What is the charge on an electron antineutrino and during what process is an electron antineutrino produced?

D

Which of the following lists the particles emitted during radioactive decay in order of increasing ionizing power? 

A. γ, β, α
B. β, α, γ
C. α, γ, β
D. α, β, γ

A

The mass of nuclear fuel in a nuclear reactor decreases at the rate of $8 \mathrm{mg}$ every hour. The overall reaction process has an efficiency of $50 \%$. What is the maximum power output of the reactor?

A.  $100 \mathrm{MW}$

B.  $200 \mathrm{MW}$

C.  $100 \mathrm{GW}$

D.  $200 \mathrm{GW}$

A

The discrimination index was below the desired 0.2 with a high number of blank responses and many candidates choosing each of the options. This is a question requiring consideration of units using 10^-6 for mg to kg and also remembering to allow for efficiency.

A pure sample of nuclide A and a pure sample of nuclide B have the same activity at time t = 0. Nuclide A has a half-life of T, nuclide B has a half-life of 2T.

What is $\frac{\text{activity of A}}{\text{activity of B}}$ when t = 4T?

A.  4

B.  2

C.  $\frac{1}{2}$

D.  $\frac{1}{4}$

D

Which Feynman diagram describes the annihilation of an electron and its antiparticle?

A

A detector measures the count rate from a sample of a radioactive nuclide. The graph shows the variation with time of the count rate.

The nuclide has a half-life of 20 s. The average background count rate is constant.

What is the average background count rate?

A.  1 s⁻¹

B.  2 s⁻¹

C.  3 s⁻¹

D.  4 s⁻¹

C

Which is the correct Feynman diagram for pair annihilation and pair production?

D

The Feynman diagram shows an interaction between a proton and an electron.

What is the charge of the exchange particle and what is the lepton number of particle X?

B

In the Rutherford-Geiger-Marsden scattering experiment it was observed that a small percentage of alpha particles are deflected through large angles.

Three features of the atom are

I.   the nucleus is positively charged

II.  the nucleus contains neutrons

III. the nucleus is much smaller than the atom.

Which features can be inferred from the observation?

A.   I and II only

B.   I and III only

C.   II and III only

D.   I, II and III

B

A radioactive nuclide X decays into a nuclide Y. The graph shows the variation with time of the activity A of X. X and Y have the same nucleon number.

What is true about nuclide X?

A.  alpha (α) emitter with a half-life of t

B.  alpha (α) emitter with a half-life of 2t

C.  beta-minus (β⁻) emitter with a half-life of t

D.  beta-minus (β⁻) emitter with a half-life of 2t

D

The carbon isotope $\frac{14}{6}$C is radioactive. It decays according to the equation

$\frac{14}{6}$C → $\frac{14}{7}$N + X + Y

What are X and Y?

B

This question was well answered by candidates, with a high discrimination index.

A pure sample of iodine-131 decays into xenon with a half-life of 8 days.

What is $\frac{\text{number of iodine atoms remaining}}{\text{number of xenon atoms formed}}$ after 24 days?

A.  $\frac{1}{8}$

B.  $\frac{1}{7}$

C.  $\frac{7}{8}$

D.  $\frac{8}{7}$

B

The majority of candidates correctly selected option B. This question had the highest discrimination index on the HL paper.

A neutron is absorbed by a nucleus of uranium-235$\left({}_{92}{}^{235}\text{U}\right)$. One possible outcome is the production of two nuclides, barium-144$\left({}_{56}{}^{144}\text{Ba}\right)$ and krypton-89$\left({}_{36}{}^{89}\text{Kr}\right)$.

How many neutrons are released in this reaction?

A.  0

B.  1

C.  2

D.  3

D

Answer C 2 neutrons, was the most popular choice suggesting that candidates failed to read the question properly and missed 'a neutron is adsorbed' at the beginning.

The diagram shows atomic transitions E₁, E₂ and E₃ when a particular atom changes its energy state. The wavelengths of the photons that correspond to these transitions are ${\lambda }_1$, ${\lambda }_2$ and ${\lambda }_3$.

What is correct for these wavelengths?

