Libris Britannia 4/science library(b).zip/science library(b)/SCIENTIF/0830.ZIP/SPECTRUM.DOC

Text File | 1987-11-02 | 17KB | 293 lines

General Program Description

     Included on this disk are the following spectral analysis programs:
GAMMA.COM, ENRAD.COM, ALPHA.COM, and XRAY.COM.

     GAMMA and ENRAD are programs to display gamma emission spectral data.
ALPHA is intended to display alpha emission spectral data.  XRAY can display
x-ray diffraction pattern spectral data.  Sample spectra are included on this
disk.  These programs will display spectral data on the hi-resolution color
graphics screen and allow the user to examine it.  He/she can expand or
contract the spectrum and print it by using a print screen utility.  Selected
areas of the spectrum can be integrated, and peaks in a gamma or alpha
spectrum can be identified by comparison with an isotope library.  Any program
is started by typing the following command to the DOS:

       command [filespec]

where command is either GAMMA, ENRAD, ALPHA, or XRAY; and where [filespec] is
a spectral file.  If the filespec is not included on the command line, then
the program will prompt the user to supply one.  Drive and path may be
included.  The spectral file must be in a particular format in order for the
program to properly read it (see section on file format).  The program then
reads the spectral file if it exists; if not, it will ask the user to supply
an existing filespec.


Program Operation

     Let's explore the operation of one of the spectral analysis programs by
looking at one of the sample spectra provided on the disk.  Type the following
command to get started:

     ENRAD corew4.ccs

We will start with the ENRAD program (ENRAD stands for environmental
radiation).  Corew4.ccs is a gamma spectrum of a sediment core taken from the
bottom of the Calcasieu Lake in southwest Louisiana.  We expect to see only
naturally occurring gamma emitters, so we choose to use the ENRAD program.
ENRAD will read this spectral file.
     Next, the program will read in the isotope library file. (At this time,
XRAY does not include any kind of library file.)  This file must be present on
the default drive.  These files contain isotopic information which the program
uses to identify peaks in the gamma or alpha spectra.  (See section on Isotope
Libraries for a description of these files.)
     Next, the program searches for a file containing the detector geometry
coefficients.  This file is called COEFFS.TXT.  It currently contains five
geometries (see section on coefficients file).
     Next, the program will search the default drive for a file which has the
same filename and an extension of .CFG.  This file contains answers to the
questions asked by the program concerning whether or not to connect the dots
making up the spectral plot, and vertical scaling of the data.  If this file
is not present, the program prompts the user for this information.  The
questions asked are:
     "Connect dots? (Y/N)".  Type Y or N in response to this question.
     "Logarithmic plot? (Y/N)".  If the answer is Y, the program will scale
the data and display the spectrum.  If the answer is N, the program will ask
the user to input a scaling factor.  If the user just presses RETURN or enters
a zero, then the data will be scaled so that the largest value in the spectrum
will appear full scale on the graphic plot.  Choosing a smaller value will
result in expansion of the y÷axis.  After the data is scaled, the spectrum is
displayed on the graphic screen and the user can begin to examine it.
     We should see the dots not connected and a logarithmic plot.  The
vertical line near the middle of the screen is the graphic cursor.  It can be
moved by pressing the left and right arrow keys.  It can be moved faster by
holding down the control key and pressing the arrow keys.  As the cursor is
moved, its position is constantly updated on a status line near the bottom of
the screen.  The cursor's channel number is shown.  This is its position
within the spectral file.  For this particular spectrum, there are 1024
channels.  The energy corresponding to this channel is calculated and shown
(in units of kilo electron volts) if this spectrum has been calibrated.  This
calibration data is stored along with the spectrum.  Finally, the counts in
this channel are shown.
     The graphic screen is a window through which we are looking at the
spectrum.  To move the window to the right, press the PgUp key.  To move the
window to the left, press the PgDn key.  Look at the help screen by pressing
the / or ? key.  When you are ready to quit the program, press control-Q.  The
program will return to the DOS.  A description of the function keys is given
below.

