1. Introduction 2. The abundances of the elements 3. Some simple nuclear physics - Geiger and Marsden - Rutherford and Nuclear Reactions - Chadwick and.

1. Introduction

2. The abundances of the elements

3. Some simple nuclear physics - Geiger and Marsden - Rutherford and Nuclear Reactions - Chadwick and the neutron - The need for accelerators - Why radioactive decay?

4. Where do they come from? - Big Bang - Star formation - Main Sequence Stars - Explosive Events5. Searching for Superheavy Elements - Element 112 and beyond.

Chemical Element Composition by Weight Oxygen 65 Carbon 18 Hydrogen 10 Nitrogen 3 Calcium 1.5 Phosphorus 1.0 Potassium 0.35 Sulphur 0.25 Sodium 0.15 Magnesium 0.05

Cu,Zn,Se,Mo,F,Cl,I,Mn,Co,Fe 0.70

Li,Sr,Al,Si,Pb,V,As,Br trace levels

Chemical elements in the body

The abundances of the elements in the Solar System

Note:- Logarithmic scale

The Abundances of the Elements for A = 70 - 210

Note the double peaks atN = 46/50, 76/82, 116/126

They are due to productionby the two separate processes – the slow ( s ) and rapid ( r )neutron capture processes

Relative Abundance of elements in Earth’s upper crust

The Beginnings of Nuclear Physics

Before and After Geiger and Marsden

E.Rutherford

J.J.Thomson

H.Geiger and E.Marsden

Manchester University

Proc.Roy.Soc A82 (1909)

proton

neutron

electron

} nucleus

u ud

proton

udd neutron

uu ee

dd

The Atom

u - up quarku - up quarkd - down quarkd - down quarke - e - electronelectron- neutrino- neutrino

u - up quarku - up quarkd - down quarkd - down quarke - e - electronelectron- neutrino- neutrino

e

e

First Controlled Nuclear Reaction

Rutherford’s last major piece of work at Manchester

A follow up to some work of E.Marsden in Rutherford’s lab.

- Alpha particles passing through H gas seemed to produce long range particles.

Source of α - particles

ZnS Screen

Thin metal plate

Source of α - particles

ZnS Screen

Thin metal plate

First Controlled Nuclear Reaction

With CO2 or O2 in the chamber no.of scintillations on ZnS screen fell with stopping power of the gas but if N2 was introduced no. of scintillations with brilliance of H-scintillation (proton) went up.

Conclusion he had observed the first controlled nuclear reaction or transmutation

14N + 4He 17O + p

The Radioactive Decay Law

1902 – Rutherford and Soddy deduced from careful observations that the rate of disintegration of a radioactive substance followed an exponential.

dN/dT = -λN or

N = N0 exp(-λt)

1903 – They suggested that Radium was a disintegration product and since it was always present in Uranium minerals it had to come from Uranium decay. It was not long before the whole natural decay chains from U and Th to Lead (Pb) were unravelled.

Frederic Soddy (1877-1956)

n

n

p

p

n

f2f1

The need for Accelerators

• When close together two nucleons attract each other strongly and so nuclei interact strongly

• As a result studying reactions is fine but two positively charged particles repel one another

• In order to make them interact we must give them enough energy, we must accelerate them.

Incident particle

Radiation

Radiation

Cloud Chamber

Chadwick’s Experiments

The Elements of Nuclear Structure

1932 – Heisenberg immediately interpreted the nucleus as consisting of protons plus neutrons and isotopes have a natural explanation in terms of having the same no. of protons and different nos. of Neutrons. e.g 1H – 1 proton nucleus of Hydrogen 2H – 1 proton + 1 neutron nucleus of deuterium 3H – 1 proton + 2 neutrons nucleus of tritium

1932 – Discovery of Neutron

1932 – Explanation of Beta Decay [Pauli]

1932 – Discovery of positron by C.D.Anderson, which had been predicted by P.A.M.Dirac

Proton Drip Line

Neutron Drip Line

Super Heavies

Fewer than 300 nuclei

Another View of the Nuclear Landscape

Neutron masses plotted versus N and ZFor the light nuclei

E = mc2

So the valley represents the nuclei with the lowesttotal energy.

