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.}
No comments:
Post a Comment
If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation