Nuclear Physics Research At Surrey …from pure to applied and everything in between..
What is (nuclear physics) research ? (i.e., why bother at all ?) • Pure fundamental, knowledge-driven inquisitive search for understanding…. • To help obtain a basic, fundamental understanding of how things work. • Part of the basic cultural fabric of society, research for research sake, beauty in nature, parallels to the arts. • Usefulness….generation of income, to enhance the quality of life,
Some areas…. • Pure, fundamental nuclear physics research: • Exotic nuclei, some very ‘big science questions’ • What are the limits of nature ? • Underlying nuclear theory • Some surprises (e.g., nuclear halos) • How were the chemical elements created ? • Trapping (and releasing) nuclear energy.
Some more areas? • (Some) applications of fundamental nuclear physics research: • Environmental / nuclear waste monitoring. • Gamma-ray spectrometry..let’s play ‘find the uranium’ • Instrumentation development, new detectors, • Surrey ion-beam centre (PIXE, PIGE) • Looking at diseases (arthritis with nuclear probes) • Looking inside stuff….
A recent survey of General Public in UK asked: • “The nuclei of atoms make up 99.99% of all matter. So what are they made of? • Electrons • Quarks • Photons • Neutrinos • DNA” • Only 2% knew correct answer!! Is it surprising that the general public does not know this? Should we be worried? Does is matter??? ANSWER: Quarks.
Atoms (‘indivisible’) …… ~10-10 m, electrons (and their orbital structure) determine chemistry of the elements, e.g., NaCl Nuclei…..~10-14m across, protons determine the chemical element (Z); neutron number (N) determines the mass, (A = N+Z). > 99.9 % of the mass of the atom is in the nucleus. Nucleons (protons and neutrons ~10-15m) have a substructure, three quarks in each nucleon (‘ups’ and ‘downs’)…but they don’t exists on their own.
Chart of the Nuclei 6 5 4 Z = No. of Protons 3 2 11B 12C 13C 10B 9Be 1 0 6Li 7Li 6 7 8 9 11Be 12Be 8He 3He 4He 9Li 7B 13B 14B 15B 15C 16C 17C 10C 8Li 14C 9C 6Be 12B 9B 7Be 10Be 11C 6He 8B 5Li 10Li 11Li 14Be 1H 2D 3T n 0 1 2 3 4 5 N = No. of Neutrons
Signal for existence of tetraneutron in 14Be breakup reaction at GANIL October 2002 issue W.Catford et al.,
Most energetically stable nuclei in the middle, More exotic, unstable nuclei at the edges…. ‘Nuclei = combinations of protons (Z) and neutrons (N). Chart of the Nuclides = a ‘2-D’ periodic table…… <300 of the (Z,N) combinations are stable and make up’everyday’ atoms. ~7,000 other combinations are unstable nuclei.
Z=43 Tc Z=61 Pm Z=84 Po Elemental composition of the Solar Nebula
218Po …formation of ‘exotic’ radioactive nuclei (in nature)…new elements created e.g., Pa, Actinium, Radium, Radon, Polonium etc.
The Natural Decay Chain for 238U ‘Radium’ ‘218At =Radium B’ 210Po =Radium ‘F’ Radon =‘Emanation’ C’ ‘218Po =Radium A’ E C D C’’ Aside: information here is used extensively in environmental monitoring; + radioactive dating – age of the earth ~109 yrs…evidence for evolution....
For a ‘typical’ nucleus, Nuclear Volume A (= number of protons and neutrons) Since for a sphere, V = 4R3/3 Thus nuclear radius, R A1/3 R= (1.2 x10-15m) A1/3 Rutherford Scattering experiments showed this relation to hold for all nuclei studied….so what’s new to learn…. Then… 1985 – the strange case of ‘Lithium -11’ (note stable lithium isotopes are Lithium-6 and Lithium-7)
Lithium beam detector target The probability of a beam of ‘neutron-rich’ lithium-11 isotopes colliding on carbon target was much larger than expected.
