Physics Basics Flashcards
What is the term to describe two atoms whose nuclei contain the same number of protons but different numbers of neutrons?
Isotopes
What is the term to describe two atoms whose nuclei contain the same number of neutrons but different numbers of protons?
Isotones
What is the term to describe two atoms whose nuclei contain the same number of nucleons but differ in their nuclear energy states?
Isomers
What is the mass of an amu (atomic mass unit)?
1/12 the mass of a C-12 atom = 1.66x10-27 “in between” weight of proton/neutron
What is an electron volt (eV)?
The kinetic energy acquired by an electron passing through a potential difference of 1V
What is the energy equivalent (E0) [E=mc2] of an electron at rest?
E0 = 0.511 MeV
What is the energy equivalent [E=mc2] of 1 amu?
931.5 MeV
Electrons can exist only in those orbits for which the angular momentum of the electron is an integral multiple of ____.
h/2π (h = Planck’s constant = 6.626x10-34 J-sec)
What is the maximum number of electrons in an orbit?
2(n2)
What are valence electrons?
Electrons in the outermost shell (lowest binding energy)
What impact does the Z of an atom have on the Coulomb forces/binding energy of electrons?
Higher Z = higher binding energy due to greater nuclear charge
What are the four fundamental forces of nature, in order of strength?
- Strong nuclear force (strongest)
- Electromagnetic force
- Weak nuclear force
- Gravity
What equation describes the amount of energy carried in a photon?
E = hv (h = Planck’s constant = 6.626x10-34 J-sec)
As the wavelength of a photon becomes shorter, what happens to frequency? Energy?
As wavelength shortens…
- Frequency - higher
- Energy - higher
What is the A of an atom (i.e. I-131)? What is the Z of an atom?
A = mass number = number of nucleons Z = atomic number = number of protons **In a stable nucleus, A should = 2*(Z)
What is the Half Value Layer (HVL)? What equation describes this?
HVL = amount of material required to attenuate beam to 1/2(E0) HVL = [-ln(0.5)/u] where u(mu) is a constant of the material
What is pair production? What is the threshold energy of the incident photon required for pair production to occur?
Pair production = photon passes close to nucleus, resulting in energy conversion into positron-electron pair Threshold energy = >/=1.022 MeV
What is the energy dissipated by an ionizing event?
~33eV
What is the difference between x-rays and gamma-rays?
x-rays produced extranuclearly, g-rays produced intranuclearly **otherwise identical in nature and properties
Where to x- and game-rays fall on the electromagnetic spectrum?
Short-wavelength end
What are alpha particles?
Nuclei of helium atoms consisting of two protons and two neutrons with a net positive charge Can be produced by an accelerator or by decay of heavy nucleotides (i.e. uranium, radium)
Which sources of radiation are directly ionizing? Indirectly ionizing?
charged particles - directly ionizing (sufficient kinetic energy to disrupt atomic structure of absorber) electromagnetic radiation - indirectly ionizing (when absorbed, give up energy produce fast-moving charged particles that produce damage)
What is the Compton process?
Incident photon strikes outer shell electron, ejecting the electron (transfer of kinetic energy) and diverting the path of the now lower energy incident photon (scattering)
Following a Compton interaction, is the wavelength of the scattered photon higher or lower than that of the incident photon?
lower (lower energy)
An interaction proceeds as follows: an incident photon strikes an inner-shell electron, giving up all of its energy and resulting in ejection of the electron from its shell. What type interaction has just occurred?
Photoelectric effect
An interaction proceeds as follows: an incident photon strikes an inner-shell electron, giving up all of its energy (ie photoelectric effect) and resulting in ejection of the electron from its shell. What is the result of this ejection?
- Electron from an outer shell “drops down” to fill the vacancy - Emission of characteristic x-rays by this transfer of energy
The mass absorption coefficient for which of the following process varies based on Z: -Compton process -photoelectric effect
photoelectric effect
What is a free radical?
atom/molecule with an unpaired orbital electron in the outer shell
Which sources of radiation are directly ionizing? Indirectly ionizing?
charged particles - directly ionizing (sufficient kinetic energy to disrupt atomic structure of absorber) electromagnetic radiation - indirectly ionizing (when absorbed, give up energy produce fast-moving charged particles that produce damage)
What is the Compton process?
Incident photon strikes outer shell electron, ejecting the electron (transfer of kinetic energy) and diverting the path of the now lower energy incident photon (scattering)
What is the photoelectric effect?
