High purity Germanium detector design related clarifications

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
John Futter
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Re: High purity Germanium detector design related clarificat

Post by John Futter » Fri Aug 25, 2017 7:53 pm

Dennis
No TEFLON is no good in this use
teflon creeps in fact it would have to be the worst plastic for creep
Also it is too good an insulator so one cannot define the surface electric field therefore you need greater clearances when using teflon as an insulator
one of the best insulators for this kind of use is acryllic followed by G10.
Of course when these detectors were designed G10 had not been invented
Nowadays especially for superconducting magnets the internal support structures are made from very thick G10
Our mechanical workshop at work NC machines alot of G10 for HTS110
https://www.scottautomation.com/hts-110/

Jerry Biehler
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Re: High purity Germanium detector design related clarificat

Post by Jerry Biehler » Sat Aug 26, 2017 3:06 am

I have found G10 used in a lot of cryo cooled devices like superconducting magnets and EDX units. Probably the best choice.

Stinks to high heaven and is hell to machine though.

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Richard Hull
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Re: High purity Germanium detector design related clarificat

Post by Richard Hull » Sat Aug 26, 2017 7:23 am

G10 is one of the finest tool dullers and fine edge removers I have ever had the displeasure of dealing with. Get out your diamond hones after machining this stuff.
I made a number of rotary spark gap disks from this stuff and insulator bars. Drilling a lot of holes, too.

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Fusion is the energy of the future....and it always will be
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Re: High purity Germanium detector design related clarificat

Post by Jerry Biehler » Sat Aug 26, 2017 8:21 am

If I remember right we cut the stuff with PCD coated end mills. The shop was 200k sq ft and just walking in you could tell someone was running the stuff. Ugh.

AshishGopalakrishnan
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Re: High purity Germanium detector design related clarificat

Post by AshishGopalakrishnan » Tue Aug 29, 2017 9:16 am

Thank you everyone for your suggestions. This has been very informative and helpful.

Based on the responses and some more research into this topic, I came up with the following theoretical conclusions:
Regarding the triangular plate, it could crack due to the following possible reasons:
-Mechanical load applied on the support
-Loads due to stresses due to thermal cycling
-Material that could not withstand either of these of both

I am attaching images that show the triangular plate and a stack of clear plates that also mechanically support the crystal. These stack of clear plates fit tightly in the bore of the detector's end cap.
Stack of clear plates with label.JPG
Image showing stack of clear plates at the detector's end cap
Supports with labels.JPG
Image showing both the supports
As a final step in this case study, I am trying to design a new crystal support system using Solidworks. This new design has to satisfy the following constraints:
- Survive when handled roughly (should not crack)
- Withstand different temperatures (cryogenic temperatures, 100 C bake, thermal cycling)
- Provide insulation
- Minimize material outgassing
- Should be installable in existing detectors that have this cracked plastic plate problem

The last point is a major constrain that has to be taken into consideration. Based on this problem statement that was given to me, I am attaching a file that shows my interpretations regarding the last constraint. Since it has to be installed on existing designs, the following image shows some parameters that will stay in the new design.
Image with design constraints.JPG
Image showing some design related constraints
New design ideas:
1) Mechanical support:
As I have mentioned in previous post, the triangular plate cracks even with gentle handling. Hence, assuming that the load is not uniformly distributed in the existing design, I was planning to include another layer in between the top and bottom layer to provide more support. I have included a figure where I would have pointed out this for better understanding.
Design concept example with actual setup.JPG

2) Materials used:
Based on various suggestions, I shortlisted the following materials to be taken into consideration for the new design and chose the best material by comparing their ability to meet the constraints (withstand mechanical and thermal loads):
-Polycarbonate
-Plexiglas
-Ceramic
-Teflon
-G10

3) Design process:
I have drawn 5 more sketches in a similar fashion, and with different arrangements. To design in solidworks, I will be choosing the one design that satisfies all constraints. In the image that shows one of my sketches, I included a middle layer thinking that it would not fail because of the weight of the system.

