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Dysprosium Activation?

Posted: Wed Mar 22, 2017 10:54 pm
by Garrett Young
Has anyone activated Dysprosium? This calculator (https://www.ncnr.nist.gov/resources/activation/) indicates that given equivalent mass even over a short period (minutes) it has a higher activation than Rhodium.

Dy-164 (28.26% natural occurrence) has a very high cross section to thermal neutrons.
Dy164-N,G-SIG.gif
Dy164-N,G-SIG.gif (6.39 KiB) Viewed 6797 times
Dy-165m has a half life of 74.2 seconds so it would activate fairly quickly, but it looks like the decay is either an isomer transition to Dy-165 (97.8%) or 1.286 MeV beta (2.2%). (Ref: http://nucleardata.nuclear.lu.se/toi/nu ... iZA=660465) My question: Does the IT emit an easily detectable 108 KeV gamma or would the 1.286 MeV beta be the primary detection?

Dy-165 has a half life of 140 minutes and is a beta emitter (1.286 MeV)

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 2:14 am
by John Futter
Garret
buy some from metallium and try it out

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 10:53 am
by Jon Rosenstiel
Garrett,

Yes, 20 minutes in the neutron oven at 4.0E+06 TIER.



Jon Rosenstiel

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 11:09 am
by Garrett Young
Jon,

Awesome work! How many grams was your sample?

I assume the activated sample also emitted a large amount of beta radiation as well.

I'm concerned, based on your results, that activation with short runs (2-3 minutes) at low neutron rates (200-400k/sec) will be challenging to detect. There would be little difference in the Dy-165m activation level in 3 minutes versus 20 minutes, but obviously the neutron rate would have a significant effect.

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 1:40 pm
by Jon Rosenstiel
Garrett,

The chunk I used was 123 grams.


Don't know about beta emission as I didn't try facing it up to a GM counter.

How long do you have to wait between runs? If it's not too long just keep hitting it as hard and as fast as you can. Dy-165's 2.3-hour half-life does give you a little wiggle room.

Jon Rosenstiel

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 2:03 pm
by Richard Hull
I always look for only beta from my activations. Jon has an EDAX system and a good PMT with NaI:Tl xtal will not look nearly as clean or as bold. I have a gamma spec and use it a lot. It has a 5" bicron scintillator/PMT combo, which I consider a big too big for my use and often revert to my 3" bicron gamma detection xtal/PMT combo.

Jon's work is plus-ultra and this often puts what he shows out of the reach of the casual activator even with a good PMT- gamma spec system.

I have searched the span of the elements and Silver, Indium and Rhodium are the easy ones. Enrico Fermi loved Rhodium best of all. Fast to activate and quick to be reusable (dead).

Rhodium is a bit expensive and silver is the best of all for Beta work and Indium gives a good Gamma spec. as well as beta.

If you ever hit just 1.0e6 TIER and can hold or just hover around that figure for 30 or more minutes, a whole world of activation will unfold before you. That long a blast of Neutrons and x-radiation will demand shielding or remote operation since that world hovers around 40kv applied, in most fusors.

Richard Hull

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 3:35 pm
by Garrett Young
Maybe I'm misinterpreting the data but looking at https://www.orau.org/ptp/PTP%20Library/ ... RDy165.htm it seems that, with the increased cross section, Dy-165m should emit detectable (gamma 1, beta 3) radiation with a simple Geiger counter even with low neutron rates.

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 10:13 pm
by Garrett Young
I acquired a small piece of Dysprosium and ran some tests and early indication is that the sample was activated. I ran for 5 minutes and slightly lower power (TIER 250k n/s) on three separate tests spaced by 30 mins and on each occasion the 1 minute count was 4.8 deviations higher than the following 5 minute background counts. The Fluke Biomedical Geiger counter is fairly sensitive with the pancake style probe.

I assume that the Dy-165m is the primary radiator.

Re: Dysprosium Activation?

Posted: Mon Mar 27, 2017 10:44 am
by Garrett Young
I've been doing more research on why the activation of Dy was so prominent in my setup (low neutron rate, small sample, short time) and found that it's really about the internal conversion coefficient of Dy165m. (Raw internal conversion coefficient data: http://bricc.anu.edu.au/index.php)
The decay of 165Dym to 165Dy has a large internal conversion coefficient i.e. most decays are by emission
of an orbital electron rather than the 108.16 keV γ photon. It is because of this fact that the 165Dym activity can be recorded with a GM counter
(p. 10 http://www.physics.usyd.edu.au/~senior- ... xpt_23.pdf)

If you add up all the CE emission rates due to gamma 1 (https://www.orau.org/ptp/PTP%20Library/ ... RDy165.htm) you get 0.95 Bq s-1 which is equal the main beta decay rate (beta 11) from Ag 110. Couple this activity level with the higher cross section and slightly longer half life of Dy165m (compared to Ag110) and you have a excellent activation material when coupled with sensitive GM counter (note: I used a rubber band to securely hold the flat pouch of Dy to the pancake window for maximum detection).

Re: Dysprosium Activation?

Posted: Mon Mar 27, 2017 4:54 pm
by Richard Hull
I'll have to give DY a shot. The internal conversion blasting out an orbital electron would demand a mica windowed GM tube I would imagine.

Richard Hull

Re: Dysprosium Activation?

Posted: Mon Mar 27, 2017 5:12 pm
by Garrett Young
Here is the probe I'm using: http://www.flukebiomedical.com/biomedic ... ?pid=54801 (which does have a mica window)

Re: Dysprosium Activation?

