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
• gt 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.
forces strength range (fm) exchange particle mass (eV) charge spin
gravitational 6x10-39 infinite graviton? 0 0 2
weak 1x10-6 2x10-3 W, Z 91x109 1,0 1
electromagnetic 7x10-3 infinite photon 0 0 1
strong 1 1.5 pion 35x106 0 1
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
Antiparticles

• 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.

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 AZN
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
Isotopes same Z 40Ca, 42Ca, 44Ca often,
isotope used instead of nuclide isotopes have
same Z, so same number of electrons gt same
chemistry use radioactive isotope in place of
stable one can monitor decay for tracer
studies
Isotones same N 40Ca, 42Ti, 44Cr Isobars same
A 42Ca, 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?