218 Po …formation of ‘exotic’ radioactive nuclei (in nature)…new elements created e.g., Pa, Ac, Ra, Rn, PooPoo
‘ 218 Po =Radium A’ ‘ 218 At =Radium B’ C D E 210 Po =Radium ‘F’ Radon =‘Emanation’ ‘Radium’ C’ C’’ The Natural Decay Chain for 238 U Aside: information here is used extensively in environmental monitoring; + radioactive dating – age of the earth ~10 9 yrs…evidence for evolution....
‘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. Most energetically stable nuclei in the middle, More exotic, unstable nuclei at the edges ….
How Far Can We Go ? What are the ‘nuclear limits’ ? 2 proton radioactivity What is the heaviest element ? How are the heavier elements formed ?
Physics aims and regions for the Stopped RISING Campaigns (2006-8)
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…. 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. gamma ray decay
For a ‘typical’ nucleus, Nuclear Volume A (= number of protons and neutrons) Since for a sphere, V = 4 R 3 /3 Thus nuclear radius, R A 1/3 R = (1.2 x10 -15 m) A 1/3 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)
The probability of a beam of ‘neutron-rich’ lithium-11 isotopes colliding on carbon target was much larger than expected. Lithium beam target detector
Nuclear ‘halos’ and Borromean Nuclei…. 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….
4n4n 4n4n Borromean Halo states tetraneutron Proton dripline
(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? K-electrons L-electrons T1/2 = 10.4 s 205 Au 126 202 Pt
Nuclear Excited States – Nuclear Spectroscopy (recall). 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. gamma ray decay
Evidence for nuclear shell structure….. energy of 1 st excited state in even-even nuclei….E(2 + ). What do we expect ?
large gaps in single-particle structure of nuclei…MAGIC NUMBERS = ENERGY GAPS
(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? K-electrons L-electrons T1/2 = 10.4 s 205 Au 126 202 Pt N=82 N=126
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=126 N=82 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….
Elements Z=116 and 118 discovered from fusion of Calcium ions on radioactive targets of Californium and Curium (Oganessian et al., Phys. Rev. C74 (2006) 044602). Periodic table has increased by 26 elements since Rutherford’s work on Uranium and Thorium decays.
Facility for Anti-Proton and Ion Research (FAIR) To be constructed at the current GSI site, near Darmstadt, Germany Will bring currently ‘theoretical nuclear species’ into experimental reach for the first time.
(some) Nuclear Physics Research c. 2009. Nuclei comprise 99.9% of all matter we can see in the Universe and are the fuel that burns in stars. A comprehensive description of nuclei requires theoretical and experimental investigations of rare isotopes with unusual neutron-to-proton ratios. These nuclei are labeled exotic, or rare, because they are not typically found on Earth. They are difficult to produce because they usually have extremely short lifetimes. The goal of a comprehensive description and reliable modeling of all nuclei represents one of the great intellectual opportunities for physics in the twenty-first century.
(‘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?