STELLAR NUCLEOSYNTHESIS OF
ELEMENTS HIGHER THAN ATOMIC NUMBER 30, (NI)
By:Clarence L. Dulaney
A: INTRODUCTION
It is pretty well established
that stellar energy is produced by fusion reactions forming elements up to
atomic number 30, (Ni). [1, 2, 3, 4]. No
further energy or fusion occurs for elements above 30Ni.[4.320] (Note: 4 is the reference number and 320 is the page
number).
That higher elements than 30Ni
are produced even in the sun is indicated by Novotony’s
[1.47ff] “Table of Abundances” based on spectral data from sunspots and the
solar photosphere. Obviously some
mechanism must exist to produce these higher elements (up to 92U).
B, Addition of “Neutrons” to Heavy
Elements
The current theory has
addition of “neutrons” in a step-by-step fashion to form the higher
isotopes. Clayton [2.Chapter 7] gives a
detailed account of the process, although he is a bit vague about where the
“neutrons” come from particularly in stars as light as the sun. He is also vague about how the heavy nuclei
and “neutrons” come in contact. (this, along with some comments about what “neutrons”
actually are will be addressed in a subsequent paper.)
“Neutrons” can add with
essentially no energy because they have no charge. They are not accelerated to high velocities
in the high temperature of the stellar atmospheres. They are added to a given atomic number up
to the point where an unstable nucleus is formed. Then a B- is emitted and the next higher atomic number element
is produced. The neutron capture is
“slow” with the b- emission being
relatively fast. The overall process is
called the “s-process”.
30Ni62 + 0n1
= 30Ni63* = 31Cu63
=b-. 31Cu63
+0n1
= 31Cu64 etc.
is an example of the process.
As evidence for the
s-process, spectral lines of 43Tc and 61Pr have been
found in spectra from “s-type” red-giant stars[5]. Both of these elements have no ”stable” isotopes and are not found naturally on earth or
in the solar abundances.
Pathways ro
produce most stable isotopes of the heavy elements have been shown to be
possible [2] There
are some isotopes however that cannot be reached by the s-process. See Lilley, [4.332] for evidence that there
is a problem with
40Zr96 and with 42Mo100. Other problems concern “stable” isotopes of 90Th
and 92U.
Theory has it that these
isotopes are made by the “r-process”, so named for the rapid addition of a
large number of “neutrons” that leads to bypassing possible unstable
nuclei. Generally, only in nova type
explosions are enough “neutrons” available for the “r-process “ to occur. With the large number of “neutrons”, the
addition proceeds to transuranic isotopes. These isotopes spontaneously undergo
fission. As an example, 97Bk
could disintegrate to 48Cd and 49In.
Nowever,
Novotny’s Table show that
some of the r-process elements show up in the solar atmosphere, so the process
must stop before transuranic isotopes are formed, (or
very large number of :neutrons” are produced on the sun.) This topic will also be addressed in the
next paper.
There is one other possible
process called the “p-process” that produces isotopes with higher ratios of
protons to neutrons than the
s- or r-processes.
Actually it should be called the g-process.[6].
See the next paper.
SUMMARY
No energy is produced (other
than a small “binding” energy) in addition of “neutrons’ to elements higher
than 30Ni in stellar atmospheres.
Current theory has it that
higher atomic weight isotopes are formed by addition of “neutrons” one-by-one, Once an unstable
isotope is formed, the next higher atomic number isotope is formed by b- decay.
Two pathways are proposed,
the “s-process” and the “r-process”. The
former involves slow addition of “neutrons” followed by fast emission of b-..
The “r-process” involves
rapid addition of large number of “neutrons” which skips over some unstable
nuclei.
By one process or the other all stable isotopes
up to 92U are formed.
REFERENCES
1.
e. Novotony, “Introduction to Stellar Atmospheres and
Interiors”,
2.
3.
J. M. Paschakoff, “Astronomy, From the Earth to the Universe,”,
4.
J. Lilley,
“Nuclear Physics, Principles and Applications” John Wiley &Sons, NY, 2001
© September 14, 2007 Clarence L. Dulaney