Transcript PPT - James Madison University

The Nucleosynthesis of
Chemical Elements
Dr. Adriana Banu, James Madison University
January 22, Saturday Morning Physics’11
Big questions
We knew for long time that our energy comes from Sun!
1.But what produces it in the Sun?
Gravity (which governs planets motion)?!
Chemical reactions like on Earth (fuel burning, explosions...)?!
In the 1930s we got the answer: nuclear reactions!
Namely fusion!
What about the other stars?!
2. How were/are the chemical elements created?
(nucleosynthesis) The answer is still: nuclear reactions!
But which reactions?! How they proceed?!
3. Did nucleosynthesis stop, or continues today?
“If in some cataclysm, all of scientific knowledge were to
be destroyed, and only one sentence passed on to the next
generations of creatures, what statement would contain
the most information in the fewest words?
Everything is made of atoms.”
-Richard Feynman
Nobel Prize in Physics, 1965
“If you want to make an apple pie from scratch, you must
first create the universe…”
“We are star-stuff…”
- Carl Sagan
• From Aristotle to Mendeleyev
In search of the building blocks of the universe…
Greek philosophers
water
4 building blocks
18th-19th century Lavoisier, Dalton, …
air
distinction between compounds
and pure elements
atomic theory revived
fire
earth
92 building blocks
(chemical elements)
Periodic Table of Elements
1896 Mendeleyev
not to scale
Atom = nucleus + electrons
-e
(10-10 m)
+Ze
Nucleus = protons + neutrons
(10-14 m)
• Modern “Alchemy”: radioactivity
1896 Becquerel discovers radioactivity
The Nobel Prize in Physics 1903
A. H. Becquerel
Pierre Curie
Marie Curie
 emission of radiation from atoms
 3 types observed: ,  and 
“transmutation”
(Helium)
• Chart of the Nuclides
~ 3000 currently known nuclides
~ 270 stables only !
~ 7000 expected to exist
Z
118
Sn
50
68
Color Key:
Stable
+ emission
- emission
 particle emission
Spontaneous fission
N
A
X
Z
N
A chemical element (X) is uniquely identified by
the atomic number Z !
Nuclides that have the same Z but different N are called isotopes !
Mass number: A = N + Z
• Nuclear Masses and Binding Energy
The binding energy is the energy required to dissasemble a
nucleus into protons and neutrons.
It is due to the strong nuclear force!
M ( Z , N ) = Zm p + Nm n - BE
mp = proton mass, mn = neutron mass,
m(Z,N) = mass of nucleus with Z protons and N neutrons
Thanks to E=mc2,
tiny amounts of mass convert into huge energy release…
He-4
(2 protons + 2 neutrons)

Radium-226
(88 protons + 138 neutrons)
Radon-222
(86 protons + 136 neutrons)
1 kg of radium would be converted into 0.999977 kg of radon and alpha particles.
The loss in mass is only 0.000023 kg = 23 mg!
Energy = mc2 = mass x (speed of light)2
= 0.000023 x (3 x 108)2 = 2.07 x 1012 joules.
Equivalent to the energy from over 400 tonnes of TNT!!!
1 kg Ra (nuclear)  4*105 kg TNT (chemical)
238Pu
• Modern “Alchemy”:nuclear fusion and fission
The process through which a large
nucleus is split into smaller nuclei is
called fission.
Fusion is the opposite!
Fission and fusion are a form of
elemental transmutation because
the resulting fragments are not
the same element as the original
nuclei.
Nuclear fusion occurs
naturally in stars !
• Nuclear Reactions
A1
Z1
X + Z2 Y  A + B
A2
A3
Z3
Conservation laws:
A4
Z4
A1 + A2 = A3 + A4
(mass numbers)
Z1 + Z2 = Z3 + Z4
(atomic numbers)
Amount of energy liberated in a nuclear reaction (Q-value):
Qval = [(m1 + m2) – (m3 + m4)]c2
initial
definition
final
Qval > 0: exothermic process (release of energy) in stars
Qval < 0: endothermic process (absorption of energy)
• Stability and Binding Energy Curve
Qval >0
fission
Qval >0
fusion
Qval <0
fusion
• What Is the Origin of the Elements?
• Nucleosynthesis: the synthesis of Elements through Nuclear Reactions
Two original proposals:
(full) Big-Bang nucleosynthesis
all elements formed from protons and neutrons
sequence of n-captures and  decays
soon after the Big Bang
Stellar nucleosynthesis
elements synthesised inside the stars
nuclear processes
well defined stages of stellar evolution
Alpher, Bethe & Gamow (“  ”)
Burbidge, Burbidge, Fowler & Hoyle (B2FH)
Phys. Rev. 73 (1948) 803
Rev. Mod. Phys. 29 (1957) 547
The Nobel Prize in Physics 1967
The Nobel Prize in Physics 1983
Which one is correct?