The nuclei up on the sides of the valley are unstable and willdecay successively until theyreach the bottom and hencestability.

Our raw materials for nuclearPhysics are the atomic nuclei atthe bottom of the valley-there are283 stable or long-lived isotopes we can find in the Earth’s crust or atmosphere

Proton Drip Line

Neutron Drip Line

Super Heavies

Fewer than 300 nuclei

Where were the elements made?In essence only H and He were made in the Big Bang in the ratio H : He = 75: 25 by mass

All other elements were either made in stars or in the laboratory.

Gravity

H burning heats core

Stars form in collapsing clouds of gas and dust

Core temp. ~ 1.5 x 107 K

The proton-proton chain

1H + 1H = 2H + e+ +1H + 1H = 2H + e+ +1H + 1H = 2H + e+ +

1H + 1H = 2H + e+ + (B)1H + 2H = 3He + (C)

1H + 1H = 2H + e+ + (A)

1H + 2H = 3He + (D) 3He + 3He = 4He + 1H + 1H + (E)

Thus the sequence of reactions turns 4 protons into an alpha particle.

1H + 1H + 1H + 1H 4He + 2e+ + 2e + 3

Since the alpha particle is particularly tightly bound this process ofturning 4 protons into an alpha releases about 26 MeV of energy.It is this energy which heats the stellar interior,allows it to withstandthe gravitational pressure and causes it to shine!

1.Once a star’s hydrogen is used up its future life is dictated by its mass

2.During the H-burning phase the star has been creating He in the core by turning four protons into a He nucleus plus electrons and neutrinos.

3.Once H burning stops in the centre the star contracts and some of the potential energy is turned into heat. If the core temperature rises far enough then He burning can begin.

After the Main Sequence

1010 years

The Earthwill be

engulfed!!

++ 12C + 16O

Red Giant(3000ºK

Red)

H burning

Core temp now 108 K

Gravitación

Etoile massive supergéante

C. THIBAULT (CSNSM)

H He

C O

Ne Na Mg

Al Si P S

Fe

If the star is eight times more massive than the Sun

Strong Force

SUPERNOVA

White Dwarf

H, N, O¡¡only!!

(Hubble)Fluorescence

Helix Planetary Nebula in the constellation of Aquarius

Death of a Red Giant:SUPERNOVA – SN1987A

October 1987 1056 Joules of energy

This happened 170000 years ago in the nearest galaxy

Binding Energy per nucleon as a function of Nuclear Mass(A)

The End of Fusion Reactions in Stars

A = 56

•When two nuclei fuse together energy is released up to mass A = 56 Beyond A = 56 energy is required to make two nuclei fuse.•As a result we get the burning of successively more massive nuclei in stars.First H, then He, then C,N,O etc.•In massive stars we eventually end up with different materials burning in layers with the heaviest nuclei burning in the centre where the temperature is highest.•When the heaviest(A = 56) fuel runs out the star explodes-Supernova

[Remember E = mc2]

Principe de la nucléosynthèse

C. THIBAULT (CSNSM)

616058

59

59

5756 5855

protons

26 Fe 54

27 Co

28 Ni

29 Cu

62

63 65

•• Capture d’un neutron •• Radioactivité –

epn

neutrons30 4035

64

Il y a compétition entre

Principle of Nucleosynthesis

Capture of a neutron

Competition between two processes

Radioactivity

Part of the Slow Neutron Capture Pathway

In Red Giant Stars neutrons are produced in the 13C( 4He,n) 16O or22Ne(4He,n)25Mg reactions.The flux is relatively low.As a result there is time for beta decay before a second neutron is captured.The boxes here indicate a stable nuclear species with a particular Z & N.Successive neutron captures increase N. This stops when the nucleus created is unstable and beta decays before capture.

The pathways for the s- and r-processes

S-process:Neutron flux is low so beta decay occurs before a second neutron is captured.We slowly zigzag up in mass.

R-process:Neutron flux is enormous and many neutrons are captured before we get beta decays back to stability.

The Abundances of the Elements for A = 70 - 210

Note the double peaks atN = 46/50, 76/82, 116/126

They are due to productionby the two separate processes

S – process &R-process.

