Silver Activation From Hell - 18MeV Clinac.

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.
Post Reply
RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 1:49 pm
Real name:

Silver Activation From Hell - 18MeV Clinac.

Post by RobertTubbs »

I took the day to play with a few Clinacs in town and thought I'd share what is probably the hottest silver activation on record here.

The procedure was to sandwich a 1 troy-ounce .99 fine Vienna Philharmonic between two wax bricks and nuke it from orbit with the 18MeV Linac in photon mode.

Activation after 10 minutes was beyond the scope of the Ludlum-12 Ratemeter/thin window NaI so I numbed it alittle with a generic 6993 GM tube which still pegged initially. According to the dose calibrated (for Cs-137) Eberline on hand at the hospital the coin was reading 50-60mRem/hr just before the Eberline bought the farm.

After 2 hours it was ~2,000 CPM on the surface with the 6993 tube.

After 4 Hours it was ~200 CPM on the suface with the 6993 tube.

Here's a video of the activation: http://youtu.be/wsiclNmrD7U

Here's a video of the coin at 2 hours: http://youtu.be/1V7-ZDGg8LM

Here's a video of the coin at 4 hours: http://youtu.be/rf0ZT9BrNCk

It's been almost 5 hours and it's still singing....

[Pictured is a different machine, one that was getting some TLC.]

Enjoy,
RT
Attachments
328294_2621549509004_1563208816_32215179_1558523881_o.jpg
User avatar
Steven Sesselmann
Posts: 2127
Joined: Wed Aug 10, 2005 9:50 pm
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Steven Sesselmann »

Robert,

For those of us who are less familiar with this kind of Linac, would you like to share what this machine is used for, how you get access to play with it, and what nuclear reaction is taking place between the machine and the silver coin to make it radioactive.

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 7:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Carl Willis »

Interesting experiment, Robert. That's some quite-hot silver.

Steven, Robert will have to fill in the details particular to his equipment, but broadly these are electron linear accelerators made for external-beam radiotherapy, one of the leading methods for treating cancer. The electron beam is usually a few dozen microamps accelerated through an RF coupled-cavity waveguide to energies as high as 25 MeV. Most treatments use the poly-energetic bremsstrahlung beam created by the electrons striking a high-Z target as in a diagnostic x-ray tube, and I suspect that's in place for Robert's experiment. Photons of such high energy can break apart nuclei in what are referred to as photonuclear reactions. The (g,n) reactions are particularly common. 1.7-MeV photons will blow a neutron out of beryllium; 2.2-MeV photons will blow a neutron out of deuterium; 6-7 MeV photons will blow a neutron out of most anything. At 18 MeV, there are many photons with energies exceeding the photoneutron threshold in the accelerator's target and collimator. Most of the neutrons are probably born in the head of the linac for this reason.

Illy Sommer posted on a similar activation experiment involving simply a Geiger counter:
viewtopic.php?f=13&t=6248#p34692

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277
User avatar
Steven Sesselmann
Posts: 2127
Joined: Wed Aug 10, 2005 9:50 pm
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Steven Sesselmann »

Carl,

Are you suggesting that neutrons are a byproduct in this machine, and that high energy gamma rays are what is required for the cancer treatment?

Further you say that 1.7 Mev photins will dislodge neutrons from Beryllium, is this an energy specific reaction, or are you saying that anything over 1.7 Mev will do it?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 7:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Carl Willis »

Hi Steven,

Yes, neutrons and radioisotopes are undesirable byproducts, although their contribution to the overall healthy-tissue dose in a typical treatment is small.

The energies I mentioned are thresholds, below which that particular photonuclear reaction won't happen and above which it is kinematically allowed (though the cross-section tends to be very low just above the threshold).

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277
RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 1:49 pm
Real name:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by RobertTubbs »

Carl kindly covered everything of significance in this context, the only thing I'd stand to say is that in photon mode these machines are accelerating beam currents between 20-50mA resulting in a dose of approximately 700Rads/minute. I don't know exactly what the continuum of X-Rays looks like on these machines but I imagine they've been engineered to produce X-Ray energies as homogeneous as possible depending on what energy mode they're locked into.

RT
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: Silver Activation From Hell - 18MeV Clinac.

Post by George Schmermund »

Why is there a rabbit in the background?
Anything obvious in high vacuum is probably wrong.
RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 1:49 pm
Real name:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by RobertTubbs »

Haha, Tyler had to email me a photoshopped picture to really see it. The object in the screen of the Clinac 6EX is an arm holding a camera.

I can assure you no rabbits were harmed in the process of yesterday's shenanigans.

