nuclear reactions

Question 1

discovered nuclear reactions (fission)

Answer 1

1939 hahn and strassmann, bombarded uranium with neutrons and discovered nuclear fission. lisa meitner also part of team (mother of the atomic bomb)

Question 2

fission bomb

Answer 2

atomic bomb consists of at least 2 fissile materials of critical mass. when they are brought together suddenly an uncontrolled chain reaction occurs with an enormous release of energy

Question 3

nuclear fission

Answer 3

the splitting of a large nucleus into 2 smaller nuclei of roughly the same size with the release of energy and neutrons

Question 4

fission fragments

Answer 4

products of fission. the neutrons released are fast and can produce further fission

Question 5

chain reaction

Answer 5

occurs if a neutron from an atom that has undergone fission produces further fission

Question 6

critical size

Answer 6

by increasing the size of a sample you will reach a point where a chain reaction can occur i.e. enough neutrons available

Question 7

fissile

Answer 7

a source that will undergo fission e.g. U-235

Question 8

fermi

Answer 8

built the first nuclear reactor, chicago pile 1 in 1942. first power plant then built in 1950, EBR-1

Question 9

fuel rod

Answer 9

natural uranium or enriched with U-235

Question 10

moderator

Answer 10

made of graphite or heavy water, slows down the neutrons to produce further fission in U-235

Question 11

control rods

Answer 11

made from steel with boron. absorb neutrons in the core to slow down the reaction.

Question 12

shielding

Answer 12

usually lead, stops radiation escaping

Question 13

coolant

Answer 13

takes heat from the core to the heat exchanger. heat exchanger uses heat to produce steam and thus electricity

Question 14

environmental impact of fission reactors

Answer 14

-mining U ore: releases radon gas
-accidents in the reactor: problems with containment e.g chernobyl
-treatment of spent fuel rods (nuclear reprocessing): problems with transporting and fuelling
-radioactive waste: remaining waste products must be stored securely for long time (long T1/2)

Question 15

health hazards of ionising radiation

Answer 15

-skin burns
-cataracts, leukemia etc
-genetic birth defects
-death

Question 16

radiation damage depends on

Answer 16

-type of rad
-activity of source
-duration of exposure
-type of tissue irradiated

Question 17

minimising risks of radiation

Answer 17

-reduce time spent when using them
-tongs, shielding, protective clothing

Question 18

background radiation

Answer 18

we are all exposed to some radiation. this comes from outer space (cosmic rays), rocks in the earth’s crust e.g. radon gas, man made radioactive materials. 87% comes from natural sources

Question 19

nuclear fusion

Answer 19

this is the joining of two small nuclei to form a larger nucleus with the release of energy.

-can only occur if the 2 nuclei are forced together with enough force to overcome the coulomb repulsion between them
-energy released keeps the reaction going

Question 20

hydrogen bomb

Answer 20

uncontrolled (cold) fusion reaction example. initial high temps needed are reached by small fission bomb inside

Question 21

fission vs fusion

Answer 21

-less radioactive waste produced
-no possibility of uncontrolled runaway reaction
-deuterium readily available in oceans and can be extracted cheaply

Question 22

E = mc^2

Answer 22

mass form of energy –> mass & energy are related quantities. mass can be converted into energy + vice versa.

Question 23

mass energy conversion

Answer 23

m(products) > m(reactants) –> energy supplied
m(r) > M(p) –> energy given out
energy released as kinetic energy or gamma rays or both