Activation at Five Paces
Posted: Tue May 27, 2008 6:59 pm
Neutron activation at 15-feet using a Hirsch-Farnsworth fusor? Yes sir! But I did have to push my fusor pretty hard, and I did use an easy to activate material (indium foil).
Activation time (fusor run time) for this experiment was 42 minutes at an output (TIER) of ~3.8E+06 n/s. Due to overheating issues the 42-minute run was broken up into three segments with 20-minute cool-down periods between the first and second and second and third runs. (Carl’s water-cooling scheme is starting to look pretty good)!
To determine if activation had occurred I used a 2-inch pancake detector and a Ludlum 2200 scaler / ratemeter to count the betas given off by the activation product. (54.3-minute In-116m). To minimize the effects of variation in the natural background count 90-minute count times were used.
The In-115 >> In-116m reaction has a thermal neutron cross-section of ~154 barns and a resonance integral of ~3200 barns. The piece of indium used for this experiment was ~two inches in diameter and had a thickness of ~0.025-inches. The indium was placed in my UHMW “neutron oven” which was located 15-feet (5-paces) from my fusor.
(Some pix of the neutron oven):
viewtopic.php?f=13&t=5817#p34261
Data:
90-minute count on indium foil before activation: 41.1 cpm.
90-minute count on indium foil immediately after activation: 44.6 cpm.
90-minute count on indium foil 4-hours after activation period: 41.2 cpm.
I should note that I ran this experiment several times using various fusor run times, and in each and every instance the count immediately after activation was always higher than the count before activation.
Doing a few neutron flux calculations proved quite interesting as well:
Fusor output: 3.8E+06 n/s total isotropic emission rate.
Flux at 15-feet: 1.4 neutrons / sq-cm / second.
To achieve that same flux (1.4 n / sq-cm / s) 15 cm from my fusor’s poissor (my normal activation distance) my fusor would need to be producing ~4000 n/s TIER. Not a lot of output to achieve measurable activation.
Jon Rosenstiel
Activation time (fusor run time) for this experiment was 42 minutes at an output (TIER) of ~3.8E+06 n/s. Due to overheating issues the 42-minute run was broken up into three segments with 20-minute cool-down periods between the first and second and second and third runs. (Carl’s water-cooling scheme is starting to look pretty good)!
To determine if activation had occurred I used a 2-inch pancake detector and a Ludlum 2200 scaler / ratemeter to count the betas given off by the activation product. (54.3-minute In-116m). To minimize the effects of variation in the natural background count 90-minute count times were used.
The In-115 >> In-116m reaction has a thermal neutron cross-section of ~154 barns and a resonance integral of ~3200 barns. The piece of indium used for this experiment was ~two inches in diameter and had a thickness of ~0.025-inches. The indium was placed in my UHMW “neutron oven” which was located 15-feet (5-paces) from my fusor.
(Some pix of the neutron oven):
viewtopic.php?f=13&t=5817#p34261
Data:
90-minute count on indium foil before activation: 41.1 cpm.
90-minute count on indium foil immediately after activation: 44.6 cpm.
90-minute count on indium foil 4-hours after activation period: 41.2 cpm.
I should note that I ran this experiment several times using various fusor run times, and in each and every instance the count immediately after activation was always higher than the count before activation.
Doing a few neutron flux calculations proved quite interesting as well:
Fusor output: 3.8E+06 n/s total isotropic emission rate.
Flux at 15-feet: 1.4 neutrons / sq-cm / second.
To achieve that same flux (1.4 n / sq-cm / s) 15 cm from my fusor’s poissor (my normal activation distance) my fusor would need to be producing ~4000 n/s TIER. Not a lot of output to achieve measurable activation.
Jon Rosenstiel