Atomic And Nuclear Physics

Front 1

Each type of atom that contains a unique combination of protons and neutrons is called a ___

Back 1

nuclide

Front 2

______ are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons.

Back 2

Isotopes

Front 3

The total number of protons in the nucleus of an atom is called the _____ of the atom, and is given the symbol Z.

Back 3

atomic number

Front 4

The ______ of the nucleus is the total number of nucleons, that is, protons and neutrons in the nucleus. The mass number is given the symbol A and can be found by the equation Z + N = A.

Back 4

mass number

Front 5

____ are negatively-charged particles that have 1/1835 the mass of the hydrogen atom.

Back 5

Electrons

Front 6

______ are relatively large particles that have almost the same mass as a hydrogen atom and a positive charge equal in magnitude (but opposite in sign) to that of the electron.

Back 6

Protons

Front 7

______ have almost the same mass as the proton, but are electrically neutral

Back 7

Neutrons

Front 8

Atoms consists of a dense nucleus of protons surrounded by electrons traveling in discrete orbits at fixed distances from the ______.

Back 8

nucleaus

Front 9

_____ used the knowledge of the atomic particles to give us a model of the atom.

Back 9

Bohr

Front 10

An electron in one of these orbits or shells has a specific or discrete quantity of energy (quantum). When an electron moves from one allowed orbit to another allowed orbit, the energy difference between the two states is emitted or absorbed in the form of a single quantum of radiant energy called a photon.

Back 10

Bohr Atom

Front 11

Opposites attract; like charges repel
Electrical force between two protons that are separated by a distance of 10 -20 meters is about 1012 newtons

Back 11

Electrostatic forces exist between charged particles

Front 12

between two protons that are separated by a distance of 10 -20 meters is about 10 -24 newtons. Exist between any two objects that have mass

Back 12

Gravitational forces

Front 13

A strong attractive force that is independent of charge. It acts equally only between pairs of neutrons, pairs of protons, or a neutron and a proton
This force has a very short range; it acts only over distances approximately equal to the diameter of the nucleus (10 -13 cm). The attractive nuclear force between all nucleons drops off with distance much faster than the repulsive electrostatic force between protons

Back 13

Nuclear Force

Front 14

______ is defined as Uranium in which the isotope Uranium-235 has a concentration greater than its natural value (0.72%).

Back 14

Enriched Uranium

Front 15

The enrichment process will also result in the byproduct of depleted ______.
Commercial Fuel - 3% to 5%
Navy Reactors – 92% to 95%
Weapons Grade - > 90%

Back 15

Uranium

Front 16

________ is defined as Uranium in which the isotope Uranium-235 has a concentration less than its natural value.
Although _______ is referred to as a by-product of the enrichment process, it does have uses in the nuclear field and in commercial and defense industries.
Depleted < 0.72%

Back 16

Depleted Uranium

Front 17

Depleted = ______%

Back 17

< 0.72%

Front 18

The difference between the mass of the atom and the sum of the masses of its parts is called the _______

Back 18

mass defect (delta m).

Front 19

_____is defined as the amount of energy that must be supplied to a nucleus to completely separate its nuclear particles (nucleons).

Back 19

Binding energy

Front 20

1 amu is equivalent to _____ of energy
Binding energy can then be calculated.

Back 20

931.5 MeV

Front 21

_____ is the emission of alpha particles (helium nuclei)
When an unstable nucleus ejects an alpha particle, the atomic number is reduced by 2 and the mass number decreased by 4.

Back 21

Alpha decay

Front 22

_____ is the emission of electrons of nuclear rather than orbital origin.
These particles are electrons that have been expelled by excited nuclei and may have a charge of either sign.

Back 22

Beta Decay

Front 23

Beta Decay: If both energy and momentum are to be conserved, a third type of particle _____ must be involved.
The ________ is associated with positive electron emission, and its antiparticle, the ______, is emitted with a negative electron.

Back 23

the neutrino / antineutrino

Front 24

Negative electron emission, represented as -e, -, or simply as e- or -, effectively converts a neutron to a proton, thus increasing the atomic number by one and leaving the mass number unchanged.
This is a common mode of decay for nuclei with an excess of neutrons, such as fission fragments below and to the right of the neutron-proton stability curve

Back 24

Beta Minus

Front 25

Positively charged electrons are known as positrons.
Except for sign, they are nearly identical to their negatively charged cousins.
When a positron, represented as +e, +, or simply as e+ or +, is ejected from the nucleus, the atomic number is decreased by one and the mass number remains unchanged.
A proton has been converted to a neutron.

