4.1 Physics relevant to radiotherapy

Question 1

Describe the structure of an atom

Answer 1

• Protons and Neutrons grouped together in a nucelus
• Surrounded by negatively charged Electrons in different energy shells
• If there are the same number of Protons and Electrons then the atom has no charge
• The attraction between the negatively charged Electrons and positively charged Protons holds them in the structure = Electromagnetic Force

This is the Rutherford-Bohr model

Question 2

What is the notation for atoms?

Answer 2

a
X
z

a = mass number = protons + neutrons
X = element (chemical symbol)
z = atomic number = number of protons = defines the element

Question 3

What is the Mass number?

Answer 3

The number of protons and neutrons added together

Question 4

What is an Isotope?

Answer 4

The same element will always have the same number of protons but can have different numbers of neutrons

e.g. Carbon will always have 6 protons but can have 6 or 7 neutrons making
C-12 or C-13

This is an ISOTOPE

P = Protons the same

Question 5

What is the Atomic number?

Answer 5

The atomic number is the number of protons in an element

This defines which element it is e.g. 6 protons = Carbon

Question 6

What is an Isobar?

Answer 6

Isobars have the same mass number but different numbers of protons

ISOBARS = same A

Question 7

What is an Isotone?

Answer 7

Same number of neutrons
ISOTONE = Neutrons

Question 8

What is an Isomer?

Answer 8

Isomer is where two atoms have the same A and Z but differ in their arrangement of energy levels

ISOMER = Energy levels

Question 9

What is Binding Energy?

Answer 9

Binding energy is the energy it takes to release an electron from an atom

Question 10

What two factors impact Binding Energy?

Answer 10

1. How close the electron is to the nucleus - inner electrons have a higher binding energy
2. How many protons are in the nucelus and therfore how strong the positive charge of the nucleus is

Question 11

What are the electron shells and what is their Principle Quantom Number (n)?

Answer 11

K n=1
L n=2
M n=3
O n=4

Question 12

How does the Principle Quantom Number determine how many electrons can be in each shell?

Answer 12

2n^2

so…
K = 2(1)^2=2
L = 8
M = 18
N = 32
O + = 32

Question 13

What are the 4 electron orbitals?

Answer 13

s - can hold 1 pair of electrons (2)
p - can hold 3 pairs of electrons (6)
d - can hold 4 pairs of electrons (8)
f - can hold 7 pairs of electrons (14)

Question 14

What are Valence Electrons?

Answer 14

Electrons that are in the outermost shell of an atom and can participate in the formation of a chemical bond