Hello, so I am trying to make a sealed Na22 source. The usual way is to put in a drop or two of the salt solution, where some of the Na of NaCl is radioactive, on a kapton sheet of 10 micron. Then you cover it with another identical kapton sheet and seal the edges using glue. This is the standard way. Jerzey Dryzek talks about it nicely here. This kapton + Na22 source is sanwiched between two identical samples for positron lifetime experiment.
Now, the problem with Kapton is that its usage is limited upto ~ 500 C which is its melting point. So, what are the alternatives for Kapton if one wants to use this source in high temperature experiments (say around 1400 C). I have tried once with Tungsten foil of 1-2 micron thickness. It worked nicely in the begining but then slowly the Na22 started leaking out from the pin hole in the foil or cracks in it. Eventually, one day it tore. So, what are the other options? I am thinking of making a similar source with micron thick tungsten foil but then cover it with another micron thick tungsten foil. This might work but will have slightly higher 'source correction'. That is not a big problem though. Does anybody have any suggestion as to what other ways might there be to make a high temperature Na22 source for positron lifetime experiments?
thank you
saurabh mukherjee
http://www.ifj.edu.pl/~mdryzek/page_r21.html
https://www.researchgate.net/profile/Jerzy_Dryzek
Can you use tantalum/titanium etc
Manufacturing is described in attached document
Thank you for the reply, Mushtaq. But the pdf you attached describes how to make a UHV compatible source for positron beam. What I am looking for is basically a good substitute for kapton using the process as described by Jerzy Dryzek in source preparation (link attached in my original question).
We have used metal foils such as Ni in the past (not at 1400 C) that are spot welded at perimeter using a thicker "window frame" around it for strength. This is not vacuum tight. My preference would be to minimize the source effect by depositing Na22 directly on my sample sandwich. This may not be an option if you need the samples to be contamination free.
I think the source embedded inside the glass can meet your requirements. In this case you can also avoid the metallic materials. I is helpful not only for high temperature measurements but also for measurements in liquid samples.
Conference Paper Preparation of Na-22 positron source embedded in the glass f...
Dave, Thank you for the reply. I was talking to Dhanadeep Dutta and he actually told me about how you make sources using Ni foils. I have some questions though- 1. how thick is the foil? 2. Do you use a general purpose spot welding machine (i have attached a picture that I think we have in our lab) ? 3. Did you have problem with slow leaking of source from the foil?
saurabh
Pushkar,
Thank you for the reply. So the 600 C temperature mentioned in your paper - is it because the glass transition temperature of soda lime glass is ~ 570 C. So, in that case wont that be the limit of the temperature it can go upto? Basically, I am trying to sort of repeat this work- " Investigation of vacancy formation and phase transformations in uranium by positron annihilation " ARTICLE in JOURNAL OF NUCLEAR MATERIALS 88:273-278 · FEBRUARY 1980.
saurabh
Narendra, I am not very sure about the time but lets say an hour at each temperature. Now, since its a temperature scan , the whole thing will take probably 1-2 day. so, roughly 12 hours at high temperature.
saurabh
I don't remember the precise Ni foil thickness but it did stop 10-20% of positrons. Your spot welder looks to be too big. We have a 0-250 Watt-sec lab grade spot welder that can do rather delicate work. We did not need to be particularly delicate here because we were spot welding the heavier metal frame that had the thin Ni foil in between. We spot welded as close as possible to the inner edge of the frame (close to the foil) but we did not spot weld directly onto the thin foil. These thin foils where thick enough (perhaps too thick) such that they did not leak through--we did not get samples contaminated. However, I do recollect that the source material (under some environmental conditions that I do not recall) did move radially outward such that some of the source seemed to be under the heavier frame--thus the intensity of positrons stopping in our sample is less as some fraction of positrons stopped in the Ta frame.
Follow Gidley approach. Select well annealed foils for non-detectable holes. NaCl boils about 1400 degC so an enclosed source will have increased volume and pressure as temperature rises and the hole(s) expand radially. Your source correction will be interesting depending on the required accuracy and precision for a given lifetime. Your systematic analysis may be interesting reading!
Thank you for the reply, Jim. I did not consider the boiling point of NaCl so thanks for pointing that out. That puts an upper limit on the temperature. I will try the way suggested by Dave.
saurabh
Why you don't try to quench the samples after heating in the furnace for a reasonable time and to measure them at room temperature afterwards? It will froze the defects and phase composition at the heating temperature. We have used such a methodic to investigate defects in different materials at varied conditions e.g. "Positron Annihilation Measurements of Quenched-in Defects in Ni", Physics Letters A, v. 138, n. 1,2 (1989) 65-68.
Hello Ivaylo
what you suggest can be done. I was trying to reduce the hassle because annealing & quenching at every step might involve some work. This way, you automate the whole system and come back after 1-2 day.
saurabh
Hello Ivaylo
what you suggest can be done. I was trying to reduce the hassle because annealing & quenching at every step might involve some work. This way, you automate the whole system and come back after 1-2 day.
saurabh
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