Back 25

Beta Plus

Front 26

Nuclei having an excess of protons may capture an electron from one of the inner orbits which immediately combines with a proton in the nucleus to form a neutron.
The electron is normally captured from the innermost orbit (the K‑shell), and, consequently, this process is sometimes called K‑capture.

Back 26

Electron Capture

Front 27

The usual method for an excited nucleus to go from the excited state to the ground state is by the emission of a gamma. However, in some cases the gamma ray (photon) emerges from the nucleus only to interact with one of the innermost orbital electrons and, as a result, the energy of the photon is transferred to the electron.

Back 27

Internal Conversion

Front 28

The conversion electron is ejected from the atom with kinetic energy equal to the gamma energy minus the binding energy of the orbital electron.
An orbital electron then drops to a lower energy state to fill the vacancy, and this is accompanied by the emission of characteristic x‑rays.

Back 28

Internal Conversion

Front 29

Commonly occurs immediately after particle emission; however, the nucleus may remain in an excited state for a measurable period of time before dropping to the ground state at its own characteristic rate.

Back 29

Isomeric transitions

Front 30

A nucleus that remains in such an excited state is known as a nuclear isomer because it differs in energy and behavior from other nuclei with the same atomic number and mass number.
The decay of an isomer to a lower energy level is called an isomeric transition.
It is also possible for the excited isomer to decay by some alternate means, for example, by beta emission.

Back 30

Isomeric Transition

Front 31

______ is the property of certain nuclides of spontaneously emitting particles or gamma radiation.
The decay of radioactive nuclides occurs in a random manner, and the precise time at which a single nucleus will decay cannot be determined. However, the average behavior of a very large sample can be predicted accurately by using statistical methods.

Back 31

Radioactivity

Front 32

This probability per unit time that an atom of a nuclide will decay is known as the radioactive decay constant, .
The units for the decay constant are inverse time such as 1/second, 1/minute, 1/hour, or 1/year.
These decay constant units can also be expressed as second-1, minute-1, hour-1, and year-1.

Back 32

Radioactive Decay Constant

Front 33

The time for half the radioactive nuclei in any sample to undergo radioactive decay. After two half-lives, there will be one fourth the original sample, after three half-lives one eighth the original sample, and so on.

Back 33

Radioactive Half-life

Front 34

A _____is a unit of measure of the rate of radioactive decay equal to 3.7 x 1010 disintegrations per second. This is approximately equivalent to the number of disintegrations that one gram of radium-226 will undergo in one second

Back 34

Curie

Front 35

A _____ is a more fundamental unit of measure of radioactive decay that is equal to 1 disintegration per second. Currently, the curie is more widely used in the United States, but usage of the becquerel can be expected to broaden as the metric system slowly comes into wider use.

Back 35

becquerel

Front 36

The conversion between curies and becquerels is ____
_

Back 36

1 curie = 3.7 x 1010 becquerels

Front 37

Exists when a radioactive nuclide is decaying at the same rate at which it is being produced.
Since the production rate and decay rate are equal, the number of atoms present remains constant over time.

Back 37

Radioactive Equilibrium

Front 38

Occurs when the parent nuclide and the daughter nuclide decay at essentially the same rate.
For _______ to occur, the parent must have a long half‑life when compared to the daughter. An example of this type of compound decay process is barium-140, which decays by beta emission to lanthanum-140, which in turn decays by beta emission to stable cerium-140.

Back 38

Transient Radioactive Equilibrium

Front 39

In an _____ reaction between a neutron and a target nucleus, there is no energy transferred into nuclear excitation
Momentum and kinetic energy of the "system" are conserved although there is usually some transfer of kinetic energy from the neutron to the target nucleus. The target nucleus gains the amount of kinetic energy that the neutron loses

Back 39

elastic scattering

Front 40

In the elastic scattering reaction, the laws governing the reaction are:

Back 40

Conservation of Momentum ( mv )

Conservation of Kinetic Energy ( ½ mv2 )

Front 41

In ______, the incident neutron is absorbed by the target nucleus, forming a compound nucleus.
The compound nucleus will then emit a neutron of lower kinetic energy which leaves the original nucleus in an excited state.