• Big Bang Nucleosynthesis
• occurred within the first 3 minutes of the
Universe after the primordial quark-gluon plasma
froze out to form neutrons and protons
• BBN stopped by further expansion and cooling
(temperature and density fell below those required
for nuclear fusion)
• BBN explains correctly the observed mass abundances
of 1H (75%), 4He (23%), 2H (0.003%),3He (0.004%), trace
amounts (10-10%) of Li and Be, and no other heavy elements
Mass stability gap at
A=5 and A=8 !!!
A=8
BBN
No way to bridge the
gap through sequence
of neutron captures during BB …
A=5
After that, very little happened in
nucleosynthesis for a long time.
temperature and density too small !!!
It required galaxy and star formation via
gravitation to advance the synthesis of heavier
elements.
matter coalesces to higher temperature and density…
Because in stars the reactions involve mainly
charged particles, stellar nucleosynthesis is a
slow process.
• Stellar life cycle
+
metals
element
mixing
DEATH
explosion
Stars
thermonuclear
reactions

Interstellar gas
BIRTH
gravitational contraction
 energy production
 stability against collapse
 synthesis of “metals”
• Hydrogen Burning
• slow or fast (explosive) H-burning
• almost 95% of all stars spend their lives burning the H in their core (including
our Sun). Our Sun is a slow nuclear reactor (a fusion reactor we could not make!)
until hydrogen fuel is depleted  the life time of
our sun depends on the nuclear reaction rates
life time of stars depends on their mass: at larger masses burn faster! We are lucky!
• Helium Burning: Carbon formation
• BBN produced no elements heavier than Li due to the absence of a stable
nucleus with 8 nucleons
• in stars 12C formation set the stage for the entire nucleosynthesis of
heavy elements
How is Carbon synthesized in stars?
T ~ 6*108 K and  ~ 2*105 gcm-3



4He
+ 4He  8Be
8Be
unstable
( ~ 10-16 s)
8Be
+ 4He  12C
• Helium Burning: Oxygen formation
• Oxygen
production from carbon:
+ 4He →16O + 
Carbon consumption !
12C
Reaction rate is very small  not all C is burned, but
Oxygen production is possible and Carbon-based life
became possible…
• Nucleosynthesis up to Iron
A massive star near the end of its lifetime has “onion ring” structure
Carbon burning
12C
 T ~ 6*108 K
 ~ 2*105 gcm-3
+12C -> 20Ne + 4He + 4.6 MeV
23Na + 1H + 2.2 MeV
Neon burning
9
 T ~ 1.2*10 K
 ~ 4*106 gcm-3
+  -> 16O + 4He
20Ne + 4He -> 24Mg + 
20Ne
Oxygen burning
16O
9
 T ~ 1.5*10 K
 ~ 107 gcm-3
+ 16O -> 28Si + 4He + 10 MeV
31P + 1H + 7.7 MeV
Silicon burning
9K
 T ~ 3*10
8
-3
 ~ 10 gcm
major ash: Fe
stars can no longer convert mass into
energy via nuclear fusion !
• Nucleosynthesis beyond Iron
It was
987,000,000,000,000,000 MILES Away !
987 QUADRILLION MILES
• Abundance of the Elements
Almost 5 billion
Features:
• 12 orders-of-magnitude span
• H ~ 75%
years ago, our solar
system began the
• He ~ 23%
with its gravitation
collapse…
• C  U ~ 2% (“metals”)
journey
If we look around us today, we can see what elements
were in our interstellar cloud…
• Abundance of the Elements
Data sources:
Earth, Moon, meteorites,
stellar (Sun) spectra, cosmic rays...
Fe
Features:
• 12 orders-of-magnitude span
• H ~ 75%
• He ~ 23%
• C  U ~ 2% (“metals”)
Au
Abundance of elements and isotopes are UNIQUE finger prints of
various cosmic processes. To interpret and understand them, diverse
and vast nuclear physics knowledge is needed!!! Not fully solved!
U.S. Nuclear Science
[Today and for the Next Decade]
General goal:
Explain the origin, evolution, and structure of the
visible matter of the universe—the matter that makes
up stars, planets, and human life itself.
The Science – Physics of Nuclei and
Nuclear Astrophysics
• What is the nature of the nuclear force that binds protons
and neutrons into stable nuclei and rare isotopes?
