Atomic Physics — Free IB MYP5 Physics Questions

1QuestionAtomic number (Z) and mass number (A)Concept Practice

3 marks~5 minCriterion A

The diagrams below show two simplified atomic models of carbon isotopes.

Diagram 1: nucleus with 6 protons and 6 neutrons; 6 electrons orbiting.
Diagram 2: nucleus with 6 protons and 7 neutrons; 6 electrons orbiting.

a

State the atomic number

Z

for both isotopes. [1]

b

Deduce the mass number

A

for each isotope and identify each diagram as carbon-12 or carbon-13. [1]

c

Explain why these two atoms are isotopes of the same element, despite having different mass numbers. [1]

Solutions

2QuestionActivity and count rate (basic idea)Concept Practice

2 marks~3 minCriterion A

A Geiger–Müller (GM) tube is connected to a counter and placed close to a radioactive source. The counter displays 150 counts per second.

a

Identify the physical quantity measured by this GM tube setup. [1]

b

State the value and unit of this quantity as shown by the counter. [1]

Solutions

3QuestionDefinition of radioactivityConcept Practice

2 marks~3 minCriterion D

Technetium-99m (

^{99m}

Tc) is a radioactive isotope widely used in hospitals. It emits gamma radiation and has a half-life of approximately 6 hours.

a

Outline how

^{99m}

Tc is used in medical imaging to diagnose organ function. [1]

b

Evaluate one societal benefit or limitation of using radioactive isotopes such as

^{99m}

Tc in medicine. [1]

Solutions

4QuestionBackground radiation: Natural sources (cosmic, rocks), Artificial sourcesConcept Practice

2 marks~3 minCriterion A

The diagram shows three sources contributing to background radiation: a cosmic ray entering Earth's atmosphere, a rock containing uranium, and a medical X-ray machine.

a

Identify the two natural sources of background radiation shown in the diagram. [1]

b

Identify the artificial source of background radiation shown in the diagram. [1]

Solutions

5QuestionNature of each radiation: Mass, charge, speedConcept Practice

2 marks~3 minCriterion A

A student investigates how the deflection of alpha particles changes with the voltage applied between two parallel charged plates. The particle speed is kept constant throughout.

a

Identify the independent variable in this investigation. [1]

b

Identify the dependent variable in this investigation. [1]

Solutions

6QuestionConcept of nuclear forces: Strong nuclear force (basic idea)Concept Practice

2 marks~3 minCriterion A

The diagram shows a helium-4 nucleus containing two protons and two neutrons. Arrows indicate the electrostatic repulsion acting between the two protons due to their positive charges.

a

Identify the force responsible for holding the nucleus together despite this repulsion. [1]

b

Explain why this force does not cause the entire nucleus of a large atom, such as uranium-238, to collapse into a single point. [1]

Solutions

7QuestionDisposal of radioactive waste (basic idea)Concept Practice

2 marks~3 minCriterion D

Used cobalt-60 needles from hospitals are classified as low- to intermediate-level radioactive waste. After the source activity falls below safe operational limits, the needles must be disposed of safely.

a

State one method used to dispose of low- to intermediate-level radioactive waste from hospitals. [1]

b

Discuss one societal impact arising from the long storage time required for this type of radioactive waste. [1]

Solutions

8QuestionBiological effects in Cell damage/ Cancer risk/ DNA mutationConcept Practice

2 marks~3 minCriterion A

The diagram below shows three types of ionising radiation, labelled X, Y, and Z, each stopped by a different material. Radiation X is stopped by paper, radiation Y is stopped by a few millimetres of aluminium, and radiation Z requires thick lead to be significantly attenuated.

a

Identify which label (X, Y, or Z) represents gamma radiation. [1]

b

Explain why gamma radiation requires thick lead to stop it, while alpha radiation is stopped by paper. [1]

Solutions

9QuestionAtomic number (Z) and mass number (A)Assessment Practice

5 marks~8 minCriterion A

A mass spectrometer analyses element X and detects three isotopes:

Peak 1	$m/z = 84$	relative abundance $= 0.5\%$
Peak 2	$m/z = 86$	relative abundance $= 9.9\%$
Peak 3	$m/z = 88$	relative abundance $= 89.6\%$

a

Calculate the weighted average atomic mass of element X using:

