Physics Exam 1

The small energy values of quanta or **photons** are usually expressed in ______ (eV)

electronvolts

a particle representing a quantum of light or other __electromagnetic__ radiation; carries energy proportional to the radiation frequency but has zero rest mass.

photon

1 eV = ?

1\.60 X 10^-19 J

Which decay equation is this?

alpha; ***charge and number of nucleons must be conserved, must be the same on right and left sides of the equation***

Which decay equation is this?

beta minus

Which decay equation is this?

beta positive; the **positron** is ejected from the nucleus; the neutron remains in the nucleus so the atomic mass remains the same, but the atomic number decreases by one

Which decay equation is this?

electron capture

Which decay equation is this?

gamma

Which decay scheme is this?

beta minus

Which decay scheme is this?

beta positive; the difference between mass-energy of parent neutral atom and daughter neutral atom must be at least two times the electron mass energy (1.02 MeV) for positron emission; parent atom emits a positron and must rid itself of an atomic electron to become a neutral atom

Which decay scheme is this?

electron capture

Which decay scheme is this?

internal conversion

•Suppose that a radioactive parent isotope X decays to a daughter product D with a half-life Tp  

• D decays to G with a half-life Td  

If Tp>Td then after some period of time the ratio of the activity of D to the activity of X will approach a constant value

radioactive equilibrium

Which type of equilibrium is Tp≫Td?

secular

Which type of equilibrium is Tp≳Td?

transient

•occurs when Tp >> Td

•After some time, the activity of the daughter becomes equal to the activity of the patient

secular equilibrium

•Occurs when the half-life of the daughter is somewhat less than the parent

•After a long time the decay curves become almost parallel to one another and the apparent half-life of the daughter becomes the same as the half-life of the parent and the ratio of the activities reaches a constant value

transient equilibrium

nuclei are composed of nucleons, which are what?

protons and neutrons

__ have a single unit of positive charge and _____ are neutral

protons, neutrons

atomic number (Z)= ?

number of protons

mass number (A)= ?

number of protons - number of neutrons

___ can only have specific discrete energies. __ in different shells have different energies that are unique to each element. ___ are bound to atom, so energies are negative

electrons

It takes a _____ amount of energy to free the electrons from the atom (ionization)

positive

Electrons in inner shells are ____ tightly bound to atom than outer shell electrons

more

Higher Z means more or less tightly bound inner electrons?

more

Ground state of an atom is the ____ possible energy configuration of electrons

lowest

occurs when 1 or more electrons occupy a higher energy state than they would if in ground state

excited state

occurs when 1 or more electrons receive so much energy (at least the atomic binding energy for the shell) that they are removed from the atom

ionization

•Electrons can make transitions between shells

•Transition from lower to high energy state occurs if atom absorbs energy equal to difference between energy levels

•Atom is left with excess energy à excited state

•Transition to lower energy states are possible if vacancy in lower energy shell

•Electron in higher energy shell will rapidly drop down and fill vacancy

•Energy is released as a ____ ______

photon emission

The number of electrons and their configuration determines the ____ _____ of an element

chemical properties

____ _____ involve the sharing or exchange of outer electrons between atoms

chemical reactions

dense, positively charged body consisting of protons and neutrons (called nucleons)

nucleus

Mass of proton and neutron are _______

comparable

Mass of electron is about ____ times smaller

2000

A= ?

atomic mass number (number of nucleons)

Z= ?

atomic number (number of protons)

X= ?

chemical symbol

How do you find the number of neutrons?

N=A-Z

Number of _____ determines chemical identity of element

protons

Number of ____ determines its chemical behavior

electrons

•Same A (number of __**p**__rotons) but different N (number of neutrons)

isotope

•Same __**A**__ (number of nucleons) but different Z (number of protons)

isobar

Same A and Z, but nucleus is in an excited state called a __**m**__etastable state that has a long lifetime

isomer

same number of __**n**__eutrons

isotone

•The atomic mass unit (*u*) corresponds to an energy of ______

931MeV

•1 *u* is roughly the mass of a ______

nucleon

What is this an example of?

isobar

What is this an example of?

isotone

What is this an example of?

isomer

***an excited state that has a relatively long lifetime***

metastable

*If the percentage change in distance from the source is small, the percentage change in the intensity of a radiation beam is approximately _____ the percentage change in distance*

twice

well-collimated beam, detector placed far from attenuating material so that no scattered photons may enter the detector

narrow beam attenuation

___ is the linear attenuation coefficient; has units of inverse distance and depends on the energy of the radiation and the attenuating medium

µ

•The thickness of specified material necessary to attenuate intensity of beam to half its original value for narrow beam geometry; depends on energy of beam and material that beam traverses

half value layer

•The ______ HVL (HVL2) is the additional thickness necessary to reduce beam intensity by another factor of 2

second

•As a _______ beam penetrates the material, it usually becomes “hardened” and so it is generally true that HVL2 > HVL1

polyenergetic

•For a _______ beam, HVL2 = HVL1

monoenergetic

tera (T)

