I don't have industrial linacs but they are sort of similar to medical linacs, hopefully what I include is sort of helpful. ummm HVL in steel is what varian define their beam qualities since a linatron has energies in the megavoltage range ranging from about 1 to 15 MeV (MV).  I would assume you know that bit. Depending on which linatron you have you will have a HVL that ranges from 15mm steel to about 33mm steel for nominally 15MV. Ideally you want to establish a narrow beam geometry, you will need to create some sort of collimator and the attenuation plates should be placed close to the collimator at a large distance from the detector. see a couple of diagrams in here; http://www.uthgsbsmedphys.org/radoncres/09-measurementofradiation-quality.pdf  It is also an idea to have an appropriate buildup cap on the detector according to the nominal energy. I am sure you would know that you now measure the open beam, then attenuate the beam with subsequent layers of steel. Remembering as you add more steel you will change the energy spectrum of the beam creating a harder beam. I would assume you have; https://www.varian.com/sites/default/files/resource_attachments/LinatronAppManual7.pdf which covers some of the above. Best of luck

Hi Lindsay:

Thank you for taking the time to write a so detailed answer. I was aware of the document by Varian. However, they do not detail there if they include a steel plate as initial thickness before adding steel plates to measure the HVL. It seems that it is traditional to add a 1/2-in steel plate to harden the beam in this type of industrial linacs when measuring the HVL (in fact, what Varian states as HVL is not the first HVL, but the so called equilibrium HVL). My simulations seem to agree with this, but I just wanted to be sure of the experimental setup used by Varian in the commissioning.

Thanks and regards,

Marcelino

Marcelino I figured you would know the docs, I have only seen linatrons in the paperwork but had a colleague who repaired then for Varian at a govt munitions factory. I could understand the addition of the steel plate to harden the beam since it would rid the beam of a lot of the low energy and make imaging a whole lot easier. In fact on one of the data sheets Varian show a beam flattening filter which of course would not only improve the beam shape but also harden the beam. I know in the medical world the Varian flattening filter free linacs still have a insert in the beam line to "rid the beam of low energy". Cheers

Lindsay

got to ask what the heck is a medical physicist doing with a linatron anyway?

You are right, Lindsay. The Linatron also includes a flattening filter as an option, which, according to information from Varian webpage, is simply a disc. The FFF beams of Varian clinical linacs definitely must include some sort of insert as you say, to remove low energy contributions. I attach you a link to an interesting paper on this subject.

Regards,

Marcelino

Article A geometrical model for the Monte Carlo simulation of the Tr...

Good question! I The subject of my thesis is on Monte Carlo simulation applied to radiotherapy but a side project about the Linatron arosed... A good simulation practice...