{Year 2} Chapter 11 - Radioactive Decay [Complete]

Question 1

What is a metastable state?

Answer 1

When an atom or nucleus is left for an extended period of time in a state that is not the one of least energy for it - e.g. when the electrons are not in the ground state, or when protons or neutrons are sometimes left on a higher energy level due to emitting a radioactive particle

Question 2

When does gamma emission take place?

Answer 2

After the processes of either beta or alpha emission, or K-capture

Question 3

What is the notation used to tell when an atom/element is in a metastable state?

Answer 3

An m next to its mass number, e.g. Silver-107m

Question 4

What is K-capture, and why is it called as such?

Answer 4

The lowest electron energy level in the atom is called the K shell. These electrons are often very close to, or even pass through, the nucleus. Sometimes, they can become captured and turn a proton into a neutron, resulting in the emission of a neutrino

Question 5

In beta+ emission what particles are emitted?

Answer 5

A neutrino, as well as the beta+ particle itself - a fast moving positron

Question 6

In beta- emission what particles are emitted?

Answer 6

An antineutrino, as well as a the electron

Question 7

What nucleus is emitted during alpha decay?

Answer 7

A helium one

Question 8

In what type of element is alpha emission most commonly found?

Answer 8

Ones which are rich in protons - having atomic numbers most commonly exceeding 82

Question 9

How can alpha particles be used as a source of energy?

Answer 9

They are placed within a solid, but since they cannot get through it, their energy dissipates within it before they can exit, resulting in the energy being transferred to the solid and heating it up

Question 10

What are two ways that radiation can be used to treat cancer?

Answer 10

From the outside of the body inwards, by sending gamma rays from a source into the tumour and rotating the source around it // From the inside out, by putting a piece of the radioactive (beta) source within the tumour and letting it kill the tumour

Question 11

What are Carbon-14 and Argon-40 used for?

Answer 11

To date archaeological remains and rocks respectively

Question 12

What is the main activity equation?

Answer 12

Activity = decay constant (lambda) x number of nuclei (N) = 0.693N/half life

Question 13

What is the equation linking half life and ln2?

Answer 13

Half life (T1/2) = ln2 / decay constant (lambda)

Question 14

What is a half-life?

Answer 14

The time it takes for half of the nuclei in one radioactive sample to decay

Question 15

What is the decay equation?

Answer 15

N = Number of nuclei at the beginning x e^(-lambda x time)

Question 16

What is the equation for rate of decay?

Answer 16

Difference in nuclei number / Difference in time = - lambda x number of nuclei

Question 17

What is the mass of one mole of an element with an atomic mass of 30?

Answer 17

30 grams exactly

Question 18

What is the decay constant of a radioactive source?

Answer 18

The probability of a nucleus decaying per unit time

Question 19

What is the activity of a radioactive source?

Answer 19

The amount of disintegrations per second => A = decay constant x number of nuclei

Question 20

What are the two buzzwords when it comes to describing radioactive decay?

Answer 20

It is both random and spontaneous

Question 21

What is a good comparison to show the random nature of probability?

Answer 21

To throw 600 die - would think that 100 of them would face upwards on 6, and the rest on other numbers, but in reality it would vary from this and would not turn out perfectly with the 100 on 6 and rest evenly distrubuted

Question 22

On the plot of N against Z, where is which decay?

Answer 22

Alpha, Beta+ and K-capture happen below the line, and just Beta- happens above it (it is recommended you draw a graph to help here)

Question 23

What is technetium-99m used for and why is it so good?

Answer 23

Technetium-99m is used as a gamma-emitting diagnostic tracer in patients. It has an ideal half-life of 6 hours - making it a high emitter but for a conveniently short time, but the element it is derived from, molybedenum-99, has a long enough half- life to get to the hospital easily where it can be separated. The technetium is in a metastable state - which is why the m is next to its 99.