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Fusor V... A calibration report from HEAS 2020

Posted: Tue Oct 06, 2020 8:22 pm
by Richard Hull
At HEAS, a few days ago, Bob Reite, (pronounced "right"), brought his calibrated rem ball capable of determining the instantaneous and average mrem/hr rate in a neutron flux field. This has allowed for a far more accurate determination of the fusor V capabilities including flux figures and TIER figures allow for an accurate instantaneous flux value as well as a true average flux over a period of time during a run. As you will see, the instantaneous flux values during a particularly great 1 minute counting run can be well over twice the average flux over a period of 5 minutes! Both of which could be seen and recorded on Bob's superior Eberline neutron controller/counter attached to his rem ball.

Data taken down in the best run of fusor V on October 3rd at HEAS as witnessed by as many as 6 people during a 15 minute active run and silver activation.

Highest 1 minute activation count on my 3He detector and digital counter system... 157,960 CPM
Highest recorded instantaneous mrem/hr rate during the above run..... 4.01 mrem/hr
Average recorded mrem/hr rate over the last 5 minutes of 2.48 mrem/hr
Silver activation, first 10 second silver GM count 128 counts over that short period. Old record was 105 counts

The data taken is displayed below along with the decay graph of the two neutron activated silver isotopes.

Run data:

10.8 microns....35kv....7ma.....24,879 CPM

note: the above 10 runs took 15 minutes with some minor adjustments made between each run It is figured the last 5 measurements made up the 5 minute average on Bob's counter for the 2.48 mrem/hr rate.
The 157,960 run did indicate an instantaneous value at one point of 4.01 mrem/hr instantaneous. The graph of this run's silver activation is seen below.

Now to resolving and computing flux and a future multiplication factor.

I will use the average of the entire run to determine both the future multiplier of a median average count over a run as a ratio to determine average flux and average count.
However, I will use the ratio (later to be computed) for the highest one minute count to represent the maximum TIER attained.

First, the run average is computed.

The rem ball has a calibration curve to relate its mrem/hr readings to a flux. The graph indicates that the ball detects a net flux of 9.5 neutrons per sq cm per second as an indication of 1 mrem/hour.
The average over 5 minutes in the above run was 2.48 mrem/hr. Thus, the average flux was 9.5 X 2.48 = 23.56 n/

This flux was measured in the Rem ball 44 cm from the fusor. This distance was measured by Bob Reite and confirmed by Richard Hull in a second measurement.

To arrive at the average TIER, the fixed distance of 44 cm becomes the radius "r" of the TIER measurement sphere. Assuming uniform emission and no reflection, scattering or absorption of neutrons by the steel in the fusor or surrounding objects, we now compute the area of the detection sphere. 4 Pi r^2 = 24,328 sq cm.

As 1 sq cm at 44cm represent a flux of 23.56 the "Average TIER" for the above run over 5 minutes is 23.56 X 24,328 = 573,179 neutrons per second. The average count over the period is the sum of the last 5 readings which is 144,074 This makes for an averaging multiplication factor of 573,179/144,074 = 3.98 this will be used in future as the multiplier of the average run count to determine all future "Average TIER" run outputs.

Now to compute the best one minute run resultant flux and TIER based on the greatest instantaneous recorded mrem/hour during that 157,960 cpm run.

The instantaneous flux is 9.5 X 4.01 = 38.1 n/cm sq/sec.
The detection sphere has the same computed area as in the average example. 24,328 sq cm
Thus, the instantaneous or best TIER for the 157,960 cpm one minute fusion is 38.1 X 24,328 = 926,896 neutrons/sec TIER or just short of the mega mark. The instantaneous multiplier in future of the best 1 minute neutron count might be assumed to be 926,328/157,960 = 5.86


Using the calibrated REM ball the average TIER over a run of 5 minutes might be best computed in future with a multiplier of 3.98 times the average of the last 5 one minute cpm neutron counts.
The instantaneous one minute TIER, based on a superlative 1 minute count, might be assumed to be 5.8 times the one minute count.

Only the average flux and average TIER bears on the overall ability to activate any isotope with a half-life over 2 minutes.
The instantaneous flux and TIER represents but a fleeting period of a top output rate for the fusor.

As the remball has tied its result to the counts produced by the fixed 3He system I currently use, the multipliers of 3.98 and 5.8 will be applied in future for the averaged 5 minute run Tier and the instantaneous peak TIER during a specific 1 minute superior count during the run, respectively.


I will endeavor to repair my PNC-1 lately calibrated neutron counter to cross check the above. Some hope of obtaining data from a bubble detector or my future 5-inch BC-720 PMT system seems possible as well. Until such time, I shall use the reduced multipliers above which are much more in line with reality.

Using my crude, but abortive attempt at calculation base on the stated cps/nv value on the 3He resulted in a 2.42 multiplier was a bit off, but that is old news now and in the past.

Richard Hull

Re: Fusor V... A calibration report from HEAS 2020

Posted: Wed Oct 07, 2020 11:27 pm
by Richard Hull
Bill Kolb did his normal analysis of the HEAS best run on activation of silver by fusor V. I attach it below. Bill felt the background was lower, but I felt the activation was exceptional enough, (best ever), that the noise floor rose above the old background line due to following the increased activation. This is really noticeable in the long decaying Ag110

The main post above with the new data is a great improvement and may have flaws, even in it, but it is what we have to work with and better and more well grounded than what preceded it.

Richard Hull