Name: _______________________________________________

CS P1 H Radioactivity

Date:

Time: 20 minutes

Total marks available: 20

Total marks achieved: ______

Questions Q1.

State what is meant by the term 'half-life'.

(1)

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(Total for question = 1 mark)

Q2.

Early in the twentieth century, scientists fired a beam of alpha particles at thin gold foil.

Figure 2 shows the main parts of their experiment with some results.

Figure 2

Explain how the results of the experiment shown in Figure 2 support the nuclear model of an atom.

(3)

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(Total for question = 3 marks)

Q3.

Figure 1 is a diagram of three atoms.

Figure 1

Give reasons why these atoms are isotopes.

(2)

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(Total for question = 2 marks)

Q4.

Figure 1 is a diagram of three atoms.

Figure 1

Some unstable isotopes emit alpha particles.

Which of these describes an alpha particle?

(1)

A a hydrogen nucleus

B a hydrogen atom

C a helium nucleus

D a helium atom

(Total for question = 1 mark)

Q5.

What is the approximate size of a hydrogen atom?

(1)

A 10–3 m

B 10–10 m

C 10–19 m

D 10–31 m

(Total for question = 1 mark)

Q6.

Figure 7 shows the nuclei of four atoms.

Figure 7

Which two nuclei have the same number of neutrons?

(1)

A plutonium-238 and uranium-235

B uranium-235 and americium-238

C uranium-234 and americium-238

D americium-238 and plutonium-238

(Total for question = 1 mark)

Q7.

Some rocks containing potassium were formed many millions of years ago.

There was no argon-40 in the rocks when they were formed.

When scientists analyse samples of these rocks, they find small amounts of argon-40 trapped inside.

The graph shows how the relative amounts of potassium-40 and argon-40 change over time.

(i) Use the graph to find the half-life of potassium-40.

(1)

half-life = ........................................................... million years

(ii) Scientists analyse a sample taken from inside a rock.

They find that there is exactly 3 times as much argon-40 as there is potassium-40. Use the graph to find the age of the rock.

(2)

age of rock = ........................................................... million years

Q8.

Many different types of radioactive isotope are used for the diagnosis and treatment of medical conditions.

(i) Iodine-123 is used as a radioactive tracer to diagnose thyroid problems.

Complete the sentence by putting a cross ( ) in the box next to your answer. This tracer must have a half-life of

(1)

A a few days

B a few hours

C less than a second

D several weeks

(ii) Pellets which contain radium-223 can be put inside the body to treat cancers.

Radium-223 has a half-life of 11.4 days and emits alpha radiation. Explain why radium-223 is suitable for use inside the body to treat cancers.

(3)

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Q9.

One isotope of the element potassium is potassium-40.

A nucleus of potassium-40 is represented by:

(i) Complete the sentence by putting a cross ( ) in the box next to your answer.

The number of neutrons in a nucleus of potassium-40 is (1)

A 19

B 21

C 40

D 59

(ii) Which of these symbols is correct for the nucleus of a different isotope of potassium?

Put a cross ( ) in the box next to your answer. (1)

(iii) A sample of potassium-40 is left for a long time.

Some of the potassium-40 nuclei will emit gamma radiation as they turn into argon-40 nuclei. Argon-40 nuclei never change. Describe what information this gives about the isotope potassium-40.

(2)

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Q1. No Examiner's Report available for this question Q2. No Examiner's Report available for this question Q3. No Examiner's Report available for this question Q4. No Examiner's Report available for this question Q5. No Examiner's Report available for this question Q6. No Examiner's Report available for this question Q7.

(i-ii)

Most candidates could find the half-life from the graph and many went on to double this value to correctly

answer the second part.

In part (ii) a large number of candidates clearly used the graph to identify the point where the amount of argon was three times the amount of potassium (i.e. at 75/25) to arrive at the correct answer but an equally large number simply multiplied the half-life by 3 and so failed to score any marks.

Results Plus: Examiner Comments This candidate clearly knew how to interpret the graph and arrived at the right answer for the full 2 marks.

Results Plus: Examiner Tip If you are reading values from a graph it is always a good idea to draw lines with a ruler: like this candidate did. Examiners award at least 1 mark for showing the correct method even if the final answer is incorrect.

Q8.

(ii)

Candidates needed to know the properties of alpha radiation and then apply this to the treatment of cancers. When considering the half-life this should be related to the time necessary for effective treatment or that the pellets do not have to be removed.

This response score two marks.

Results Plus: Examiner Comments The alpha radiation is described as 'strongly ionising' which gets one mark and also as 'not very penetrating', this gets a second mark. Although the alpha radiation is described as 'will severely damage the tumar' just damage is not sufficient for the third mark, destroys tumours or mutates cells is required. No mark is awarded for the reasoning behind the short half life as it did not relate to the treatment.

Results Plus: Examiner Tip Learn the properties that each type of radiation and how these can effect human tissue.

This response scores three marks.

Results Plus: Examiner Comments This response makes no mention of half life but gets marks for:

strongly ionising

won't penetrate into the body past the cancers.

cancer cells will be killed off.

Results Plus: Examiner Tip Apply the properties of alpha radiation to the situation given in the question.

Q9.

(iii)

Candidates could achieve marks a number of ways in this question. The most common

observation was that the isotope was unstable and/or radioactive, followed by recognition that it had a long half-life. Some of the more able candidates wrote that the decay must be random because only some nuclei had decayed in that time.

Results Plus: Examiner Comments This answer correctly identifies a long half-life and gains 1 mark.

Results Plus: Examiner Comments This response was awarded 1 mark for recognising that it must be unstable and a second mark for the fact that this means it is radioactive.

Mark Scheme

Q1.

Q2.

Q3.

Q4.

Q5.

Q6.

Q7.

Q8.

Q9.