5 Nuclear physics (5.1 -5.2.2)

Question 1

structure of an atom

Answer 1

a positively charged nucleus and negatively
charged electrons in orbit around the nucleus

Question 2

how may atoms form positive ions?

Answer 2

by losing electrons

Question 3

how may atoms form negative ions?

Answer 3

by gaining electrons

Question 4

relative charges of protons, neutrons, and electrons

Answer 4

proton: +1
neutron: 0
electron: -1

Question 5

proton number/atomic number

Answer 5

number of protons in the nucleus
(number of protons in a neutral atom should be the same as number of electrons)

Question 6

mass number/nucleon number

Answer 6

sum of the number of protons and neutrons in the nucleus

Question 7

Nuclides

Answer 7

type of atom with a specific number of neutrons and protons

Question 8

nuclide notation

Answer 8

chemical symbol: X
proton number Z
nucleon number: A

Question 9

to find number of neutrons

Answer 9

nucleon number - proton number

Question 10

isotope

Answer 10

are atoms of the same element that have equal number of protons but a different number of neutrons

Question 11

why do isotopes tend to be more unstable?

Answer 11

due to their imbalance of protons nad neutrons
- more likely to decay to achieve stability

Question 12

How does rutherford’s experiement provide evidence for:
a very small nucleus surrounded by mostly empty space

Answer 12

A majority of them go through the atom, because the atom is mostly empty space
While a very small number are deflected back because the nucleus is very small

Question 13

How does rutherford’s experiement provide evidence for:
A nucleus containing most of the mass of the atom

Answer 13

Some of the a-particles scattered back, caused by the small, dense nucleus

Question 14

How does rutherford’s experiement provide evidence for:
A nucleus that is positively charged

Answer 14

Some alpha particles are deflected through small atoms
Happens because the positive alpha particles are repelled by the positive nucleus which contains most of the mass

Question 15

Rutherford’s experiment procedure

Answer 15

Scattering of alpha particles by a sheet of thin metal

(Expected - alpha particles to travel through the gold foil and maybe change direction a small amount)

Question 16

Results of rutherford’s experiment

Answer 16

• most of the alpha particles PASSED STRAIGHT THROUGH the foil
• some of the alpha particles CHANGED DIRECTION but continued through the foil
• a few of the alpha particles BOUNCED BACK off the gold foil

Question 17

ionisation

Answer 17

the addition or removal of an electron from an atom

Question 18

Nuclear fission

Answer 18

the splitting of a large, unstable nucleus into two smaller nuclei

Question 19

Nuclear fission process

Answer 19

a neutron collides with an unstable nucleus, causing the nucleus to split into two smaller nuclei (daughter nuclei) as well as two or three neutrons
- gamma rays are emitted

Question 20

How to know if an nuclide equation is fission

Answer 20

there’s a neutron on the left and two daughter nuclei on the right

Question 21

Nuclear fusion

Answer 21

when two light nuclei join to form a heavier nucleus

Question 22

why is nuclear fusion hard to reproduce on earth

Answer 22

requires extremely high temperatures to maintain
- happens in stars

Question 23

Example of a nuclear fusion equation

Answer 23

Two hydrogen nuclei fusing to form a helium nucleus

Question 24

where does the energy for nuclear fusion come from

Answer 24

a very small amount of the particles mass is being converted to energy
- E = mc^2
(energy = mass x speed of light squared)

Question 25

background radiation

Answer 25

the radiation that exists around us at all times

Question 26

sources that make a significant contribution to background radiation

Answer 26

a) radon gas (in the ari) b) rocks and buildings c) rood and drink d) cosmic rays

Question 27

How can ionising radiation be measured

Answer 27

using a detector connected to a counter

Question 28

what is count rate

Answer 28

number of decays per second (counts/s)

Question 29

Examples of devices used to measure ionising radiation

Answer 29

Geiger-Muller tube (or GM tube) Photographic film Ionisation chamber scintillation counters spark counters

Question 30

Issues using radioactive isotopes with long half lives to release energ

Answer 30

ECONOMIC - high cost of storage - reduction in touirsm - loss of farming produce - reduction of land SOCIAL - fear of cancer - sickness in people/animals ENVIRONMENTAL - crop mutation - leakage into water supplies

Question 31

when is an atom unstable?

Answer 31

when it doesn't have enough binding energy to hold the nucleus together permanently due to the imbalance of neutrons and protons

Question 32

Describe the emission of radiation

Answer 32

spontaneous and random in direction

Question 33

Alpha particles (what, charge, range, penetration and ionisation)

Answer 33

What: helium nucleus (2 protons and 2 neutrons) Charge: 2+ Range in air: few cm Penetration: stopped by paper Ionisation: High

Question 34

Beta particles (what, charge, range, penetration and ionisation)

Answer 34

What: fast-moving electron Charge: -1 Range in air: few 10s of cm Penetration: stopped by as few mm of aluminium Ionisation: medium

Question 35

Gamma rays (what, charge, range, penetration and ionisation)

Answer 35

What: EM wave Charge: 0 Range in air: infinite Penetration: REDUCED by a few mm of lead Ionisation: low

Question 36

What do ionising effects depend on

Answer 36

Kinetic energy and Electric charge

Question 37

How does kinetic energy affect the ionisation effect?

Answer 37

Higher the kinetic energy of the raidaiton, the more ionising it is - alpha has highest mass and is most ionising (think 1/2mv^2)

Question 38

How does electric charge affect the ionisation effect?

Answer 38

Greater the charge the more ionising - alpha has largest charge and is most ionising

Question 39

Alpha particles and ionising effect

Answer 39

Most ionising : they leave a dense trail of ions behind them, affecting virtually every atom they meet, because of this they lose their energy and so have a short range (short range = relatively harmlessm but dangerous if ingested)

Question 40

When will a particle be deflected in an electric field

Answer 40

if it has charge (so not gamma)

Question 41

When will a particle be deflected in a magnetic field

Answer 41

if it has charge and is moving perpendicular to it

Question 42

Alpha particles are deflected towards what (magnetic field)

Answer 42

the negative plate as they have a positive charge

Question 43

Beta particles are deflected to what (magnetic filed)

Answer 43

positive plate as they have negative charge

Question 44

Gamma rays are deflected to what (magnetic field)

Answer 44

Not deflected, travels straight between the plates as they have no charge

Question 45

Why are alpha particles deflected less (and travel further) than beta particles in magnetic fields

Answer 45

Alpha particles are heavier than beta particles

Question 46

radioactive decay

Answer 46

change in an unstable nucleus that can result in the emission of alpha particles or beta particles or gamma radiation - changes are spontaneous and random

Question 47

what happens to the nucleus during alpha or beta decay

Answer 47

the nucleus changes to that of a different element

Question 48

define half life (of a particular isotope)

Answer 48

the time taken for half the nuclei of that isotope in any sample to decay