IGCSE Physics (0625) 5.2.4 Half-life Paper 3

Question

A nucleus of americium-241 has the nuclide notation shown.

\(^{241}_{95}\) Am

(a) (i) Determine the number of neutrons in a nucleus of americium-241.
number of neutrons =…………………………………………………………………………………………….
(ii) Determine the charge on a nucleus of americium-241.
charge =………………………………………………………………………………………………….

(b) Americium-241 decays by emitting α-particles.
Put a tick in the box next to each correct statement.

(c) Americium-241 has a half-life of 432 years.A sample contains 16 mg of americium-241.Calculate the time it takes until only 4.0 mg of americium-241 are left in the sample.
time = ………………………………………. years

Answer/Explanation

Answer:
(a)
(i)
146
(ii)
positive
95

(b) tick in 3rd box
tick in 4th box

(c) idea of 2 half-lives
(432 × 2) = 864 (years)

Question

Astatine-210 is a radioactive material. The nucleus of astatine can be represented by the symbol shown.

                                                                  \(^{210}_{85}\)At

(a) Complete the table to describe the nucleus of astatine-210.

type of particle

number of particles

charge on particle

neutron

positive

(b) Astatine-210 has a half-life of 8 hours.
(i) The count rate of a sample of astatine-210 is measured over 24 hours.
On Fig. 12.1, sketch a line to show how the count rate changes over the 24 hours.

                                       

(iii) The mass of a sample of astatine-210 is 0.500 kg.
Calculate how long it takes for 0.375 kg of the sample to decay.
decay time = ……………………………………….. hours

    Answer/Explanation

    Answer:
    (a) (neutron) – 125 – neutral
    proton(s) – 85 – (positive)

    (b)(i) curve of negative gradient, gradient decreasing
    curve with negative gradient starts on y axis
    (b)(ii) 0.125 (kg) (remaining)
    two half-lives indicated
    16 hours

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