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Question 18N.3.hl.TZ0.22

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Date November 2018 Marks available [Maximum mark: 5] Reference code 18N.3.hl.TZ0.22
Level hl Paper 3 Time zone TZ0
Command term Calculate, Explain, Suggest Question number 22 Adapted from N/A
22.
[Maximum mark: 5]
18N.3.hl.TZ0.22

Nuclear isotopes are used in the treatment of cancer.

(a)

Alpha particles are more damaging to human cells than any other nuclear radiation and yet they are used in targeted alpha therapy (TAT).

Explain how TAT is relatively safe to use in the treatment of dispersed cancers.

[2]

Markscheme

«alpha emitter» carried to/selectively absorbed by cancer cells «by antibody, carrier drug, protein» ✔

 

low penetrating power

OR

short range ✔

 

Do not accept just “targets cancer cells and does not affect healthy cells”.

Gamma radiation is also used in radiotherapy.

(b.i)

Technetium-99m ( 43 99 m Tc ) has a half-life of 6.0 hours. Calculate the percentage of  43 99 m Tc  remaining in a sample of the radioisotope after two days.

[2]

Markscheme

ALTERNATIVE 1:

« 40 6.0 =» 8  t 1 2 /8 half-lives «required» ✔

% remaining = «(0.5)8 × 100 =» 0.39 «%» ✔

 

ALTERNATIVE 2:

λ = « 0.693 6.0 =» 0.1155 ✔

% remaining = «100 × e–0.1155 × 48 =» 0.39 «%» ✔

 

Award [2] for correct final answer.

Accept “0.32 «%»” in ALTERNATIVE 2.

(b.ii)

Suggest why the percentage of technetium-99m remaining in the human body two days after injection will be lower than that calculated in (b)(i).

[1]

Markscheme

removed by excretion ✔

 

Accept any method of excretion.

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