[labnetwork] Hazard due to x-ray production in e-beam evaporators?

[Joseph E. Palmer]

Aaron,

      It has been some years since I worked at the Nuclear Physics Lab 
at Rutgers University (with an 8MeV Van De Graff particle accelerator), 
but I will relay what I know.  10 keV x-rays are barely able to make it 
past the chamber walls.  Of course, this depends upon the proximity of 
the gun to the chamber walls, their thickness, and the material they are 
constructed from.  It is always good to confirm this with a Geiger Counter.

      Over years that I have been here at Princeton, occasionally 
someone from our own EHS is sent over to measure the amount of radiation 
being produced by our tools, and they have never been able to get a 
reading over background.  You would get a larger dose of radiation while 
standing in front of the bananas (K40) at Shop Rite, sleeping next to 
someone (C14), living in Denver, Co, or flying in an airplane.  I don't 
mean to belittle their concern; when involved in any research that 
involves the possibility of radiation exposure, keeping track of your 
cumulative dosage is important.  In short, I am generally not concerned 
with anything lower than 10keV.

Regards,

Joe Palmer

On 5/27/2020 11:21 PM, Aaron Hryciw wrote:
> Dear colleagues,
>
> One of the users in our open-access facility recently expressed 
> concern about x-ray production in electron-beam evaporation systems.  
> Since the typical acceleration voltage in our e-beam systems is 7–10 
> kV, he was concerned that bremsstrahlung and characteristic x-rays 
> would be generated during deposition, with a maximum energy of 7–10 
> keV (soft to hard x-rays), and that these x-rays would pose a health 
> and safety hazard to an operator standing next to the viewport for ~30 
> minutes.
>
> A literature search yielded a few reports describing radiation damage 
> to sensitive devices from x-rays produced during an e-beam 
> metallization step, but I did not find any mention of related health 
> and safety considerations.  While some x-rays are undoubtedly 
> produced, presumably there are reasons why they are not hazardous to 
> an operator (e.g., perhaps total x-ray output is very small, majority 
> of x-ray spectrum is low energy, x-rays do not penetrate stainless 
> steel chamber walls or viewport windows, etc.).  I would like to 
> answer this user with specific physical arguments as to why the hazard 
> is insignificant, however, so any advice you could offer to this end 
> would be greatly appreciated.  Many thanks.
>
> Cheers,
>
>  – Aaron
>
> __
>
> Aaron Hryciw, PhD, PEng
>
> Fabrication Group Manager
>
> University of Alberta - nanoFAB
>
> W1-060 ECERF Building
>
> 9107 - 116 Street
>
> Edmonton, Alberta
>
> Canada T6G 2V4 Ph: 780-940-7938
>
> www.nanofab.ualberta.ca <http://www.nanofab.ualberta.ca/>
>
>
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-- 
Joseph E. Palmer
Chief of Operations for the MNFL
PRISM, Princeton University
Contact:
Office (Tuesdays and Thursdays): 609-258-4706
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