Re: Short video clip of 18" x18" Lichtenberg Figure being discharged (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 27 Feb 2007 11:26:43 -0600
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Short video clip of 18" x18" Lichtenberg Figure being discharged
    (fwd)

Dave,

Interesting question - possible x-ray generation via runaway electrons! 
We didn't think to bring radiation measuring equipment. Unfortunately, 
the only radiation measuring device I have is a Geiger Counter, and it's 
unlikely that this would have detected any short x-ray pulses during 
discharges, if they existed.

However, the folks at the accelerator facility did provide me with a 
quartz fiber direct reading pocket dosimeter which I had to wear for the 
entire day (we used almost 8 hours of beam time). During this time I 
probably discharged 700-800 specimens. I just checked with the facility 
- the device was a Nuclear Associates Model 138, 0 - 200 mR dosimeter. 
This is similar to the following model from Arrow-Tech. The device is a 
quartz fiber electrometer that's initially charged to about 200 volts. 
X-rays or gamma rays will partially remove charge, permitting the device 
to directly measure cumulative exposure to radiation. This particular 
device was sensitive to x-ray photons between 16 keV and 6 MeV:
http://www.arrowtechinc.com/Catalog_pdf/lrdosimeter.pdf

At the end of the day, the dosimeter was checked by their radiation 
physicist, and it (apparently) didn't register an abnormal amount of 
radiation. Unfortunately, I didn't think to record the actual reading at 
the time - I'll have to do so on our next run. Interestingly, similar 
dosimeters have in fact been used to detect the presence of low energy 
x-rays from nanosecond high pressure air discharges as described in a 
number of papers in the literature.

Since my dosimeter did not register a significant accumulated dose, this 
may imply that runaway electrons were not being generated during our 
discharges. Or, since the discharges occur primarily inside the PMMA, 
perhaps any low energy x-rays were subsequently absorbed by the 
surrounding acrylic before they could irradiate the dosimeter (and me!). 
In any event, it looks like discharging Lichtenberg Figures does not 
cause x-ray sunburns...  :^)

Bert





High Voltage list wrote:
> Original poster: Steven Roys <sroys@xxxxxxxxxx>
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Mon, 26 Feb 2007 18:08:40 -0500
> From: David Speck <Dave@xxxxxxxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Re: Short video clip of 18" x18" Lichtenberg Figure being discharged
>     (fwd)
> 
> Bert,
> 
> Very neat video of the Lichtenberg  genesis process.  I'll look forward 
> to seeing the video of the actual irradiation process, if you can post 
> that as well. 
> 
> Have you checked to see if any X-rays are generated during the discharge 
> process?  I know that you are supposed to have low pressures to get 
> significant X-ray production, but if you are playing with 2 MV and 200 
> amps, that's a pretty hefty beam current.  Even if X-ray production was 
> very inefficient, with that kind of drive power, I wonder if you are 
> zapping yourself when you discharge one of the blocks.
> 
> Dave
> 
> High Voltage list wrote:
>> Original poster: Steven Roys <sroys@xxxxxxxxxx>
>>
>>
>>
>> ---------- Forwarded message ----------
>> Date: Fri, 23 Feb 2007 10:27:47 -0600
>> From: Bert Hickman <bert.hickman@xxxxxxxxxx>
>> To: High Voltage list <hvlist@xxxxxxxxxx>
>> Subject: Short video clip of 18" x18" Lichtenberg Figure being discharged
>>
>> Hi All,
>>
>> I just uploaded a short video clip of an 18" X 18" X 1" Lichtenberg 
>> Figure being discharged to You Tube. This particular specimen was 
>> brought by local coiler Jeff Larson during our 2005 "Captured Lightning" 
>> production run. The video was captured and edited by Terry Blake:
>> http://www.youtube.com/watch?v=FWOst4VwwEU
> 
> 
> 
> 


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