\bar{A} = \frac{\sum (m/z \times \text{relative abundance})}{\sum \text{relative abundance}}

Show all working. [2]

b

Deduce the identity of element X from your result and state its atomic number

Z

. [1]

c

The three peaks all share the same atomic number

Z

yet differ in mass number

A

. Analyse how this is possible, and explain why the most abundant isotope does not necessarily determine the value of

Z

. [2]

Solutions

10QuestionEnergy levels and electron transitionsAssessment Practice

8 marks~12 minCriterion B

When a hydrogen atom's electron drops to a lower energy level, it emits a photon whose wavelength reveals the energy difference between those levels.

Lyman series (transitions to

n = 1

):

n = 2 \to 1

: 121.6 nm,

\quad n = 3 \to 1

: 102.6 nm,

\quad n = 4 \to 1

: 97.2 nm,

\quad n = 5 \to 1

: 95.0 nm

Balmer series (transitions to

n = 2

):

n = 3 \to 2

: 656.3 nm,

\quad n = 4 \to 2

: 486.1 nm,

\quad n = 5 \to 2

: 434.0 nm,

\quad n = 6 \to 2

: 410.2 nm

Use

\Delta E = \dfrac{hc}{\lambda}

, where

h = 6.63 \times 10^{-34}

J s and

c = 3.00 \times 10^{8}

m s

^{-1}

.

a

Calculate the energy of the photon emitted in the

n = 3 \to 2

transition. [2]

b

Using your answer to (a) and the data above, deduce the energy of the photon emitted in the

n = 3 \to 1

transition without using the 102.6 nm value directly, then compare your result with the value obtained from 102.6 nm. [3]

c

The Lyman series wavelengths decrease from 121.6 nm to 95.0 nm as the upper level rises from

n = 2

to

n = 5

, yet the decreases get smaller with each step. Analyse how both series together support the conclusion that energy level spacing decreases as

n

increases. [3]

Solutions

11QuestionEnergy levels and electron transitionsAssessment Practice

5 marks~8 minCriterion C

In the Franck–Hertz experiment, electrons are accelerated through mercury vapour. The graph shows collected current versus accelerating voltage, with current peaks at 4.9 V, 9.8 V, and 14.7 V.

Given:

h = 6.63 \times 10^{-34}

J s,

c = 3.00 \times 10^{8}

m/s,

1 \text{ eV} = 1.60 \times 10^{-19}

J.

a

Calculate the wavelength of the photon emitted when a mercury atom returns to its ground state after absorbing 4.9 eV. [2]

b

Explain why the current drops sharply after each peak rather than decreasing gradually. [1]

c

Evaluate the extent to which the pattern of peaks in the Franck–Hertz data supports Bohr's model of quantised energy levels. [2]

Solutions

12QuestionBohr model (energy levels)Assessment Practice

8 marks~12 minCriterion A

The Lyman series of hydrogen emission occurs when electrons fall to the ground state (

n = 1

). The first three lines have wavelengths:

n = 2 \to 1

:

121.6 \text{ nm}

n = 3 \to 1

:

102.6 \text{ nm}

n = 4 \to 1

:

97.3 \text{ nm}

A graph of

\dfrac{1}{\lambda}

(in

10^6 \text{ m}^{-1}

) against

\dfrac{1}{n^2}

(upper level) is plotted, giving a linear trend with

y

-intercept

1.097 \times 10^7 \text{ m}^{-1}

.

Use:

\dfrac{1}{\lambda} = R\!\left(\dfrac{1}{1^2} - \dfrac{1}{n^2}\right)

,

R = 1.097 \times 10^7 \text{ m}^{-1}

,

h = 6.63 \times 10^{-34} \text{ J s}

,

c = 3.00 \times 10^8 \text{ m s}^{-1}

,

1 \text{ eV} = 1.60 \times 10^{-19} \text{ J}

.

a

Explain why the series limit corresponds to the

y

-intercept of this graph. [2]

b

Deduce the series limit wavelength in nm. [3]

c

Evaluate the ionisation energy of hydrogen in eV using

E = hc/\lambda

, and assess the reliability of the experimental data by comparing your result with the accepted value of

13.6 \text{ eV}

. [3]

Solutions

13QuestionDalton’s modelAssessment Practice

5 marks~8 minCriterion C

A pure sample of element X is analysed. The graph below shows mass (in atomic mass units, u) versus number of atoms for this sample.

