Chapter 5 RADR

Protective housing

provides solid, stable mechanical support. It is lead lined and serves as an electrical insulator and thermal cushion

What helps dissipate heat away from the tube?

oil bath and cooling fans

xrays are produceds in what direction?

isotropically (in all directions)

Leakage radiaton

ionizing radiation escaping through protective sheilding

Anode has

anode target and induction motor

Cathode has

focusing cup and filament

What is the main purpose of the enclosure?

maintain a vaccum within the tube

What is the glass envelope made out of and why?

borosilicate, because it is heat resistant

Sun tanning

bronze glass discoloration from vaporized tugsten

Purpose of the anode

provides the target for electron interactions to produce x-rays and is an electrical and thermal conductor

What are the 2 designs of anode?

stationary anode and rotating anode

Stationary anode

a design consisting of a tungsten button embedded into a copper rod and the target area does not move

What is the disadvantage of the stationary anode?

electrons continously strike the exact small focal area, causing extreme rapid heat build up that can physically damage or melt the target

Rotating anode

spreads the tremendous heat produced over a larger surface area rather that striking a single spot

what is the rotating disc made out of?

molybdenum coated with tungsten and mounted on a copper shaft

why is the shaft copper?

because it conducts heat and electricity excellently

why is molybdenum used?

because it is a light but strong alloy that blocks heat from rotor bearings

why is a tungsten coating used?

because it has a very high melting point of 6152F, 3400 and a high atomic number of 74 that improves efficiency

why is rhenium added to tungsten?

to increase thermal capacity and tensile strength

what are the 2 parts of the induction motor?

stator and rotor

Stator

is made up of electromagnets arranged in pairs around the rotor

Rotor

made of an iron core surrounded by coils and operated by mutual induction to rotate the anode

Line-focus principle

by angling the face of the target, a large actual focal spot is maintained to spread heat load and create a small effective focal spot to improve image detail

what are is being bombarded by the filament electrons?

the actual focal spot

smaller the are of origin =

sharper the image

Anode heel effect

a phenomenon where the x-ray beam intensity is reduced on the anode side of the tube

Purpose of the cathode

provides the source of electrons needed for xray production

Thorium

is a radioactive metallic element that is added to increase thermionic emission and extend filament life

what is the focusing cup mad of?

nickel

what can the radiographer select at the console?

kVp, mAs, and focal spot size

Space charge

a cloud of electrons near the filament that limit additional electron emission because the electrons repel

Space charge effect

self limiting factor

what is SID?

source-to-image receptor distance

What 3 things are needed to produce xrays?

1. a large potential difference 2. a vehicle which kinetic energy can ride 3. a place for interaction

why is the electron cloud attracted to the anode target?

because of the huge potential difference

Factors that shorten the xray tube life

1. frequent use of high exposure factors 2. long exposure 3. overload of the filament

Factors that extend tube life

1. warm-up 2. do not prep rotor excessively 3. do not rountinely use extremes of exposure factors