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