Graph data — Number of atoms (

\times 10^{23}

) : 0, 1, 2, 3, 4; Mass (u): 0, 20.18, 40.36, 60.54, 80.72

a

Deduce the average mass of one atom of element X from the graph. Show your working. [2]

b

Explain why Dalton's atomic model would predict an integer value for the mass per atom, and identify what feature of the graph contradicts this prediction. [1]

c

Analyse how the existence of isotopes modifies Dalton's model to account for the non-integer mass you calculated in (a). [2]

Solutions

14QuestionBohr model (energy levels)Assessment Practice

8 marks~12 minCriterion D

Technetium-99m (Tc-99m) is a radioactive isotope widely used in hospitals for imaging internal structures. It emits gamma radiation, detected by specialised cameras to diagnose conditions such as cancer. Tc-99m has a half-life of 6 hours. The energy of an emitted gamma photon is given by

E = hf

, where

h = 6.63 \times 10^{-34}

J s. Some patients require up to 3 scans per year throughout their lives.

a

Explain how a gamma photon is emitted from an excited Tc-99m nucleus, using the Bohr model of energy levels. [2]

b

A gamma photon emitted by Tc-99m has a frequency of

3.0 \times 10^{19}

Hz. Calculate the energy of this photon in joules. [2]

c

Evaluate the ethical justification for exposing a patient to repeated Tc-99m scans (3 per year). In your answer, state one assumption that underpins your evaluation. [4]

Solutions

15QuestionDalton’s modelAssessment Practice

2 marks~3 minCriterion D

Dalton's atomic theory states that all atoms of a given element are identical in mass and properties.

a

Outline one real-world application of this assumption. [1]

b

Dalton's theory cannot fully account for the behaviour of chlorine in precise industrial chemical reactions. Discuss one limitation of his model that explains this, and state how it affects reaction accuracy. [1]

Solutions

16QuestionDefinition of radioactivityAssessment Practice

5 marks~8 minCriterion C

The graph shows the number of uranium-238 nuclei remaining in a sample over time. The half-life of uranium-238 is 4.5 billion years. The sample initially contains

8.0 \times 10^{22}

nuclei. Uranium-238 decays through a series of steps, ultimately producing one lead-206 nucleus per uranium-238 nucleus.

a

Using the graph, deduce the number of uranium-238 nuclei remaining after 9.0 billion years. [1]

b

Calculate the number of uranium-238 nuclei that have decayed after 9.0 billion years, and explain how the concept of half-life supports your answer. [2]

c

A student claims that

6.0 \times 10^{22}

lead-206 nuclei have formed after 9.0 billion years. Evaluate this claim, using the definition of radioactivity and the structure of the uranium-238 decay series in your reasoning. [2]

Solutions

17QuestionFactors affecting decay (none – randomness)Assessment Practice

3 marks~5 minCriterion C

The graph below shows the number of undecayed nuclei in a radioactive sample plotted against time. A smooth exponential curve represents the theoretical decay, while individual data points show the measured values.

a

State what is meant by the term random in the context of radioactive decay. [1]

b

Explain why the measured data points do not lie perfectly on the smooth exponential curve. [1]

c

A second, much larger sample of the same isotope is measured under identical conditions. Analyse how the scatter of data points around the smooth curve would differ, and justify your reasoning. [1]

Solutions

18QuestionDecay series (basic idea)Assessment Practice

4 marks~6 minCriterion A

A sample initially contains

1.00 \times 10^{20}

atoms of pure Uranium-238 (

^{238}_{92}

U). Uranium-238 undergoes alpha decay to Thorium-234 (

^{234}_{90}

Th) with a half-life of

4.47 \times 10^{9}

years. Thorium-234 then undergoes beta decay to Protactinium-234 (

^{234}_{91}

Pa) with a half-life of 24.1 days. Assume every Thorium-234 atom decays to Protactinium-234 before any further decay occurs.

a

Construct the nuclear equation for the alpha decay of Uranium-238 to Thorium-234. [1]

b

Calculate the number of Uranium-238 atoms remaining after

4.47 \times 10^{9}

years. [1]

c

After

4.47 \times 10^{9}

years, a scientist claims that the number of Protactinium-234 atoms present equals the number of Uranium-238 atoms that have decayed. Justify this claim, and state the number of Protactinium-234 atoms present. [2]

