Nuclear physics

Question 1

Nucleon

Answer 1

particle in the nucleus

Question 2

Atomic number (Z)

Answer 2

number of protons

Question 3

N

Answer 3

number of neutrons

Question 4

Mass number

Answer 4

protons and neutrons

Question 5

Nuclide

Answer 5

a particle with a particular mass number

Question 6

Isotopes

Answer 6

nuclides of the same element, same number of protons but different neutrons

Question 7

evidence for isotopes

Answer 7

bainbridge mass spectrometer;charged atoms are fired at a specific velocity passed by an opposite plate and landing at different places reveals having different isotopes

Question 8

Interactions in a nucleus

Answer 8

Coulomb interactions and nuclear interactions

Question 9

Coulomb interactions

Answer 9

A charged particle will never enter the nucleus because as the distance to it reached 0, then the repulsion would be infinitely large.

Question 10

Nuclear interactions

Answer 10

Where the coulomb repulsion is overcome, as on sun, but much larger gravities.

Question 11

Stability of nuclei

Answer 11

if strong force and coulomb repulsion are balanced; if not, unstable
for it to be stable neutrons must be ≥ number of protons (because coulomb force goes further than strong force)

Question 12

unified atomic mass unit

Answer 12

1/12 of the mass of a carbon-12 atom

Question 13

Energy-mass equivalence

Answer 13

mass and energy are equivalent in that a change in mass can also be regarded in the same change in energy
E=mc^2

Question 14

MeVc^-2

Answer 14

equivalent to 1 atomic mass unit

Question 15

mass defect

Answer 15

difference in mass between mass of nucleus and the mass of separate nucleons

Question 16

nuclear binding energy

Answer 16

energy required to separate the nucleus into different components (MeV)
E=mc^2 (binding energy= mass defect* c^2)

Question 17

radioactive decay

Answer 17

when an unstable nucleus emits an alpa or beta particle or gamma ray photon resulting in a daughter nucleus which is more stable

Question 18

characteristics of radioactive decay

Answer 18

random and spontaneous (with less nuclei, probability does not change and the number of decays reduce)

Question 19

half-life

Answer 19

time taken for the initial activity of the radioactive sample to halve

Question 20

radioactive decay law

Answer 20

the rate of decay is proportional to the number of undecayed nuclei (dN/dt=-λ(decay constant)*N(number of undecayed nuclei))
N=N0e^(-λt)

Question 21

Activity (rate of decay same)

Answer 21

A=-dN/dt=λN=λN0e^(-λt)

Question 22

Measuring the half-life of an isotope (long)

Answer 22

number of decays by time
mass of the sample and calculating the number of atoms N
using A=λN to calculate λ constant
using T1/2= ln2/λ

Question 23

carbon-14 dating

Answer 23

once an organism has died, the amount of carbon-14 will fall with decay, which can be used to tell how old it is

Question 24

why is C-14 dating possible

Answer 24

c14 is unstable, but c12(also present) is stable (proportion constant in living)
neither can be replenished after death
c14 decays

Question 25

limitations of Carbon-14 dating

Answer 25

after 5000 years, the activity is too small to be measured

Question 26

Measuring geological time

Answer 26

age of rocks can be determined by the decay of Uranium-238 to lead-206
(the rock must contain uranium as an impurity in its structure, but reject lead so all that is left is results of the decay)
the half life is approximately the age of the earth

Question 27

alpha decay

what, why, how

Answer 27

an alpha particle (2 protons+2 neutrons) (also described as the nucleus of a helium-4)
causes transmutation
tends to be emitted by nuclides with too many neutrons for stability

Question 28

transmutation

Answer 28

alpha decay causing a change in element

Question 29

properties of alpha particles

Answer 29

travel at about 10^7ms^-1
deflected by electric and magnetic fields (double positive charges)
low penetration
causes intense ionization (change of charge from e- changes)

Question 30

beta decay for a proton in a nucleus

Answer 30

beta + particles (positrons, or antimatter of an electron (same mass, opposite charge)) and neutrino (v)(neutral particle with little or no mass) are emitted

Question 31

beta decay for a neutron

Answer 31

beta particle (electron) and antineutrino

Question 32

beta decay

Answer 32

both types are transmutations
beta+ because of too few electrons
beta because of too many electrons

Question 33

properties of beta particles

Answer 33

typically at 10^8ms^-1
deflected by electric and magnetic fields as expected for a single negative
causes moderate ionization
medium penetration

Question 34

gamma decay

Answer 34

gamma ray (part of electromagnetic spectrum)
does not cause transmutation
after alpha or beta decay, the exited state may gamma decay to reduce energy

Question 35

properties of gamma rays

Answer 35

travel at 3*10^8
not deflected by electric and magnetic fields
cause little ionization
high penetration

Question 36

nuclear energy levels (evidence)

Answer 36

alpha particles always emitted at same speed from a nuclide. gamma rays always emitted with same energy.

Question 37

biological effects of ionizing radiation

Answer 37

may damage dna (can be repaired, but if not could cause cancerous cells)
short term: could cause burns in high dosage; could kill organs
long term: risks of cancer, but no link between dosage and type of cancer

Question 38

induced nuclear reactions

Answer 38

the reactions can be forced by by striking a stable nucleus with another nucleus, particle or gamma ray photon

Question 39

nuclear fission

Answer 39

when a stable nucleus absorbs a slow moving neutron making it unstable and causing a split into two large fragments and some neutrons
the importance of neutron emission is possible chain reactions

Question 40

estimation of the energy produced by fission/fusion

Answer 40

=the increase in binding energy (binding energy of mother nucleus is seen as negative)

Question 41

Nuclear fusion

Answer 41

combing of two nuclei, which results in high levels of energy emission

Question 42

evaluation of fusion

Answer 42

possible because the binding energies of two low mass nuclei can fuse to create a larger nuclei of higher binding energy.
coulomb repulsion prevents it working, and requires the collision to happen at high speeds causing the energy released to mainly be kinetic energy
attractive because of large quantities of deuterium and tritium (H-2+H-3) and much less radioactive waste, but extremely hard to make it happen and remain constant

Question 43

thermonuclear reactions

Answer 43

reactions that require immense heat to keep the reaction occurring, happens in a star.

Question 44

problems involving mass defect and binding energy

Answer 44

E=mc^2
Mass defect= total mass of separated nucleons- mass of nucleus
Sometimes given in atomic masses, so incorporate electrons
Atomic mass= nuclear mass+(Zmass of electron); therefore Mass defect= (Zmass of proton)+(Nmass of a neutron)- (Atomic mass-(Zmass of electron)

Question 45

Measuring a short half life

Answer 45

lnA by time

Question 46

beta energy spectra

Answer 46

continuous with a range of speeds (thus energy levels) up to a maximum. the anitneutrino takes remaing energy away