I apologize to everyone who Matthew did not even give a chance to think but the excuse is that Matthew is really good! 
 
It was a saturation of the I_t current amplifier. Another sign of that is too sharp a rise of the edge right after the pre-edge - it is when the I_t signal  drops below the saturation limit.
 
A comment: the last time NSLS had 20h of stored beam lifetime was in the 20th century, I think, but it is besides the point.
Anatoly
 
 
-----Original Message-----
From: Matthew Marcus [mailto:mamarcus@lbl.gov]
Sent: Thursday, April 03, 2008 9:30 PM
To: anatoly.frenkel@yu.edu; XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Brainteaser

The most obvious explanation for why the post-edge scans line up and the pre-edges don't is that the transmission chamber
current amp or V/F is saturated and reads a fixed value below the edge.  As the ring current decays, I0 goes down while
It is fixed below the edge, so ln(I0/It) decreases as observed.  With this explanation, and noting that ln(I0/It)
decreased by about 0.05 in an hour, I infer that the stored-beam lifetime is ~20hr.
    mam
----- Original Message -----
From: Anatoly Frenkel
To: anatoly.frenkel@yu.edu ; 'XAFS Analysis using Ifeffit'
Sent: Thursday, April 03, 2008 6:13 PM
Subject: [Ifeffit] Brainteaser

Attached is a brainteaser which I think is cute. Too late for the April fool's day but still... 
Some comments: three consecutive scans of the same sample were taken in this order: scan 1, 2 and 3. Duration: 30 minutes per scan.
 
If these data look unusual to you please tell us why and what could've happened in this experiment. 
 
Those of you who send first three correct answers will be acknowledged!
 
Anatoly
 
 

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