RUMP: General Concepts
Buffers and Data Files
RBS experimental and simulation spectra are stored in RUMP in a set of
internal buffers. These buffers are reused on a rotating basis to accommodate
new spectral data. Twelve buffers are configured in the PC version, each
with a maximum of 1024 channels of data (mainframe versions generally increase
the buffer size to 2048 channels). The buffers are numbered from -1 through
10. The first two buffers, -1 and 0, are always reserved for temporary
calculations (-1) and for spectral simulations (0). The remaining ten buffers
hold experimental spectra, copies of simulations or temporary calculations
(PERT). Buffers are referred to by either number or by content (the filename
of the corresponding data). At any point in time, one buffer is designated as
the MAIN or ACTIVE buffer. This designation is important in that many
commands, for example THICKNESS, operate only on the ACTIVE buffer. The
ACTIVE buffer may be changed using commands such as GET or POINTAT
and can be identified using the BUFFERS command. The first two special
buffers -1 and 0 cannot, in general, be retained as the ACTIVE buffer.
Buffers are actually data structures containing not only the spectral
information (counts per channel), but also experimental parameters required
to analyze the data. These experimental parameters describe the incident
particle, the beam energy, charge integration, scattering geometry, etc. This
information is stored on a per buffer basis and may be modified using commands
described in this manual.
RUMP data files correspond closely to the buffer structure. The most recent
version of the data file utilize a format which is machine independent,
allowing direct binary exchange of data files between different mainframe and
micro implementations of RUMP. An appendix to this section describes the
internal data file format in detail. The old format, written using FORTRAN
unformatted I/O records, is still recognized by the READ commands. Buffers
are filled with experimental data by reading the files using GET, REAL, PLOT or OVERLAY. The ACTIVE buffer can be saved, with the
current buffer experimental parameters, using REWRITE, SAVE or
WRITE commands.
Specifying Elements
Elements names are required in many of the commands to RUMP. Internally,
RUMP maintains a list of 92 elements with isotope masses, abundances, and
atomic density. Elements are specified by their common one or two letter
symbol such as Si or O. Full names are not permitted. A specific isotope
can also be specified for most commands by using the format 28Si or 31Si. (An
obsolete format Si+28 is also still supported.) If the isotope is listed in
the internal tables, the actual mass for the element is used. Otherwise, the
specified atomic weight will be used as the atomic mass. 42Si is valid in
RUMP but don't expect meaningful results.
Charged beams are specified in the same manner except for the addition of
plus signs after the symbol. 4He++ is the symbol for normal double plus
backscattering alpha particles.
SIM and PERT
RUMP includes a very fast and powerful, if not overly friendly, simulations
package referred to as SIM. SIM couples with an even less friendly package
called PERT which automatically varies parameters describing the simulation to
reach a ``best fit'' with a given experimental spectrum. Both SIM and PERT
are sub-processors under RUMP with their own set of commands and data files.
There is no command to do a simulation; simulations are automatically
performed when necessary using experimental parameters from the ACTIVE spectra
and elements and layer thicknesses from a ``sample description''. Commands
within SIM are primarily directed to generating the sample description and
modifying some of the simulation parameters. PERT is solely concerned with
the search procedure.
Last modified: November 3, 1996
Michael O. Thompson (mot1@cornell.edu)