Energy_Monitor affects final intensity?

[artus at obiwan.kri.physik.uni-muenchen.de]

Hello Kristian,

I have just encountered a strange result with my last job:

The instrument looks like source, guide, Cu monochromator and several
detectors at the sample position. To investigate more precisely what
happens to the energy distribution I added another E_monitor just in
front of the monochromator. But then the final intensity at the sample 
position drops by a factor of about 2/3!!! This difference is a
factor of 20 larger then the error. This happens also with fixed
seed. Running with -s 2 gives

Detector: psdsamar_I=2.11443e+06 psdsamar_ERR=44571.6
Detector: psdsam_I=213670 psdsam_ERR=14286.2
Detector: divsamar_I=1.90489e+06 divsamar_ERR=43010.2
Detector: divsam_I=200795 divsam_ERR=13871.7

with E_mon in front of the monochromator and

Detector: psdsamar_I=3.58938e+06 psdsamar_ERR=57710.6
Detector: psdsam_I=364115 psdsam_ERR=18388.7
Detector: divsamar_I=3.11014e+06 divsamar_ERR=54681.8
Detector: divsam_I=333511 divsam_ERR=17787.5

without.

It seems as if the E_monitor is absorbing neutrons??? Isn't it 
supposed not to do so!? Am I wrong somewhere?

Attached is the input file with E_mon in front of the monochromator:

Georg
*************

DEFINE INSTRUMENT 4075M23CU422()

DECLARE
%{
/* Mosaicity used on monochromator */
double mono_mosaic_v = 20;
double mono_mosaic_h = 20;
/* Q vector for bragg scattering with monochromator */
double mono_q = 8.517; /* Cu 422 1AA */
double mono_r0 = 0.3;
double thetam = 42.67;
double tthetam;
%}

INITIALIZE
%{
  tthetam = 2 * thetam;
%}

TRACE

COMPONENT a1 = Arm()
  AT (0,0,0) ABSOLUTE

COMPONENT source = Source_flux(
	radius = 0.050,
	dist = 2.000,
	xw = 0.040, yh = 0.075,
	E0 = 81.804,	/* = 1A*/
	dE = 1.636,	/* entspricht deltalambda / lambda = 1E-02 */ 
	flux = 3.63E+12)
  AT (0,0,0) RELATIVE a1

COMPONENT part1 = Guide2(
	w1 = 0.040,
	h1 = 0.075,
	w2 = 0.038644,
	h2 = 0.073982,
	l = 0.780,
	R0 = 1.0,
	Qc = 0.0214,
	alpha = 5.617,
	mh = 3,
	mv = 2,
	W = 0.0033)
  AT (0,0,2) RELATIVE a1 

COMPONENT part2 = Guide2(
	w1 = 0.038644,
	h1 = 0.073982,
	w2 = 0.036522,
	h2 = 0.072392,
	l = 1.220,
	R0 = 1.0,
	Qc = 0.0214,
	alpha = 5.617,
	mh = 3,
	mv = 2,
	W = 0.0033)
  AT (0,0,2.782) RELATIVE a1 

COMPONENT part3 = Guide2(
	w1 = 0.038644,
	h1 = 0.072392,
	w2 = 0.020,
	h2 = 0.060,
	l = 9.500,
	R0 = 1.0,
	Qc = 0.0214,
	alpha = 5.617,
	mh = 3,
	mv = 2,
	W = 0.0033)
  AT (0,0,4.202) RELATIVE a1

COMPONENT a2 = Arm()
  AT (0,0,9.9) RELATIVE part3
  ROTATED (0,tthetam,0) RELATIVE a1

COMPONENT enmon = E_monitor(
        xmin = -0.01,
        xmax = 0.01,
        ymin = -0.03,
        ymax = 0.03,
        Emin = 80.992,
        Emax = 82.628,
        nchan = 10,
        filename = "enmon.out")
  AT (0,0,9.88) RELATIVE a1

COMPONENT cumono = Monochromator(
	zmin = -0.15,
	zmax = 0.15,
	ymin = -0.03,
	ymax = 0.03,
	mosaich = mono_mosaic_h,
	mosaicv = mono_mosaic_v,
	r0 = mono_r0,
	Q = mono_q)
  AT (0,0,0) RELATIVE a2 ROTATED (0,thetam,0) RELATIVE a1

COMPONENT psdsamar = PSD_monitor(
        xmin = -0.01,
        xmax = 0.01,
        ymin = -0.03,
        ymax = 0.03,
        nx = 20,
        ny = 60,
        filename = "psdsamar.out")
  AT (0,0,2) RELATIVE a2

COMPONENT psdsam = PSD_monitor(
        xmin = -0.005,
        xmax = 0.005,
        ymin = -0.005,
        ymax = 0.005,
        nx = 10,
        ny = 10,
        filename = "psdsam.out")
  AT (0,0,2) RELATIVE a2

COMPONENT divsamar = Divergence_monitor(
        xmin = -0.01,
        xmax = 0.01,
        ymin = -0.03,
        ymax = 0.03,
        nh = 45,
        nv = 45,
        h_maxdiv = 0.375,
        v_maxdiv = 0.375,
        filename = "divsamar.out")
  AT (0,0,2) RELATIVE a2

COMPONENT divsam = Divergence_monitor(
        xmin = -0.005,
        xmax = 0.005,
        ymin = -0.005,
        ymax = 0.005,
        nh = 45,
        nv = 45,
        h_maxdiv = 0.375,
        v_maxdiv = 0.375,
        filename = "divsam.out")
  AT (0,0,2) RELATIVE a2

COMPONENT ensamar = E_monitor(
        xmin = -0.01,
        xmax = 0.01,
        ymin = -0.03,
        ymax = 0.03,
        Emin = 80.992,
        Emax = 82.628,
        nchan = 10,
        filename = "ensamar.out")
  AT (0,0,2) RELATIVE a2

COMPONENT ensam = E_monitor(
        xmin = -0.005,
        xmax = 0.005,
        ymin = -0.005,
        ymax = 0.005,
        Emin = 80.992,
        Emax = 82.628,
        nchan = 10,
        filename = "ensam.out")
  AT (0,0,2) RELATIVE a2

END