Particles and Nuclides

Question 1

What is the specific charge of a particle?

Answer 1

The charge per unit mass, and the units are Ckg-1

Question 2

What is the charge and mass of a proton?

Answer 2

• Charge: +1.60 x 10-19 C

- Mass: 1.673 x 10-27kg

Question 3

What is the charge and mass of a neutron?

Answer 3

• Charge: 0 C

- Mass: 1.675 x 10^-27

Question 4

What is the charge and mass of an electron?

Answer 4

• Charge: -1.60 x 10^-19

- Mass 9.11 x 10^-31

Question 5

Why are there some unstable and stable nuclei?

Answer 5

1. For nuclei to be stable there is the strong nuclear force between the protons and neutrons which is stronger than the electromagnetic repulsion between the protons
2. The strong nuclear force also acts between neutrons as otherwise it would be easy to remove neutrons from the nuclei

Question 6

What is the strong nuclear force?

Answer 6

1. Hold the nuclei together and keeps them stave

2. It is attractive up to distance of about 3 fm and repulsive at range of about 0.4 fm

Question 7

Whta is the separation of the nucleons in a stable particle?

Answer 7

1. At separations of about 0.4 fm, the magnitude of the strong nuclear force is zero and the force is neither attractive or repulsive
2. This is the equilibrium portions for the nucleons where the resultant force on each nucleon is zero
3. In a stable nucleon, this the separation of each nucleon
4. At a separation of 3fm, the strong force is dropped to zero

Question 8

What is alpha decay?

Answer 8

-Emission of two protons and two neutrons which are joined together (a helium nucleus)

Question 9

How do unstable nuclei become more stable?

Answer 9

By the process of radioactive decay: alpha, beta, gamma

Question 10

What is beta decay?

Answer 10

Decay of a neutron into a proton and an electron and an antineutrino, which are subsequently emitted from the nucleus

Question 11

What is gamma emission?

Answer 11

Involves the protons and neutrons inside the nucleus losing energy and emitting a gamma photon as part of the process

Question 12

What are neutrinos and antineutrinos?

Answer 12

• The neutrino, is a natural almost mass less fundamental subatomic particle that rarely interacts with matter
• The antineutrinos are antiparticles of the neutrino
• There are three forms of neutrino: the electron neutrino; the muon neutrino and the tau neutrino

Question 13

What is the cloud chamber?

Answer 13

• To detect ionising nuclear radiation (beta, alpha, gamma)
• Created artificial clouds by rapidly explaining air saturated with water vapour inside a sealed chamber
• Pass X-Rays through chambers and the X rays leave wide cloudy tracks inside the chamber (did this as he suspected clouds form on charged particles in the atmosphere)

Question 14

What are the results of the cloud chamber with alpha, beta, gamma?

Answer 14

1. Highly Ionising Alpha: leaves broad, straight definite length tracks
2. Ionising beta: left thin straight or curved tracks (depending on how high their energy was)
3. Weakly ionising gamma: left no tracks at all

Question 15

What is the spark counter?

Answer 15

• Only detects highly ionising alpha particles
• When the air particles are ionising by the alpha particles the charged particles produced cause a spark to be formed, and that spark jumps across the 5000V gap between the gauze and the wire
• The spark can be seen, heard and counted by an observer or with a microphone
• Useful to show that alpha particles have v short range in air

Question 16

Why does beta and gamma not show up in a spark counter?

Answer 16

Beta and gamma do not ionise enough of the air between the metal gauze and the thin wire underneath

Question 17

What is a Geiger Muller counter?

Answer 17

1. Ionising radiation enters the GM tube through thin mica window (alpha or beta) or through the window or sides of the counter (gamma)
2. Low pressure inert gas inside the detector (helium, neon or argon) is ionised producing a cascade of changed particles that are attracted to oppositely charged electrodes
3. The small pulse of current produced by the moving charge is detected by the electronic counter, which registers a ‘count’
4. GC can detect alpha, beta, gamma and spark and cloud can’t do all

Question 18

What is rest mass energy?

Answer 18

It is the amount of energy related by converting all of the mass of a particle at rest into energy using E=mc^2, where m is the rest mass of the particle and C is the speed of light

Question 19

What is a mega electron volt?

Answer 19

Usually the energy of nuclear particles is given in there units and it is equivalent to 1.6 x 10^-19 J

Question 20

What are antiparticles?

Answer 20

1. All particles have a corresponding antiparticle
2. Each particle-antiparticle pair has the same mass and therefore the same rest-mass energy, but they have opposite properties such as their charge
3. They are fundamental particles

Question 21

What happens during a particle antiparticle interaction?

Answer 21

1. When a particle meets its corresponding antiparticle their will annihilate and they total mass is converted to energy in the form of two gamma ray photons
2. Two photons are always producing during particle-antiparticle annihilation in order to conserve momentum
3. The total energy of the gamma photon is equal tot eh total rest energies of the particle-antiparticle pair in order to conserve energy

Question 22

What is pair production?

Answer 22

1. The opposite process to annihilation and in this case a photon with enough energy can interact with a. large nucleus and be converted direction into a particle-antiparticle pair
2. The rest energy of an electron (and therefore a positron) is 0.51MeV and so in order to create this pari the ton must have enough energy to create both particles so 1.02 MeV.

Question 23

Why is there a minimum energy for paid production?

Answer 23

Energy of photon needs to provide at least the rest masses of the electron and the positron

Question 24

How do mercury atoms become excited in a fluorescent tube?

Answer 24

1. Electrons passing through tube collide with electrons in mercury atoms
2. Transferring energy/atom gains energy from collision
3. Causing orbital electrons/ electrons in mercury atom to move to higher energy level

Question 25

Explain how the excited mercury atoms emit photons in a fluorescent tube

Answer 25

1. Each excited electron relaxes to a lower energy level

2. Emitting a photon of energy equal to the energy difference between the levels