Exam 1: Rad Physics

How are electron shells identified?

labeled inside to outside, alphabetically starting with k

How do you determine the maximum number of electrons in the outer most shell?

2n², where n is the number of the electron shell from the nucleus

What is an isotope?

Same number of protons

What is an isotone?

Same number of neutrons

What is an isobar?

Same number of both protons plus neutrons (mass #)

What is the smallest unit of an element that RETAINS all the properties of an element?

An atom

What is an isomer?

Identical atom at an excited state

What is the atomic number?

Number of protons = Z number

What is the mass number?

Approx. number of nucleons (protons and neutrons) = A number

What characteristic of waves is constant for electromagnetic waves?

Velocity- electromagnetic waves all travel at the speed of light

What are the units for speed?

Meter/sec

What are the units for wavelength?

Meters

What are the units for frequency?

Hertz

What variables are identified in the wave equation and how are they related to each other?

• Velocity = frequency x wavelength

• Velocity of all E M radiation is c (speed of light)

• Velocity is directly proportional to frequency and wavelength

• Frequency and wavelength are inversely proportional to each other

When comparing 2 types of electromagnetic energy, can you determine which has the longest/shortest wavelength?

Yes, longer wavelength = lower frequency and lower energy

What is the acronym for the electromagnetic spectrum?

Can Granny X Use Vinegar in Minute Rice

What is the electromagnetic spectrum in order to shortest wavelength to longest?

Cosmic, Gamma, X-ray, Ultraviolet Light, Visible Light, Infra-red, Microwaves, Radio Waves

What is the speed of light?

3 × 10^8 m/s

What are the characteristics of electromagnetic photons?

• They can travel through a vacuum

• They can excite and/or ionize matter

• They have a velocity equal to the speed of light

• They are illustrated as sinusoidal waves

• They possess both wave and particle characteristics

• They are arranged in an orderly spectrum according to frequency and wavelength

What is a photon?

The smallest quantity of any type of electromagnetic raiation

What is a hertz?

Unit of frequency, 1 Hz = 1 cycle/second

What happens at the filament?

Thermionic emission, materials are thoriated tungsten, molybdenum, & rhenium

What is thermionic emission?

The ejection of electrons from the surface of a wire due to increased hear, causes an electron cloud or space charge surrounding the wire

What is the actual focal spot size?

The physical area of the anode that the electrons hit

What is the effective focal spot size?

The area of the focal spot that is projected out of the tub toward the object being radiographed

What happens at the anode?

X-ray production, this is because the speeding electrons are stopped suddenly and the KE has to go somewhere

What problems can filament vaporization cause?

• tube arcing

• filament breakage

What factors control the size of the effective focal spot?

• filament size (which also controls the size of the actual focal spot)

• target angle

What is the purpose of the focusing cup?

To narrow the thermionic cloud as it is driven to the anode, narrowing the thermionic cloud improves spatial resolution

What material is the focusing cup made of?

Nickel (or molybdenum)

What charge does the focusing cup have during normal operation?

Negative, making it biased so it compresses the electron cloud

What charge does the focusing cup have when it is being used as a switch in a grid-controlled tube?

Positive, so the electrons in the cloud stick to the focusing cup instead of crossing the tube, effectively turning off the x-rays

What are the parts of the cathode assembly?

• filament (source of electrons)

• focusing cup (compresses electron cloud)

What factors must be considered when choosing the material for the filament?

• high melting point

• temperature for thermionic emission

What are the three layers of an anode disk?

• Tungsten-rhenium alloy (where x-rays are produced)

• Molybdenum disk (provides support and heat dissipation)

• Graphite backing (prevents warping and heat transfer to rotor and bearings)

What factors must be considered when choosing the material for the anode?

• Atomic number (higher atomic # for more efficient x-ray production)

• High melting point (to prevent pitting)

• High heat-conducting ability (to cool quickly)

What are the locations of thermionic emission and photon production?

Filament- thermionic emission

Anode (actual focal spot)- photon production

What purposes does the glass envelope serve?

Contains the vacuum

What device is used to rotate the anode?

Induction motor, composed of the rotor inside the glass envelope and the stator outside

What components make up the device used to rotate the anode?

The rotor and the stator

How does filament size impact the effective focal spot size?

Bigger filament, bigger effective focal spot (this controls the size of the actual focal spot)

How does the anode target angle impact the effective focal spot size?

Steeper angle (smaller degrees), smaller effective focal spot

What does a dual focus x-ray tube have?

Two filaments

When considering the distribution of x-rays across the x-ray tube, when imaging a part of uneven thickness, the bigger part should be placed under which portion of the x-ray tube?

The thickest part should be placed under the cathode (fat cat) becuase the anode absorbs some of the x-rays on that side

How fast do regular anodes rotate?

3,600 rpm

How fast does high capacity anodes rotate?

10,000 rpm

What design features help the rotating anode dissipate heat?

• Diameter of the disk

• Speed of rotating the disk (rpm)

• Angling the focal track to take advantage of the line focus principle

If an atom is ionized, what has happened?

An electron has been knocked out of orbit

What is the target angle in most x-ray tubes?

12 degrees (range of 5-15 degress)

What is the accumulation of electrons in the area around the filament called?

Space charge

Which side of the x-ray tube is positive?

Anode

Which side of the x-ray tube is negative?

Cathode

What are the three aspects of the tube housing?

• Steel housing (protects from rough handling)

• Dielectric oil (protects against electrocution and cools the tube)

• Lead lining (protects against radiation going in weird directions)

What aspect of the tube housing prevents electrocution?

Dielectric oil

What are the 2 purposes of the dielectric oil in the tube housing?

• to prevent electrocution

• to cool the tube

What is meant if an x-ray tube is described as biased?

Focusing cup is more negative than the filament

What is the meaning of isotropic?

In all directions, x-rays are emitted from the anode in all directions

What is the maximum permissible leakage radiation from the x-ray tube housing?

100 mR/hr at 1 meter

What is a vacuum?

A space from which air has been removed

What is the process of the x-ray creation?

• electricity flows through the filament, causing it to heat up and release electrons

• electricity is applied to both ends of the tube and the released electrons travel from the cathode to the anode, accelerating and gaining KE in the process

• speeding electrons are stopped by the anode, where the excess KE is released as x-rays

What are three basic characteristic of the wave equation?

Wavelength, frequency, & velocity

The chemical element is determined by the number of ____ in the atom.

Protons

A period in the periodic table is…

the principal quantum number

The ____ of electromagnetic radiation is constant.

Velocity

Two identical atoms that exist at different energy states are called ____.

Isomers

If the frequency of a wave is 1,000 hertz and is traveling at 50,000 m/sec, then its wavelength is…

50 m

Isotopes have ____ mass numbers and ____ atomic numbers.

Different; the same

The smallest particle that has all the properties of an element is a(n) ____.

An atom

Groups of the periodic table…

represent elements with the same outer electron configuration.An electron is ____ charged and has a mass of ____ amu(s).

An electron is ____ charged and has a mass of ____ amu(s).

negatively; 0.000548

Carbon has an atomic number of 6. One of its isotopes has a mass number of 14. The number of neutrons in this isotope is…

8

The smallest quantity of any type of electromagnetic radiation is a(n) ____.

Photon

The nuclear particles that distinguish one element from another are the…

# of protons

An atom has an atomic number of 18 and a mass number of 38. Letting P = the number of protons and N = the number of neutrons, which of the following atoms is the isotope of this atom?

P = 18, N = 21

Quarks may behave according to the ____ theory.

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