A.  ${\lambda }_1>{\lambda }_2>{\lambda }_3$

B.  ${\lambda }_1={\lambda }_2+{\lambda }_3$

C.  $\frac{1}{{\lambda }_1}=\frac{1}{{\lambda }_2+{\lambda }_3}$

D.  $\frac{1}{{\lambda }_1}=\frac{1}{{\lambda }_2}+\frac{1}{{\lambda }_3}$

D

In a hydrogen atom, the sum of the masses of a proton and of an electron is larger than the mass of the atom. Which interaction is mainly responsible for this difference?

A. Electromagnetic

B. Strong nuclear

C. Weak nuclear

D. Gravitational

A

The ${\pi }^{+}$ meson contains an up ($u$) quark. What is the quark structure of the ${\pi }^{-}$ meson?

A. $ud$

B. $u\overline{d}$

C. $\overline{u}d$

D. $\overline{u}\overline{d}$

C

Nuclide X can decay by two routes. In Route 1 alpha (α) decay is followed by beta-minus (β^–) decay. In Route 2 β^– decay is followed by α decay. P and R are the intermediate products and Q and S are the final products.

Which statement is correct?

A.  Q and S are different isotopes of the same element.

B.  The mass numbers of X and R are the same.

C.  The atomic numbers of P and R are the same.

D.  X and R are different isotopes of the same element.

B

The following decay is observed.

μ⁻ → e⁻ + v_μ + X

What is particle X?

A.   γ

B.   $\overline{v}$_e

C.   Z⁰

D.   v_e

B

Carbon (C-12) and hydrogen (H-1) undergo nuclear fusion to form nitrogen.

${}_6{}^{12}\text{C+}{}_1{}^1\text{H →N+}$ photon

What is the number of neutrons and number of nucleons in the nitrogen nuclide?

B

This question was well answered by HL candidates, although a significant number of candidates incorrectly identified the number of neutrons present in the nitrogen nuclide.

White light is emitted from a hot filament. The light passes through hydrogen gas at low pressure and then through a diffraction grating onto a screen. A pattern of lines against a background appears on the screen.

What is the appearance of the lines and background on the screen?

D

The diagram shows the emission spectrum of an atom.

Which of the following atomic energy level models can produce this spectrum?

A

With a low difficulty index, most candidate responses were divided between (incorrect) responses C and D. Students appeared to select more familiar energy level diagrams rather than the diagram that best correlated with the emission spectrum given.

What is correct about the Higgs Boson?

A.     It was predicted before it was observed.

B.     It was difficult to detect because it is charged.

C.     It is not part of the Standard Model.

D.     It was difficult to detect because it has no mass.

A

Gamma ($\gamma$) radiation

A.  is deflected by a magnetic field.

B.  affects a photographic plate.

C.  originates in the electron cloud outside a nucleus.

D.  is deflected by an electric field.

B

Identify the conservation law violated in the proposed reaction.

                                                 p⁺ + p⁺ → p⁺ + n⁰ + μ⁺

A.     Strangeness

B.     Lepton number

C.     Charge

D.     Baryon number

B

In the nuclear reaction X + Y → Z + W, involving nuclides X, Y, Z and W, energy is released. Which is correct about the masses (M) and the binding energies (BE) of the nuclides?

C

Which of the following leads to a paradigm shift?

A. Multi-loop circuits

B. Standing waves

C. Total internal reflection

D. Atomic spectra

D

During the nuclear fission of nucleus X into nucleus Y and nucleus Z, energy is released. The binding energies per nucleon of X, Y and Z are $B_{\text{X}}$ , $B_{\text{Y}}$ and $B_{\text{Z}}$ respectively. What is true about the binding energy per nucleon of X, Y and Z?

A.  $B_{\text{Y}}$ > $B_{\text{X}}$ and $B_{\text{Z}}$ > $B_{\text{X}}$

B.  $B_{\text{X}}$ = $B_{\text{Y}}$ and $B_{\text{X}}$ = $B_{\text{Z}}$

C.  $B_{\text{X}}$ > $B_{\text{Y}}$ and $B_{\text{X}}$ > $B_{\text{Z}}$

D.  $B_{\text{X}}$ = $B_{\text{Y}}$ + $B_{\text{Z}}$

A

A sample of a pure radioactive nuclide initially contains $N_0$ atoms. The initial activity of the sample is $A_0$.

A second sample of the same nuclide initially contains $2N_0$ atoms.

What is the activity of the second sample after three half lives?

A.  $\frac{A_0}{2}$

B.  $\frac{A_0}{4}$

C.  $\frac{A_0}{6}$

D.  $\frac{A_0}{8}$

B