Bushong's high-frequency heat unit multiplier is 1.4, not 1.45
Key takeaways
- In Bushong: high frequency 1.4, three-phase 1.4 with no split by pulse count, single phase 1.0.
- HU = kVp x mA x s x factor.
- At 80 kVp, 300 mA and 0.1 s, high frequency gives 3,360 HU and single phase gives 2,400 HU.
- Bushong 11th ed. prints none of 1.35, 1.41 or 1.45 as a heat factor.
In Bushong, the factor is 1.4 for high-frequency generators and for three-phase generators, with no split by pulse count. Single phase uses no multiplier, which is the same as 1.0.
HU = kVp x mA x s x factor
One heat unit is the product of 1 kVp, 1 mA and 1 s, and three-phase and high-frequency units make more heat at the same settings (Bushong 11th ed., PDF pp.139-140).
How the generators compare
Worked at 80 kVp, 300 mA and 0.1 s. Bushong says only “three-phase”, so we apply its factor to both pulse counts:
| Generator | Voltage ripple | Factor in Bushong | Heat units |
|---|---|---|---|
| Single phase | 100% | 1.0 | 2,400 HU |
| Three phase, 6 pulse | about 14% | 1.4 | 3,360 HU |
| Three phase, 12 pulse | about 4% | 1.4 | 3,360 HU |
| High frequency | about 1% | 1.4 | 3,360 HU |
Bushong’s factor doesn’t change with ripple once you leave single phase. High frequency has less ripple than 12 pulse, but both use 1.4.
What about 1.35, 1.41 and 1.45?
An earlier version of this page taught a separate factor for each waveform: 1.35 for 6 pulse, 1.41 for 12 pulse and 1.45 for high frequency. We’ve seen these values in study material online that we don’t cite as a source. None of the radiography textbooks we hold prints 1.45 as a heat factor, so we can’t say where it came from.
We searched the full text of Bushong 11th ed. It gives a single factor of 1.4 for both three-phase and high-frequency, and prints none of 1.35, 1.41 or 1.45 as a heat factor. It gives one value, 1.4. We have since retired the three-value set across Radtechprepper, and our formula pages use 1.4.
ARRT® doesn’t publish a factor. Its registry outline lists “basic principles”, “phase, pulse and frequency” and “tube loading” under the x-ray generator, so we can’t say what any one exam item would use. If a practice question offers only 1.35, 1.41 or 1.45, it isn’t using Bushong’s factor. Check it against your program’s text.
What heat units are for
Heat units tell you how much heat a planned exposure puts into the anode. You compare that load against the tube’s limits on its charts. Our page on how to read a tube rating chart covers the single-exposure check and the cooling charts. Our page on x-ray production efficiency explains why nearly all the energy ends up as heat.
Where to practice this
The Image Production guide uses the same 1.4 factor in its tube section. For the wider picture, read the Equipment Operation and QA chapter, then try the equipment practice questions.
Frequently asked questions
What is the heat unit multiplier for a high-frequency generator?
1.4 in Bushong's textbook, which gives one factor of 1.4 for both three-phase and high-frequency equipment. Single phase needs no multiplier.
What is the multiplier for three-phase 12-pulse?
1.4 in Bushong, the same as high frequency. Bushong gives one three-phase factor and doesn't split it by pulse count.
How do you calculate heat units on a high-frequency generator?
Using Bushong's factor, multiply kVp x mA x seconds x 1.4. At 100 kVp, 300 mA and 0.1 s, that is 4,200 HU.
Why does the page address say 145?
An earlier version of this page taught 1.45. That value was retired because the textbook doesn't support it. The address stayed the same so old links keep working.
Sources
Found an error? Email [email protected] with the page and the source.
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