;+
; PROJECT:
;	SDAC
; NAME: 
;	Aluminum
;
; PURPOSE:
;	This procedure computes the correction factor for BATSE count rate attenuation due to an
;	oblique angle through the Al entrance window.
;
; CATEGORY: 
;	BATSE
;
; CALLING SEQUENCE:
;	ALUMINUM, Cos_zenang, Correction
;
; CALLS:
;	none
;
; INPUTS:
;       Cos_zenang: cosine of the angle between detector axis and Sun
;
; OPTIONAL INPUTS:
;	none
;
; OUTPUTS:
;	Correction: To compensate for decrease in rate with increasing angle
;	due to increased absorption, the observed rate is divided by "Correction"
;
; OPTIONAL OUTPUTS:
;	none
;
; KEYWORDS:
;	none
; COMMON BLOCKS:
;	none
;
; SIDE EFFECTS:
;	none
;
; RESTRICTIONS:
;	none
;
; PROCEDURE:
;	Interpolates on a pre-determined table for a power-law of 4
;
; MODIFICATION HISTORY:
;	Version 1, ras, 1991
;	Version 2, ras, 1996, documentation added
;
;-


pro aluminum, cos_zenang, correction
;return the aluminum correction factor as a function of angle
;the cosine of the zenith angle dependence has already been removed
;The correction factor is returned as a 4 element vector.
;These factors have been computed for a power-law of 4 with
;these edges:
;
;	23.0000      57.0000
;	57.0000      115.000
;       115.000      310.000
;       310.000      2000.00
;
ang = [0.,18.19,25.84,31.79,36.87,41.41,45.57,49.46,53.13,56.63,60.]

corr = reform([1.00000,      1.00000,     1.00000,     1.00000, $    
	0.980078,     1.00236,     1.01219,     1.04000, $
	0.959945,     1.00459,     1.02428,     1.07767, $
	0.918787,    0.994695,     1.02723,     1.11875, $
	0.859851,    0.970751,     1.01715,     1.15791, $
        0.791347,    0.942840,     1.00629,     1.20141, $    
	0.715697,    0.907824,    0.988454,     1.24331, $    
	0.636383,    0.866618,    0.964055,     1.27733, $    
	0.560160,    0.830950,    0.947251,     1.31729, $    
	0.491289,    0.791721,    0.922256,     1.37093, $
	0.435114,    0.755767,    0.896818,     1.41187], 4,11)
correction = fltarr(4)
for i=0,3 do correction(i)= interpol(corr(i,*),cos(ang/!radeg),cos_zenang)
;
end