worksheet_32.doc

32 Worksheet (A2) Data needed to answer questions can be found in the Data, formulae and relationships sheet.  1 State the nature of X-ra y radiation.

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 2 The enery of an X-ray photon is !" #e$. a b

%alculate the enery of the photon in &oules. %alculate the wa'elenth of the X-rays.

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 3 (ne of the interaction mechanisms between X-rays and matter is the photoelectric effect.  )ame the two other interaction mechanisms.

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 4 State one main difference between the imaes produced by a normal X-ray machine and by a %*T scan.

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 technique.  5 riefly eplain what is meant by a non-invasive te

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 6 State what is meant by ultrasound.

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 7 The speed of ultrasound in soft tissue is +.! #m s +. a b

%alculate the wa'elenth of ultrasound of frequency +./ 01. 3se your answer to part a to eplain why hih-frequency ultrasound is suitable for medical scans.

 8 Define acoustic impedance.

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 9 The table below shows useful data for bioloical materials. Material

Density / ! m"3

soft tissue

+"4"

+!5"

+.46

muscle

+"7!

+!8"

+.7+

 bone

(

5"""

4.5"

 blood

+"4"

+!7"

+.44

#peed o$ ultr ultras asou ound nd / m s"%

&coustic impedance  Z  / %'6 ! m"2 s"%

%alculate the density of bone. %alculate the percentae of intensity of ultrasound reflected at the blood9soft tissue  boundary. :*ssume the wa'es are incident at riht anles to the boundary. boundary.;; c 0=> scanner.

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%% ?rotons ha'e a precession frequency of 5" 01 in a stron uniform manetic field. a b c

Describe what is meant by precession. State the frequency of the radio frequency :=@; radiation that will cause the protons to resonate. 3se your answer to b to  to determine the wa'elenth of the =@ radiation.

*S and * Ae'el ?hysics

(riinal material B %ambride 3ni'ersity ?ress 2"+"

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%

32 Worksheet (A2)

%2 riefly describe the production of X-rays and eplain why an X-ray spectrum may consist of a continuous spectrum and a line spectrum.

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%3 The intensity of a collimated X-ray beam is 2!" C m 2. a b

Define intensity. The diamete diameterr of the X-ray X-ray beam beam is 5." mm. mm. %alcula %alculate te the power transmitted transmitted by the the beam. beam.

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%4 Desc Descrribe ibe wh what is meant eant by a co contra ntrast st mediu edium m and and sta state why why it is used used in X-r X-ray scan scans. s.

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%5 The potential difference between the cathode and the anode of an X-ra y tube is /" #$. %alculate the minimum wa  w a'elenth of the X-rays emitted from this tube.

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%6 The photoelectric effect is one of the attenuation mechanisms by which X-ray photons intera interact ct with with the the atom atomss in the the body body.. Descr Describe ibe some some of of the charac character teristi istics cs of this this mechan mechanism. ism.

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17 * collimated X-ray beam is incident on a metal bloc#. The incident intensity of the beam is I".

Draw a s#etch raph to show the 'ariation with thic#ness  x of the intensity  I  of the beam. b Crite down an epression for the intensit y I in terms of I" and  x. :manetic resonance imain; to obtain dianostic information about internal body structures.

23 X-=ays, ultrasound and 0=> are all used in medical dianosis. State one situation in which each of these techniques is preferred and i'e reasons, one in each case, for the choice.

Total

*S and * Ae'el ?hysics

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Score

(riinal material B %ambride 3ni'ersity ?ress 2"+"

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E

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