IGCSE Physics (0625) 5.2.3 Radioactive decay Paper 4

Question

(a) State the proton number, nucleon number and the value of the charge on an α-particle.
proton number …………………………………………………………………………………………………………..
nucleon number …………………………………………………………………………………………………………
charge ………………………………………………………………………………………………………………………

(b) A nucleus of strontium-90 consists of 38 protons and 52 neutrons. Strontium-90 is radioactive
and decays by β-emission to an isotope of yttrium. The symbol for strontium is Sr and the
symbol for yttrium is Y. Write down the nuclide equation of this decay.

(c) The half-life of radon-220 is 56 s. A sample of radon-220 is in a container. After 112 s the mass
of radon-220 is 9.2 mg.
Calculate the mass of the original sample.
mass = ……………………………………………..

Answer/Explanation

Answer:

(a)
2
4
+2

(b) 
nucleon numbers 90 on both sides of equation 
Sr and proton number 38 on left AND Y and proton number 39 on right

(c) (original mass = 4 / 9.2 =) 37 mg 
2 half-lives

Question

(a) An iodine isotope \(^{131}_{53}\) I decays by  β -emission to an isotope of xenon (Xe).

(i) State the number of each type of particle in a neutral atom of \(^{131}_{53}\) I.
protons ……………………. neutrons ……………………. electrons
(ii) State the symbol, in nuclide notation, for the xenon nucleus.
………………………………………………………………………………………………………………………

(b) The background count rate of radioactivity in a laboratory is 30 counts / min.

A radioactive sample has a half-life of 50 minutes. The sample is placed at a fixed distance from a detector. The detector measures an initial count rate from the sample, including background, of 310 counts / min.

On Fig. 10.1, plot suitable points and draw a graph of the count rate from the sample, corrected for background, as it changes with time.

Answer/Explanation

Answer:
(a) (i) Protons: 53 neutrons: 78 electrons: 53 
(ii)
\(^{131}_{54}\)Xe

(b) Points plotted at 3 of: 0s, 50 s, 100s, 150s 
3 corrected counts/minute plotted at any from :
(0, 280)
(50, 140)
(100, 70)
(150, 35) 
Graph drawn as curve through correct points

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