Solutions

19QuestionHalf-life Interpretation of decay graphsAssessment Practice

4 marks~6 minCriterion B

The decay of a radioactive sample is shown in the graph below. The activity (counts per minute) is recorded every 5 seconds.

a

[2 marks] Use the data points from the graph to describe the pattern of how the activity changes over time.

b

[2 marks] Determine the half-life of this radioactive sample. Explain how you used the pattern to find it.

c

[2 marks] Predict the activity after 35 seconds. Justify your prediction using the pattern observed.

Solutions

20QuestionHalf-life DefinitionAssessment Practice

1 mark~2 minCriterion B

Interpret the decay graph of a radioactive isotope. The graph shows activity (counts per minute) on the y-axis and time (minutes) on the x-axis. Data points are: at t=0 min, activity = 800 cpm; t=10 min, 400 cpm; t=20 min, 200 cpm; t=30 min, 100 cpm; t=40 min, 50 cpm; t=50 min, 25 cpm; t=60 min, 12.5 cpm.

a

[2 marks] Describe the pattern in how the activity changes every 10 minutes. Generalize this pattern into a rule that relates activity to the number of 10-minute intervals elapsed.

b

[2 marks] Determine the half-life of this isotope from the graph. Explain how you used the pattern to find it.

c

[2 marks] Predict the activity at t=70 minutes. Justify your prediction using the pattern you identified in part (a).

Solutions

21QuestionActivity and count rate (basic idea)Assessment Practice

7 marks~11 minCriterion D

A hospital uses iodine-131 (half-life

T = 8

days) for thyroid scans. A patient receives an initial activity

A_0 = 40

MBq. The legal public-exposure limit is 1 MBq at 1 metre. Patients are advised to avoid public transport for 2 weeks after treatment. Biological elimination reduces the effective half-life to approximately 5 days. The hospital performs 50 scans per week; each patient excretes 5% of their initial dose into the sewage system during the first week.

A = A_0 \times \left(\frac{1}{2}\right)^{\frac{t}{T}}

a

Using the decay formula above, deduce the number of days after treatment at which the patient's activity falls to the legal limit of 1 MBq. Use the physical half-life of 8 days. [2]

b

Using your answer to (a) and the effective half-life of 5 days, evaluate whether the 2-week guideline provides sufficient protection for pregnant women and children travelling on public transport. [3]

c

Calculate the total activity released into the sewage system by the hospital per week, then evaluate whether this poses a significant environmental risk. [2]

Solutions

22QuestionBackground radiation: Natural sources (cosmic, rocks), Artificial sourcesAssessment Practice

6 marks~9 minCriterion B

A sealed rock sample emits radiation. The background count rate in the laboratory is

15

cpm. The table below shows the total count rate (including background) measured over eight days.

Time (days):

0,\ 2,\ 4,\ 6,\ 8

Total count rate (cpm):

255,\ 135,\ 75,\ 45,\ 30

a

Calculate the corrected count rate at each time point. Show your working. [2]

b

Deduce the half-life of the radioactive isotope. Show your reasoning. [2]

c

A technician claims the rock sample will be safe to handle (corrected count rate below

8

cpm) after

16

days. Evaluate this claim using a calculation. [2]

Solutions

23QuestionDeflection in electric and magnetic fieldsAssessment Practice

8 marks~12 minCriterion D

A nuclear reprocessing facility stores

\text{Cs-137}

and

\text{Sr-90}

in a storage pond. To reduce long-term waste, a mass spectrometer separates these isotopes: ions are accelerated to the same speed

v

and enter a uniform magnetic field

B

, where the magnetic force provides the centripetal force, causing each ion to follow a circular path. Both isotopes form singly charged ions (

q = 1.6 \times 10^{-19}\ \text{C}

).

a

Deduce which isotope has the larger radius of curvature in the magnetic field. [2]

b

Explain how the separation of

\text{Cs-137}

creates both a benefit for long-term waste management and a security risk. [3]

c

Evaluate the environmental limitations of using a mass spectrometer for large-scale isotope separation, discussing at least two distinct limitations. [3]