10^12

giga (G)

10^9

mega (M)

10^6

kilo (k)

10^3

hecto (h)

10^2

deka (da)

10^1

deci (d)

10^-1

centi (c)

10^-2

milli (m)

10^-3

micro (µ)

10^-6

nana (n)

10^-9

pico (p)

10^-12

*____ _____* are based on the metric system since most countries use the metric system

SI units

An x-ray machine has two major components

x-ray tube and generator

X-rays are produced inside tube and exit tube through the

window

Generator supplies __ and ___ to the tube

current, voltage

_____ are created when a beam of electrons, accelerated inside the evacuated x-ray tube, strikes a target at the end of the tube

x-rays

When electrons strike the target, a fraction of their kinetic energy is converted to x-rays and the remaining KE is converted to _____

heat

Electrons have to be accelerated through a large potential difference because they have to gain enough KE to produce ____ ____

energetic x-rays

•_______ are produced when electrons are accelerated between the cathode (negative electrode) and anode (positive electrode) in an evacuated metal or glass tube, and strike the anode at the end of the tube

x-rays

•When electrons strike the target (which is embedded in the anode) a large fraction of their energy is dissipated as _____

heat

•The remainder is converted to _____

x-rays

The _____ has a heated filament that gets very hot, like a toaster wire

cathode

The electrons are boiled off the cathode filament and are accelerated toward the _____

anode

•Most diagnostic tubes use _____ (W) for the target material

tungsten

Why is the high melting point of tungsten (3370C) beneficial?

the electron beam produces a high heating rate

Why is the high Z of tungsten beneficial?

it has a high efficiency for x-rays production

the _____ is commonly made of copper with tungsten target embedded in it

anode

•Copper is a _____ heat conductor

good

When an electron strikes the target of an x-ray tube (or in a linac), it interacts with the ______ in the target. It can interact with either atomic electrons or the atomic nucleus

matter

•______ electron interacts with an outer or an inner shell electron

incoming

•_____ shell electrons can be excited to higher-level energy states

outer

•They will then drop back to their original states and emit low-energy photons. These photons will be absorbed quickly in the target, and their energy converted to _____

heat

•Outer shell electron could be ejected from the atom, and the atom is ____

ionized

•Ejected electron will move through target material, interacting with other atoms, and will find another atom missing an outer shell electron and “______” with that atom and a low energy photon, whose energy will be absorbed

recombine

•Occasionally a high-energy bombarding electron will eject an inner shell electron (K or L shell)

•There will be a vacancy that can be filled by outer shell electrons dropping down

•Inner shell electrons are very tightly bound, so the energy released when outer shell electrons drop down to fill an inner shell vacancy will be high (classified as x-rays)

•Some of the higher energy x-rays may escape from the target without being absorbed

•They will have discrete energies that are characteristic of the atom from which they are emitted (unique for each element)

characteristic x-rays

Incident electron with kinetic energy E0 ejects an orbital electron and leaves from the collision with energy E0 – ΔE, where ΔE is the sum of the energy imparted to the ejected electron and the energy used to overcome the binding energy of that electron

A hole is left by the departed orbital electron and a higher shell electron drops to fill that vacancy in the lower shell, giving off a characteristic photon with energy equal to the difference in the binding energies for the shells

characteristic x-rays

When a bombarding electron passes close to an atomic nucleus in the target, it will be accelerated as a result of the electrical attractions between the electron and the nucleus

Accelerated charges generate electromagnetic radiation

Radiation will be emitted by the electron over a wide range of energies

Maximum energy of the emitted x-rays is equal to the total kinetic energy of the bombarding electron

Bremsstrahlung emission

bremsstrahlung radiation means what in German?

braking radiation

At large angles with respect to electron beam for low-energy x-ray beams (diagnostic) but strongly peaked in the forward direction for therapeutic energies

Bremsstrahlung directional dependence

In a typical target both ___ ___ and _____are produced

characteristic x-rays, bremsstrahlung

x-rays with discrete wavelengths that are uniquely characteristic of the distinct energy levels of the atom from which they come. these result when a bombarding electron ejects an inner shell electron in the target medium.

characteristic x-rays

when bombarding electron passes close to an atomic nucleus in the target, it will be accelerated as a result of the electrical attraction between the and the nucleus. accelerate charges generate electromagnetic radiation. radiation will be emitted by the electron in this process over a wide range of energies. this radiation is called bremsstrahlung, which means “braking radiation” in German. the maximum x-ray is eqaul to the total kinetic energy of the bombarding electron.

bremsstrahlung (continuous) x-rays