PROJECT:  CHIANTI

      CHIANTI is an Atomic Database Package for Spectroscopic Diagnostics of
      Astrophysical Plasmas. It is a collaborative project involving the Naval
      Research Laboratory (USA), the University of Florence (Italy), the
      University of Cambridge and the Rutherford Appleton Laboratory (UK). 

 NAME

    KARZAS_XS()

 EXPLANATION

    Outputs the photoionization cross-section at the wavelengths WVL for 
    ionization of an N,L electron with ionization energy IONIZ_EN, 
    calculated using the Karzas & Latter (ApJS 6, 167, 1961) formulation. 
    The bound-free gaunt factor is derived from the tables of Karzas & 
    Latter.

 INPUTS

    WVL    Wavelengths (in angstroms) for which cross-sections are 
           required (1-D array).

    N      Principal quantum number of the electron being removed in the 
           ionization.

    L      The orbital angular momentum of the electron being removed in the 
           ionization.

    IONIZ_EN  The ionization energy (in cm^-1) of the electron being 
              removed.

 OPTIONAL INPUTS

    PE      Allows the PE array from READ_KLGFB to be directly input to 
            KARZAS_XS thus avoiding the need to read the K&L data 
            repeatedly for many ions. Requires KLGFB to also be input.

    KLGFB   Allows the KLGFB array from READ_KLGFB to be directly input to 
            KARZAS_XS thus avoiding the need to read the K&L data 
            repeatedly for many ions. Requires PE to also be input.

 OUTPUT

    The photoionization cross-section for the ionization of the outer 
    electron in units of mega-barns (Mb = 10^-18 cm^2) at the input 
    wavelengths. E.g., for Fe XIII (ground configuration 
    1s2.2s2.2p6.3s2.3p2) it is the cross-section for the removal of the 
    3p electron.

 CALLS

    READ_KLGFB

 HISTORY

    Ver.1, 24-Jul-2002, Peter Young
 CALLS:
 CALLED BY
	freebound_ion

 Name        :
	Klein
               
 Purpose     : 
	This function returns the Klein-Nishina differential Compton scattering cross-section 
	in cm^2 electron^(-1) sr^(-1).
               
 Category    : Spectra
               
 Explanation : Klein-Nishina formula from Zombeck
               
 Use         : result = KLEIN( e, mu )
    
 Inputs      : 
	E - Energy in keV
	Mu- cosine of the angle between the incident and scattered photons
               
 Opt. Inputs : None
               
 Outputs     : None

 Opt. Outputs: None
               
 Keywords    : 
	TOT - total Compton xsec cm^2/electron
	ENEW- Energy of Compton scattered photon
 Calls       : ***
	xsec
 CALLED BY:
	KLEIN_ELCTRN
 Common      : None
               
 Restrictions: Either "E" or "Mu" may be vectors, but not both.
	Need more work to reconcile the differential and total cross-sections.
	ras, 21-May-1996               
 Side effects: None.
               
 Prev. Hist  : Taken from SPEX directory

 Modified    : 
	Version 1, ras 2-Mar-1996

 Name        :
	KLEIN_ELCTRN
               
 Purpose     : 
	This function returns the Klein-Nishina differential Compton scattering cross-section 
	in cm^2 electron^(-1) sr^(-1) as a function of the kinetic energy of the 
	scattered electron.
               
 Category    : Spectra
               
 Explanation : Klein-Nishina formula from Zombeck
               
 Use         : result = KLEIN_ELECTRN( E, K )
    
 Inputs      : 
	E - Energy in keV
	K - vector of kinetic energies of scattered electrons
               
 Opt. Inputs : None
               
 Outputs     : None

 Opt. Outputs: None
               
 Keywords    :              tot=tot, mu=mu, wmu=wmu, enew=enew
	TOT - total Compton xsec cm^2/electron
	ENEW- energy of scattered photon (E-K)
	WMU - indices of valid kinetic energies, K
	MU  - Compton scattering angle, relative to incident photon direction

 Calls       : ***
	Klein
 CALLED BY:
	RESP_CALC response calculation
 Common      : None
               
 Restrictions: 
 Side effects: None.
               
 Prev. Hist  : 

 Modified    : 
	Version 1, ras 2-Mar-1996