     F1 LEFT Pressing the F1 key will place a marker on the left side of a
region of interest.
     F2 RIGHT Pressing the F2 key will place a marker on the right side of a
region of interest.
     (Any time both LEFT and RIGHT marks are placed on a region of interest,
this spectral region will be integrated and the results shown on a status line
near the bottom of the screen.  Shown are the LEFT and RIGHT channels, the
gross area and the net area.  The net area is calculated by drawing a baseline
from the left to the right mark, and subtracting the area below the baseline
from the gross area.)
     F3 EXPAND Pressing the F3 key will expand the display.  The channel under
the cursor will try to stay near the middle of the graphic screen.
     F4 CONTRACT Pressing the F4 key will contract the display.  The channel
under the cursor will try to stay near the middle of the graphic screen.
     F5 IDENT Pressing the F5 key will cause the program to search through
the library, trying to find a match for the energy under the cursor.  At the
end of the search, the number of matches will be displayed near the bottom of
the screen.
     F6 RESULT Pressing the F6 key will display the results of the most
recent search.  Examine one of the library entries by typing its number, or
return to the display by pressing RETURN.  If you type a valid number, then
you are presented with all of the isotope's data stored in the library.  Also
shown is the mass of the sample and geometry.  The detector efficiency and
amount of isotope in the sample are calculated and shown.  You now have the
option of printing this information on the printer, if desired, press Y,
otherwise press N or RETURN.  The isotope amount is calculated using one of
the following equations:

pCi/g =            Net.area x  1 x 1012                              (Eq. 1)
         Live x Det.eff x t.p x 3.7 x 1010 x mass

     Net.area is the net area of the spectral region, 1 x 1012 is the
number of pico units, Live is the live time in seconds, Det.eff is the
detector efficiency, t.p is the transition probability, 3.7 x 1010 is the
number of disintegrations per Curie, and mass is the sample mass in grams.

ppm =         Net.area/Live x At.wt x 1 x 106                        (Eq. 2)
       Ab x t.p x Det.eff x flux x mass x c.s x Avog x irr x cool

     Net.area is the net area of the spectral region, Live is the live time in
seconds, At.wt is the atomic weight in grams per mole, 1 x 106 is the number
of parts in one million, Ab is the isotopic abundance, t.p is the transition
probability, Det.eff is the detector efficiency, flux is the neutron flux in
neutrons per cm2 per second, mass is sample mass in grams, c.s is the cross
section in barns, Avog is Avogadro's number, irr is the activation factor, and
cool is the decay factor:

   irr = (1-(exp(-(ln(2)/HalfLife) x lenirr )))        (activation factor)
     HalfLife and lenirr (length of irradiation) are in hours,
   cool = (exp(-(ln(2)/HalfLife) x cooltime x 24 ))    (decay factor)
     HalfLife is in hours and cooltime is in days.

     The isotopic amounts for naturally occurring isotopes are calculated
using equation 1 (in programs ENRAD and ALPHA), while isotopes from thermal
neutron activated samples are calculated using equation 2 (in the program
GAMMA).

     F8 SCALE Pressing the F8 key will allow changing the plot parameters,
such as connected dots and vertical scale.
     F9 -MORE- Pressing the F9 key will present a second set of functions.

     F1 ENERGY Pressing the F1 key will display the energy calibration factors
near the bottom of the screen.  These are the channel zero energy and the
energy per channel.  Both are in units of kev.
     F2 TIME Pressing the F2 key will display the count times near the bottom
of the screen.  These are clock and live times in seconds.  The percent dead
time is calculated from these times.
     F3 MEMORY Pressing the F3 key will display the available memory.
     F4 HEADING Pressing the F4 key will display the heading information that
is stored along with the spectral file.
     F5 DETEFF Pressing the F5 key will cause the program to plot the
efficiency curves for the various detector geometries that are currently
defined.
     F6 SAVE Pressing the F6 key will cause the program to write the entire
spectral file back to disk.  This is useful if the spectrum is recalibrated
and then the user wishes to store the new calibration coefficients.
     F7 CALIB Pressing the F7 key will allow the user to recalibrate the
spectrum.  The program will prompt the user with instructions printed near the
bottom of the screen.  First, move the cursor to a peak of known energy, press
the RETURN key, and enter the energy (in kev).  Then, move the cursor to a
second peak of known energy, press the RETURN key, and enter the energy (in
kev).  The program will calculate the channel zero energy and the energy per
channel and display them near the bottom of the screen.  These new
coefficients can be stored with the spectrum by pressing the F6 SAVE key.
     F8 LOAD Pressing the F8 key will cause the program to prompt the user for
another file name.  This spectral file will be loaded and displayed.
     F9 -MORE- Pressing the F9 key will present the first set of functions.


