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Prelims > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

1
Q

beta -

A

n -> p + e- + v_bar

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2
Q

beta +

A

p -> n + e+ + v

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3
Q

electron capture

A

p + e- -> n + v

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4
Q

activity - production + decay

A

R(1 + e^(-lambda t)), R = N0 sigma I

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5
Q

barns to m^2

A

1b = 10^-28 m^2

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6
Q

amu to kg

A

1 u = 1.66054 x 10^-27

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7
Q

average binding energy of a nucleon

A

8 MeV

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8
Q

uncertainty principle

A

as distribution of momentum increases (lower momentum) distribution of position decrease (is everywhere)

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9
Q

what is the range of the nuclear force?

A

6fm

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10
Q

in an incident energy vs xs graph, what do the oscillations mean?

A

comes from energy being quantized. each spike represents a state. as energy increases there are more states, until there get to be such a dense number that it is represented as a smooth line.

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11
Q

What is the peak of the binding energy curve? Where is there a spike?

A

Iron 56 is the Peak, spike at He4

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12
Q

equation for radius of a nuclide

A

R = R0A^1/3

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13
Q

what is the force behind gamma decay?

A

electromagnetic

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14
Q

what’s the force behind beta decay?

A

the weak force

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15
Q

exposure rate

A

activity/distance^2

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16
Q

greys to joules/kg to rad

A

1 gy = 1 j/kg=100rad

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17
Q

what quantities can be related to each other via the uncertainty principle?

A

momentum and position, energy and time, angular momentum and angle

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18
Q

how are energy and cross section related?

A

as neutron slows down (lower energy) it has a higher cross section

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19
Q

When does the wave function look like an exponential decay

A

when E < U0

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20
Q

When does the wave function look oscillatory?

A

when E > U0

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21
Q

can we usually ignore binding energy of the electron?

A

yes

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22
Q

what are some ways you can show a nuclide is unstable using mass data?

A

Check to see if either type of beta decay is energetically favorable.

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23
Q

growth of daughter activities

A

dN2 = L1N1dt - L2N2dt, N2(t) = N0 L1/(L2 -L1)(e^-L1t - e^-L2t)

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24
Q

what assumption about growth of daughter can we make when L1 &laquo_space;L2?

A

e^-L1t = 1 which gives N2(t) = N0 L1/L2(1 - e^-L2t)

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25
Q

what is secular equilibrium?

A

in a decay chain, as time gets large, nuclei are decaying at the same rate they are being produced.

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26
Q

why is alpha decay rare at nuclei of A = 56?

A

That’s the peak of the binding energy curve. Alpha particles are less likely to break off when binding energy is high. You can also calculate Q value there and see that it is not positive.

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27
Q

Q for electron capture

A

Q = [m(x) - m(x’)]c^2 - Bn

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28
Q

Q for beta -

A

Q = [m(x) - m(x’)]c^2

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29
Q

Q for beta +

A

Q = [m(x) - m(x’) - 2m_e]c^2

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30
Q

de Broglie wavelength

A

lambda = h/p, relates wavelength and momentum

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31
Q

fermi beta decay

A

no change in parity or spin.

32
Q

gamow teller

A

0 or 1 spin change, no parity change

33
Q

first forbidden decay

A

delta J = 0, 1, 2, delta pi = 1

34
Q

second forbidden decay

A

delta J = 2, 3, delta pi = 0

35
Q

third forbidden

A

delta J = 3, 4 delta pi = 1

36
Q

fourth forbidden

A

delta J = 4, 5 delta pi = 0

37
Q

find allowed multipolarity

A

every integer in between abs(J_i - J_f) and J_i + J_f, if parity changes must be odd L for electric, even for magnetic. Opposite for no parity change.

38
Q

how does an increase in multipole order correspond to strength?

A

Increase in multipole order corresponds to a reduction in strength by approximately 10^-5

39
Q

what’s the relationship between energy and velocity?