Back 41

inelastic scattering

Front 42

The nucleus will usually, by one or more gamma emissions, emit this excess energy to reach its ground state.
For the nucleus that has reached its ground state, the sum of the kinetic energy of the exit neutron, the target nucleus, and the total gamma energy emitted is equal to the initial kinetic energy of the incident neutron.

Back 42

Ineleastic Scattering

Front 43

In ______ the incident neutron enters the target nucleus forming a compound nucleus. The compound nucleus then decays to its ground state by gamma emission

Back 43

radiative capture

Front 44

In a ______ reaction the incident particle enters the target nucleus forming a compound nucleus. The newly formed compound nucleus has been excited to a high enough energy level to cause it to eject a new particle while the incident neutron remains in the nucleus.

Back 44

particle ejection

Front 45

The measure of how far the energy level of a nucleus is above its ground state

Back 45

Excitation Energy (E sub exc)

Front 46

The ______ is the minimum excitation energy required for fission to occur.
For fission to be possible, the change in binding energy plus the kinetic energy must equal or exceed the critical energy (BE + KE > Ecrit).

Back 46

critical energy (E sub crit)

Front 47

A ______ is composed of nuclides for which fission is possible with neutrons of any energy level. What is especially significant about these nuclides is their ability to be fissioned with zero kinetic energy neutrons (thermal neutrons).
Keyword “thermal neutrons”
Subset of fissionable material

Back 47

fissile material

Front 48

A fissile material is composed of nuclides for which fission is possible with neutrons ____. What is especially significant about these nuclides is their ability to be fissioned with zero kinetic energy neutrons (thermal neutrons).
Keyword “thermal neutrons”
Subset of fissionable material

Back 48

of any energy level

Front 49

A _______ is composed of nuclides for which fission with neutrons is possible. All fissile nuclides fall into this category. However, also included are those nuclides that can be fissioned only with high energy neutrons.
Keyword “High (fast) neutron”

Back 49

fissionable material

Front 50

A fissionable material is composed of nuclides for which _______. All fissile nuclides fall into this category. However, also included are those nuclides that can be fissioned only with high energy neutrons.
Keyword “High (fast) neutron”

Back 50

fission with neutrons is possible

Front 51

Because several of the fissile nuclides do not exist in nature, they can only be produced by nuclear reactions (transmutation). The target nuclei for such reactions are said to be _______
______ are materials that can undergo transmutation to become fissile materials.

Back 51

Fertile material

Front 52

______ process where neutron absorption reactions that do not result in fission lead to the production of new nuclides

These nuclides can, in turn, be transmuted again or may undergo radioactive decay to produce still different nuclides. The nuclides that are produced by this process are referred to as _________ products

Back 52

Transmutation

Front 53

______ If a reactor contains fertile material in addition to its fissile fuel, some new fuel will be produced as the original fuel is burned up, All US Light Water Reactors are _______

Back 53

Conversion / “Converters”

Front 54

______ Reactors that are specifically designed to produce fissionable fuel are called_______. In such reactors, the amount of fissionable fuel produced is greater than the amount of fuel burnup.

Back 54

Breeding / "breeder" reactors

Front 55

delta m=
m(sub)p=
m(sub)n=
m(sub)e=
m(sub)atom=
Z=
A=

Back 55

delta m= mass defect (amu)
m(sub)p= mass of a proton (1.007277 amu)
m(sub)n= mass of a neutron (1.008665 amu)
m(sub)e= mass of electron (0.000548597 amu)
m(sub)atom= mass of nuclide X (amu)
Z= atomic number (number of protons)
A= mass number (number of nucleons

Front 56

Binding Energy per Nucleon: As the atomic number and the atomic mass number increase, the _______ within the nucleus increase due to the greater number of protons in the heavy elements.

Back 56

repulsive electrostatic forces

Front 57

Why only Heavy Nucleon’s easily fissionable?

Back 57

The heaviest nuclei require only a small distortion from a spherical shape (small energy addition) for the relatively large coulomb forces forcing the two halves of the nucleus apart to overcome the attractive nuclear forces holding the two halves together.

