Nuclear Physics

Question 1

What were the results of Rutherford’s alpha particle scattering experiment

Answer 1

most of the alpha particles passed through the foil with little or no deflection
a small number of alpha particles were deflected through angles of more than 90 degrees

Question 2

What were Rutherford’s interpretations of his results?

Answer 2

most of the atom’s mass is concentrated in a small region, the nucleus, at the centre of the atom
The nucleus is positively charged as it repels alpha particles (which are positively charged particles) that approach it too closely

Question 3

what is the count rate?

Answer 3

the number of counts divided by the time taken. (no of counts per second).

Question 4

Explain the geiger tube

Answer 4

see textbook

Question 5

range of gamma radiation in air?

Answer 5

follows inverse square law

Question 6

What does gamma radiation consist of

Answer 6

high energy photons

Question 7

What is intensity?

Answer 7

the radiation energy per second passing normally through unit area

Question 8

Why is a gamma photon emitted?

Answer 8

if a nucleus has too much energy after it has emitted an alpha or beta particle

Question 9

How does ionising radiation affect living cells?

Answer 9

it can destroy cell membranes which cause the cells to die.

It can damage vital molecules such as DNA

Question 10

What is the difference between somatic effects and genetic effects?

Answer 10

somatic- affects the health of the affected person

genetic- affects the health of future offspring

Question 11

what is the half-life?

Answer 11

the time taken for the mass oil the isotope to decrease to half its initial mass. This is the same as the time taken for the number of radioactive nuclei to halve.

Question 12

What is the activity?

Answer 12

the num per of nuclei of the isotope that disintegrate per second.

Question 13

What are the units of activity?

Answer 13

Bq

Question 14

What is the decay constant?

Answer 14

the probability of an individual nucleus decaying per second

Question 15

What is carbon dating?

Answer 15

the determination of the age or date of organic matter from the relative proportions of the carbon isotopes carbon-12 and carbon-14 that it contains.

Question 16

What is Argon dating?

Answer 16

method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock.

Question 17

What is a radioactive tracer?

Answer 17

it is used to follow the path of a substance through a system. The radioactive isotope in the tracer should have a half life which is stable enough for it to be measured and short enough to decay quickly after use. It should emit B or gamma radiation so it can be detected outside the flow path.

Question 18

state 3 industrial uses of radioactivity

Answer 18

engine wear
thickness monitoring
Power sources

Question 19

sketch a typical N-Z graph

Answer 19

see textbook

Question 20

Why do B- emitters occur to the left of the stability belt of an N-Z graph?

Answer 20

because the isotopes are neutron-rich compared with stable isotopes

Question 21

Why do B+ emitters occur to the left of the stability belt of an N-Z graph?

Answer 21

because the isotopes are proton-rich compared with stable isotopes

Question 22

what is a technetium generator?

Answer 22

it is a device that produces a source that emits gamma radiation only. see textbook for further details.

Question 23

What is binding energy?

Answer 23

the work that must be done to separate a nucleus into its constituent neutrons and protons

Question 24

What is mass defect?

Answer 24

the difference between the mass of the separated nucleons and the mass of the nucleus

Question 25

What is the binding energy per nucleon?

Answer 25

the average work done per nucleon to remove all the nucleons from a nucleus

Question 26

What is nuclear fission?

Answer 26

the process in which a large unstable nucleus splits into two fragments which are more stable than the original nucleus. The binding energy per nucleon increases in this process.

Question 27

What is nuclear fusion?

Answer 27

the process of making small nuclei fuse together to form a larger nucleus. The binding energy per nucleon increases in this process.

Question 28

Explain the process of nuclear fission

Answer 28

a nucleus absorbs a neutron and splits into two approximately equal fragments. this event releases energy and two or three neutrons. These neutrons can go on and cause further fission events, thus leading to a chain reaction.

Question 29

Why is energy released in a fission event?

Answer 29

this is because the fragments repel each other as they are both positively charged, with sufficient force to overcome the strong nuclear force trying to hold them together. The fragment nuclei and fission neutrons therefore gain kinetic energy. the two fragment nuclei are smaller and therefore more tightly bound than the original nucleus. I.e. they have more binding energy. The energy released is equal to the change of binding energy.

Question 30

What is a thermal nuclear reactor?

Answer 30

It uses process of nuclear fission. It contains control rods evenly spaced in the reactor core. The reactor core also contains control rods and a coolant (water at high pressure). It is connected to a heat exchanger. A pump is used to force the coolant through the reactor core, where it is heated. It is then put through the heat exchanger where it produces steam to drive turbines that turn electricity generators to produce electricity.

Question 31

What is the function of the control rods?

Answer 31

to absorb neutrons and prevent a chain reaction event.

Question 32

What is the function of a moderator in a reactor?

Answer 32

to slow the neutrons down

Question 33

What is the critical mass?

Answer 33

the minimum mass of a fissile material in order for a chain reaction to occur

Question 34

Describe the safety features in a nuclear reactor

Answer 34

The reactor core is a thick steel vessel which can withstand the pressure and temperature swell as absorbing some of the B and gamma radiation. The core is in a building with very thick walls to absorb radiation that escape the reactor vessel (gamma). Every reactor has an emergency shut down system (insert control rods into core). Sealed rods are removed from reactor by remote handling devices.

Question 35

How is high-level radioactive waste disposed?

Answer 35

the spent fuel rods are removed from reactor by remote handling devices and placed into cooling ponds for up to a year because they continue to release heat. The radioactive waste is then stored in sealed containers in deep trenches