Protactinium-234 (²³⁴₉₁Pa) is a radioactive isotope of protactinium that decays to uranium-234 (²³⁴₉₂U).

1. (a)Compare the nuclide notation ²³⁴₉₁Pa with the nuclide notation ²³⁴₉₂U and deduce what this shows about what is emitted from a nucleus of protactinium-234 as it decays to uranium-234. Place a tick (✓) in the appropriate boxes of Table 9.1 to show what is deduced from comparing the nuclide notations.[2]
2. (b)(i)The most abundant isotope of protactinium is protactinium-231. Explain, by referring to their nuclear compositions, why protactinium-231 and protactinium-234 are both isotopes of the same element.[1]
3. (b)(ii)Explain, by referring to their nuclear compositions, why protactinium-231 and protactinium-234 are different isotopes of that element.[1]
4. (c)(i)A teacher places a radiation detector on a bench in a school laboratory and switches it on. The teacher measures and records the background radiation count rate. Describe what is meant by 'background radiation' and state two significant sources of the count rate recorded by the teacher.[3]
5. (c)(ii)The teacher moves a sample of protactinium-234 so that it is next to the detector. Suggest one precaution that ensures that the sample is moved in a safe way.[1]
6. (c)(iii)The count rate is measured every 20s with the sample present, and then corrected for background radiation. Fig. 9.1 shows a graph of the corrected count rate against time for the protactinium-234 sample. [Figure 9.1] The curve is the best-fit line. Explain why many of the crosses do not lie on the curve.[2]
7. (c)(iv)Using Fig. 9.1, determine the half-life of protactinium-234. Show your working.[3]
8. (c)(v)The uranium-234 formed from the protactinium-234 is also radioactive. Its half-life is many thousands of years. Explain why the radiation from uranium-234 does not affect the count rates measured in this experiment.[2]

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