# Size of bremsstrahlung radiation fields generated by linear accelerators

## Summary:

What determined the size of radiation fields produced by for example, pulsed-power, linear accelerators?
Hi everyone, sorry we are talking about pulsed power accelerators again. In this context, it is about the HERMES III again.

According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf HERMES III, a 16 terawatt pulsed power accelerator at Sandia National Labs, which fired electron beams with peak energy (currently) at 22 MeV and 730 ka current that later converted into Bremsstrahlung radiation is used to irradiate very large outdoor area and very large test objects such as military tanks to simulate nuclear explosion gamma ray radiation effects on whole weapon systems and large armoured vehicles. What determined the size of the Bremsstrahlung radiation fields? Is it simply the size of the accelerator or the voltage and current of the electron volt regardless the size of the accelerator?

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Baluncore
2019 Award
What determined the size of the Bremsstrahlung radiation fields? Is it simply the size of the accelerator or the voltage and current of the electron volt regardless the size of the accelerator?
You need to express yourself more clearly, so we can understand your question.
What do you mean by "size" of a radiation field ?
How can an electron volt have a voltage and current ?

The number of photons that radiate out from the target is proportional to the beam current.
That field falls off with distance by the inverse square law.
The intensity pattern of the field is determined by the geometry of the target relative to the electron beam.

wonderingchicken
You need to express yourself more clearly, so we can understand your question.
What do you mean by "size" of a radiation field ?
How can an electron volt have a voltage and current ?

The number of photons that radiate out from the target is proportional to the beam current.
That field falls off with distance by the inverse square law.
The intensity pattern of the field is determined by the geometry of the target relative to the electron beam.
Sorry for not being clear. What I mean by radiation field size is the height, width and length of the radiation field after the electrons are converted into high energy bremsstrahlung. There is a mistake in my last sentence as you noted (i.e. the voltage and current of the electron volt). I should rephrase it like this, "What determined the size or dimension (e.g. height, width, length, etc.) of the Bremsstrahlung radiation fields? Is it simply the size of the accelerator or the voltage and current of the diode regardless the size of the accelerator?" Anyway, thank you for the responses.

You said the following, "The number of photons that radiate out from the target is proportional to the beam current."

Ok, so the more current the more photons coming out of the source. Is this related to the dimension of the radiation field? More current means larger radiation field?

"That field falls off with distance by the inverse square law.
The intensity pattern of the field is determined by the geometry of the target relative to the electron beam."

Baluncore
2019 Award
What I mean by radiation field size is the height, width and length of the radiation field after the electrons are converted into high energy bremsstrahlung.
A radiation field does not have a height, width and length. Radiation radiates like a fan in 3D. You must employ a spherical coordinate system, centred on the emitter. Radiation goes on out forever, the energy density of the “beam” progressively being reduced. The “beam pattern” gives the relative energy radiated in different directions.

A radiation field does not have a height, width and length. Radiation radiates like a fan in 3D. You must employ a spherical coordinate system, centred on the emitter. Radiation goes on out forever, the energy density of the “beam” progressively being reduced. The “beam pattern” gives the relative energy radiated in different directions.

Sorry for that. I got confused by those "large area" and "small area" radiation simulator (for example here https://rb.gy/accexo the CASINO accelerator is "used when high intensity, small area exposures are needed" while the other accelerator PHOENIX is "used with lower intensity, where large area exposures are needed"), so I thought "large area" radiation simulator generated "larger" radiation field while the "small area" radiation simulator only irradiated smaller areas by generating "smaller" radiation field. In addition, "large area" radiation simulator seems to be big in size while "small area" radiation simulator is smaller. So, that's where I got the impression that larger accelerators such as HERMES III generated "larger" radiation field while smaller accelerators generated "smaller" radiation field. English isn't my first language, so pardon me.

If you see the figures in page 40 here in this link https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf I believe the upper figure showed the indoor mode while the lower figure showed the outdoor mode (HERMES III have two test cells, indoor test cells and outdoor test cells). If you compare both images, the radiation field of the outdoor mode seems to be very large. So, I'm wondering what methods that are used to achieve that. In my opinion, I believe it is due to the size of the diode. Correct me if I'm wrong.

hutchphd
Why, in the name of heaven, are you interested in producing fluxes of high energy radiation over large areas efficiently????
"Aw shucks I'm just interested" does not do it for me.

