PHY431 Midterm Spring 2000
1
5/2/2000
Short-Answer Questions
1. Define alpha, beta, and gamma radiation. For each type, write down an example of a reaction in
which such radiation is emitted.
alpha radiation
: emission of strongly bound 2p-2n cluster (He nucleus):
238
U
→
234Th
+
α
beta radiation
: emission (or capture) of electron plus neutrino, or emission of positron plus neu-
trino:
64
Cu
→
64
Ni +
e
−
+ e
+
+
ν
e
is
β
−
radiation.
gamma radiation
: emission of high-energy photons from nuclear de-excitation
2. In what experimental features does scattering of alpha particles as observed by Rutherford differ
significantly from predictions from the Thomson “plum-pudding” model of the atom?
occasional large-angle scatters, which could not occur in a Thomson model.
3. For Rutherford scattering off an Aluminum (
A
=27,
Z
=13) foil, calculate the alpha particle energy
for which deviations from the Rutherford scattering formula ought to occur.
for
K
> (
e
2
/4
πε
0
)(
zZ/R
) = (1/137)(2
×
13/(1.2
×
27
1/3
fm)) = 10.4 MeV (ignoring the size of the
α
)
4.
List all the known leptons, their spins, and their electric charges.
All are spin-½ fermions; the charged leptons:
e
−
,
µ
−
,
τ
−
and the uncharged neutrinos:
e
,
,
.
5.
List all the known quarks, their spins, and their electric charges.
All are spin-½ fermions; the charge +
2
/
3
quarks:
u
,
c
, t, and the charge
−
1
/
3
quarks:
d
,
s
,
b
.
6. List the interactions that
quarks and leptons have (an-
swer
Y
or
N,
or specify):
7.
List the carriers,
with spin and charge
, of the
(i)
Electromagnetic force: photon:
γ
, charge 0, spin 1
(ii)
Weak interaction:
W
±
,
Z
0
, spin 1
(iii)
Strong interaction: 8 gluons, charge 0, spin 1
8.
Describe two experimental methods used to study the nu-
clear charge distribution.
i)
electron scattering off nuclei
ii)
muonic atoms
9.
Sketch the expected nuclear charge density as function of
radius for a spherically symmetric
A
=58 nucleus. Label
the axes with the proper nuclear density (MeV/fm
3
) and
distance scales (fm).