radiation

Question 1

nuclear binding energy

Answer 1

energy required to separate the nucleus into its consistents

Question 2

example of binding energy and the interchangableness of mass and energy

Answer 2

when measuring the mass of nucleus and the mass of its consistents, the mass of the nucleus is always lower, the difference is known as the mass defect/deficit. the mass that is lost and converted into energy and released when the nucleons fuse to form a nucleus

Question 3

fission

Answer 3

splitting of a large nucleus into two daughter nuclei. it occurs in very large nuclei, which are unstable, and occurs completely randomly, however it can also be induced. energy is released during fission because smaller nuclei have a higher binding energy per nucleon.

Question 4

which nuclei undergo fusion or fission

Answer 4

nuclei smaller than iron undergo fusion, nuclei larger than iron undergo fission

Question 4

fusion

Answer 4

the opposite of fission, it is where two smaller nuclei join together to form one large nucleus. it only occurs in fairly small nuclei. energy is released during fusion because the larger nucleus has a much higher binding energy per nucleon. Fusion releases more energy than fission however fusion can only occur at very high temperatures

Question 5

binding energy per nucleon

Answer 5

the binding energy of the nucleus divided by the number of nucleons in the nucleus

Question 6

the conditions for fusion

Answer 6

Extremely high temperatures: A massive amount of energy is required to overcome the electrostatic force of repulsion between nuclei, as they are both positively charged
very high densities: Make sure that there are enough colliding protons undergoing fusion

Question 7

control rods

Answer 7

absorb neutrons to prevent them going to induce further fission reactions-the further the rods are inserted, the ore neutrons absorbed and so fewer reactions occur

Question 8

the moderator

Answer 8

responsible for slowing down neutrons released in fission reactions so they can reach thermal speeds and go on to induce further fission reactions

Question 9

fuel rods

Answer 9

consist of a fissile material- each rod contains less than the critical mass and so reactions don’t become uncontrolled

Question 10

coolant

Answer 10

carries away the thermal energies produced by the reactions to generate steam and turn generators to generate electricity

Question 11

dermal neutron

Answer 11

slow moving neutron so it can be absorbed to induce fission

Question 12

critical mass

Answer 12

the minimal amount of fissile substance needed to maintain a steady flow of fission reactions

Question 13

Background radiation

Answer 13

when taking readings of a radioactive source it is important to measure the background radiation first, then subtract this value to find the corrected count, which is the actual count rate caused by the source

Question 14

sources of background radiation

Answer 14

-radon gas: released from rocks
-artificial sources: caused by nuclear weapons testing and nuclear meltdowns
-cosmic rays: enter the earths atmosphere from space
-rocks containing naturally occurring radioactive isotopes

Question 15

radiation

Answer 15

where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable

Question 16

alpha radiation (α)

Answer 16

helium nucleus, 2-10 cm range in air, highly ironising, absorbed by paper

Question 17

beta radiation (β)

Answer 17

fast moving electron, 1m range in air, weakly ionising, absorbed by a few mm of aluminium

Question 18

gamma radiation (γ)

Answer 18

EM wave, infinite range in air, very weakly ionising, absorbed by lead or thick concrete

Question 19

how can you find which type of radiation is being emitted from a source

Answer 19

1) using a GMtube , find the background rate
2) place the source near the GM tube and find its count rate
3) place paper between the source and GM tube, if the count rate falls by a lot, the emission is alpha
4) repeat this using aluminium and or lead depending on results

Question 20

the random nature of nuclear decay

Answer 20

radioactive decay is a random and spontaneous process meaning you can’t predict when the next decay will occur. A given radioactive nucleus will have a constant decay probability denoted by λ. λ is the probability of a nucleus decaying per unit time. can be found by finding the change in the number of nuclei of a sample per time, over the initial number of nuclei.
∆N/∆t=-λN

Question 21

effect of exponential decay

Answer 21

because decay is exponential, the time taken for the number of nuclei to halve will be constant
N=Noe^ λt
lnN=lnNo-λt
ln(0.5No)=lnNo-λt
λt=ln2

Question 22

activity

Answer 22

the number of nuclei that decay per second, this is proportional to the number of nuclei (N) in the sample, where the decay constant (λ) is the constant of proportionality: A= λN