Introduction to Radiochemistry

1. Introduction to Radiochemistry NUSC 341-3

2. Forces in Matter and the Subatomic Particles Chapter 1

3. What is Nuclear Science? Nuclear science: study of structure, properties, and interactions of atomic nuclei at fundamental level. nucleus – contains almost all mass of ordinary matter in a tiny volume understanding behavior of nuclear matter under normal conditions and conditions far from normal a major challenge extreme conditions existed in the early universe, exist now in the core of stars, and can be created in the laboratory during collisions between nuclei (TRIUMF) Nuclear scientists investigate by measuring the properties, shapes, and decays of nuclei at rest and in collisions. This course covers low energy, or low temperature, nuclear science => properties of the nucleus

4. Why should we bother?

5. Interactions • Electromagnetic e- (lepton) bound in the atoms by the electromagnetic force • Weak interaction Neutrino observed in beta decay. • Strong interaction Quarks are bound in together by the strong force in nucleons. Nuclear forces bind nucleons into nuclei. • Gravitation Gravitational interaction between the elementary particles is in practice very small compared to the other three.

6. Interactions The forces of elementary particle physics are associated with the exchange of particles. An interaction between particles is characterized by both its strength and its range. 1 fm = 10-15 m Force between two objects can be described as exchange of a particle – particle transfers momentum and energy between the two objects, and is said to mediate the interaction graviton – not yet observed pions or pi mesons – between nucleons

7. Standard Model • Attempts to explain all phenomena of particle physics in terms of properties and interactions of a small number of three distinct types. • Leptons: spin-1/2 • Quarks: spin-1/2 • Bosons: spin-1; force carriers These are assumed to be elementary.

8. Standard Model

9. Hadrons Hadrons: any strongly interacting subatomic particle; composed of quarks. There are 2 categories: • Baryons: fermions, make of 3 quarks • Mesons: bosons, made of quark, antiquark

10. Electron (e-) – Positron (e+) Particles and antiparticles (such as the pair highlighted in pink) are created in pairs from the energy released by the collision of fast-moving particles with atoms in a bubble chamber. Since particles and antiparticles have opposite electrical charges, they curl in opposite directions in the magnetic field applied to the chamber. Antiparticles

11. Antiparticles

12. Building Blocks • Molecules consists of atoms. • An atom consists of a nucleus, which carries almost all the mass of the atom and a positive charge Ze, surrounded by a cloud of Z electrons. • Nuclei consist of two types of fermions: protons and neutrons, called also nucleons. • Nucleons consists of three quarks. e = 1.6022 x 10-19 C

13. 1 Å = 10-10 m 1 fm = 10-15 m

14. 3 quarks baryons mn = 1.6749 x 10-27 kg = 939.55 MeV = 1.008665 u mp = 1.6726 x 10-27 kg = 938.26 MeV = 1.007276 u Charge: 0 Charge: e

15. The Nucleus The atomic nucleus consists of protons and neutrons Protons and neutrons are generally called nucleons • A nucleus is characterized by: • A: Mass Number = number of nucleons • Z: Charge Number = number of protons • N: Neutron Number Determines the Element Determines the Isotope Of course A=Z+N Usual notation: Mass number A 12C Element symbol – defined by charge numberC is Carbon and Z = 6 So this nucleus is made of 6 protons and 6 neutrons

16. Mass • Nuclear and atomic masses often given in u: atomic mass unit • 12.000 u = 12 daltons mass of a neutral 12C atom • 1 u = 1.6605 x 10-27 kg • Mass and energy are interchangeable – E = mc2 where energy usually expressed in MeV • 1 MeV = 1.602 x 10-13 J • 1 u = 931.5 MeV/c2

17. isodiaphors Z isotopes isobars isotones Isotopes: same Z40Ca, 42Ca, 44Ca often, ‘isotope’ used instead of ‘nuclide’ isotopes have same Z, so same number of electrons => same chemistry use radioactive isotope in place of stable one – can monitor decay for tracer studies Isotones: same N40Ca, 42Ti, 44Cr Isobars: same A42Ca, 42Ti, 42Cr Isodiaphors: same neutron excess 42Ca, 46Ti, 50Cr

18. Classification of Nuclides • Stable nuclei: 264; 16O • Primary natural radionuclides: 26; very long half-lives; 238U with t1/2 = 4.47 x 109 y • Secondary natural radionuclides: 38; 226Ra t1/2 = 1600 y decay of 238U • Induced natural radionuclides: 10; cosmic rays; 3H t1/2 = 12.3 y; 14N(n,t)12C • Artificial radionuclides: 2-4000, 60Co, 137Cs…

19. Periodic Table

20. Chart of Nuclei • plot of nuclei as a function of Z and N • “Not just one box per element”

21. Chart of Nuclides http://www.nndc.bnl.gov/chart/

22. …or Segre Chart • plot allows various nuclear properties to be understood at a glance, similar to how chemical properties are understood from the periodic chart • ~ 2500 different nuclei known • 270 stable/non-radioactive • theorists guess at least 4000 more to be discovered at higher neutron numbers, higher mass • limits – • proton-rich side (left of stable): proton dripline cannot add another proton, it “drips” off dripline is known/accessible to experiments • neutron-rich side (right of stable): neutron dripline cannot add another neutron, it “drips” off dripline is unknown – neutron-rich nuclei difficult to produce/study • mass (above stable) – cannot add another proton or neutron limit unknown – again, difficult to produce/study • “island of stability” predicted near Z = 114; not yet observed

23. Natural Decay Chains

24. Thorium Decay Chain (4n + 0) 1.4 x 1010 y

25. (4n + 2) 4.5 x 109 y

26. The Actinium Decay Series (4n +3) • 235U  … 207Pb (7 alphas and 4 betas) 7.04 x 108 y

27. An Extinct Natural Decay Chain • Neptunium decay series (4n + 1) • 237Np (t1/2 = 2.14 x 109 y ) …209Bi

28. End of Chapter 1 Any questions?