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Dysprosium Activation?

Posted: Thu Mar 23, 2017 2:54 am
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
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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 6:14 am
by John Futter
Garret
buy some from metallium and try it out

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 2:53 pm
by Jon Rosenstiel
Garrett,

Yes, 20 minutes in the neutron oven at 4.0E+06 TIER.
Dysprosium.jpg
Jon Rosenstiel

Re: Dysprosium Activation?

Posted: Thu Mar 23, 2017 3:09 pm
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 5:40 pm
by Jon Rosenstiel
Garrett,

The chunk I used was 123 grams.
Dy 005a.jpg
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 6:03 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 7:35 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: Fri Mar 24, 2017 2:13 am
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 2:44 pm
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 8:54 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