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June 2007

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Subject:
From:
"Hlava, Paul" <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Date:
Thu, 7 Jun 2007 13:53:38 -0600
Content-Type:
text/plain
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JEOL Probe Users Listserver

Moderator: Ellery Frahm, [log in to unmask],
Electron Microprobe Lab, University of Minnesota

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*

All,

	Yes, disconnect the power.  Then you can safely let it warm up.

	In order to speed the warm-up process, we have vacuumed the LN2
out of our Dewars.  (I have to admit, this is a lot less exciting that
blowing out the LN2!)  (Clean out the canister first to facilitate
dumping of the LN2.)  Be sure to wear proper gloves, etc. and do let the
hose warm up before trying to bend it, afterwards.  If you leave the
vacuum going long enough , you also get some of the condensate.  You
must follow up with a swab (clean cloth on a wooden dowel) to get the
last residual moisture and dirt.

	A thin coating of ice in the system isn't much of a problem.
The main LN2 Dewar culprit's) are small particles of water ice
introduced by frost falling into the Dewar.  The particles have a
specific gravity just a bit greater that the LN2 (~0.9 versus ~0.8)and
they tend to act as boiling stones and thereby "dance" on the bottom.
This introduces microphonics into your signal and causes your spectral
peaks to broaden.

P


Paul F. Hlava
Senior Member of Technical Staff
Electron Microprobe Laboratories

Sandia National Laboratories
MS - 0886
Albuquerque, NM 87185-0886
505/844-1890
505/884-2974 FAX 

-----Original Message-----
From: JEOL-Focused Probe Users List [mailto:[log in to unmask]] On
Behalf Of Ron Rasch
Sent: Thursday, June 07, 2007 12:55 AM
To: [log in to unmask]
Subject: Re: [PROBE-USERS] Safe ways to de-ice a liquid nitrogen cooled
EDS

JEOL Probe Users Listserver

Moderator: Ellery Frahm, [log in to unmask], Electron Microprobe Lab,
University of Minnesota

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*

Hi Jens,

A shame about your iced up EDS detector; very annoying for light
elements and L lines.

I believe you cannot warm up a SiLi EDS detector under power, but I
believe it is OK to warm up a SiLi EDS detector if it is not under
power. I have done it myself a few times with success. My general
procedure is:

To warm up EDS:
(A) Turn OFF the power on the EDS detector control box. I turn off
everything that is connected to the detector, the one that supplies the
HV bias is the most important.

(B) After a suitable pause, I carefully unplug all the leads and
connectors to the EDS detector unit itself. Mine has a multi-pin plug
and a BNC (HV) plug. I use electrical tape/electrical boxes to secure
and insulate all the loose bits and bobs.

(C) Then let the EDS detector warm up slowly. This may take a few days
or more. I put up signs saying "DO NOT FILL EDS DETECTOR - DO NOT
CONNECT TO POWER" etc. Some people blow out/warm up the LN2 from the
detector with air, but this can be dangerous if done too vigorously, as
it can shower the whole lab with LN2. I usually take the lid off the EDS
detector to speed up the warming. I also tie some cloth around the
outside of the dewar to catch the condensate. I have always left my
detector connected to the SEM and under vacuum.

(D) When the detector is warm, then make sure it is dry inside the
dewar. Ice inside the dewar causes noise. The ice on the detector should
now be gone. I clean out any solid debris from the dry dewar.

To cool down EDS:
(E) Fill the EDS detector dewar with LN2, and let it cool down for at
least two hours. Top up the LN2 after one hour just to make sure it has
enough LN2.

(F) After you are sure the EDS is cold, and have double checked all the
power sources are still off, then reconnect all the plugs and leads to
the EDS detector.

(G) Turn on power to the EDS control box.

(H) Check and calibrate. I use copper (a Cu TEM grid) at 20kV with a
20-30% dead time. In my system the Cu L line should be more than twice
the Cu K line.

A few words of caution:
Please use all care and common sense. Remember I have not seen your
system. Some electrical components may still hold a charge after
disconnecting. There may be local electrical licencing issues. Be aware
of the safety issues with liquid nitrogen, cryo-burns and the
displacement of oxygen.

Finally, when I worked out my plan of attack, I described the detail of
what I wanted to do and sent it to the local EDS agent. They read it and
offered their opinion and approval before I proceeded.

I hope this helps - at least as a starting point.

cheers,
Ron



Quoting "Jens C. Andersen" <[log in to unmask]>:

> JEOL Probe Users Listserver
>
> Moderator: Ellery Frahm, [log in to unmask], Electron Microprobe Lab, 
> University of Minnesota
>
> Post a message: send your message to [log in to unmask]
>
> Unsubscribe: send "SIGNOFF PROBEUSERS" to [log in to unmask]
>
> On-line help and FAQ: http://probelab.geo.umn.edu/listserver.html
>
>
>
> *
>
> Dear colleagues.
>
> I'm looking for information on how to safely de-ice an EDS detector.  
>  The detector is of the lithium drifted silicon detector type that   
> cannot be brought up to room temperature.
>
> Any advice is appreciated.
>
> Thanks,
>
> Jens
>
>
> Jens C. Andersen
> Camborne School of Mines
> School of Geography, Archaeology, and Earth Resources University of 
> Exeter Cornwall Campus Penryn, Cornwall TR10 9EZ United Kingdom Tel. 
> +44 (0)1326 371 836 Fax. +44 (0)1326 371 859
>
> http://www.exeter.ac.uk/cornwall/csm
>
> Visit the virtual Skaergaard intrusion at http://www.skaergaard.org

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