X-ray Tube Output: 80μGy/mAs at 1m, 900µGy/s @1m

[BobP]

Homework Statement

(The question is in the image attached)

(c) An X-ray unit in the cardiac catheter labs has an output of 80µGy/mAs at 1 meter when the unit is set at 100 kVp. After adding 0.3mm Cu to the beam the photon intensity is reduced to a quarter and tends to vary in proportion to kV3 (i.e. kV to the power of 3). What would be the output rate at 80cm from the tube focus for a
continuous beam at 80 kV p and 5 mA ?
(d) The same unit as in c) is now used for an acquisition run. The protocol uses 15 frames per second with a 10ms pulse width at 100kV without the copper filtration and a 20 x 20cm square field. The detector distance is 1m from the tube. If the measured output rate at 1m is 900 µGy/s what is the peak tube current of each pulse? What DAP reading in cGycm2 would be measured in 10 seconds of acquisition?

Homework Equations

none relevant

The Attempt at a Solution

Please can someone confirm if my answers are correct
(c) 80 μG/mAs
(Working: 20 * (1/0.8)² * (80/100)³ * 5)

(d)
Current = 750 mA
DAP reading = 360 cGycm²

Thank you

 

[gleem]

first part looks good.

Second part in order to achieve an output of 900uG/sec when the output is 80yGy/mas you need how many ma on average for continuous operation to achieve that output? Since the the tube operates only a fraction of the time (duty cycle is what?) the current must be higher than the average right?

 

[BobP]

first part looks good.

Second part in order to achieve an output of 900uG/sec when the output is 80uGy/mAs you need how many mA on average for continuous operation to achieve that output? Since the the tube operates only a fraction of the time (duty cycle is what?) the current must be higher than the average right?

If I have 900 uGy/sec when I have 80 uGy/mAs and the machine is on for 150ms in total over a 1 second period
Then I have
80 * mA per second = 900
Therfore mA = 11.25 mA

BUT as the current is not always on the actual mA is

mA * 15 * 10 * 10^-3 = 11.25 SO
Answer = 75 mA

But for part (ii)
If output is 900 uGy/sec and I run the machine for 10 seconds then I have a dose of 9000 uGy
With an area of 400 cm2 I have a DAP of 9000 uGy * 400 = 3.6 Gy cm^2 = 360 cGycm^2

So I got the mA wrong initially but the DAP correct.
Is my answer now correct?
Thanks

 

[gleem]

looks good

 

[BobP]

looks good

Thank you for your help :)