Nuclear physics Flashcards Preview

Physics > Nuclear physics > Flashcards

Flashcards in Nuclear physics Deck (46):
1

Nucleon

particle in the nucleus

2

Atomic number (Z)

number of protons

3

N

number of neutrons

4

Mass number

protons and neutrons

5

Nuclide

a particle with a particular mass number

6

Isotopes

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

7

evidence for isotopes

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

8

Interactions in a nucleus

Coulomb interactions and nuclear interactions

9

Coulomb interactions

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

10

Nuclear interactions

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

11

Stability of nuclei

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)

12

unified atomic mass unit

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

13

Energy-mass equivalence

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

14

MeVc^-2

equivalent to 1 atomic mass unit

15

mass defect

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

16

nuclear binding energy

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

17

radioactive decay

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

18

characteristics of radioactive decay

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

19

half-life

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

20

radioactive decay law

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)

21

Activity (rate of decay same)

A=-dN/dt=λN=λN0e^(-λt)

22

Measuring the half-life of an isotope (long)

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

23

carbon-14 dating

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

24

why is C-14 dating possible

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

25

limitations of Carbon-14 dating

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

26

Measuring geological time

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

27

alpha decay
(what, why, how)

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

28

transmutation

alpha decay causing a change in element

29

properties of alpha particles

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)

30

beta decay for a proton in a nucleus

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

31

beta decay for a neutron

beta particle (electron) and antineutrino

32

beta decay

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

33

properties of beta particles

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

34

gamma decay

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

35

properties of gamma rays

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

36

nuclear energy levels (evidence)

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

37

biological effects of ionizing radiation

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

38

induced nuclear reactions

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

39

nuclear fission

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

40

estimation of the energy produced by fission/fusion

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

41

Nuclear fusion

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

42

evaluation of fusion

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

43

thermonuclear reactions

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

44

problems involving mass defect and binding energy

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+(Z*mass of electron); therefore Mass defect= (Z*mass of proton)+(N*mass of a neutron)- (Atomic mass-(Z*mass of electron)

45

Measuring a short half life

lnA by time

46

beta energy spectra

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