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LETSPEC: Linear Energy Transfer (LET) Spectra

Overview

The LETSPEC module of the CREME96 transforms input particle fluxes, which are functions of kinetic energy, into spectra which are functions of Linear Energy Transfer (ie., stopping power or dE/dx). An LET spectrum is required as an input for the CREME96/HUP program, which calculates the rates of single-event effects (SEEs) due to direct-ionization.

Inputs

In general, the input to LETSPEC will be a .tfx from the TRANS program, which transports fluxes through shielding. However, .flx files from the FLUX program can also be used in order to make calculations without shielding. (In general, such calculations are not recommended. See shielding thickness.)

Other inputs to the LET spectrum calculation are:

Outputs

.LET

The primary output from LETSPEC is an integral LET spectrum (in a file called "something.let"). This file contains the integral linear energy transfer (LET) spectrum. That is, as a function of LET (in MeV-cm2/g) it gives the flux of particles (in nuclei/m2-s-sr) whose LET exceeds the specified value. The .let file also contains header information which documents the inputs and parameters which produced it. You can examine this header information to make sure, for example, that you've selected the .let file you want.

The special format of the CREME96 .let files suppresses the LET values. This format can be decoded into a two-column table (with LET in MeV-cm2/g) in the first column and integral flux in nuclei/m2-s-sr in the second column) using the TABLE routine. You can download this two-column table to your own PC for plotting with your own software. At the top of this LETTAB file will be header information (with a "%" in the second column of each header line). Note that you may have to delete some or all of these lines before passing the file to your plotting software.

.LET files track the flux at LET values from 1 to 1.1 x 105 MeV-cm2/g. These values cover the full range of stopping powers produced by nuclei in Nature, from relativistic protons to stopping uranium nuclei (provided that these species are included in your input file.)

.DLT

As a secondary output, LETSPEC can also produce a differential LET spectrum (in a file called "samething.dlt"). This .dlt file is optional, since it is not needed for subsequent CREME96 SEU rate calculations. This file contains the differential flux of nuclei (in nuclei/m2-s-sr-(MeV-cm2/g)) vs. linear energy transfer (LET, in MeV-cm2/g).

The special format of the CREME96 .dlt files suppresses the LET values. This format can be decoded into a two-column table (with LET in MeV-cm2/g) in the first column and differential flux in nuclei/m2-s-sr-(MeV-cm2/g) in the second column) using the TABLE routine. You can download this two-column table to your own PC for plotting with your own software. At the top of this table will be header information which documents the inputs and parameters which produced it (with a "%" in the second column of each header line). Note that you may have to delete some or all of these lines before passing the file to your plotting software.

The .dlt spectrum is calculated by numerical differentiation of the integral LET spectrum in the corresponding .let file. The present differentiation algorithm leads to some "wiggles" at the level of a few percent which are numerical artifacts.

The differential LET spectrum contains sharp discontinuities. These discontinuities are real and appear at the minimum and maximum LETs produced by each nuclear species. These discontinuities may not be handled properly by some plotting software.

.dlt files track the flux at LET values from 1 to 1.1 x 105 MeV-cm2/g. These values cover the full range of stopping powers produced by nuclei in Nature, from relativistic protons to stopping uranium nuclei (provided that these species are included in your input file).

See also: Plotting CREME96 Spectra

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