Averagesupernova and wonderingchicken
Why, in the name of heaven, are you interested in producing fluxes of high energy radiation over large areas efficiently????
"Aw shucks I'm just interested" does not do it for me.
I don't have any background in engineering or even physics so I don't even know how to build one. Relax. I just got confused by the terms "large area" and "small area" radiation simulator, and I wonder by what ways they achieve to get larger or smaller radiation fields. Is it simply by current and voltage regardless the size of the accelerator, or is it depends on the size of the accelerator or some of its parts. That's it.

Baluncore
2019 Award
Baluncore any thoughts?
I really don't understand what you are on about here.

It is meaningless to refer to a larger field or a smaller field. A field has many parameters. Just which parameter you are referring to must be explicitly identified. Until you stop using the term field and start referring to the technical parameters of the field, you will confuse yourself and anyone who reads what you write.

You need to study the specifications of radiation beam patterns and apertures before you scramble your understanding any further.

I cannot agree or disagree with what I cannot understand.

hutchphd
OK. But there is no particular magic here. The larger and smaller "radiation fields" are just the difference between a fire hose and a lawn sprinkler. More current produces more Xrays. It is not clear to me why this is interesting.
I think thjis is a semantic issue.

wonderingchicken
I really don't understand what you are on about here.

It is meaningless to refer to a larger field or a smaller field. A field has many parameters. Just which parameter you are referring to must be explicitly identified. Until you stop using the term field and start referring to the technical parameters of the field, you will confuse yourself and anyone who reads what you write.

You need to study the specifications of radiation beam patterns and apertures before you scramble your understanding any further.

I cannot agree or disagree with what I cannot understand.
Maybe the appropriate term is radiation beam, just like what you have stated just now. Sorry. The reason why I refer them as "fields" is because I thought of beam as a narrow rod-like while field is more like a widening wave, and as you can see in page 39-40 here https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf the radiations don't look like a laser which is narrow at all.

But there are such things as larger area and small area radiation simulator which you can see here https://rb.gy/accexo , which leads me think "oh so the large area accelerator generated "larger" radiation beam so it can irradiate larger areas while the small area generated "smaller" radiation beam so it can't irradiate large areas". But after thinking for awhile, photons have no definite boundaries so I can see why you're confused by "larger" and "smaller" radiation.

So, I think what makes an accelerator can irradiated very large areas or small areas don't depend on the "size" of the radiation but depends on the size of the accelerator especially the source (e.g. diode and anode converter target). If the source is large, then it can irradiate very large areas and if the source is small then only small areas can be irradiated. Correct?

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OK. But there is no particular magic here. The larger and smaller "radiation fields" are just the difference between a fire hose and a lawn sprinkler. More current produces more Xrays. It is not clear to me why this is interesting.
I think thjis is a semantic issue.
Noted you said "The larger and smaller "radiation fields" are just the difference between a fire hose and a lawn sprinkler" so it depends on the size of the source (i.e. the size of the diode of an accelerator). Correct?

The HERMES III is a huge 22 MeV (peak voltage), 730 ka (peak current) accelerator so it can irradiated very large areas due to its very large size which is the size of a small subway train, but if the size of an accelerator is small but yet it have similar voltage and current as the HERMES III, can it irradiated large areas?

hutchphd
The correct answer is yes it could. Whether or not it can and does depends upon a myriad of design and operational details specific to the instrument. Power=(current)x(voltage)
Incidentally X-ray production relies on more than bremsstrahlung. For most electron beam targets production depends heavily upon characteristic resonances in the inner atomic electrons in the target. Check the link.

wonderingchicken
The correct answer is yes it could. Whether or not it can and does depends upon a myriad of design and operational details specific to the instrument. Power=(current)x(voltage)
Incidentally X-ray production relies on more than bremsstrahlung. For most electron beam targets production depends heavily upon characteristic resonances in the inner atomic electrons in the target. Check the link.
So, in conclusion, size is not important but what is most important is the power (current and voltage). Then, that means this submicron wires irradiated by petawatt lasers that generated hundreds of MeV gamma rays https://www.pnas.org/content/115/40/9911 can also irradiate very large areas just like the bigger HERMES III judging by the voltage that is produced (hundreds of MeV gamma rays which is higher than 22 MeV peak voltage by the HERMES III) but I'm not sure about the current that is produced by the process.

hutchphd