Incident photon strikes inner shell electron and is entirely absorbed, providing sufficient energy to overcome binding energy and extra kinetic energy. The vacancy is immediately filled by an outer shell electron, producing characteristic x-rays
Which of the following depends on the Z of the material? 1) Compton process 2) photoelectric effect
Photoelectric effect
What equation describes the kinetic energy of an electron ejected through a photoelectric interaction?
hv - E(B) hv = energy of incident photon E(B) = binding energy of electron
How does the mass absorption coefficient for photoelectric absorption correlate to Z?
appx Z^3
A radioactive nuclide has Z > 82. How is this species most likely to decay?
Emission of alpha particle
What is an alpha particle composed of?
2 protons, 2 neutrons (helium nucleus)
A radioactive nuclide undergoes alpha decay. What impact does this have on the mass number (A) and atomic number (Z) of the atom?
A decreases by 4 (2 protons, 2 neutrons) Z decreases by 2 (2 protons)
What is the general reaction for alpha decay?
(A,Z)X –> (A-4, Z-2)Y + (4,2)He + Q Q = disintegration energy, appears as kinetic energy of alpha particle and product nucleus
What does the activity of a radioactive material describe?
Number of disintegrations per unit time =gN where gamma is the decay constant
What units can be used to describe radioactive activity?
1 Bq = 1 disintegration per second 1 Ci = 3.7E10 Bq (1mCi = 3.7E7 Bq)
Given the decay constant (g) for a radioactive nuclide, what is the half-life?
T1/2 = 0.693/g
All elements with Z > ___ are radioactive.
Z > 82
All naturally occurring radioactive elements can be grouped in to 3 series: uranium, actinium, and thorium. These series all terminate at stable isotopes of what element?
All terminate at stable isotopes of lead (A = 206, 207, and 208)
What is the half-life of Co-60?
5.26yrs
Co-60 emits two monoenergetic photons (g-rays) of what energy? Avg energy?
1.17 and 1.33 MeV Avg = 1.25 MeV
What is the HVL (Pb) for 60-Co?
11mm Pb
What is the half-life of Sr-90? Y-90?
28.9 yrs
90-Sr emits ___ rays of what energy?
Beta-rays, 2.27MeV
What is the physical half-life of 131-I? What else is needed to calculate the effective half-life?
T1/2 = 8d Biological half-life is required to calculate effective halflife 1/Teff = 1/Tphys + 1/Tbio
What is the rest mass of a proton? A neutron?
E=mc2
Proton = 938 MeV
Neutron = 939 MeV
What is the mass defect? What is the energy equivalent (E=mc2) of this value?
Mass difference between an atom and the sum of its constituent parts (ie, the energy required to form an atom)
Energy equivalent = binding energy of the nucleus
What is the binding energy of an electron?
Minimum energy required to rip electron from atom
As the number of protons in a given element increases to >20, what happens to the neutron:proton ratio?
Elements with Z>20 have a greater neutron:proton ratio
What equation describes the decay constant (lambda)?
Lambda = Ln(2)
t1/2
=the probablility that a single nucleus within an element will undergo decay in a given time
*negative in exponential decay equation because probability decrease over time
What is activity (A) and what are its units?
Activity = rate of decay
Unit = Bq (1 disintegration/sec)
1 Curie (Ci) = 3.7x1010 Bq
What is the Emax of B-particles emitted from Sr-90?
2.27 MeV
What is the half-life of Sr-90?
t1/2 = 28 years
1 Ci = ??? Bq
1Ci = 3.7 x 1010 Bq
1Bq = 1 disintegration/sec
How can the mean life (Ta) of a radioactive atom be determined?
Ta = 1.44 x t1/2
In an element with a high n/p ratio (ie too many neutrons), what are the products of ß decay?
conversion of neutron –> proton
emission of electron (ß-/negatron), antineutrino, and Q (disintegration energy)
What type of B decay results in emission of an antineutrino?
ß- decay
What type of B decay occurs in an element with a low n/p ratio (ie too many protons)?
B+ decay
conversion of proton –> neutron
emission of B+, neutrino, and Q
Positron (B+) is inherently unstable and destined for annhilation event, thus ultimately emitting 2x0.511 MeV photons
What nuclear processes can result in an element with an excess of protons?
Positron emission
Electron capture
How is 99mTc produced?
99mTc has short t1/2 of 6hrs, so must be supplied as 99Mo
99Mo is supplied to hospitals after extraction from the neutron-irradiated uranium (235U) targets