Solutions

24QuestionBackground radiation: Natural sources (cosmic, rocks), Artificial sourcesAssessment Practice

6 marks~9 minCriterion D

A family is choosing between granite countertops and standard concrete for their kitchen renovation. Granite contains trace amounts of uranium-238, which decays to produce radon-222 gas. The granite emits radon at

0.1\ \text{Bq kg}^{-1}

; the kitchen will contain

50\ \text{kg}

of granite. Standard concrete emits radon at

0.02\ \text{Bq kg}^{-1}

;

200\ \text{kg}

will be used. Inhaling radon delivers an annual dose of

0.01\ \text{mSv}

per

\text{Bq}

of activity.

a

Calculate the annual radon dose for each material option. [2]

b

Deduce which material poses the greater radon health risk, and explain why the difference in calculated doses may not be meaningful in practice. [2]

c

Discuss the limitations of using only these calculated doses to decide which material is safer for the family. [2]

Solutions

25QuestionComparison of properties pentrating power/ionization power/ biological damageAssessment Practice

5 marks~8 minCriterion A

A radiation simulation records the following data for alpha, beta, and gamma radiation travelling through air before striking a 2.0 mm lead shield.

Distance travelled in air before reaching the shield (cm):
Alpha: 4.0 — Beta: 120 — Gamma: exits simulation (> 1000)

Energy deposited in lead (MeV per mm of lead):
Alpha: 1.2 — Beta: 0.3 — Gamma: 0.05

Ionisation events in air (events per mm of travel):
Alpha: 40 000 — Beta: 100 — Gamma: 1

a

Calculate the total energy deposited by each radiation type in the 2.0 mm lead shield. [1]

b

Using the ionisation data and the distances travelled in air, explain the relationship between a particle's stopping distance and its rate of energy transfer to matter. [2]

c

Justify why alpha radiation causes the greatest biological damage despite having the least penetrating power. [2]

Solutions

26QuestionDeflection in electric and magnetic fieldsAssessment Practice

3 marks~5 minCriterion C

The diagram below shows the trajectories of alpha, beta, and gamma radiation entering a uniform electric field directed vertically downward.

a

State the charge of each type of radiation. [1]

b

Using the relationship

F = qE

, explain why alpha and beta particles deflect in opposite directions in this field. [1]

c

A student claims that a more massive alpha particle will always deflect less than a beta particle in the same electric field, regardless of their speeds. Justify whether this claim is correct. [1]

Solutions

27QuestionDetection methods: Geiger-Müller counter, Photographic filmAssessment Practice

3 marks~5 minCriterion C

A Geiger–Müller (GM) tube is placed at increasing distances from a small radioactive source in air. The graph shows count rate (counts per second) plotted against distance

d

from the source.

a

State the inverse-square law for radiation intensity from a point source. [1]

b

Explain why the count rate measured by the GM tube decreases as

d

increases, linking the inverse-square law to the fixed detection area of the tube's window. [1]

c

A student claims that doubling the distance will halve the count rate. Evaluate this claim. [1]

Solutions

28QuestionApplications of isotopes: Medical (tracers, cancer treatment), Industrial uses, Carbon dating (basic idea)Assessment Practice

6 marks~9 minCriterion A

Technetium-99m is a radioactive isotope widely used in medical imaging. A sample has an initial activity of 200 MBq. The graph below shows how the activity changes over time.

a

Deduce the half-life of technetium-99m from the graph. [2]

b

Calculate the decay constant

\lambda

, using

\lambda = \dfrac{\ln 2}{t_{1/2}}

. State the units of

\lambda

. [2]

c

A hospital requires the activity to remain above 25 MBq to produce a usable image. Using the graph, interpret whether a sample prepared 4 days before a scan can still be used. Justify your answer with reference to both the graph and the half-life. [2]

Solutions

29QuestionNeutron-to-proton ratioAssessment Practice

6 marks~9 minCriterion B

The graph of neutron number (

N

) versus proton number (

Z

) for all known stable isotopes displays the band of stability and the line

N = Z

.

