From dd Thu Oct 23 09:41:39 2003
To: mwb
Subject: Re: ACIS OBF distance and ECS diameter
Cc: cgrant@benz.mit.edu, goeke, hermanm@space.mit.edu
Content-Length: 3251


Mark,  (Hi Bob, Catherine, and Herman!)

 Thanks for the info on ECS: 12+/-2mm accuracy etc is
fine: my purpose is to have an idea of how much of the
OBF is "sampled" by a pixel in the ECS observations:
with a source diameter of 1 mm [8 mm Ti/Al] at a distance
of 50 mm (+/-4) the cone of x-rays hitting a pixel
intercepts the OBF in a circle of size:

OBF_samp_dia = 12/500  * 1 [or 8]

             = 0.024 mm  [or  0.19 mm]

So the ECS data for Mn L/K is (in principle) able to
sample thickness/density variations in the OBF at ~0.03 mm
scale (requiring data per pixel) or larger (by averaging
over some number of pixels)...  (Of course I mean variations
in the contaminant on the OBF in particular!)  And the 
Al/Ti data could sample at scales of 0.2 mm and larger
(8x8 pixel regions or larger) to look for variation...

  By the way, do you (Catherine) also monitor Ti L/K
ratio (~0.45 keV) or is there a filter on the source etc?
Actually the contaminant effect at 0.45 keV is not so
much more than at 0.7 but would add another data point  
to energy dependance of deviation from "Herman's" model...

  Note in contrast the astrophysical measurements have
the HRMA beam going through the OBF and given its f-ratio
the beam has a diameter (shell 1) of 

OBF_HRMA_beam = 12 / 8.3[f-ratio] = 1.44 mm diameter

as it goes through the OBF so the astrophysical measurements
are averaged over this spatial scale...

  OK, thanks again for getting back to me, 

 -Dan

- - - Re:
From: "Mark W. Bautz" <mwb>
Message-Id: <200310222050.QAA23291@space.mit.edu>
Subject: Re: ACIS OBF distance and ECS diameter
In-Reply-To: <200310211914.PAA22872@spectra.mit.edu> from Dan Dewey at "Oct 21, 2003 03:14:16 pm"
To: dd (Dan Dewey)
Date: Wed, 22 Oct 2003 16:50:04 -0400 (EDT)
Cc: goeke (Robert F. Goeke)

Dan,
> 
> Hi Mark (and Bob),
> 
>   Off hand do you know about how far the ACIS OBF is
> from the CCD focal plane ?  I saw a diagram that
> makes me think it is in the 0.5 to 3cm range...
It is about 12mm from the "vertex" of the tilted chips in the I-array
to the surface of the filter, and very nearly the same distance from 
S3 to the spectrometer obf. These numbers are good to 2mm, I would say.
We can always look at a drawing if you'd like.

> 
>   And Catherine says there are 3 External Cal Sources:
> Fe/Mn, Ti, and Al located about 46 cm from the
> focal plane roughly on-axis (within 10cm or so) - right?
There are 3 sources; my records indicate the distance is more 
like 53.3 cm, but this number is based on an uncontrolled drawing. 
I will check into this unless Bob tells me he is sure of the answer.
> 
>  And lastly, what is the "size" (exit diameter) of these
> ECS sources?  About 5 mm ?
Each source is in an Isotope Products lab A-2 capsule. For the
Mn source, which irradiates the focal plane directly, the radioactive 
material is spec'ed to be contained  within a 1mm diameter circle
at the center of the capsule. For the Al and Ti sources, an annulus
plated with  Fe55  irradiates a target disk. Photons leaving the target
disk pass through the center hole in the annulus. This hole is 8mm in
diameter. This "hole" is actually bevelled, though; see ACIS dwg
36-40212.02

The cal source assy dwg, is 36-40212.

Hope this helps.
mark