Fusor Forums

Newcomers might be interested in this neutron activation experiment. When W-186 (one of the several naturally occurring 'stable' tungsten isotopes) is neutron irradiated some of the atoms pick up an extra neutron to become W-187 which is radioactive and can be measured easily with amateur equipment.

To make it even more interesting, the short half life of about 24 hours is dramatic.

Metal foil activation is directly applicable to Fusors as it is one of the standard primary tool to detect and measure neutron flux.

As this experiment develops, updates will be posted in this remote folder:

http://www.qsl.net/k0ff/01%20Nuclear%20 ... ctivation/

George Dowell

edit 5July2015- added Am-Be document

Nice plot of the activity for the activated W. Most fusors can't run long enough to activate Tungsten noticeably wihtout a special high sensitity gamma spec or GeLi detector. We tend to stick with Silver, Indium, Manganese and a couple of others with high cross section and very short half lives under 10 minutes or so. Rhodium would be fabulous if you could get enough to play with.

Richard Hull

George I ran across your site searching for GR-130 DOS software some time ago, a big thanks for making it available. With the software I was able to understand the file format for a custom nuclide identification library, honestly, it is something that should be done in a desktop but I had fun doing it just the same.

I have been wondering if gamma rays transfer energy to atoms in an all or nothing kind of way, or if they can be somewhat moderated. Do a few inches of lead widen the Full Width Half Max of a gamma peak and is there any chance of detecting a 6MeV gamma with a 3MeV instrument?

Thanks
Peter

Hi Peter, please send me a direct email so we don't clutter up the board with non fusor stuff.

George Dowell

GEOelectronics@netscape.com

Peter Schmelcher wrote:George I ran across your site searching for GR-130 DOS software some time ago, a big thanks for making it available. With the software I was able to understand the file format for a custom nuclide identification library, honestly, it is something that should be done in a desktop but I had fun doing it just the same.

I have been wondering if gamma rays transfer energy to atoms in an all or nothing kind of way, or if they can be somewhat moderated. Do a few inches of lead widen the Full Width Half Max of a gamma peak and is there any chance of detecting a 6MeV gamma with a 3MeV instrument?

Thanks
Peter

Hi George

Having so low counts, I see a risk of electronic drift.
Can you design the experiment in order to avoid any changes in response?

Remember, this forum is all about radiation detection. Not just neutrons. Gamma Spec talk is always welcome as that is how we work with activated materials for identification.

GM counters, PMTs, Neutron detection counters or methodology are all viable in this forum. Fusion radiation detection efforts are very diverse and most radiation topics can readily be discussed here. As long as they can be used in part or fully for detection of fusion or radiation found in activation products.

Richard Hull

Thanks for the clarification Richard.

I'm interested in all aspects of nuclear and atomic ionizing radiation and electromagnetic non ionizing radiation detection and shielding.

George Dowell

Richard Hull wrote:Remember, this forum is all about radiation detection. Not just neutrons. Gamma Spec talk is always welcome as that is how we work with activated materials for identification.

GM counters, PMTs, Neutron detection counters or methodology are all viable in this forum. Fusion radiation detection efforts are very diverse and most radiation topics can readily be discussed here. As long as they can be used in part or fully for detection of fusion or radiation found in activation products.

Richard Hull

picture shows the first 12 hour scan and another 12 hour scan after 4 Days= 4 half lives of W-187.



George Dowell

George
Those spectra are the best answer to my question.
Congratulations!
Roberto

Very nice work George... nice clean spectra. What are you using as a neutron source?

Jon Rosenstiel

Electronci drift is there, to be sure and this is due to the A to D converters. This is taken up and corrected for by using a check source each data accumulation session to adjust your amplifier detection threshold and or gain to center the check source's known peak precisely prior to running an unknown or re-running a long, low count re-count days later. Part of the art of gamma spec work.

Again, much excellent gamma spec work has been done here in this forum over many years with activated materials.

Richard Hull

Jon Rosenstiel wrote:Very nice work George... nice clean spectra. What are you using as a neutron source?

Jon Rosenstiel

Hi Jon.

More to come but the working conditions in a nutshell were/are:



Target- 70g WC (tungsten carbide) tool part.

Source- isotopic @20e8 n/s (11/2014), distance 5”".

Moderator- 2"” 200 series S.S., 1""” air gap, 2” water.

Time on source 37 Hr.

Cooldown in hot cell/ transportation cycle- 4 Days



Detector- Bicron 1.75M2/2 FWHM 6.3% @ 661.7 keV-in custom lead shield,

Detector Base- custom made 14 pin base with 1 transistor preamp (Note1)

MCA- URSA II @ 4K channels set for 0-4000 keV range. Run times 1 hour, 6 hour, 12 hour, repeated on 24 hour cycle.











Note 1- I'’ve adopted 2 versions of this base as a standard for 3M14 based integral tube/crystals such as the Bicron. One includes the preamp, the other is all-passive. Both versions now standardized to include only SHV connectors for HV and BNC connectors for Signal.-



Link to PMT Base project, 2N3906 transistor is a good fit:

http://www.qsl.net/k/k0ff/PMT%20Base%20 ... %20PREAMP/



Same base without preamp, gives really good overall performance:

http://www.qsl.net/k/k0ff/PMT%20Base%20 ... %20PREAMP/







George Dowell

Two 12 hour scans, separated by 5 half-lives in time, subtracted from one another. The first scan was the baseline activity, taken as soon as the sample was available and was loaded as "LIVE SPECTRUM" to make this picture.

For 5 more days, another 12 hour scan was taken and saved. Activity at the 5 half-life point has all but vanished. That scan was loaded as "BACKGROUND SPECTRUM" and subtracted from the first scan via the URSA II software function.

This picture then represents the difference between the original scan and the 5 half-life scan. This also removes the minor background counts from distant K-40 and Tl-208 (from Th-232) sources. Essentially the idea is to show what was in the sample when it arrived but is no longer there 5 half-lives later.

I was expecting to see residual W-185, but so far it's presence has eluded the investigation.

The data will be uploaded to the aforementioned remote site so if anyone wants to, they can download the URSA II program designed for your computer platform and then download my raw data .usf files.



George Dowell

Richard Hull wrote:Electronci drift is there, to be sure and this is due to the A to D converters. This is taken up and corrected for by using a check source each data accumulation session to adjust your amplifier detection threshold and or gain to center the check source's known peak precisely prior to running an unknown or re-running a long, low count re-count days later. Part of the art of gamma spec work.

Again, much excellent gamma spec work has been done here in this forum over many years with activated materials.

Richard Hull

Understood Richard and thanks for mentioning that.

For this study the probe was stabilized to operating temperature for about 1 week before, and the MCA has not been shut off since. Of course hour by hour and day to night temperature fluctuations are still present.

The initial energy calibration was done with Cd-109 (Ag-109m X-Rays ~22keV), Am-241 @ 59.5, Cs-137 @ 661.7 and Co-60 @ 1173.2, 1332.5 and the sum peak checked at 2505.7. This particular MCA will allow 12 point calibrating, but I always keep the # points to a minumun, to bracket the area of energy being studied.

I acknowledge the work done by the advanced amateurs here on FUSOR.NET and can credit their input for helping me to get started since I joined here in 2003.

George Dowell

George, my posting was for the fellow who posted wondering about drift in the instrument over time. I knew your calibration would be right on.

Richard Hull

Richard
Thanks for the explanation.
George
Great work!

Regards
Roberto