Three isotopes lie within the band of stability:

Carbon-12	$Z = 6$	$N = 6$
Iron-56	$Z = 26$	$N = 30$
Lead-208	$Z = 82$	$N = 126$

a

Deduce the neutron-to-proton ratio (

N/Z

) for each of the three isotopes above. [3]

b

Interpret the difference in

N/Z

between Carbon-12 and Iron-56 in terms of nuclear stability. [1]

c

Analyse the trend in

N/Z

across the three isotopes and explain, using the concept of nuclear forces, why heavy stable nuclei require a greater proportion of neutrons than light stable nuclei. [2]

Solutions

30QuestionApplications of isotopes: Medical (tracers, cancer treatment), Industrial uses, Carbon dating (basic idea)Assessment Practice

4 marks~6 minCriterion C

A patient is injected with 200 MBq of technetium-99m for a bone scan. The half-life of technetium-99m is 6 hours.

The activity at time

t

is given by:

A = A_0 \left(\frac{1}{2}\right)^{\frac{t}{T}}

where

A_0

is the initial activity and

T

is the half-life.

a

Calculate the activity remaining after 18 hours. Show all working. [2]

b

A radiographer states: "After 30 hours, the activity will be less than 10 MBq, making the tracer ineffective for imaging." Evaluate this claim, supporting your answer with a calculation. [2]

Solutions

31QuestionApplications of isotopes: Medical (tracers, cancer treatment), Industrial uses, Carbon dating (basic idea)Assessment Practice

3 marks~5 minCriterion D

The graph shows the percentage of carbon-14 (

^{14}

C) remaining in an organic sample plotted against time (years). The curve begins at 100% at

t = 0

, falls to 50% at

t = 5730

years, to 25% at

t = 11\,460

years, and to 12.5% at

t = 17\,190

years.

a

Use the graph to deduce the half-life of carbon-14. [1]

b

Explain the relationship between time elapsed and the percentage of

^{14}

C remaining shown by the graph. [1]

c

A piece of ancient wood contains 25% of its original carbon-14. Deduce the age of the wood and justify why carbon-14, rather than a isotope with a much shorter half-life, is more suitable for dating objects thousands of years old. [1]

Solutions

32QuestionApplications of isotopes: Medical (tracers, cancer treatment), Industrial uses, Carbon dating (basic idea)Assessment Practice

2 marks~3 minCriterion A

Carbon-14 (

^{14}

C) is used in radiocarbon dating of ancient organic material. Both carbon-12 (

^{12}

C) and carbon-14 (

^{14}

C) have 6 protons.

a

State which isotope is radioactive and identify the subatomic particle whose differing number causes this instability. [1]

b

A sample of ancient wood contains only

^{14}

C and

^{12}

C. Deduce why the ratio of

^{14}

C to

^{12}

C decreases over time, but the number of

^{12}

C atoms remains constant. [1]

Solutions

33QuestionDefinition of isotopesAssessment Practice

2 marks~3 minCriterion D

Technetium-99m (

^{99m}

Tc) is widely used in nuclear medicine imaging. It is produced in hospital generators from the decay of molybdenum-99 (

^{99}

Mo).

a

Identify the type of radiation emitted by

^{99m}

Tc and explain why this nuclear property, together with its half-life of 6 hours, makes it suitable for diagnostic imaging. [1]

b

Evaluate one limitation of using

^{99m}

Tc in clinical settings, considering both its nuclear properties and practical consequences for patient access. [1]

Solutions

34QuestionNotation of isotopes (e.g., ¹⁴C)Assessment Practice

4 marks~6 minCriterion D

A museum uses carbon-14 dating to estimate the age of a wooden artifact. Carbon-14 is represented by the notation

^{14}_{6}\text{C}

, where the half-life of

^{14}_{6}\text{C}

is 5730 years. Analysis indicates the artifact is approximately 50,000 years old.

a

State two assumptions that must be made for carbon-14 dating to yield an accurate age. [2]

b

The artifact is claimed to be 50,000 years old. Discuss why this age estimate is likely to be unreliable, referring to the half-life of

^{14}_{6}\text{C}

and the impact on measurement accuracy. [2]

Solutions

35QuestionDisposal of radioactive waste (basic idea)Assessment Practice

8 marks~12 minCriterion C

Three identical sealed waste drums — Drum A, Drum B, and Drum C — each contain a different radioactive isotope. A Geiger counter recorded the radiation level at the surface of each drum every 5 days for 30 days. The results are shown in the graph below.