Posted: Mon Mar 27, 2017 11:53 pm
by Garrett Young
New Run - Changed Measurement Equipment

5 minute run, 218k n/sec average
~0.5 gram Dysprosium, 15 cm distance to cathode
Data taken with RDA-3A beta scintillation detector and Ortec 4890 PreAmp/Amp/SCA

Peak CPM ~2x background average and 6+ standard deviations
Dy165.png
IMG_1580.png

Re: Dysprosium Activation?

Posted: Tue Mar 28, 2017 10:56 am
by Garrett Young
It's unclear why the peak activity is delayed by 5 minutes. If this was a transition from Dy165m to Dy165 then the activity wouldn't have decayed as quickly after the peak (?). Potentially some other interaction with the setup is causing erroneous results.

Re: Dysprosium Activation?

Posted: Tue Mar 28, 2017 11:42 pm
by Garrett Young
Still getting odd decay numbers with the beta scintillation detector. The counts are clearly higher with neutron activated Dy than without, but the data is not intuitive. Does anyone have thoughts on this?

Re: Dysprosium Activation?

Posted: Wed Mar 29, 2017 12:27 am
by Michael Hughes
Related to my other thread on PoBe, I was able to activate dysprosium-164 to Dy-165 using 10 mCi of PoBe sources. The Dy was a baggie of 25g of Dy2O3, which I activated for about a day in my neutron oven and then taped around the GM tube of a GMC-320.

Since I'm working under different conditions than fusioneers are (much lower flux, but much longer activation and counting times letting me test higher half-life nuclides), I look for smaller deviations above average background counts over longer periods of time. I haven't tried finding Dy-165m and failed at finding anything statistically significant with silver, but I definitely got a detectable amount of Dy-165.

A t-test comparing the average of the GM counts from the first half-life against the background average (3.01 cpm above background) found an extremely significant increase at p < 10^-12, although the second and third half-lives weren't significantly above background (p=0.06 and 0.07 respectively). I defined the background as the average of everything from 5 half-lives until I stopped the test at about 12 half-lives of Dy-165 (total of 28 hours of counting). Only the first 7 are shown:

Image

So, given my puny flux of something like 10k n/s, I think that the fusioneers here who are getting >250k n/s and who can run for more than a few minutes should easily be able to find Dy-165 in addition to Dy-165m. Then again, I'm not totally sure how far away the activated material can be in a fusor neutron oven - obviously the oven would have to be outside the fusor itself, and then there would be at least 10 cm or so of plastic on all sides. I get to place my target material directly on top of the PoBe source, which is a huge advantage given the inverse square law. How far away do you guys have to place your target material from the center of the fusor?

Re: Dysprosium Activation?

Posted: Wed Mar 29, 2017 2:41 pm
by Richard Hull
10-12CM is the norm from the central grid to the center of the neutron oven and material to be activated. The central grid is not the only source of neutrons in a fusor as the source is more difuse and the oven, itself, only incepts a fraction of the neutrons. A very complex situation. A neutron oven to intercept 100% of the fusor neutrons would have to enclose the entire device. ( A virtual impossibility due to expense and numerous mechanical issues.)

Richard Hull

Re: Dysprosium Activation?

Posted: Wed Mar 29, 2017 11:41 pm
by Michael Hughes
Yeah, I realized that neutron emission from fusors is pretty much isotropic and that the oven can't cover the entire fusor or anything, but not that some of the fusion happens outside the grid. I hadn't thought about just how badly the inverse-square law hinders neutron activation with a fusor though.

Taking a fusor running at 250k n/s, and an activation target 10cm from the center of the grid (which I'll pretend is where all the fusion takes place), you would have 250000/(4*pi*(10 cm)^2) = 199 n/s/cm^2, whereas my targets are directly on top of the PoBe source, so let's say 10k n/s at an average distance of 1 cm would yield 796 n/cm^2/s.

Still, though, I'm kind of uncertain about how it all works out within the moderator given that both fusor and alpha-Be sources require something like 18 collisions with H atoms to get down into the thermal range, which presumably means that there are neutrons wandering around throughout the moderator and only some of them find their way to the target. So I'm not sure how a given fast neutron flux converts to a thermal neutron flux. I posted a related thread in New User Chat.

Re: Dysprosium Activation?

Posted: Fri Mar 31, 2017 12:46 pm
by Richard Hull
I have noted that in the average 6" spherical fusor you need to be producing about 500k n/s iso to do a good amount of easy activation. One million n/s iso will be necessary for advanced activation. This assusmes an eight inch cube of HDPE as a neutron oven placed in virtual contact with the fusor shell. Naturally, an assiduous, dedicated researcher with a fusor can get by with lower numbers than noted above.

Richard Hull

Re: Dysprosium Activation?

Posted: Sat Apr 01, 2017 1:09 am
by Garrett Young
It seems short term activation produces erratic counts (but statistically significant compared to background to a high confidence factor).

I decided to target Dy-165 activation by repeating the cycle of running for 4 minutes at ~300k n/s and cooling down for 10 minutes a total of 5 times (60 mins total time). This strategy has produces intuitive results with persistent activity.
Dy165.png

Re: Dysprosium Activation?

Posted: Sat Apr 01, 2017 12:56 pm
by Richard Hull
The size of Garrett's fusor is rather small compared to most fusors and he is intercepting far more neutrons in the moderator than others at 300k n/s iso. The few extra cm, closer to a larger oven does make a difference. In fusor activation, it is all about how many fast neutrons you can put into the largest moderator possible.

Richard Hull