Coefficients File

     The file called COEFFS.TXT contains the detector geometry coefficients.
The format of the file is described as follows.  The first line of the file
contains the number of geometries in the file.  Each geometry is given:
 A)  two coefficients, called a and b.  These coefficients are used to
     determine the detector efficiency at any given energy by solving this
     equation:

          Det.Eff. = a * energyb

     (**NOTE** This equation gives erroneous efficiencies for energies below
     about 100 kev.)  These coefficients can be determined by counting a
     radioactive standard (available from the National Bureau of Standards),
     and plotting the ratio of detected activity to known activity versus
     energy.  This data can be fitted to the above equation using a least
     squares method.  This method is carried out for each detector geometry
     used, and the data is put into the coefficients file.
 B)  the title, or name, of the geometry.  This is usually a number, 1, 2,
     etc., for each geometry used.


Configuration File 

     A configuration file can be created to avoid having to answer the plot
questions every time a spectral analysis program is run.  If this file is
present on the default drive, then the program will take answers to the plot
questions from this file.  The configuration file should contain two or three
pieces of information.  The first character should be Y or N, and is the
answer to the question "Connect dots? (Y/N)".  The second character is also
either Y or N, and is the answer to the question "Logarithmic plot? (Y/N)".
If the second character is Y (which means that log plot is selected), then
that is all the configuration file needs to contain.  If the second character
is N (which means that log plot is not selected), then a numeric value will
have to be provided.  To cause the spectral analysis program to always scale
the spectrum to the largest value, enter a zero here; otherwise, any non-zero
value can be entered.  The simplest method of creating a configuration file is
illustrated here: (user input is italicized; <CR> means to press the RETURN
key)

                                        Comments
     A>copy con gamma.cfg <CR>  copy from console to configuration file
       NN0<F6>  <CR>            <F6> means press the F6 key
         1 File(s) copied         response from DOS


Spectrum Acquisition

     The spectrum will have to be acquired from a multi-channel analyzer or
similar instrument, and then processed into the particular format required by
the analysis program.  The program called ACQUIRE3.BAS is a program written in
BASIC which was designed to operate with a model 5400 multi-channel analyzer
built by Norland/Ino-Tech, using a serial interface.  It will ask for some
heading information to be stored along with the spectrum, and then will
display some instructions before acquiring the spectrum.  This program is very
picky and probably will have to be modified to work with other equipment.  But
it should give a rough idea on how to write a program to acquire and process a
spectrum.


Spectral File Format 

     The spectral file must be in a particular format in order for the
programs GAMMA, ENRAD, and ALPHA to read them properly.  The program XRAY has
slightly different file format requirements.  In the following, the string
called "miscellaneous" will be printed on the top line of the graphic screen.
Usually the title of the spectrum is put here.
     For the GAMMA, ENRAD, and ALPHA programs the format is as follows:

   Name of variable           variable type        description
     irrdate                    string[80]      date of irradiation
     irrtime                    string[80]      time of irradiation
     colldate                   string[80]      date of collection
     colltime                   string[80]      time of collection
     misc                       string[80]      miscellaneous
     flux                       real            neutron flux in units of
                                             neutrons per cm2 per second
     mass                       real            sample mass in grams
     geom                       integer         detector geometry
     lenirr                     real            length of irradiation in hours
     cooltime                   real            cooling time in days
     chzen                      real            channel zero energy in kev
     ench                       real            energy per channel in kev
     numchan                    integer         number of channels in spectrum
     clock                      real            clock time in seconds
     live                       real            live time in seconds
     counts                     real            counts in channels 2 through
                                              numchan.  Channels 0 and 1 are
                                              assumed to contain the clock and
                                              live times, respectively.
     <EOF>                                      end of file.


     The following file format applies to the program XRAY.COM:

   Name of variable           variable type        description
     misc                       string[80]      miscellaneous
     startang                   real            starting angle of scan
     endang                     real            ending angle of scan
     angincr                    real            angle increment
     CTime                      integer         count time in seconds
     ...
     numchan                    integer         number of channels
     counts                     real            counts in channels 1 through
                                              numchan
     <EOF>                                      end of file.


Isotope Libraries

     Three isotope libraries are included.  They are NTHERM2.TXT, ENRAD2.TXT,
and NATALP2.TXT.  They include information such as atomic number and atomic
mass of isotopes, cross section and abundance of parents, and emission
energies and transition probabilities.  Up to 24 energies and transition
probabilities are included with each isotope.  This data has been collected
from General Electric Nuclide Chart.
     The library NTHERM2.TXT contains isotopes which are produced by thermal
neutron irradiation.
     The library ENRAD2.TXT contains isotopes which are naturally occurring
gamma emitters.  The isotopes are products of the uranium and thorium decay
chains.
     The library NATALP2.TXT contains isotopes which are naturally occurring
alpha particle emitters.