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Friday, October 25, 2019

A graph of nucleon number A against proton number Z is shown in Fig. 7.1.


Question 15
A graph of nucleon number A against proton number Z is shown in Fig. 7.1.


Fig. 7.1

The graph shows a cross (labelled P) that represents a nucleus P.

Nucleus P decays by emitting an α particle to form a nucleus Q.
Nucleus Q then decays by emitting a β particle to form a nucleus R.

(a) On Fig. 7.1, use a cross to represent
(i) nucleus Q (label this cross Q), [1]

(ii) nucleus R (label this cross R). [1]


(b) State the name of the class (group) of particles that includes the β particle. [1]


(c) The quark composition of one nucleon in Q is changed during the emission of the β particle.
Describe this change to the quark composition. [1]
[Total: 4]





Reference: Past Exam Paper – November 2018 Paper 23 Q7





Solution:
(a)
(i) Q plotted at (82, 210)

{21484P             - - - >   AZQ      +          42α
Proton number and nucleon number should be conserved.

214 = A + 4
A = 214 – 4 = 210

84 = Z + 2
Z = 84 – 2 = 82

The emission of an α-particle from a nucleus will cause the proton number to decrease by two and the nucleon number to decrease by four.}

(ii) R plotted at (83, 210)

{21082Q - - ->                AZR      +          0-1β

210 = A + 0
A = 210

82 = Z – 1
Z = 82 + 1 = 83}


(b) lepton(s)

{The β particle is a lepton. It is not made up of quarks, so it is not a hadron.}


(c)
up down down changes to up up down
or udd uud
or down changes to up
or d u         

{The nucleus Q is 21082Q.
Number of proton in Q = 82
Number of neutron in Q = 210 – 82 = 128

Nucleus R is 21083R.
Number of proton in R = 83
Number of neutron in Q = 210 – 83 = 127

So during the decay of Q into R, a neutron is changed into a proton.
Quark composition of neutron = udd
Quark composition of proton = uud

A d-quark has changed into a u-quark.}

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