WIELKIM WYBUCHU I W

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Wstęp do Fizyki Jądra Atomowego i cząstek elementarnych

VII. NUKLEOSYNTEZA W WIELKIM WYBUCHU I W

GWIAZDACH

Jan Królikowski

krolikow@fuw.edu.pl,

pok. 123 w Pawilonie IPJ

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Źródłem cytatów po

angielsku jest artykuł o nukleosyntezie w

Wikipedii:

http://en.wikipedia.org/wiki/

Stellar_nucleosynthesis

J. Królikowski: Wstęp do Fizyki Jądra i

Cząstek Elementarnych IIIr. ind. 2

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Nukleosynteza lekkich jąder (do Li i Be) dokonywała się w WW i w gwiazdach,

wszystkie ciężkie jądra zostały wytworzone w gwiazdach.

Do A=57 (żelazo)- maksimum energii wiązania na nukleon B/A- możliwa była fuzja. Jadra

cięższe powstały na skutek bardziej

skomplikowanych procesów- łańcuchów

reakcji z neutronami i rozpadów jąder poza ścieżką stabilności.

Wybuchy gwiazd powodowały

rozprzestrzenienie się pierwiastków we

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Rozpowszechnienie nuklidów

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Procesy w gwiazdach; podróżowanie po tablicy nuklidów

Potrzebujemy:

Mas, czasów życia przekrojów czynnych Itp.. W OBSZARACH DALEKICH OD ŚCIEŻKI STABILNOŚCI

100Sn

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Obfitości pierwiastków w Układzie Słonecznym

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Nukleosynteza w WW

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Gwiazdy

Odkrycie mechanizmów fuzji jądrowej:

– Okno Gamova (G. Gamov, 1928) – Cykl pp (H. Bethe, 1939)

– Cykl CNO (C. F. von Weizsaeker, 1938)

– Cieższe nuklidy do Fe i rzadkie procesy R i S (F.

Hoyle, 1946-54 , Burbridge, Burbridge, Fowler, Hoyle (B

²

FH), 1957, "Synthesis of the Elements in Stars".

Reviews of Modern Physics 29 (4): 547–650):

• Spalanie C, N, O, Si

• Procesy R i S z udziałem neutronów w jądrach ciężkich

gwiazd (ew. gwiazd neutronowych)nuklidy n-nadmiarowe

• Wychwyt protonów (Rp) i fotodezintegracja (P) nuklidy p-

nadmiarowe

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Przykład: Czerwony Olbrzym przed wybuchem jako SN

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Podstawa proces pp (Bethe)

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Przenikanie przez barierę

Okno

Gamowa

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Neutrina ze Słońca- testowanie SSM

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Po spaleniu wodoru…

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Po spaleniu wodoru i helu:

C. F. von Weizsaeker

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Spalanie C, O i Si

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Proces S(low)

The S-process was seen to be needed from the relative abundances of isotopes of heavy elements and from a newly published table of abundances by Hans Suess and Harold Urey in 1956. Among other things, this data showed abundance peaks for strontium, barium, and lead, which, according to quantum mechanics and the nuclear shell model, are particularly stable nuclei, much like the noble gases are chemically inert. This implied that some

abundant nuclei must be created by slow neutron capture, and it was only a matter of determining what other nuclei could be accounted for by such a process. A table

apportioning the heavy isotopes between S-process and R-process was published in the famous B²FH review paper in 1957.^[1] There it was also argued that the S-process occurs in red giant stars. In a particularly illustrative case, the element technetium, with a longest half-live of 4.2 million years, had been discovered in S-, M-, and N-type stars in 1952.^[2][3]. Since these stars were thought to be billions of years old, the presense of technetium in

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Proces S zachodzi w gwiazdach AGB

0.6 M

_S

<M<10 M

_S

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Powolny wychwyt neutronu

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Proces R(apid)

Immediately after a core-collapse supernova, there is an extremely high neutron flux (on the order of 10²² neutrons per cm² per second) and temperature, so that neutron captures occur much faster than beta-minus decays far from stability, meaning that the r-process "runs up" along the neutron drip line. The only two hold-ups inhibiting this process of climbing the neutron drip line are a notable decrease in the neutron-

capture cross section at nuclei with closed neutron shells, and the degree of nuclear stability in the heavy-isotope region, which terminates the r-process when such nuclei become readily unstable to spontaneous fission (currently believed to be in the

neutron-rich region near A = 270 (number of nucleons) in the chart of nuclides). After the neutron flux decreases, these highly unstable radioactive nuclei quickly decay to form stable, neutron-rich nuclei. So, while the s-process creates an abundance of stable nuclei with closed neutron shells, the r-process creates an abundance of nuclei about 10 atomic mass units below the s-process peaks, as the r-process nuclei decay back towards stability on a constant A line in the chart of nuclides.

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Szybki wychwyt protonów (proces Rp)

The rp-process (rapid proton capture process) consists of consecutive proton captures onto seed nuclei to produce heavier elements^[1]. It is a nucleosynthesis process and, along with the s process and the r process, may be responsible for the generation of many of the heavy elements present in the universe. However, it is notably different from the other processes mentioned in that it occurs on the proton-rich side of stability as opposed to on the neutron-rich side of stability.

The end point of the rp-process (the highest mass element it can create) is not yet well established, but recent research has indicated that in neutron stars it cannot progress beyond tellurium.^[2] The rp-process is inhibited by alpha decay, which puts an upper limit on the end point at ¹⁰⁵Te, the lightest observed alpha decaying nuclide^[3], though lighter isotopes of tellurium could potentially be proton-bound and alpha decaying.

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Fotodezintegracja jąder (proces P)

When the p-process was originally proposed in the famous "B²FH paper" in 1957,^[1]

the physics of the process itself was not understood. The authors believed that most atomic nuclei heavier than iron, which are generally neutron-rich, were

created by the s-process and r-process, both mechanisms for creating neutron-rich nuclei through neutron capture. However, it was observed that some proton-rich nuclei cannot be produced by the s- or r-process (e.g. ¹⁹⁰Pt or ¹⁶⁸Yb). This simple observation suggested that there must be a process for creating certain heavy proton-rich nuclei, and so it was called simply the proton-process, or p-process for short. It is interesting to note that the process as it is now understood actually has nothing to do with proton capture as the name might suggest, and thus it should not be confused with the rp-process, which does involve proton capture.

Sometimes the rp-process is mistakenly referred to as the p-process, because the nomenclature, for historical reasons, is slightly misleading