration between Hoyle and Fowler soon followed, with Fowler even coming to Cambridge. This helped to explain the rate of the process, but the rate calculated by Salpeter seemed too low at the temperatures expected in supernovas.
This state completely suppresses single gamma emission, since single gamma emission must carry away at least 1 unit of angular momentum. Carbon is a necessary component of all known life. Some scholars argue the 7.
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Fred Hoyle argued in that the Hoyle resonance was evidence of a "superintellect";  Leonard Susskind in The Cosmic Landscape rejects Hoyle's intelligent design argument. Other scientists reject the hypothesis of the multiverse on account of the lack of independent evidence. From Wikipedia, the free encyclopedia. Nuclear fusion reaction chain converting helium to carbon.
It is not to be confused with alpha process. Main article: Big Bang nucleosynthesis. Main article: Fine-tuned universe. Astrophysics Library 3rd ed. New York: Springer. Hoyle said that because the energy of three alpha particles creates carbon with more energy than it needs, this extra energy must be equal to an excited state of carbon, allowing it to decay to its ground state and remain stable. Experiments later proved him right, but the resonance introduced its own problems. It occurs at a very particular value, 7.
Revised rates for the stellar triple-alpha process from measurement of 12C nuclear resonances.
Vary it by 0. Hoyle and others argued that this means our universe must have been fine-tuned for life. That resonance could have occurred at a range of energies, and the fact that it just happened to occur at the point we needed it to for our existence makes us astonishingly lucky. The odds of this happening at random are very low, and some argue that the only way to explain it is if our universe is just one of many in a multiverse.
In that case, each universe could have slightly different values for the fundamental constants of physics. For this to happen would require a change in the binding energy of beryllium-8 of less than 0.