Dead Time

Dead time is the percentage of time that your detector is unable to record events either from material considerations (light transport), electronics (very slow ADC), or online data processing.  In determining the GARRn (see PNNL 18903 if intrested . . .) we measure the response of our films to a mixed spectra.  The additional gamma flux causes a bunch of low energy counts that aren't present in the pure neutron field, which increases the dead time.  This then cases the spectra to shift to lower energies with a larger gamma flux.

As more sources are added the dead time went to ~5%. 

 However, as you can see by the tail, events are still taking place at high channel numbers, they are just not being sampled as frequently.  Kinda neat now the recording of spectra can be thought of a monte carlo sampling. If we increase the LLD from channel 150 to 1,000 then we see that this artifact disappears (mostly).

Higher LLD decreases the dead time, causing a more accurate sampling. No idea why the 6uCi is shifted to the right.

Further in Monte Carlo world, I've been trying to prove the optimal Battleship (board game) game play based on minimizing the discrepancy.  They use this same idea in quasi-random number generators, where the pick the random values in a predetermined sequence which minimizes the region that is not sampled; for example the Halton Sequence is base two on the interval (0 1] is 1/2, 3/4,1/4,5/8,3/8,7/8,1/8, etc.

I'm trying to update to Geant4.5 to use their new constructors (I want to avoid defining my own sensitive detector and related hit classes) so I'm back to trying to get Geant4 to work in Visual Studio.  It really seems to be full proof, but somewhere I am messing up at the final build, probably because I installed my make tools in Program Files, which has a space in it so won't be treated a properly in a relative path.

CHAMPIONS

IM ULTIMATE CHAMPIONS!

Jeffy's Friends Team Members:

• Jeffrey
• Richy
• Harrison
• Fong
• Timmy
• Alex
• Trent
• Carter
• GT

WHOOO!

Cranes

They are doing construction behind Pasqua, which involves a crane!  Cranes are very cool.

Crane!

The base of the crane is counter weighted with cement

This Crane is called "Papa Bear"

Gamma Interaction Simulations

One of the drawbacks of using MCNPX is a lack of control for the physics options, and its refusal to implement certain features.  So I have taken to playing around with Geant4 again, which means I get to make awesome pictures.

50 Events in a Plastic Scintillator

The results even seem correct, so I guess I'm on the correct track! (Get it, track . . .).   Next step is to add a photo cathode behind it and implement hits collections and sensitive detectors. I've also started to write my thesis; I think I am starting to look forward to getting away from Rocky Top.

In other news our IM Ultimate suffered our first defeat of the season after a very sluggish, hammer throwing, who needs defense first half.  We should still have the head to head and point diff, so I am still on track to win a T-Shirt.

Points Progression

I was following the twitter feed of CMU ultimate last weekend at Queen city and was  surprised by the number of runs in their games.  It might not have been real (old folks have bad memories), but I decided to look at my stats from the UT games in terms of score progression.

The above busy little graph shows the progression of score for various UT games.  A good game for a team is like "The Program's" game against us - we only scored 3 points.  A bad game is the UCF game, where UCF scored 7 points in a row.

I think this gives a pretty good idea of how your O and D lines perform; over many games you want to be in the lower right rather than the upper left, and you definitely do not want vertical streaks, they signify a large number of O line breaks.

Maybe if I get bored (I told myself I was going to write my master thesis this weekend; I even got a bottle of scotch) I will mine Pitt's twitter feed to see how a good team performs.

The Solution to Pollution is Dillution

Rocky Flats (Wikipedia)

Rocky Flats was a nuclear weapons production site (hydrogen bomb and plutonium) until 1992.  As with most of the national lab associated with the weapons program  they had leakage of radioactive material into the environment.  (Is there a weapon's lab that didn't have a release?)  One such release exceeded the EPA's limits for soil contamination by a little bit, so the Rocky Flat's solution was just to till the group; dilute the contamination to below the EPA limits.  This didn't fly, and eventually Rocky Flats had to clean up their mess.

This brings up an interesting point; why was it a problem to dilute the pollution to below the EPA limit?  Almost all of the NRC operating limits are not determined by the amount of radioactivity you release, but rather how much you release per volume / mass or the dose, which depends on the per volume / mass you are in contact with (for the exact values, see 10 CFR - there is some good stuff in there).   Their probably shouldn't be so much leeway in the codes - a hard amount of radioactivity released (in activity, broken down by isotope) should be set.

How many messes do you clean up by diluting?

Weekend Follies: Boosting Detector Performance

I've been playing with using different geometries and materials to boost the perforamance of our detector.  If you encase our detector in Stainless Steel (SS-316) you get around a 0.3% increase in in the absolute detection efficiency, compared to air.  After some hunting I discovered this is because of the (n,2n) reaction in nickel.  If you encase the detector in highly enriched uranium you then get a 35% increase.  However, this amount of encasing requires over 100 kilograms of HEU; for comparison Little Boy used 64 kg U.

In other news UCF had a very strong performance at Warm-Up.    I hope they can do a repeat at Easterns; hopefully the South East can get more than one bid.