Nuclear ‘halos’ and Borromean Nuclei…. J.S. Al-Khalili & J.A. Tostevin, Phys. Rev. Lett. 76 (1996) 3903 Halo nuclei are examples of ‘Borromean’ systems, only bound with three Interactions…remove any one and the other two fall apart….
The neutron dripline in light nuclei proton dripline Borromean halo states 4n N=8 tetra-neutron?
How Far Can We Go ? • What are the ‘nuclear limits’ ? • What is the heaviest element ? • How are the heavier elements formed ?
What about ‘inside’ the nucleus(i.e. nuclear ‘structure’) ? • Can we see ‘inside’ the nucleus ? • What does it tell us?
gamma ray decay • Nuclear states labelled by spin and parity quantum numbers and energy. • Excited states (usually) decay by gamma rays (non-visible, high energy light). • Measuring gamma rays gives the energy differences between quantum states. Nuclear Excited States – Nuclear Spectroscopy. Nuclei can exist in either the ground state or an excited state Each nucleus is different….but groups of structural patterns do appear….
Evidence for nuclear shell structure…..energy of 1st excited state in even-even nuclei….E(2+). What do we expect ?
large gaps in single-particle structure of nuclei…MAGIC NUMBERS = ENERGY GAPS
N=82 N=126 • (SOME) BIG NUCLEAR PHYSICS’ QUESTIONS TO BE ADDRESSED • Does the ordering of nuclear quantum states change ? • How robust are the magic numbers? • What are the limits of nuclear existence? T1/2 = 10.4 s 205Au126 K-electrons L-electrons 202Pt
A (big!) problem, can’t reproduce the observed elemental abundances. • We can ‘fix’ the result by changing the shell structure (i.e. changing • the magic numbers)….but is this scientifically valid ? N=82 N=126 • Need to look at N=82 and 126 ‘exotic’ nuclei in detail….
Super Heavy Elements? • Rutherford worked with decays from Thorium and Uranium the heaviest element (Z=90 & 92) known at the time. • He inferred their presence and other elements in their decay chains by characteristic alpha decay sequences….
Darmstadtium Copernicium Roentgenium
Robust theoretical predictions of nuclear quantum shell structure in the heaviest (indeed, so far unknown) elements ….these drive future experimental investigations
Nuclear isomers: energy traps excited state half-lives ranging from nanoseconds to years [Phil Walker and George Dracoulis, Nature 399 (1999) 35]
(‘Big’) Physics Questions from the STFC Nuclear Physics Advisory Panel • What is the Nature of Nuclear Matter? • What are the limits of nuclear existence? • How do simple patterns emerge in complex nuclei? • Can nuclei be described in terms of our understanding of the • underlying fundamental interactions? • What is the equation-of-state of nuclear matter? • How does the ordering of quantum states change in extremely unstable nuclei? • Are there new forms of structure and symmetry at the limits of nuclear existence? • What are the Origins of the Elements? • How, and where, were the heavy elements synthesised? • What are the key reaction processes that drive explosive astrophysical events such as supernovae, and X-ray bursts? • What is the equation-of-state of compact matter in neutron stars? • What are the nuclear processes, and main astrophysical sites, that produce the γ-ray emitting radionuclides observed in our galaxy? • How do nuclear reactions influence the evolution of massive stars, and how do they contribute to observed elemental abundances?
The Natural Decay Chain for 238U Qa(210Pb) = 5.41 MeV Ea = 5.30 MeV E(206Pb) = 0.11 MeV T1/2 = 138 days. ‘Radium’ ‘218At =Radium B’ 210Po =Radium ‘F’ Radon =‘Emanation’ C’ ‘218Po =Radium A’ E C D C’’ BUT: Evidently, heavier (radioactive) elements like Th (Z=90) ; U (Z=92) exist ? How are they made?
= 214Pb = 214Bi