RT
Attachments
328294_2621549509004_1563208816_32215179_1558523881_o(2).jpg
User avatar
Steven Sesselmann
Posts: 2127
Joined: Wed Aug 10, 2005 9:50 pm
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Steven Sesselmann »

Robert,

700 rads converts to 7 Gray, which is 7 joules/kg

If the rabbit weighs around a 1 kg, and to fully cook it, you need to raise it's temperature to 100 C˚.

Take 100˚ less its normal body temperature 35˚ = 65˚ heating required.

The energy needed to heat one gram 1˚ is around 4.2 Joules, ergo to cook the rabbit we need.

1000 grams x 4.2 J x 65˚ = 273,000 joules

273,000 J / 7 J / 60 min = 650 hours

Have I made a mistake, or is this a really expensive way to prepare a rabbit?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 7:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Carl Willis »

Hi Steven,

Rabbit is recommended to be cooked to an internal temperature of 82 deg. C, although the tender breast is often prepared at a slightly lower temperature.

One of the difficulties facing the chef in this unique situation is the fact that rabbits are too small to achieve charged-particle equilibrium for such high-energy photons. The depth dose profile will peak toward the distant side of the bunny, but a lot of energy will still be wasted in the surroundings. If this were my task, I would first cram the animal into a vacuum-insulated Thermos bottle in order to curb heat loss. I would then surround the Thermos on the outside with a "buildup cap" of sorts, made out of any convenient material, perhaps accomplished by sinking the Thermos in a larger pot of water, in order to place the depth dose peak right in the middle of Peter Cottontail's wee rib-cage.

After cooking and before eating, it would be wise to allow the slow-roasted lapine to stand for about an hour so that N-13 produced in the flesh could decay away.

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Silver Activation From Hell - 18MeV Clinac.

Post by Richard Hull »

Potent photo neutron isotope sources used to be made in the 50's and 60's out of ultra hot 124Sb-Be mixtures. However, as with Ra-Be sources, the gamma rays especially with the 124Sb-Be sources were fearsome and could cook you really well done. Such sources were never really distributed widely and usually involved a massive container vessel with a beam port or a section of neutron oven contained within them where the item to be neutron blasted could be inserted safely. Some were referred to in older documents as neutron howitzers.

The most common, stable and safest radioisotope neutron source today is the Am241-Be mixture, making all the older photo neutron sources pretty much obsolete.

Note: In the early days of the fusor effort, in an attempt too poo-poo our work some few un-informed scientists and supposed learned detractors claimed we were making neutrons not due to true fusion, but due to the Oppenhiemer-Philips reaction which, of course, is just not possible at our energies. This is just beyond where the cross sectional fusion curve falls way off at energies above 2mev and "stripping" can occur. Here, the deuterons refuse to fuse, but can instead, shear off neutrons from each other.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
David Housley
Posts: 32
Joined: Sun Feb 20, 2011 5:07 am
Real name:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by David Housley »

While Carl is correct about the need for buildup to cook the rabbit, I suggest a much better alternative than water as the bolus material. I say wrap the rabbit carcus in plenty of bacon! Everybody KNOWS it works better with bacon Ok, I'll stop now...
Carl Willis wrote:
> Hi Steven,
>
> Rabbit is recommended to be cooked to an internal temperature of 82 deg. C, although the tender breast is often prepared at a slightly lower temperature.
>
> One of the difficulties facing the chef in this unique situation is the fact that rabbits are too small to achieve charged-particle equilibrium for such high-energy photons. The depth dose profile will peak toward the distant side of the bunny, but a lot of energy will still be wasted in the surroundings. If this were my task, I would first cram the animal into a vacuum-insulated Thermos bottle in order to curb heat loss. I would then surround the Thermos on the outside with a "buildup cap" of sorts, made out of any convenient material, perhaps accomplished by sinking the Thermos in a larger pot of water, in order to place the depth dose peak right in the middle of Peter Cottontail's wee rib-cage.
>
> After cooking and before eating, it would be wise to allow the slow-roasted lapine to stand for about an hour so that N-13 produced in the flesh could decay away.
>
> -Carl
George Dowell
Posts: 160
Joined: Fri May 09, 2003 10:30 am
Real name:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by George Dowell »

Cobalt activation. Light water moderator. George Dowell
Attachments
Screws Alone.jpg
jcs78227
Posts: 35
Joined: Mon Dec 27, 2010 5:57 am
Real name:

Re: Silver Activation From Hell - 18MeV Clinac.

Post by jcs78227 »

Speaking of those ultra hot 124Sb-Be mixtures, the 50's, and silver coin activation:

http://www.orau.org/ptp/collection/meda ... /dimes.htm

I admit much of the time the theoretical conversation here is at the edge of my physics education, but I had no idea that photonuclear reactions would be this foreign a concept.

-Jonathan
Post Reply

Return to “Neutrons, Radiation, and Detection (& FAQs)”