Front 58

Heaviest nuclei are _____

Back 58

easily fissionable compared to lighter nuclei.

Front 59

The measure of how far the energy level of a nucleus is above its ground state is called the ____.

Back 59

excitation energy

Front 60

These include nuclides that can be fissioned only with high energy neutrons

Back 60

fissionable material

Front 61

This type of reactor is designed to produce fissionable fuel

Back 61

breeding

Front 62

Describe the curve of Binding Energy per Nucleon vs mass number and give a qualitative description of the reasons for its shape.

Back 62

Because the repulsive forces are increasing, less energy must be supplied, on the average, to remove a nucleon from the nucleus. The BE/A has decreased.
The BE/A of a nucleus is an indication of its degree of stability

Front 63

The most probable pair of fission fragments for the thermal fission of the fuel uranium-235 have masses of about ______.
Note that the vertical axis of the fission yield curve is on a logarithmic scale. Therefore, the formation of fission fragments of mass numbers of about 95 and 140 is highly likely.
(obj 29)

Back 63

95 and 140

Front 64

Alpha radiation is normally produced from the radioactive decay of heavy nuclides and from certain nuclear reactions. The _______ consists of 2 neutrons and 2 protons, so it is essentially the same as the nucleus of a helium atom.

Back 64

Alpha Particle

Front 65

Because it has no electrons, the alpha particle has a charge of ____This positive charge causes the alpha particle to strip electrons from the orbits of atoms in its vicinity. As the alpha particle passes through material, it removes electrons from the orbits of atoms it passes near

Back 65

+2.

Front 66

When a high energy gamma passes close enough to a heavy nucleus, the gamma completely disappears, and an electron and a positron are formed.

Back 66

Pair Production

Front 67

The gamma interacts with an orbital or free electron; however, in this case, the photon loses only a fraction of its energy.
The actual energy loss depending on the scattering angle of the gamma. The gamma continues on at lower energy, and the energy difference is absorbed by the electron. This reaction becomes important for gamma energies of about 0.1 MeV and higher.

Back 67

Comton Scattering

Front 68

For this reaction to take place, the original gamma must have at least 1.02 MeV energy. Any energy greater than 1.02 MeV becomes kinetic energy shared between the electron and positron. The probability of pair-production increases significantly for higher energy gammas

Back 68

Pair Production:

Front 69

When a low energy gamma strikes an atom, the total energy of the gamma is expended in ejecting an electron from orbit. The result is ionization of the atom and expulsion of a high energy electron.

This reaction is most predominant with low energy gammas interacting in materials with high atomic weight and rarely occurs with gammas having an energy above 1 MeV. Annihilation of the gamma results. Any gamma energy in excess of the binding energy of the electron is carried off by the electron in the form of kinetic energy

Back 69

Photoelectric Effect

Front 70

Positively charged electrons are called _____. Except for the positive charge, they are identical to beta-minus particles and interact with matter in a similar manner.
______ are very short-lived, however, and quickly are annihilated by interaction with a negatively charged electron, producing two gammas with a combined energy (calculated below) equal to the rest mass of the positive and negative electrons.

Back 70

positrons

Front 71

Neutrons have no electrical charge. They have nearly the same mass as a proton (a hydrogen atom nucleus).
A ____has hundreds of times more mass than an electron, but 1/4 the mass of an alpha particle.

The source of _____ is primarily nuclear reactions, such as fission, but they may also be produced from the decay of radioactive nuclides.
Because of its lack of charge, the _____is difficult to stop and has a high penetrating power.

Back 71

Neutron

Front 72

A unit of measure for the rate of radio-active decay equal to 3.7 x 1010 dis-integrations per second is the ____.

Back 72

Curie

Front 73

A unit of measure for the rate of radio-active decay equal to 1 disintegration per second is the ____.

Back 73

Becquerel

Front 74

____ exists when a radioactive nuclide is decaying at the same rate at which it is being produced.

Back 74

radioactive equilibrium

Front 75

In which of the following is no energy transferred into the nuclear reaction?

Back 75

elastic scattering

Front 76

Which laws of conservation apply to an elastic collision between a neutron and a nucleus?

Back 76

conservation of momentum and kinetic energy

Front 77

In which of the following does the newly formed compound nucleus decay to its ground state by emitting a gamma?

Back 77

radiative capture