particles and radiation

Question 1

what is specific charge?

Answer 1

the specific charge of a particle is the charge divided by the mass.

Question 2

what is the strong nuclear force?

Answer 2

the strong nuclear force is the force that holds the nuclei of a stable isotope together so that they do not disintegrate. the nuclear force overcomes the electrostatic force of repulsion between the protons and the neutrons.

Question 3

what is the range of the strong nuclear force?

Answer 3

3-4fm around the diameter of a small nucleus

Question 4

when is beta radiation emitted

Answer 4

when an unstable neutron in the nucleus changes into a proton.

Question 5

when is gamma radiation emitted?

Answer 5

it is emitted by a nucleus with too much energy following alpha or beta emission.

Question 6

what is a photon?

Answer 6

a photon is a pocket of energy emitted from a source in a random direction.

Question 7

what is the photo electric effect?

Answer 7

the photo electric effect is the emission of electrons from a metal surface when a light is directed at the surface.

Question 8

how do you calculate the energy of a photon?

Answer 8

e=hf

where h is a constant refers to as the plank constant = 6.63x10 -34

Question 9

wha is the power of a laser beam and how is it calculated?

Answer 9

the power of a laser beam is the energy per second transfers by the electrons

the power of the beam = nhf
where n is the number of photons in the beam passing a fixed point each second.

Question 10

what happens when matter and antimatter particles meet?

Answer 10

they destroy each other and radiation is released.

Question 11

when is a positron emitted?

Answer 11

when a proton changes into a neutron. do not occur naturally.

Question 12

what did DIrac’s theory of antiparticles predict that every particles anti particle would do?

Answer 12

• annihilate both the particle ad itself converting the total mass into photons
• has the same rest mass as the particle
• has exactly the opposite charge to the the particle if the particle has a charge

Question 13

when does pair production occur?

Answer 13

when a photon with sufficient energy passes past a nucleus or an electron it can suddenly change into a particle and a antiparticle pair.

Question 14

what is an electron volt?

Answer 14

an electron volt is the energy transferred when an electron moves though a potential difference of one volt.

Question 15

how do you calculate the minimum energy of a photon produced in annihilation?

Answer 15

hfmin = E0

where E0 = the rest energy of the particle.

Question 16

how do you calculate the minimum energy of a photon needed for pair production?

Answer 16

hfmin = 2E0

Question 17

what is momentum?

Answer 17

mass multiplied by its velocity.

Question 18

if two protons approach each other they repel each other and then move off in different directions, why is this so?

Answer 18

the electromagnetic force between the two charged particles is due to virtual photons (can’t detect them directly). if they were intercepted then the force would stop acting.

Question 19

explain the interaction model

Answer 19

if two people are on skate boards and on of them throws a ball to the other, the one that throws the ball will recoil backwards and the one that caught the ball would also recoil backwards. in this model the ball is the virtual particle.

Question 20

what does the strong nuclear force do?

Answer 20

holds the neutrons and the protons in the nucleus together.

Question 21

when does a neutrino or an antineutrino interact with another particle?

Answer 21

a neutrino can interact with neutron and change it into a proton. a beta - particle is emitted as a result of this.
an antineutrino cab interact with a proton and change it into a neutron. here a beta + particle is created and emitted as a result off the change. these interactions are due to the exchange of particles referred to as w bosons.

Question 22

why are w bosons different to photons?

Answer 22

they have a non-zero rest mass
have a very short range of no more than about 0.001fm
are positively charged or negatively charged.

Question 23

what role does a w boson had in beta decay?

Answer 23

the w boson in each case meets a neutrino or anti neutrino, changing them into a beta - particle or a beta + particle

the w- boson decays a B- particle and an antineutrino
the w+ boson decays a B+ particle and a neutrino