L3 - Introduction To Isotopes, Radioactivity And Radiocative Decay

Question 1

What keeps the nucleus intact?

Answer 1

The neutron
- binds to proton via the nuclear force

Question 2

How was radioactivity first discovered?

Answer 2

• wrapped photographic plates in black paper
• placed phosporescent salts and uranium salts
• uranium salts caused blackening

Question 3

What is the concept of half life?

Answer 3

All readioactive elements decay with the same mathematical exponential law

Question 4

What are the 3 types of radiation?

Answer 4

• alpha
• beta
• gamma

Question 5

What are the types of radiation stopped by?

Answer 5

• alpha: few cm of air
• beta: aluminium sheet (1mm thick)
• gamma: lead (several cm, m of concrete)

Question 6

What are alpha particles?

Answer 6

Positively charged helium nuclei

Question 7

What is the best source of alpha particles?

Answer 7

Alpha decay of heavy atoms

Question 8

What is alpha decay?

Answer 8

The parent atomic nucleus decays into a different atomic nucleus

Mass number - 4
Atomic number - 2

Question 9

What is beta decay?

Answer 9

Neutron transforming into a proton, with the emission of an e- and a neutrino

Mass number =
Atomic number + 1

Question 10

What is gamma decay?

Answer 10

Produced after alpha/beta decay, daugther nucleus formed is left in an excitied state, decays to lower state by emitting a gamma ray photon

Question 11

What is the decay constant?

Answer 11

The probability that a given radioactive nuclei will decay per unit time

Question 12

What is the radioactive decay law?

Answer 12

N(t) = N(0)e - λt

Question 13

What is half life?

Answer 13

The time talen for half the radioactive nuclei in a given sample to undergo decay

Question 14

What is the decay of unstable atomic nuclei?

Answer 14

• first order decay
• differntiating
• differential is rate of change
• sub in
• half life

Question 15

What does 1Bq equal?

Answer 15

1 disintegration per second

Question 16

What does 1.0 Ci equal?

Answer 16

3.7 x10^10 Bq

Question 17

What are isotopes?

Answer 17

Atoms of the same element that have the same number of protons (atomic number) but different number of neutrons (atomic mass)

Question 18

What happens to the properties of isotopes?

Answer 18

They have the same chemical properties but different physical properties

Question 19

How do neutrons stabilise the nucleus?

Answer 19

• nuclear force binds the protons and the neutrons
• presence of neutrons reduces electrostatic repulsion of the protons to each other

Question 20

What can render a nuclide unstable?

Answer 20

Having too few or too many neutrons

Question 21

What do unstable nuvlei attempt to do?

Answer 21

Reach lower energy states by nuclear decay

Question 22

Why do different isotopes exhibit virtually identical chemical behaviours (reactivity)?

Answer 22

As the chemical behaviour is largely governed by the electronic structure

Question 23

What is the kinetic isotopes effect?

Answer 23

An exception
- bond energies are affected by the mass of the atoms that form the bond
- heavier isotopes react slower than lighter isotopes of the same element

Question 24

What happens to the potential kinetic isotope effect as the atoms become heavier?

Answer 24

Difference becomes much less, usually negligible

Question 25

What is one application of isotopes?

Answer 25

Drug metabolism
= what happens to the drug after the patient takes it

Question 26

How does isotopic labelling work during drug metabolism?

Answer 26

• isotopes introduced into drug during chemical synthesis
• see where the label ends up

Question 27

What ways can you use to identify the labelled metabolites?

Answer 27

• mass spectrometry
  = most widely used and most sensitive

Question 28

What is radiolabelling?

Answer 28

Labellimg with an unstable radionuclide
= radiation can be used to follow the tracer in the body

Question 29

Give an example of a radiolabel

Answer 29

Fludeoxyglucose (FDG)

Question 30

How does FDG work?

Answer 30

• Positron emissions are all directions, can be reconstructed into a 3D image
• any cells that have a high glucose demand will take up FDG
  = good reflection of glucose uptake by cells in the body