nuclear physics

Question 1

Describe how the strong nuclear force between two nucleons varies with the
separation of the nucleons quoting suitable values for separation.

Answer 1

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)

Question 2

An unstable nucleus can decay by the emission of an alpha particle.
(i) State the nature of an alpha particle.

Answer 2

a helium nucleus (accept 2p and 2n) (1)

Question 3

(a) The nucleus of a particular atom has a nucleon number of 14 and a proton number of
6.
(i) State what is meant by nucleon number and proton number.

Answer 3

) nucleon number is the number of protons and neutrons OR mass number
proton number is the number of protons OR atomic number

Question 4

The nucleus of a particular atom has a nucleon number of 14 and a proton number of
6.
Calculate the number of neutrons in the nucleus of this atom.

Answer 4

14 – 6 = 8

Question 5

The nucleus of a particular atom has a nucleon number of 14 and a proton number of
6.
Calculate the specific charge of the nucleus.

Answer 5

specific charge = 6 × 1.6 × 10–19 /(14 × 1.66 × 10–27 )
specific charge = 4.1 × 107
(C kg–1)

Question 6

The specific charge of the nucleus of another isotope of the element is 4.8 × 107
Ckg–1
.
(i) State what is meant by an isotope

Answer 6

isotopes are variations of an element that have same
proton/atomic number
but different nucleon number OR different number of neutrons

Question 7

The specific charge of the nucleus of another isotope of the element is 4.8 × 107
Ckg–1
Calculate the number of neutrons in this isotope.

Answer 7

4.8 × 107
 = 6 × 1.6 × 10–19 /(A × 1.66 × 10–27)
A = 6 × 1.6 × 10–19/(4.8 × 107
 × 1.66 × 10–27)
A = 12
Number of neutrons = 12-6

Question 8

What are isotopes?

Answer 8

(atoms with) same number of protons/same atomic number (1)

different number of neutrons/mass number/ nucleons

Question 9

One of the isotopes of nitrogen may be represented by N.

(i) State the number of each type of particle in its nucleus.

Answer 9

(i) 7 protons (1)
8 neutrons (1)

Question 10

State what is meant by the specific charge of a nucleus and give an appropriate unit
for this quantity.

Answer 10

the ratio of charge to mass of nucleus

C kg−1

Question 11

Nucleus X has the same nucleon number as nucleus Y. The specific charge of X is 1.25
times greater than that of Y.
(i) Explain, in terms of protons and neutrons, why the specific charge of X is greater
than that of Y.

Answer 11

number of protons and neutrons the same or number of neutrons less or
mass the same
but more protons therefore greater charge

Question 12

A stable atom contains 28 nucleons.

Write down a possible number of protons, neutrons and electrons contained in the atom.

Answer 12

number of protons = number of electrons (e.g.14) (1)

number of protons + number of neutrons = 28

Question 13

Alpha decay is a process by which an unstable isotope of an element may decay.
(i) State what is meant by isotopes.

Answer 13

same atomic number/number of protons

different mass/nucleon number/different number of neutrons

Question 14

Explain why the alpha particle, once outside the nucleus, is unaffected by the strong
nuclear force.

Answer 14

strong nuclear force is short range
no effect at distances larger 3 fm
(except any distance less than 10 fm)

Question 15

Under certain conditions a γ photon may be converted into an electron and a positron.
(a) What is this process called?

Answer 15

pair production

Question 16

Explain why there is a minimum energy of the γ photon for this conversion to take
place and what happens when a γ photon has slightly more energy than this value.

Answer 16

the γ ray must provide enough energy to provide
for the (rest) mass (1)
any extra energy will provide the particle(s) with
kinetic energy (1)

Question 17

Under suitable conditions, a γ photon may be converted into two other particles rather than
an electron and positron.
Give an example of the two other particles it could create.

Answer 17

any pairing of a particle with its corresponding

antiparticle (e.g. p + anti-p )