nuclear physics

Question 1

what is mass energy equivalence

Answer 1

In Eistein’s theory of relativity:
1. mass can be converted into energy
2. energy can be converted into masse

Question 2

equation of mass-energy equivalence

Answer 2

E = m * c^2

E=energy(J)
m=mass(kg)
c=light speed

Question 3

define mass deflect

Answer 3

the difference btw the mass of a nucleus and the sum of individual masses of its protons and neutrons

Question 4

define binding energy

Answer 4

the minimum external energy required to completely separate all the neutrons and protons of a nucleus to infinity

Question 5

why is there binding energy

Answer 5

1. the mass of individual protons and neutrons is more than the nucleus formed by them
   => due to mass-energy equivalence, energy must be added to break nucleus into constituent protons and neutrons

Question 6

equation for mass deflect

Answer 6

∆m = A*m_p + (X-A) * m_n - m_total

Question 7

equation for binding energy

Answer 7

E = ∆m * c^2
E=energy
∆m=mass deflect
c=light speed

Question 8

what is binding energy per nucleon

Answer 8

1. binding energy divided by the number of nucleons
2. the higher the value => more stable the nucleus

Question 9

what to include in binding energy per nucleon graph

Answer 9

Checklist on what to include (and what not to include) in an exam question asking you to draw a graph of binding energy per nucleon against nucleon number:

• You will be expected to draw the best fit curve AND a cross to show the anomaly that is helium
• Do not begin your curve at A = 0, this is not a nucleus!
• Make sure to correctly label both axes AND units for binding energy per nucleon
• You will be expected to include numbers on the axes, mainly at the peak to show the position of iron (56Fe)

Question 10

explain what nuclear fusion and fission

Answer 10

1. fusion: 2 nuclei combine to form one heavier nucleus
2. fission: a single large nucleus divides to form 2 smaller daughter nuclei

Question 11

describe change of binding energy per nucleon with increasing proton number

Answer 11

1. small proton number:
   - force of attraction btw nucleon dominate repulsive electrostatic attraction btw protons
   - binding energy per nucleon increases as A increases (increase with very big gradient)
   - under right condition, fusion happens
2. Iron is most stable, has the highest binding energy per nucleon
3. large proton number:
   -repulsive electrostatic force btw protons dominate
   - binding energy decreases as A increases (decrease with very smaller gradient)
   - breaks large unstable nucleus into smaller, stable nuclei

Question 12

understand nucleus decay is spontaneous and random

Answer 12

1. spontaneous:
   - decay of a nucleus is not affected by other nucleus or the chemical reaction or external factors
2. random:
   - cant predict when a particular nucleus will decay and each nucleus in the sample has same chance to decay every second

Question 13

define decay constant

Answer 13

the probability that an individual nucleus will decay per unit time interval

Question 14

define activity

Answer 14

the rate of decay of nuclei of a radioactive source

Unit: becquerel (Bq) m= 1 s^-1

Question 15

equation of activity

Answer 15

A = N * λ = ∆N/∆t

A=activity
N=number of undecayed nucleus
λ=decay constant

Question 16

define half life

Answer 16

mean time taken for half of the radioactive nuclei in a sample to decay

Note:
-it is also the time for activity or count rate to half
- t1/2 is constant for each particular substance

Question 17

equation for radio active decay

Answer 17

X = X0 * e ^ (- λ * t)

X=N(number of radioactive nuclei left), A(activity) or R (count rate) at time t
X0= N, A or R at t=0
λ=decay constant (s^-1)
t=time(s)

Question 18

equation for half life

Answer 18

t1/2 = ln(2) / λ

λ=decay constant