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The Union_abs_logger_1D_space_tof_to_lambda McStas Component

12.41 The Union_abs_logger_1D_space_tof_to_lambda McStas Component

A logger of absorption along 1D of space and 1D of tof, but converted to lambda

Identiﬁcation

Author: Mads Bertelsen
Origin: ESS DMSC
Date: 19.06.20

Description

Part of the Union components, a set of components that work together and thus separates geometry and physics within McStas. The use of this component requires other components to be used.

1) One speciﬁes a number of processes using process components 2) These are gathered into material deﬁnitions using Union_make_material 3) Geometries are placed using Union_box/cylinder/sphere, assigned a material 4) Logger and conditional components can be placed which will record what happens 5) A Union_master component placed after all of the above

Only in step 5 will any simulation happen, and per default all geometries deﬁned before this master, but after the previous will be simulated here.

There is a dedicated manual available for the Union_components

This component is an absorption logger, and thus placed in point 4) above.

A absorption logger will log something for each absorption event happening in the geometry or geometries on which it is attached. These are speciﬁed in the target_geometry string. By leaving it blank, all geometries are logged, even the ones not deﬁned at this point in the instrument ﬁle. Multiple geometries are speciﬁed as a comma separated list.

This absorption logger records the absorbed intensity as a function of the measured and true wavelength. The measured wavelength is calculated from the time of ﬂight and distance travelled. This distance is a constant from source to sample added to the distance from the sample position to the detector pixel in which the event is detected. The true wavelength is calculated directly from the velocity. This information shows any error in conversion from tof to wavelength, especially from any added travelled distance from multiple scattering.

The lambda_min, max and bin parameters are used to set both the range for measured and true wavelength. If either of these, denoted lambda_m and lambda_t respectively, is set they will overwrite the lambda setting for that part. Sine most data will be along the line lambda_m = lambda_t, it is possible to record lambda_m / lambda_t as a function of lambda_t, which will be close to 1.0. This mode is selected by setting relative_measured to 1, and then the range can be selected with relative_min, max and bins.

This absorption logger needs to be placed in space, the position is recorded in the coordinate system of the logger component. Note the detection is along the y axis of the component, so it is natural to place it relative to a cylinder.

This component works as other absorption loggers, but converts the tof and position data to wavelength, which is then compared to the actual wavelength calculated from the neutron state. The neutron position used to calculate the wavelength is pixelated while the time of ﬂight is continous. The distance from source to sample is an input parameter, and the distance from sample to a detector pixel is calculated using the reference component position which should be speciﬁed with a relative component index.

It is possible to attach one or more conditional components to this absorption logger. Such a conditional component would impose a condition on the state of the neutron after the Union_master component that executes the simulation, and the absorption logger will only record the event if this condition is true.

To use the logger_conditional_extend function, set it to some integer value n and make and extend section to the master component that runs the geometry. In this extend function, logger_conditional_extend[n] is 1 if the conditional stack evaluated to true, 0 if not. This way one can check what rays is logged using regular McStas monitors. Only works if a conditional is applied to this logger.

Input parameters

Parameters in boldface are required; the others are optional.


Name	Unit	Description	Default



target_geometry	string	Comma separated list of geometry names that will be logged, leave empty for all volumes (even not deﬁned yet)	"NULL"
ref_component	1	Reference component instance index, sample position for distance calculation
yheight	m	Height of absorption logger
yn	1	Number of bins along y axis
source_sample_dist	m	Travel distance between source and sample position, used to calculate total travelled distance	0.0
lambda_min	Å	Minimum wavelength recorded (sets both lambda_m_min and lambda_t_min)	-1
lambda_max	Å	Maximum wavelength recorded (sets both lambda_m_max and lambda_t_max)	-1
lambda_bins	1	Number of wavelength bins	-1
lambda_m_min	Å	Minimum measured wavelength recorded from tof and travelled distance (overwrites lambda_min)	-1
lambda_m_max	Å	Maximum measured wavelength recorded from tof and travelled distance (overwrites lambda_max)	-1
lambda_m_bins	1	Number of measured wavelength bins	-1
lambda_t_min	Å	Minimum true wavelength recorded from tof and travelled distance (overwrites lambda_min)	-1
lambda_t_max	Å	Maximum true wavelength recorded from tof and travelled distance (overwrites lambda_max)	-1
lambda_t_bins	1	Number of true wavelength bins	-1
relative_measured	1	Default 0, records measured as function of true wavelength, if this is enabled, records measured relative to true wavelength	0
relative_min	1	Smallest value of measured / true wavelength in histogram	0.5
relative_max	1	Largest value of measured / true wavelength in histogram	1.5
relative_bins	1	Number of bins on histogram axis with measured divided by true wavelength	100
ﬁlename	string	Filename of produced data ﬁle	"NULL"
order_total	1	Only log rays that have scattered n times, -1 for all orders	-1
order_volume	1	Only log rays that have scattered n times in the same geometry, -1 for all orders	-1
logger_conditional_extend_index	1	If a conditional is used with this logger, the result of each conditional calculation can be made available in extend as a array called "logger_conditional_extend", and one would then access logger_conditional_extend[n] if logger_conditional_extend_index is set to n	-1
nowriteﬁle	1	If set, logger will skip writing to disk	0
init	string	Deprecated and unused. Accepted so that instruments written for McStas/McXtrace 3.8.7 and earlier, which name the Union_init component here, still compile.	""

12.41 The Union_abs_logger_1D_space_tof_to_lambda McStas Component

Identiﬁcation

Description

Input parameters

Links