Earth: ~1890 Kelvin: ~20-40 Myears radioactivity 1905 Rutherford => billions of years

[age: 4.55 billion years(radioactive dating)]

Radioactivity 40% of heating of Earth

picture by COMTEL

26Al all-sky map: T1/2=0.74 MyEγ =1.8 MeV continuous nucleosynthesis

Heaven:

The Elements beyond Uranium (Z = 92)

We do not find them on Earth because they are all short-lived compared with the age of the Earth [ ~ 5 x 109 years ]. So even if they have been produced in stars we

would no longer be able to find them.

However we have been able to make another 15-20 elements in the laboratory

The basic route is via Nuclear reactions with the first attempts being in the 1930s following the discovery of the neutron.

Neutron-Induced Reactions.

In the years following its discovery Rutherford’s prediction that such a particle would readily interact with nuclei was amply fulfilled.

The importance of the neutron capture reaction was highlighted by the work of E.Fermi and his collaborators. They produced many new radioactive species in this way.

They realised it should be possible to make new, heavier elements this way. For example

238U + n 239U + γ

239U 239Np + e- +

This reaction and subsequent decay does occur but it was masked by the many other activities following fission.

Hahn and Strassmann (1939) finally reported that among them their were isotopes of Ba, La and Ce. They did not take this to its logical conclusion.

Transuranic elements

1940 – McMillan and Abelson identify 23993Np

23892U + n 239

92U 23993Np 239

94Pu 23592U

β β α

23.5 m 2.3 d 2.4 x 104 y

1940 – 1960 further elements discovered in neutron capture

23994Pu 243

94Pu 24395Am 244

95Am 24496Cm

This needs high neutron flux = Nuclear weapons debris Further elements have been discovered in Heavy Ion Collisions

24998Cf + 11

5B 256103Lr + 4n

4n β n β

Transuranic elements

Pu (94), Am (95), Cm (96), Bk (97), Cf(98) all discovered at University of California,Berkeley under Seaborg

Es (99), Fm (100), Md (101), No(102), Lr (103) again discovered at Berkeley now under Ghiorso

Rf (104), Db(105), Sg(106), Bh(107) Joint Institute for Nuclear Research, Dubna,Russia – Flerov

Hs (108), Mt(109), Ds (110), Rg (111), Cn(112) at GSI under Armbruster, Munzenberg and Hoffman

Elements 113-118 still unconfirmed but Dubna under Oganessian

Copernicium

Proton Drip Line

Neutron Drip Line

Super Heavies

Fewer than 300 nuclei

208Pb

region of spherically shell stabilised nuclei(“island of stability”)

region of deformed shell stabilised nuclei around Z=108 and N=162

Elements 107-112first synthesisedand identified at GSI;New names:107 – Bh108 – Hs109 – Mt110 – Ds111 – Rg

Shell Correction Energies Eshell in the Region of Superheavy ElementsP. Möller et al.

Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04

SHIP- Recoil Mass separator at GSI, Darmstadt.

Recoilling nuclei from the target are separated from the beam particles and from each other by mass as they pass through the crossed electric and magnetic fieldsof the spectrometer. The reactions of interest are where the two nuclei fuse gently and so there is little internalenergy. As a result only 1 neutron pops out leaving the heavysuper-heavy nucleus inthe final detector.

Final detector

Needed to keep the target cool

known

27311011.45 MeV280 s

269Hs11.08 MeV110 s

265Sg9.23 MeV19.7 s

261Rf4.60 MeV (escape)7.4 s

257No8.52 MeV4.7 s

253Fm8.34 MeV15.0 s

CN277112277112

70Zn 208Pb 277112

n

kinematic separationin flight identification

by - correlationsto known nuclides

Synthesis and Identification of SHE at SHIP

Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04

Dieter-Ackermann_GSI/University_of_Mainz_-_IReS-Symposium-2004

GSIRIKEN

FLNR

high cross-sections (0.5 – 5 pb)

low cross-sections

( ≈ 35 fb)

SHE Synthesis – Present Status

D.Ackermann

Creeping up on the Superheavies at GSI

region of spherically shell stabilised nuclei(“island of stability”)

The Limits of Nuclear Existence

• Challenge: To create elements 112-116 and beyond.

