Formation of Heavy Elements

The next element in the periodic table after tin (chemical symbol Sn) is antimony (chemical symbol Sb). If122Sn captures a neutron, the result will be

123Sn

Where do elements heavier than iron come from?

Elements heavier than iron can be formed inside massive stars by absorbing neutrons, in a process called neutron capture. This is easier than fusion since neutrons are neutral and are not repelled by an atomic nucleus. Adding neutrons does not change an element but creates heavier isotopes of the same element. However, eventually when too many neutrons are added an unstable isotope is created which can then radioactively decay to another element.

Which of the following atomic numbers corresponds to an s-process element?

80

What is r- or rapid-process?

During supernova explosions, neutrons are added very rapidly to nuclei before they have time to decay. This is called the r- or rapid-process and forms the very heaviest elements. Because they are only made over a very short time periods, their abundances are extremely low.

Where do the very heaviest elements in the Periodic Table come from?

During the initial stages of a supernova explosion, huge numbers of neutrons are generated, leading to the formation of the heaviest elements. Thus these elements are actually formed after their parent stars have died!

Helium capture takes less energy than neutron capture. T/F

Flase

Which of the following is a primordial element?

Helium

What's an example of s-process?

Here is an example of the formation of the element copper, 65Cu from iron, 56Fe via the s-process. Horizontal motion to right corresponds to the neutron capture steps while diagonal motion to the upper left corresponds to the radioactive decays of unstable nuclei.

What's an example of r-process?

Here is an example of the formation of the element gold, 198Au from ytterbium, 188Yb via the r-process. Again, horizontal motion to right corresponds to the neutron capture steps while diagonal motion to the upper left corresponds to the radioactive decays of unstable nuclei. By the way, the element symbol for Ytterbium is mislabeled here. It should be Yb not Y.

What is the s- or slow-process?

Inside massive stars neutrons can be captured slowly on timescales of years. This is called the s- or slow-process and gives unstable nuclei plenty of time to decay into other elements before more neutrons are added. The s-process can form elements up to and including bismuth, 209Bi (Z = 83), the heaviest non-radioactive nucleus in the Periodic Table. Indeed the s-process is responsible for forming many of the elements intermediate to those formed by helium capture.

Very heavy elements beyond iron in the periodic table are formed in the interiors of massive stars by what process in general?

Neutron Capture

What are the formation of elements Hydrogen, Helium, Carbon, Oxygen, and iron?

Our ultimate goal is to explain where all the chemical elements come from. Let's see how were are doing so far. Hydrogen and helium, the two lightest elements make up the majority of the matter in the universe. They are mostly primordial elements having been formed in the Big Bang that created the universe. However, a small amount of additional helium is created inside stars. Low mass stars are able to form elements up to carbon and oxygen which have atomic numbers of 6 and 8 respectively while high mass stars are able to form elements up to iron which has an atomic number of 26. So as you can see, so far we have only accounted for the formation of the first 26 elements!