April 2001 anneal report for program 8841.

There was an anneal of the CCD on Apr 18, 2002, 30 days after the previous
anneal on Mar 19, 2002.  A homogeneous set of data was obtained from proposal
8841:  The CCD Hot Pixel Annealing.

Previous trends continue.  The growth rate of hot pixels continues within the
range seen for previous months.

1) The number of post-anneal hot pixels has decreased at all levels.

   > 0.1 e/s: 16438 pixels on Apr 18, 2002
   > 1.0 e/s:  3499
   > 10. e/s:   395
   
   > 0.1 e/s: 16645 pixels on Mar 19, 2002
   > 1.0 e/s:  3504
   > 10. e/s:   397
   
   > 0.1 e/s: 15803 pixels on Feb 4, 2002
   > 1.0 e/s:  3330
   > 10. e/s:   376
   
   > 0.1 e/s: 15800 pixels on Jan 9, 2002
   > 1.0 e/s:  3295
   > 10. e/s:   353


2) The *raw* post-anneal dark countrate for this anneal is 0.02648 cts/pixel.
   This compares with 0.02592 cts/pixel a month ago, and 0.02618 cts/pixel 
   a year ago.
   
3) The iterated median count rate (after iterating up to 30 times by
   eliminating pixels +/- 5*sigma) is 0.00438, up from last month.

4) The creation rates for hot pixels over this period were on the low side.

   > 0.1 e/s:  -0.1 pixels/day in Apr 2002
   > 1.0 e/s:   0.2
   > 10  e/s:   0.2

   > 0.1 e/s:  37.1 pixels/day in Mar 2002
   > 1.0 e/s:   6.9
   > 10  e/s:   1.7

   > 0.1 e/s:  25.2 pixels/day in Feb 2002
   > 1.0 e/s:   4.4
   > 10  e/s:   0.7


   > 0.1 e/s:  53.0 pixels/day 1 year ago
   > 1.0 e/s:  10.2
   > 10  e/s:   1.1


5) The rate at which new hot pixels annealed out was high, as not many new hot
   pixels were created.

   > 0.1 e/s: -5075% annealed away in the Apr 18, 2002 anneal
   > 1.0 e/s:. 183.%
   > 10  e/s:3  140%

   > 0.1 e/s:  46.0% annealed away in the Mar 19, 2002 anneal
   > 1.0 e/s:  40.0%
   > 10  e/s:    70%
   
   > 0.1 e/s:  99.5% annealed away in the Feb 4, 2002 anneal
   > 1.0 e/s:  67.9%
   > 10  e/s:   -35%


   The usual plots are attached.