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3 CREATING GEANT HITS

In AgSTAR user does not need to write a detector specific routine to create GEANT hit structure and to fill it with a useful information. Instead, a geant statements with the HITS operator, called in a block describing a sensitive volume, is used to produce a relevant GEANT hit definitions and to steer their filling at the tracking time. This statement generates all necessary GEANT calls (see GSDET and GSDETH routines, HIT 100) with their parameters as follows: The definition part of the HITS operator contains a list of information quantities, measurements, which should be saved in each GEANT hit, and their packing in one of the form 
or 

For a measurement or bin are mandatory, option and limits are optional. At present the following variables are known as measurements to the AgSTAR interface (the track point means here the middle point of the track segment producing the hit in the sensitive volume):

An integer number, following a measurement variable, is interpreted as  - the number of bits for packing the variable values. 0 means that the value is a cumulative sum, occupying a full computer word. Due to the GEANT limitation 0 can be used only in last elements of the HITS statement.

If a measurement variable is followed by a real number or an expression, it is interpreted as the packing bin size, and the number of bits, required for packing, will be calculated by the AgSTAR interface.

If the user does not provide the limits explicitly, min and/or max are determined by the AgSTAR interface using the volume dimensions. This works fine in local coordinates, but should be used with caution in global MRS coordinated.

Example: HITS VRAD xx:16:H(-25,25) yy:16:(-25,25) zz:32:(-1000,1000),
px:16:(-100,100) py:16:(-100,100) pz:16:(-100,100),
Slen:16:(0,1.e4) Tof:16:(0,1.e-6) Step:16:(0,100),
SHTN:16: Eloss:32:(0,1)

Possible measurement options are listed below. If an option is not mentioned, the alternative default solution is used. Most of the options acts on the whole list of measurements, except for option R.

3.1 Non-standard HIT elements

In a number of cases user may need in hits a specific value, unknown to the AgSTAR interface . There are two possibilities to provide such a value to AgSTAR interface : These subroutines should be described as EXTERNAL in the module header. Their first integer input argument pointer is the address of the hit descriptor array (10 words, real) in the GCBANK memory and they should return in the second real argument hit the measurement.
 


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Next: 4 DIGITISATION Up: Advanced Geometry Interface for Previous: 2 GEOMETRY DESCRIPTION


 


William J. Llope

Thu Aug 15 17:05:49 EDT 1996