Atomic structure

Question 1

Z

Answer 1

atomic number (number of protons in the atom)

Question 2

letter designated for atomic number

Answer 2

Z

Question 3

What does atomic number represent?

Answer 3

number of protons in the atom

Question 4

A

Answer 4

mass number (protons + neutrons)

Question 5

atoms with same Z, but different A:

Answer 5

Isotope, same number of protons but different number of neutrons (different number of neutrons)

Question 6

How many electrons are in the inner shell?

Answer 6

2

Question 7

What is the K-shell

Answer 7

inner most electron shell holding two electrons

Question 8

K, L, M number of electrons

Answer 8

2, 8, 18

Question 9

What is the “binding force”?

Answer 9

attractive forces between negatively charged electrons and positively charged protons.

Question 10

What electron shell has the highest binding force?

Answer 10

K-shell. strength of the binding force is inversely proportional to the square of the distance between the nucleus and the electrons

Question 11

What is the mass defect of the nucleus?

Answer 11

Difference in the mass of the individual nucleons measured separately compared to their mass when bound in the nucleus When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is less than the mass of the individual nucleons when considered separately. The difference is the binding energy of the nucleus.

Question 12

When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is _____ than the mass of the individual nucleons when considered separately.

Answer 12

When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is LESS than the mass of the individual nucleons when considered separately.

Question 13

The graph shows an estimated x-ray spectrum for a molybdenum anode x-ray tube. What do the “spikes” represent?

Answer 13

The energy emitted by a outer shell electron that has filled a K-shell vacancy (characteristic radiation).

During the production of x-rays within an x-ray tube, the accelerated electrons can strike an electron of the target directly and eject the electron. The vacancy is filled by electrons from an outer electron shell. The energy differences between the outer and inner shell is emitted as a photon. The “spike” observed on the graph is associated with the distinct energy difference of the electron energy levels that have filled the inner-shell vacancy. For diagnostic x-ray tubes only ejection of k-shell electrons is relevant, as these photons have high enough energy not to be filtered by the tube envelope and additional filtration.

Question 14

binding energy of any nuclide can be calculated by:

Answer 14

The binding energy can be calculated by subtracting the atomic weight from the sum of the weight of the individual nucleons and electrons.

The total binding energy of an atom is the total amount of energy required to hold the individual particles together, or, conversely, is the amount of energy required to break the atom apart.

Question 15

electron binding energy is defined by

Answer 15

the amount of energy required to ionize an atom

Question 16

An inner shell vacancy is filled with an electron with simultaneous release of an electron from the same atom, resulting in 2 vacancies

Answer 16

Auger effectd/Auger electron

An Auger electron is an electron that is emitted, rather than a photon, when lower level vacancies are filled. Auger electrons can be emitted from any atom. When an L-shell electron fills a K-shell vacancy, another L-shell electron can be emitted rather than a photon. The Auger electron carries off the extra energy rather than a photon, as would otherwise be expected. The emission of an Auger electron leaves 2 vacancies. In heavier atoms, cascades of photons can occur as these vacancies are filled.

Question 17

In order to maintain nuclear stability in large nuclei, what happens to A?

Answer 17

A increases (A= protons +neutrons). Specifically, neutrons increase

In order to offset the coulomb repulsion of the protons as the nuclei get heavier, additional neutrons are needed in the nucleus. Because the neutron does not have a charge but is still affected by the nuclear force, the total binding energy per nucleon increases within the nucleus. This increase also increases the stability of the atom. Thus, as the nucleus increases, a higher neutron-to-proton ratio is necessary.

Question 18

Photons with wavelengths in the electromagnetic regions that can cause ionization events do so because?

Answer 18

Absorbed energy in the atom exceeds the electron binding energy

Question 19

How does an electron lose energy in matter?

Answer 19

Electrons lose energy as they move through matter due to both collisional and radiative losses.

The electrons may collide with other particles or may lose energy due to other interactions within the electromagnetic field of the atom. An approximation of the ration of radiative energy losses to collisional energy losses is approximately (ZE/800), where E is the electron energy in MeV and Z is the atomic number of the target nuclide.

Question 20

indirect measure of photon energy or the hardness of a beam

Answer 20

Half-value layer

Question 21

isobar

Answer 21

same A (mass number), different Z (atomic number)

the way to remember:

IsobAr(same A)

Question 22

alpha particle

Answer 22

alpha particle = Helium nucleus without electrons

2 protons, 2 neutrons

2+ charge

Alpha particles are very heavy and contain high amounts of energy (4-10 MeV). Their speed is ~20000km/s and they interact with matter, causing much ionization over a very short distance.

Question 23

What is alpha decay?

Answer 23

alpha decay

an alpha particle (containing two neutrons and two protons) is ejected from the nucleus. An alpha particle is identical to the nucleus of a helium atom.

All nuclei with the atomic number (Z) greater than 82, are considered unstable. These are considered “neutron-rich” and undergo alpha decay commonly.

Alpha particles are very heavy and contain high amounts of energy (4-10 MeV). Their speed is ~20000km/s and they interact with matter, causing much ionization over a very short distance.

Question 24

What is the Z and A for an alpha particle, and how is this typically represented for elements undergoing alpha decay?

Answer 24

there are 2 protons and 2 neutrons in an alpha particle (aka, a helium nucleus)

A (mass number: protons + neutrons) = 4

Z (atomic number: protons only) = 2

Question 25

Is the number of electrons in a neutral atom denoted by A or Z?

Answer 25

Z!

Z = atomic number (number of protons)
To have a neutral atom, protons = electrons. Therefore # of electrons in a neutral atom = Z

Question 26

Isotone

Answer 26

Isotone: are atomic species that share the same number of neutrons, and differ in the number of protons.

Same Z (number of Protons) = isotoPes

Same A (number of nucleons) = isobArs

Same N (number of Neutrons) = isotoNes

Question 27

Answer 27

Isotones

Question 28

Answer 28

IsotoPes: same Z (same # of protons), different A (mass number, aka different # of neutrons)

Question 29

Answer 29

IsobAr: same A (mass number), different Z

aka, different elements with the same mass number

Question 30

Which is more pentrating: charged particulate radiation or photons?

Answer 30

photons are more penetrating than charged particulate radiation

Question 31

types of isobaric transitions

Answer 31

beta decay and positron decay isobAric means the Atomic number is the same. Z changes.

Question 32

when an unstable atomic nucleus decays by converting a neutron into a proton with the emission of an anti-neutrino:

Answer 32

beta minus decay

Question 33

type of decay

Answer 33

beta minus

Question 34

when does beta decay occur?

Answer 34

when nuclei have an ustable, excess number of neutrons relative to the number of protons.

Question 35

What nuclear decay occurs to the left of the blue line?

Answer 35

beta minus decay.

too many neutrons –> beta minus decay

Question 36

what type of nuclear decay happens towards the top of the band of stability?

Answer 36

alpha decay

too many protons and neutrons

Question 37

what type of nuclear decay happens to the right of the red line?

Answer 37

beta plus emission

Question 38

Z of _____ are structurally stable (and therefore not radioactive)

Answer 38

20