• What is the origin of simple patterns in complex nuclei?
• What is the nature of neutron stars and dense nuclear
matter?
• What is the origin of the elements in the cosmos?
• What are the nuclear reactions that drive stars and stellar
explosions?
Nuclear Physics for Astrophysics
experiments in laboratory to learn about
nuclear reaction in stars
Two big problems in nuclear astrophysics:
1. - reactions in stars involve(d) radioactive nuclei  use RNB
2. - very small energies and very small cross sections indirect methods
Comparison with
(reaction)
calculations
Measurement
at lab
energies
Extract (nuclear
structure)
information
Compare with
direct
measurements
Calculate nuclear reaction
probability
My research highlights
Astrophysical motivation
The first sources of light:
Population III stars
First stars
about 400 million yrs.
Fate of Massive Pop III Stars
G
G
pp-I,II,III
Black Hole
Collapse
H
3
G
dynamic instability
Tc  5  107 K
crit  0.02 gcm-3
CNO, rp
H
Explode
Interest in
M. Wiescher et al., 1989, Ap.J., 343 :
12N(p,)13O
Hot pp chains and rap-process chains in
low-metallicity objects
pp-I: p(p,e+)d(p,)3He(3He,2p)4He
pp-II: 7Be(e-,)7Li(p,)4He
pp-III: 7Be(p,)8B(+)8Be()4He
• process material from pp cycles into CNO nuclei
pp-IV: 7Be(p,)8B(p,)9C(+)9B(p)8Be()4He
pp-V: 7Be(,)11C(+)11B(p,2)4He
rap-I: 7Be(p,)8B(p,)9C(,p)12N(p,)13O(+)13N(p,)14O
rap-II: 7Be(,)11C(p,)12N(p,)13O(+)13N)p,)14O
rap-III: 7Be(,)11C(p,)12N(+)12C(p,)13N(p,)14O
rap-IV: 7Be(,)11C(,p)14N(p,)15O
Experimental Setup for 12N(p,)13O study
via (12N,13O) proton transfer reaction
(Faraday Cup)
Er - det
.
12
D E - det
. (PSSD)
12
N
Melamine target
C
My research @ Madison Radiation Laboratory (JMU)
• astrophysical motivation:
nucleosynthesis of heavy proton-rich elements beyond iron by
photoactivation technique using an electron linear accelerator
Measurements of photoneutron reactions induced by activation of a target
(stable nucleus), i. e. (,n) reaction rates
Medical linac
High-resolution
Germanium detectors
RESOURCES:
Existing facilities for research in Nuclear Astrophysics (North America)
LENA/TUNL
TAMU
HIS/TUNL
1.
2.
3.
4.
5.
6.
7.
8.
Michigan State University/NSCL
Oak Ridge National Laboratory/HRIBF
Argonne National Laboratory/ATLAS
Lawrence Livermore National Laboratory/NIF
TRIUMF/ISAC (Canada)
University of Notre Dame/KN Van de Graaf accelerator
Yale University/WNSL
Florida State University/Super-FN tandem/RESOLUT
Overview of main astrophysical processes
Present and Future Direction in Physics of
Nuclei and Nuclear Astrophysics
Rare Isotope Beams
Producing radioactive nuclei
Protons
Neutrons
RADIOACTIVE
NUCLEI
Actually, made by nuclear reactions with stable nuclei: Long lived to very short lived
isotopes can be produced and used to produce secondary reactions in laboratory
RIB Facilities
(Operating or Under Construction)
FRIB-facility for rare isotope beams
•Ions of all elements from protons to uranium
accelerated
“Where you could work”
(after 2018)
What is the origin of the elements in the cosmos?
p process
FRIB reach
Stellar burning
Big Bang
neutrons
NAS report: “Connecting
Quarks with the cosmos”
11 questions for the 21st century
• how where the elements from
iron to uranium made?
• In summary
• Messages to take away…
Nuclear reactions play a crucial role in the Universe:
1.
they provide the energy in stars including that of the Sun.
2.
they produced all the elements we depend on.
3.
nucleosynthesis is on-going process in our galaxy
There are ~270 stable nuclei in the Universe. By studying reactions
between them we have produced ~3000 more (unstable) nuclei.
There are ~4000 more (unstable) nuclei which we know nothing
about and which will hold many surprises and applications.
Present techniques are unable to produce them in sufficient
quantities.
It will be the next generation of accelerators
and the next generation of scientists (why not
some of you?!) which will complete the work
of this exciting research field.