Drum A: starts at 800 μSv/h, falls to near 0 by day 20.
Drum B: starts at 400 μSv/h, falls to 200 μSv/h by day 30.
Drum C: starts at 200 μSv/h, falls to approximately 180 μSv/h by day 30.

a

Deduce which drum contains the isotope with the shortest half-life and which contains the isotope with the longest half-life. [2]

b

The monitoring period ends at day 30. Calculate the expected radiation level of Drum B at day 60, and explain how the concept of half-life supports your answer. [3]

c

A worker states that Drum A is safe to handle without shielding after day 60, because its radiation level is negligible. The isotope in Drum A decays into a daughter product with a half-life of 50 years. Evaluate the worker's claim. [3]

Solutions

36QuestionSafe handling of radioactive materialsAssessment Practice

6 marks~9 minCriterion B

A student investigates how count rate from a beta source changes with distance. Using a Geiger–Müller tube, she records the following data:

Distance (cm)	5	10	15	20	25
Count rate (counts/min)	640	160	71	40	26

a

Construct a graph of count rate (y-axis) against distance (x-axis) and interpret the pattern shown. [2]

b

The student claims the relationship is an inverse square law. Justify this claim using calculations from the data. [2]

c

A technician suggests that at 30 cm the count rate will be "low enough to be safe." Evaluate this suggestion, using the mathematical model to calculate the count rate at 30 cm and discussing one limitation of relying solely on distance as a safety measure. [2]

Solutions

37QuestionBiological effects in Cell damage/ Cancer risk/ DNA mutationAssessment Practice

8 marks~12 minCriterion D

A hospital is considering replacing its X-ray system with a newer model. The new system emits 40% less radiation per scan but produces 15% higher image noise, which may require repeat scans in some cases.

a

Explain how ionizing radiation from X-rays damages DNA and increases the risk of cancer. [2]

b

A patient requires one repeat scan with the new system. Show that the patient's cumulative radiation dose is 1.2 times the original single-scan dose, and discuss why this means the reduction in radiation per scan may not proportionally reduce overall cancer risk. [3]

c

Evaluate the usefulness of the linear no-threshold (LNT) model for estimating cancer risk from low-dose medical X-ray exposures. [3]

Solutions

38QuestionNuclear accidents (case awareness)Assessment Practice

5 marks~8 minCriterion A

The Chernobyl accident released significant gamma radiation. Measured dose rates at known distances from the reactor core are:

Distance from core (m)	10	50	200
Dose rate (mSv/year)	500	20	1.25

Gamma radiation intensity follows the inverse-square law:

I \propto \dfrac{1}{r^2}

The long-term habitation safety threshold is 20 mSv/year. Each 4.5 mm thickness of lead halves gamma intensity. A proposed evacuation boundary is set at 500 m from the core.

a

Using the data point at 200 m, calculate the predicted dose rate at 500 m. [2]

b

Deduce whether the 500 m boundary meets the safety threshold for long-term habitation. [1]

c

Evaluate whether distance alone provides sufficient protection, or whether lead shielding would also be required at the 500 m boundary. Use the shielding data in your answer. [2]

Solutions

39QuestionNuclear accidents (case awareness)Assessment Practice

5 marks~8 minCriterion C

During a simulated nuclear accident, a detector measures the count rate of gamma radiation transmitted through increasing thicknesses of lead shielding. The theoretical count rate is predicted by the exponential attenuation model:

I = I_0 \, e^{-\mu x}

where

I_0 = 1000

counts/s and

\mu = 0.693 \text{ cm}^{-1}

.

Lead thickness (cm)	0.0	0.5	1.0	1.5	2.0	2.5
Experimental count rate (counts/s)	1000	720	500	350	250	180
Theoretical count rate (counts/s)	1000	707	500	353	250	177

a

Calculate the percentage deviation for each data point using:

\text{Percentage deviation} = \frac{|\text{Experimental} - \text{Theoretical}|}{\text{Theoretical}} \times 100

[2]

b

Discuss the pattern of deviations and identify their likely physical cause. [1]

c

Evaluate whether the experimental data supports the exponential attenuation model as a valid description of gamma radiation shielding by lead. [2]

Solutions

Atomic Physics — Free MYP5 Physics Practice Questions