I am not sure how my design works when it comes to withstanding thermal loads as a result of cycling and fatigue (repeated expansion and contraction). I am sure the material has a role to play. However, I was wondering if there is any way by which the thermal loads can be minimized using mechanical supports, i.e., can this be designed in way where the thermal loads acting on it are minimal?

Please let me know your feedback and suggestions on my design process. I would love to get your inputs. It would be helpful if you can suggest some references and also provide your ideas on what you feel would be the best to do for this system.

Thanks,
Ashish

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Re: High purity Germanium detector design related clarificat

Post by Rex Allers » Tue Aug 29, 2017 10:49 am

There seem to be several odd threads happening on these forums lately. I would say this is one of them.
The poster is a new member who, other than his introduction post, has only posted in this one thread that he started.

The thrust seems to be looking for thoughts on a possible mechanical design problem in one aspect of a Germanium detector. Such a detector, though a nice, complicated, rare and expensive toy, seems to be of rather limited or tangential use in fusor applications.

Here's my summary of what I see here:

- you are a mechanical engineering graduate

- doing a "case study" on Germanium detectors

- don't seem to have physical access to this detector but

- it is one of the existing designs of a detector, which is currently not being sold in the market and

- you got this information and the pic from the manufacturer

- and you will have to submit your ideas about the possible flaws in this design and also suggest possible improvements.

I'm getting a vibe that we are "helping you do your homework" or more likely this is some kind of employment audition test. Or worst case, you are really trying to design a fix for the manufacturer by pumping for information here.

Sorry if my interpretation of these things is wrong. Is there some other, less icky, purpose for this thread.
Rex Allers

AshishGopalakrishnan
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Re: High purity Germanium detector design related clarificat

Post by AshishGopalakrishnan » Tue Aug 29, 2017 6:26 pm

Rex Allers wrote:There seem to be several odd threads happening on these forums lately. I would say this is one of them.
The poster is a new member who, other than his introduction post, has only posted in this one thread that he started.

The thrust seems to be looking for thoughts on a possible mechanical design problem in one aspect of a Germanium detector. Such a detector, though a nice, complicated, rare and expensive toy, seems to be of rather limited or tangential use in fusor applications.

Here's my summary of what I see here:

- you are a mechanical engineering graduate

- doing a "case study" on Germanium detectors

- don't seem to have physical access to this detector but

- it is one of the existing designs of a detector, which is currently not being sold in the market and

- you got this information and the pic from the manufacturer

- and you will have to submit your ideas about the possible flaws in this design and also suggest possible improvements.

I'm getting a vibe that we are "helping you do your homework" or more likely this is some kind of employment audition test. Or worst case, you are really trying to design a fix for the manufacturer by pumping for information here.

Sorry if my interpretation of these things is wrong. Is there some other, less icky, purpose for this thread.



Hi Rex,

Thank you for the post! Most of your observations are indeed correct - I am new user and a mechanical engineering graduate doing a case study. However, my intentions behind posting on this thread are based out of the intent of gathering knowledge on how to solve this problem. I have not been posting anything on any of the other threads in this forum because not only am I new to this, but there are people here who have way more expertise than I do and can give more insightful suggestions to those seeking opinions. As a result, more often than not, I do feel like I don't have anything more significant to add. But if there are topics where my inputs might be valuable, I will definitely share them.

However, I am not entirely familiar with this forum given that I am new. If such discussions are not the kind that are desirable, I will completely understand.


Thanks,
Ashish

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Dennis P Brown
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Re: High purity Germanium detector design related clarificat

Post by Dennis P Brown » Wed Sep 06, 2017 1:37 pm

As a graduate (!) student you really need to use a CAD program for your 'new' design approach that incorporates the required ability to handle the thermodynamics of heat flow and stress fields as well. Hand drawings and guessing on material strengths at cryo temps is useless. Determining real stress fields for a given design/temp cycling requires good CAD software and what you are doing here is NOT how you should handle this design problem. You have learned what materials to use and design changes that could be useful so at this point, you really need to take it to a level that even a junior in college would use.

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