• • Two routes:Cold and hot fusion

• Question:Will n-rich projectiles allow us to approach closer to the anticipated centre of the predicted Superheavy nuclei.

• There is some evidence that extra neutrons enhance fusion below the barrier.The figure shows studies at Oak Ridge with 2 x 104 pps where it is clear that there is a large enhancement below the barrier.

J.F.Liang et al.,PRL91(2003)152701

• RNBs may allow us to approach the spherical N=184 shell.

But might the LHC discover yet more particles?

Well, actually, our best theories say there may be moreTo discover: Supersymmetric Particles!

The p-p chain;the reactions which power the Sun

Overall - 4p 4He + 2e- +2 + 26.7 MeV

The CNO-Cycle: In stars where we already haveC,N and O we can get hydrogenburning 4p + 2e- + 2 +26.4 MeV

The C,N and O nuclei act ascatalysts for the burning process

Hans Bethe-1938

Life Cycle of Stars and Nucleosynthesis

1. Formation from large clouds of gas and dust.

2. Centre of cloud is heated as it collapses under gravity

3. When it reaches high enough temperature then nuclear reactions can start. 4p 4He + 2e + 2ν + 26.7 MeV

4. This raises temperature further and star eventually reaches equilibrium under heating internally and gravitational collapse.

5. The process of making heavier nuclei occurs in the next stage.

After the Main Sequence

1.Once a star’s hydrogen is used up its future life is dictated by its mass.

2.During the H-Burning phase the star has been creating He in the core by turning 4 protons into a He nucleus plus electrons and neutrinos. Once the H burning stops in the centre the star contracts and some of the potential energy is turned into heat. If the core temperature rises far enough then He-burning can begin. Coulomb(electrostatic) barrier is 4 times higher for two He nuclei compared with protons.

3.Now we face again the problem of there being no stable A = 5 or 8 nuclei.

4.It turns out that we can bypass these bottlenecks but it depends critically on the properties of the properties of individual levels in Be and C nuclei.

The Creation of 12C and 16O• H and 4He were made in the Big Bang.Heavier nuclei were not produced because there are no stable A = 5 or 8 nuclei. There are no chains of light nuclei to hurdle the gaps.• How then can we make 12C and 16O?• Firstly 8Be from the fusion of two alphas lives for 2.6 x 10-16 s cf. scattering time 3 x 10-21 s. They stick together for a significant time.• At equilibrium we get a concentration of 1 in 109 for 8Be atoms in 4He. • Salpeter pointed out that this meant that C must be produced in a two step process.

• Hoyle showed that the second step must be resonant.He predicted that since Be and C both have 0+ s-wave fusion must lead to a 0+ state in 12C close to the Gamow peak at 3 x 108K.• Experiment shows such a state at 7654 keV with = 5 x 10-17s

The 7654 keV statehas / 1000

A rare set of circumstances indeed!

The Destiny of the Stars…

C. THIBAULT (CSNSM)

MainSequence

Red Giant

White Dwarf

Massive StarsSupernova

Density/

AÑOSAlgún

segundo

BrownDwarf

109

109

109

100 kg

Spectrum of Cassiopeia

We see here the remnants of asupernova in Cassiopeia.Thisradio telescope picture is takenwith theVery Large Array in New Mexico.From the measured rate of expansion it is thought to haveoccurred about 320 years ago.It is 10,000 ly away. With optical telescopes almost nothing is seen.

The inset at the bottom shows a small partof the gamma ray spectrum with a clear peak at 1157 keV,the energy of a gamma ray in the decay of 44Ti.

Abundance Predictions

known

27311011.45 MeV280 s

269Hs11.08 MeV110 s

265Sg9.23 MeV19.7 s

261Rf4.60 MeV (escape)7.4 s

257No8.52 MeV4.7 s

253Fm8.34 MeV15.0 s

CN277112277112

70Zn 208Pb 277112

n

kinematic separationin flight identification

by - correlationsto known nuclides

Synthesis and Identification of SHE at SHIP

Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04

SHE Synthesis – Status September 2004

GSIRIKEN

Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04

Ds282

FLNR