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Cauldrons in the cosmos
David Jenkins Department of Physics University of York
With thanks to Brian Fulton, York
and Marialuisa Aliotta, Edinburgh
In search of the building blocks of the Universe…
Greek philosophers 4 building blocks
earth
water
air
fire
1896 Mendeleev 92 building blocks
(chemical elements)
questions: how, where and when have the elements been made?
What are we made of?
Iron extracted at 1500 million tonnes/yr
Gold extracted at 300 tonnes/yr
Why are some elements so much more abundant than others?
Cauldrons in the Cosmos
The Big Bang…
Big bang nucleosynthesis
Occurs 1 second after Big Bang
Temperatures then cool enough to form protons and neutrons
When the temperature cools further protons and neutrons fuse to produce helium
After 3 minutes, temperature reduces to point where no more fusion occurs
13.7 billion years ago: the Big Bang
Only the 3 lightest elements were created in the Big Bang. Where did the heavier elements come from?
Cauldrons in the Cosmos
What are my ingredients?
2m high
10 µm
2 nm
In science there is only physics; all the rest is stamp collecting.
Ernest Rutherford
(30 August 1871 - 19 October 1937)
It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you.
Neutrons
James Chadwick
(20 October 1891 – 24 July 1974)
Neutrons discovered in 1932
They have almost the same mass as protons but no electric charge
Elements and Isotopes
Chemical elements have a different chemistry
We use names for them but it is just a shorthand for counting the number of protons
Isotopes have the same number of protons but different numbers of neutrons
The chemistry doesn’t really change but they are very different in terms of nuclear physics
Can I make any old nucleus by choosing different numbers of neutrons and protons?
No! - because some are more stable than others
The alchemist The alchemist tried to turn base metals into gold using techniques which we would now call “Chemistry”.
It never worked…
Why not? Nuclei have a positive charge from the protons in them and so repel
To fuse nuclei together we need high energies (temperature and densities)
The life of a Star
In regions of higher density, the primordial H and He begins to gravitationally attract
Compressing the gas causes it to heat up
Eventually the temperature at the centre gets so high that nuclear reactions start
A new Star is born!
Net effect is 4 H atoms create 1 He atom, releasing 1.6x10-13 J (about one millionth of a millionth of a Calorie)
Tiny energy release…… ….but there is LOTS of H in a star
Our sun consumes 100,000,000 tonnes of H per second!
The problem: Berylllium-8 has a half-life of 10-15 s
This process should be extremely slow…
Could not produce carbon in any quantity
Idea: We could produce Carbon-12 by fusing three Helium-4 nuclei together
Fred Hoyle
Hoyle (1953) predicted that there must be a resonance that makes the three helium nuclei fuse much more rapidly
A resonance in this context means a nuclear energy level at just the right place
In a sense, things are “just right” like the Three Little Bears’ porridge
Move the carbon energy level only a little and you can stop production of carbon in stars or
accelerate it so that stars die much faster
Would you not say to yourself, "Some super-calculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule." Of course you would . . . A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question.
But if they weren’t just right would be here to see it?!?
Cauldrons in the Cosmos
How do we reproduce the nuclear reactions involved in stars on earth?
21/25
Cosmic shower
Gran Sasso
underground halls
Radiation LNGS/surface Muons
Neutrons Photons
10-6
10-3
10-1
Background reduction in LNGS (shielding ≡ 4000 m w.e.)
22/25
LUNA’s accelerators 400 kV: LUNAII
14N(p,γ)15O 3He(4He,γ)7Be
U = 50 – 400 kV
I ∼ 500 µA for protons
I ∼ 250 µA for alphas
Energy spread ≈ 70eV
Long term stability: 5 eV/h
Cauldrons in the Cosmos
What about heavier elements?
Further stages of collapse and burning can occur, building up heavier and heavier elements
“Onion skin” structure of a late, main sequence star
The build up stops at Iron - the most tightly bound nucleus
When a star dies it expels these new elements into space.
All elements heavier than iron are generated in Supernova explosions and scattered into
space.
Modelling the explosions
Nuclear Reaction rates
MODEL
Hydrodynamical development
Astrophysical conditions (pressure, temperature
and abundances)
Abundances +
Light Curves
Observational Tests
Nuclear physics provides one of the inputs – nuclear reaction rates But which nuclear reactions are important?
Which nuclear reactions are involved?
13
1958
14
2008
2008
John Cockcroft (27th May 1897 – 18th September
1967)
Ernest Walton (6th October 1903
– 25th June 1995)
“Splitting the atom…”
Radioactive ion production (IF)
REX-ISOLDE, SPIRAL-1, HRIBF, ISAC HIE-ISOLDE, SPIRAL-2, SPES
Isotope Separation On-Line (ISOL) thick target, high yield, high quality beam
In-Flight separation (IF) thin target, chemistry independent, fast
GANIL, GSI, MSU, RIBF FAIR
10
LHC
Added Value of ISOLDE: • Cover several Physics
Domains • Possibility of high-precision
nuclear experiments • Complementary to particle
physics, • A place for many potential
new users • Easier for small countries
Common Interest with Other CERN Experiments
• Detector and Instrumentation • Computing techniques
• N-ToF, Antiprotons….
ISOLDE targets
9 9 G. D. Alkhazov et al., NIM B 69 (1992) 517, V. N. Fedosseev et al., NIM B 266, 4378 (2008), U. Koester et al., Nucl. Phys. A 701, 441 (2002)
Radioactive beam is provided by ISOL technique: 1.4-GeV protons hit thick target material Low-energy beam Singly-charged ions Isotopically pure beam Mixture of isobars
Courtesy Sebastian R
Nuclei production and selection @ ISOLDE
11
MINIBALL @ REX-ISOLDE
37
220Rn/224Ra beam @ ~2.83A.MeV
Coulex target ~2mg/cm2
Status of our understanding
Well understand (we think): The reaction rates for standard fusion reactions in
stars The broad properties of reaction networks for
explosive scenarios
Future challenges: Verifying that extrapolations to low energies are
valid for all cases e.g. carbon burning Understanding in detail the nuclear reactions
involved in supernovae The reactions that trigger runaway explosions
The cycle of life & our cosmic inheritance
Astrophysics
Nuclear Physics
Chemistry
Courtesy: M. Arnould
(EXPERIMENTAL) NUCLEAR ASTROPHYSICS
study energy generation processes in stars study nucleosynthesis of the elements
NUCLEAR PHYSICS
KEY to understand Universe at large
MACRO-COSMOS intimately related to MICRO-COSMOS
Finis
NOVA or X-RAY BURSTER
These occur in binary star systems
Hydrogen pulled off one star onto the surface of the other where it builds up
Eventually so much builds up that the reactions become an explosion
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