CAIE A-Level Physics 11.1 Atoms, Nuclei and Radiation

Practise using scattering evidence, nuclear notation, isotopes and conservation laws to explain the nucleus and alpha, beta and gamma decay.

Exam points

infer nuclear size, charge and mass concentration from alpha-scattering results and describe the nuclear atom
use nucleon/proton numbers, isotopes and A Z X notation to determine nuclear composition and charge
apply conservation of charge and nucleon number to alpha- and beta-decay equations
describe alpha, beta-minus, beta-plus and gamma radiation, including antiparticles, neutrinos and energy spectra
use the unified atomic mass unit u in nuclear and particle contexts

Covered syllabus points

11.1.1—The results of the α-particle scattering experiment the existence and small 11.1.2—A simple model for the nuclear atom to include protons, neutrons and orbital 11.1.3—Nucleon number and proton number 11.1.4—Isotopes are forms of the same element with different numbers of neutrons in 11.1.5—The notation A Z X for the representation of nuclides 11.1.6—Nucleon number and charge are conserved in nuclear processes 11.1.7—The composition, mass and charge of α-, β- and γ-radiations (both β–11.1.8—An antiparticle has the same mass but opposite charge to the corresponding 11.1.9—That (electron) antineutrinos are produced during β– decay and (electron)11.1.10—Α-particles have discrete energies but that β-particles have a continuous 11.1.11—Α- and β-decay by a radioactive decay equation of the form UT h92 238 90 234 11.1.12—The unified atomic mass unit (u) as a unit of mass

[Maximum number: 7]

Fig. 6.1 shows four alpha particles W, X, Y and Z moving towards a gold nucleus that is in thin gold foil.

Fig. 6.1 (not to scale)

(a)

The paths of particles X and Z are shown.

Complete Fig. 6.1 to show possible paths for particles W and Y.

[ 3 ]

(b)

Describe what may be inferred about the structure of an atom from the path of particle X .

[ 1 ]

(c)

When a beam containing many alpha particles is incident on thin gold foil, nearly all of the alpha particles follow paths that are similar to the path of particle Z .

Describe what may be inferred from this about the structure of an atom.

[ 1 ]

(d)

State the mass and the charge, in terms of the atomic mass unit u and the elementary charge e, of an alpha particle.

\begin{array}{r} \text { mass }=\ldots \ldots \ldots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ u ~ \\ \text { charge }=\ldots \ldots \ldots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ e ~ \\ \text { [2] } \end{array}

[ 2 ]

[Maximum number: 7]

(a)

Describe the structure of an atom of uranium-238, $\stackrel{238}{92} \mathrm{U}$ .

[ 2 ]

(b)

The decay of uranium-238 is shown by the equation

{ }_{92}^{238} \mathrm{U} \rightarrow{ }_{90}^{234} \mathrm{Th}+\mathrm{X} .

For nucleus X , calculate the ratio, in $\mathrm{Ckg}^{-1}$ , of $\frac{\text { charge }}{\text { mass }}$ .
ratio = $\mathrm{C} \mathrm{kg}^{-1}$

[ 3 ]

charge =2 e
$\left(=2 \times 1.60 \times 10^{-19} \mathrm{C}\right)$

C1

mass =4 u
$\left(=4 \times 1.66 \times 10^{-27} \mathrm{~kg}\right)$

C1

ratio $=\left(2 \times 1.60 \times 10^{-19}\right) /\left(4 \times 1.66 \times 10^{-27}\right)$ $=4.8 \times 10^{7} \mathrm{C} \mathrm{~kg}^{-1}$

A1

(c)

Two particles P and Q each consist of three quarks. These quarks are up (u) or down (d) quarks.

Particle P has no overall charge.
Particle Q has an overall charge of +2 e, where e is the elementary charge.
State the quark composition of:

[ 2 ]

(i)

particle P

[ 1 ]

(ii)

particle Q.

[ 1 ]

[Maximum number: 2]

(a)

Nucleus Q undergoes radioactive decay to form nucleus R, emitting an antineutrino and another particle X, as shown in the decay equation.

Q \rightarrow R+X+\bar{v}

[ 2 ]

(i)

State what particle is represented by X .

[ 1 ]

$\beta^{-}$ (particle) or electron

B1

(ii)

Compare the nucleon numbers of Q and R.

[ 1 ]

All question bank results loaded

Covered syllabus points

11.1 Atoms, nuclei and radiation question 1

Question (a)

Question (b)

Question (c)

Question (d)

11.1 Atoms, nuclei and radiation question 2

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

11.1 Atoms, nuclei and radiation question 3

Question (a)

Question (i)

Question (ii)