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3.2.1.2 Stable and unstable nuclei

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Time: 92

Marks: 81

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Q1. A carbon-14 nucleus undergoes β–^ decay, forming a new nucleus, releasing a β–^ particle and one other particle which is difficult to detect. (a) Write down the proton number and the nucleon number of the new nucleus. proton number ............................................................................................... nucleon number ............................................................................................. (b) Name the particle which is difficult to detect. ........................................................................................................................ (c) Name the baryons and leptons involved in the decay. baryons ........................................................................................................... leptons ............................................................................................................. (d) Give the quark structure for the neutron and the proton. neutron ........................................................................................................... proton ............................................................................................................. Hence state the quark transformation that occurs during β–^ decay. ........................................................................................................................ (Total 7 marks) Q2. (a) (i) Determine the charge, in C, of a nucleus. ............................................................................................................. .............................................................................................................

(b) An α particle is the same as a nucleus of helium, He. The equation Th Ra + α represents the decay of thorium by the emission of an α particle. Determine (i) the values of X and Y, shown in the equation, X = ..................... Y = ..................... (ii) the ratio ............................................................................................................. ............................................................................................................. ............................................................................................................. (3) (Total 6 marks) Q4. (a) An unstable nucleus, , can decay by emitting a β–^ particle. (i) What part of the atom is the same as a β–^ particle? ............................................................................................................. (1) (ii) State the changes, if any, in A and Z when X decays.

change in A ......................................................................................... change in Z. ......................................................................................... (2) (b) In the process of β–^ decay an anti-neutrino is also released. (i) Give an equation for this decay. ............................................................................................................. (1) (ii) State and explain which conservation law may be used to show that it is an anti-neutrino rather than a neutrino that is released. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (iii) What must be done to validate the predictions of an unconfirmed scientific theory? ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (Total 8 marks)

(ii) If there are eight alpha decays involved in the sequence of decays from to deduce how many β–^ decays are involved. answer = ......................................... (3) (Total 11 marks) Q6. A neutral atom of a radium isotope may be represented by. (a) (i) Name the constituents of this atom and state how many of each are present. ............................................................................................................. ............................................................................................................. ............................................................................................................. (3) (ii) Which constituent of an atom has the largest specific charge? ............................................................................................................. (1) (iii) This isotope of radium decays by β–^ decay to form an element with symbol, Ac. Write down an equation that represents this decay. (4)

(b) is a neutral atom of a different isotope of radium. State a possible value for A and for Z. A: .................................................................................................................. Z: .................................................................................................................. (2) (Total 10 marks) Q7. Alpha decay is a process by which an unstable isotope of an element may decay. (i) State what is meant by isotopes. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (2) (ii) Complete this equation for alpha decay. (2) (iii) Calculate the specific charge of an alpha particle, stating an appropriate unit.

(i) Complete the following decay equation. (1) (ii) The α particle is emitted from a stationary nucleus at a speed of 9.3 × 10^6 m s−1. Calculate the recoil speed of the daughter nucleus. recoil speed ........................... ms− (2) (iii) Show that, when a stationary nucleus decays, the kinetic energy of the recoiling cerium nucleus is only about 3% of the kinetic energy of the emitted α particle. (3) (Total 8 marks) Q9. (a) The table below contains data for four different nuclei, P, Q, R and S. Nuclei Number of neutrons Nucleon number P 5 11

Q 6 11 R 8 14 S 9 17 (i) Which nucleus contains the fewest protons? nucleus .............................................. (1) (ii) Which two nuclei are isotopes of the same element? nuclei ................................. and ................................. (1) (iii) State and explain which nucleus has the smallest specific charge. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (2) (iv) Complete the following equation to represent β–^ decay of nucleus R to form nucleus X.

(Total 1 mark)

M1. (a) 7,14 (1) (b) (anti) neutrino (1) (c) proton, neutron (1) electron, (anti) neutrino (1) (d) udd (1) uud (1) d → u (1) [7] M2. (a) (i) (charge) = 92 × 1.60 × 10– = 1.47 × 10–17^ (C) (1) (ii) (magnitude of ion charge) = 3( e ) (1) number of electrons (= 92 – 3) = 89 (1) 4 (b) X: number of nucleons [or number of neutrons plus protons or mass number] (1) 239 (1) Y: number of protons [or atomic number] (1) 94 (1) 4 [8] M3. (a) (i) neutron (1) (ii) electron (1) (iii) neutron (1) 3

or hypothesis rejected 2 [8] M5. (a) repulsive then attractive (1) short range (if distance quoted must be of order fm) (1) correct distance for cross over (accept range 0.1 – 1.0 fm) (1) 3 (b) (i) a helium nucleus (accept 2p and 2n) (1) 1 (ii) (↓92↑238) U → (↓90↑234) Th (+↓2↑4)α (1) 2 (c) (i) same atomic number/proton number (1) different number of neutrons/nucleons (1) 2 (ii) evidence of subtraction of mass number or atomic number (1) (thus atomic number decreases to) 76 (1) (atomic number of lead is 82 therefore) 6 (82 – 76) beta decays (1) 3 [11] M6. (a) (i) 88 protons (1)

140 neutrons (1) 88 electrons (1) 3 (ii) electron (1) 1 (iii) (1)(1)(1)(1) 4 (b) 228 ± 10 (1) 88 (1) 2 [10] M7. (i) same atomic number/number of protons different mass/nucleon number/different number of neutrons 2 (ii) 2 (iii) = 4.8 × 10^7 Ckg– 4 (iv) strong nuclear force is short range no effect at distances larger 3 fm

[ or give s = 0.0286 or 2.86% ] Allow ecf from values in (b)(ii). [ or = = 0.0286 or 2.86% ] When ecf is applied, 3rd^ mark is only available for answers between 2.5% and 3.5%. 3 [8] M9. (a) (i) Q / boron / B ✓ 1 (ii) P and R / R and P ✓ 1 (iii) R ✓ 6 / 14 is smallest fraction / 0.43 smallest ratio / 4.13 × 10^7 C / kg ✓ Cannot get second mark if not awarded first mark 2 (iv) One mark for each correct symbol on rhs Ignore −ve sign on e. Can have neutrino with 0,0 on answer lines Ignore any subscript on neutrino 3

(b) (i) repulsive below / at 0.5 fm (accept any value less or equal to 1 fm) ✓ attractive up to / at 3 fm (accept any value between 0.5 and 10 fm) ✓ short range OR becomes zero OR no effect ✓ Can get marks from labelled graph Don't accept negligible for 3rd^ mark 3 (ii) interaction: electromagnetic / em ✓ (virtual) photon/ γ ✓ 2 [12] M10. A [1]