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 Events 5. 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 = Note the double peaks at N = 46/50, 76/82, 116/126 They are due to production by 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 u d proton u d d neutron ued The Atom u - up quark d - down quark e - electron - neutrino - neutrino u - up quark d - down quark e - electron - neutrino - neutrino

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 CO 2 or O 2 in the chamber no.of scintillations on ZnS screen fell with stopping power of the gas but if N 2 was introduced no. of scintillations with brilliance of H-scintillation (proton) went up.  Conclusion he had observed the first controlled nuclear reaction or transmutation 14 N + 4 He 17 O + 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 = N 0 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 ( )

n n p     p  n f2f2 f1f1

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 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 1 H – 1 proton nucleus of Hydrogen 2 H – 1 proton + 1 neutron nucleus of deuterium 3 H – 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

Another View of the Nuclear Landscape Neutron masses plotted versus N and Z For the light nuclei E = mc 2 So the valley represents the nuclei with the lowest total energy. The nuclei up on the sides of the valley are unstable and will decay successively until they reach the bottom and hence stability. Our raw materials for nuclear Physics are the atomic nuclei at the bottom of the valley-there are 283 stable or long-lived isotopes we can find in the Earth’s crust or atmosphere

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 10 7 K

The proton-proton chain 1 H + 1 H = 2 H + e + +  1 H + 1 H = 2 H + e + +  (B) 1 H + 2 H = 3 He +  (C) 1 H + 1 H = 2 H + e + +  (A) 1 H + 2 H = 3 He +  (D) 3 He + 3 He = 4 He + 1 H + 1 H +  (E) Thus the sequence of reactions turns 4 protons into an alpha particle. 1 H + 1 H + 1 H + 1 H 4 He + 2e e + 3  Since the alpha particle is particularly tightly bound this process of turning 4 protons into an alpha releases about 26 MeV of energy. It is this energy which heats the stellar interior,allows it to withstand the 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

10 10 years The Earth will be engulfed!!  +  +   12 C +   16 O Red Giant (3000ºK Red) H burning Core temp now 10 8 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 Joules of energy This happened 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 = mc 2 ]

Principe de la nucléosynthèse C. THIBAULT (CSNSM) protons 26 Fe Co 28 Ni 29 Cu Capture d’un neutron Radioactivité  –   e pn neutrons 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 13 C( 4 He,n) 16 O or 22 Ne( 4 He,n) 25 Mg 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 = Note the double peaks at N = 46/50, 76/82, 116/126 They are due to production by 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 26 Al all-sky map: T 1/2 =0.74 My E γ =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 10 9 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 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 238 U + n 239 U + γ 239 U 239 Np + 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 Np U + n U Np Pu U ββα 23.5 m2.3 d 2.4 x 10 4 y  1940 – 1960 further elements discovered in neutron capture Pu Pu Am Am Cm This needs high neutron flux = Nuclear weapons debris  Further elements have been discovered in Heavy Ion Collisions Cf B Lr + 4n 4n βnβ

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 still unconfirmed but Dubna under Oganessian Copernicium

208 Pb region of spherically shell stabilised nuclei (“island of stability”) region of deformed shell stabilised nuclei around Z=108 and N=162 Elements first synthesised and identified at GSI; New names: 107 – Bh 108 – Hs 109 – Mt 110 – Ds 111 – Rg Shell Correction Energies E shell in the Region of Superheavy Elements P. 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 fields of the spectrometer. The reactions of interest are where the two nuclei fuse gently and so there is little internal energy. As a result only 1 neutron pops out leaving the heavy super-heavy nucleus in the final detector. Final detector Needed to keep the target cool

known MeV 280  s 269 Hs MeV 110  s 265 Sg 9.23 MeV 19.7 s 261 Rf 4.60 MeV (escape) 7.4 s 257 No 8.52 MeV 4.7 s 253 Fm 8.34 MeV 15.0 s CN Zn 208 Pb n kinematic separation in flight identification by - correlations to 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 GSI RIKEN 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 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 10 4 pps where it is clear that there is a large enhancement below the barrier. J.F.Liang et al.,PRL91(2003) 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 more To discover: Supersymmetric Particles!

The p-p chain;the reactions which power the Sun Overall - 4p  4 He + 2e MeV

The CNO-Cycle: In stars where we already have C,N and O we can get hydrogen burning 4p  + 2e MeV The C,N and O nuclei act as catalysts 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 4 He + 2e + 2ν 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 12 C and 16 O H and 4 He 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 12 C and 16 O? Firstly 8 Be from the fusion of two alphas lives for 2.6 x s cf. scattering time 3 x s. They stick together for a significant time. At equilibrium we get a concentration of 1 in 10 9 for 8 Be atoms in 4 He. 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 12 C close to the Gamow peak at  3 x 10 8 K. Experiment shows such a state at 7654 keV with  = 5 x s The 7654 keV state has   /    1000 A rare set of circumstances indeed!

The Destiny of the Stars… C. THIBAULT (CSNSM) Main Sequence Red Giant White Dwarf Massive Stars Supernova Density/ AÑOS Algún segundo Brown Dwarf kg

Spectrum of Cassiopeia We see here the remnants of a supernova in Cassiopeia.This radio telescope picture is taken with theVery Large Array in New Mexico. From the measured rate of expansion it is thought to have occurred 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 part of the gamma ray spectrum with a clear peak at 1157 keV,the energy of a gamma ray in the decay of 44 Ti.

Abundance Predictions

known MeV 280  s 269 Hs MeV 110  s 265 Sg 9.23 MeV 19.7 s 261 Rf 4.60 MeV (escape) 7.4 s 257 No 8.52 MeV 4.7 s 253 Fm 8.34 MeV 15.0 s CN Zn 208 Pb n kinematic separation in flight identification by - correlations to known nuclides Synthesis and Identification of SHE at SHIP Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04

SHE Synthesis – Status September 2004 GSI RIKEN Dieter-Ackermann_GSI/University_of_Mainz_-_ENAM04 Ds 282 FLNR