A

E = (1/2)mv^2

40
Q

conversion between ev and J

A

1 ev = 1.602189 x 10^-19

41
Q

what force governs alpha decay?

A

nuclear force and electromagnetic

42
Q

how does alpha decay happen?

A

Tunneling process. As the width of the barrier increases, alpha decay is less likely

43
Q

Why are alpha particles more likely to be emitted than single protons/neutrons?

A

Conservation of wave function symmetry prevents single nucleon emission. Also high binding energy of the alpha particle.

44
Q

How big is the nucleus?

A

1.75 to 15 fm. Depending on the nuclide.

45
Q

Define mass defect?

A

The number of protons + the number of neutrons - the mass of the nuclide.

46
Q

What is the ground state spin parity of even-even nuclei?

A

0+

47
Q

What is usually the first excited state spin parity of even-even nuclei?

A

2+

48
Q

After how many half-lives do we usually reach secular equilibrium?

A

5ish

49
Q

how many nucleons can be stored in each level?

A

2J + 1

50
Q

How do you find the moment of inertia in a rotational band?

A

E = (hbar^2/2I)(2J + 1) where I is the moment of inertia.

51
Q

What is the promiscuity factor?

A

How far away a nuclide is from a shell closure. P = NpNn/(Np + Nn) where Np and Nn are the numbers of valence protons and electrons.

52
Q

What are the first seven magic numbers?

A

2, 8, 20, 28, 50, 82, 126

53
Q

When is a nuclei deformed?

A

If it has promiscuity factor greater than 4.

54
Q

What state will a 0+ nucleus feed?

A

0+ since they tend to feed similar states.

55
Q

What are the units of exposure?

A

Coulombs/kg or roentgens. Conversion is 3876 roentgens = 1 C/kg

56
Q

Exposure

A

Exposure = Gamma A/r^2

57
Q

Whats the difference between dose equivalent and absorbed dose?

A

The equivalent dose calculates how much damage is expected based on the absorbed dose and type of tissue.

58
Q

What are we likely to see in a fission graph?

A

A staircase pattern spaced by about 6MeV, the binding energy of a nucleon. Beware of log log plots as you can see this better on a linear scale.

59
Q

mean lifetime

A

t = 1/lambda

60
Q

What are the different cases for pairing energy?

A

0 if A odd, if nucleus is even-even then positive, if odd-odd then negative

61
Q

what leads to the formation of quantized energy orbitals?

A

nuclear potential

62
Q

what does nlj mean?

A

describes where nucleons can be. n is the principle harmonic oscillator phonon number like a frequency. l is orbital angular momentum (because we are in 3D). j is spin.

63
Q

why is g9/2 aligned?

A

because g is 4, so it is 4 +1/2

64
Q

energy of vibrational nuclei?

A

E = n_phononE_phonon

65
Q

energy of phonon in vibrational nuclei?

A

energy of first 2+ state

66
Q

is rotation collective behavior?

A

yes

67
Q

what does the collective behavior say about the speed of transitions between the states?

A

collective is faster because all the nucleons are doing the same thing. gamma lifetimes get shorter for collective states.

68
Q

energy spacing and moment of inertia

A

inversely proportional

69
Q

typical alpha energy

A

5 MeV which means non-relativistic kinematics OK

70
Q

kinetic energy of the alpha particle

A

T_alpha = Q/(1+4/A)

71
Q

ell barrier for alpha decay

A

favors decay to same state, not as strong as for beta decay though.

72
Q

energy spectrum of alpha and beta decay

A

alpha has these peaks and there are only two particles so the linear momentum is conserved and fixed. Beta has three particles emitted and so its more of a continuum.

73
Q

what does the wavefunction affect in beta decay?

A

lifetime.

74
Q

what does a change in parity say about the permitted multipoles?

A

E odd and M even

75
Q

what does no change in parity say about permitted multipoles?

A

E even and M odd

76
Q

which multipole in gamma decay is the most intense?

A

the one with the lowest l.

Prelims (4 decks)

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