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Atom: A semiautomatic measuring system for the analysis of fission track characteristics in anisotropic minerals
Nucl. Tracks Radiat. Meas., Vol. 19, Nos I-4, pp. 255-260, 1991 Int. J. Radiat. Appl. Inatrum., Part D Printed in Great Britain
0735-245X/91 $3.00 + .00 Pergamon Press pie
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM F O R T H E ANALYSIS OF FISSION T R A C K C H A R A C T E R I S T I C S IN A N I S O T R O P I C MINERALS
M. REBETEZ, B. ZOPPIS, A. REBRAB, P. G R I L L O N , E. GENTINA and A. CHAMBAUDET Laboratoire de Mieroanalyses Nucl~.alres,U.F.R. Sciences et Techniques, 16 route de Gray, 25030 BESANCON Cedex, France
ABSTRACT We have developed a semiautomatic measuring system for the analysis of fission tracks in minerals. This system consists of an optical microscope equipped with a drawing tube which is connected to an IBM compatible computer equipped with a digitizer. ATOM is the software, developed using TURBO-PASCAL Version 4.0. It is presently used for performing data input operations of densities, lengths and orientations of tracks. It also coordinates the activities of storing and processing the data of measured tracks and it gives the results of the statistical analysis. In this way, the mineral age determination can be made either by the Population Method (I'M) or by the External Detector Method (EDM).The curves for fission track length distributions and orientations are drawn and may be printed out. This system's hardware and software are described in this paper.
KEYWORDS semiautomatic measuring system; fission tracks; dating; lengths; orientations; densities; software; optical microscopy; bitpad digitizer, microcomputer. INTRODUCTION For many years now, the fission track dating method has provided much information for carrying out chronothermometric studies of minerals such as apatite, sphene and zircon (Chambaudet et al., 1986a). The increasing number of samples to be analysed and the difficulties involved in teaching the method to new experimenters have led us to develop a semiautomatic system for analysing fission track characteristics. The parameters to be studied include the projected length of confined or surface tracks, their orientation in comparison with the crystallographic axes and the densities of tracks used for mineral age calculation. The goals of developing such a system include: - having a tool for thorough and rapid processing, providing measurements which can be reproduced, - developing open-ended data processing software to be used with low-cost, standard computers. T H E SYSTEM
galaiameam Only a few years ago, the image analysis systems used for studying SSNTD's required high-cost data processing materials (Chambaudet et al., 1984). Given current microcomputer capabilities, it is now possible to develop such software on many commonly available systems, such as the IBM-PC (Noll et al., 1988). Figure l shows how the system is set up.
255
256
M. REBETEZ et al.
/
IM
drawing tube
RS 232 serial port cursor equipped with an LED
Microscope
\
/
Bitpad digitizer
IBM compatible
Fig. 1. Diagram of track measuring system components (inspired by Dwivedi et al., 1986)
Thus, the necessary equipment is : - a microscope with a drawing tube. We use an Olympus BH2 and normally work with a magnification of x1250 (dry objective xl00, eyepiece xl0, drawing tube magnification xl.25) ; - an IBM, XT or AT compatible microcomputer. An 8088 microprocessor will suffice, but at least 640K of RAM, and a monochrome monitor with either a Hercule or an EGA card are also needed. A hard disk drive is also recommended for greater speed and increased flexibility in the use of the ATOM software; - a Benson 6440-compatible bitpad digitizer (resolution of 0.02mm) connected to the serial port of the microcomputer;, - a graphic printer (Epson LX800, 80 columns); - the ATOM software. Software
The software was developed in Turbo Pascal 4.0 (Borland Inc.). This language has the advantages of being rather simple from a programming point of view, and offering a broad range of possibilities in terms of graphics and data management, all without sacrificing speed or performance for the final user. Because of the large number of ATOM functions and amount of storage space allotted by Pascal, ATOM had to be broken up into several modules according to the software requirements. The software is designed with 13 programs for a total of 4200 lines. The user, however, is completely unaware of this decomposition: he or she needs only the execution file ATOM.EXE (110 K) and a few graphics units (90 K) to get working. Each of the 13 programs correspond to either a utility (bitpad,_ management, menu management, window management, graphics mode management, etc.), or one of ATOM s main menus. After a brief presentation of the utilities, the menus "Lengths and Angles", "PM Dan'ng" and "EDM Dating" are described in detail. ATOM UTILITIES Semiautomatic analysis of fission tracks requires the use of an optical microscope. To reduce eye fatigue (and thus the chance of errors) the experimenter must be able to isolate himself from all outside diswactions. To help, great care went in the design of ATOM to make it user-friendly and ergonomic. Thus, for example, an audible beep highlights and confirms most inputs. The Screen The graphics screen is composed of du'¢¢ windows and an information line (Fig. 2)
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM
Information
257
line
ATOM Lon(:jths / Angles study PM DatJno EDM Da~ng Calibration Bitpad Options Quit
grid
Main menu
f
F.T. data display
&
Fig. 2. Layout of the A T O M
screen
The grid is where the tracks are shown. Exactly what is observed under the microscope can be reproduced. This is also where graphs are displayed when using the graphics menus. Display of the actual grid lines is optional. The information line indicates the current operation. The menu lists the various directly accessible options. Each option is organized into tree structures. Information about the grain number, the track length, the total number to tracks input, minimum and maximum lengths, etc., is displayed in the F.T. data display area. The Granhics Cursor When the bitpad is connected, a cross on the screen reproduces the movements of the bitpad cursor as well as the LED in the eyepiece. This cross (the graphics cursor) is used for all actions carried out on the screen, whether its measuring a uack, counting, erasing, or choosing an option from the menu. The bitpad can also be disconnected. This makes additional track input impossible, but file management and statistical functions can still be done on the keyboard. Warning, Boxes and File Selectioq
In order to avoid any error in data handling and/or any information loss, warning boxes are superimposed on the screen. These special messages are designed to help the beginner learn how to use the software. These help menus can be disengaged at any time from the Option Menu. The F.T. data are recorded on the disk in files. File names are chosen by the user, following the same rules as for MS-DOS. There is afile selection box for choosing the disk unit, the directory and the file desired. The file selection and warning boxes can both be controlled with the bitpad cursor. This reduces the necessity of using the keyboard to a bare minimum. The Main Menu (Fie. 2)
The f'u'st three options are for the "Lengths and Angles", "PM Dating" and "EDM Dating" menus, and are described later. But before any track data can be input, the parameters must be entered and the bitpad must be calibrated. The "Bitpad" option is used to connect and disconnect the bitpad, and, above all, to correlate the screen grid with ~ient o f ~ e L m i ~ o l ~ e .. In .this way, all...wacks ap.p~. in the same p.lace on both grids. t.m,wrat.~.n" .opuon l~u.seo to.cml.t~'ate the bztpad using a rmcromeffic grid (5 successive measurements), or put me._c~l~'auon. coerncaent ¢In'ecuytrom the keyboard. The Opnons menu is used to change four program parameters by activing or deactivating them. The first two (display of the grid and the warning boxes) have already been discussed. The audible beeps and referential axis input are the last two parameters in the "Options" menu.
258
M. REBETEZ et aL
FISSION T R A C K ANALYSIS W I T H ATOM Fission tracks can be used to retrace the thermal history of a minerai. The history is obtained by a combination of dating - with one of the two most commonly-used methods, PM or EDM - (Chambaudet et al., 1986b) and analysis of the track length histogram (Chambaudet et al., 1986c; Rebetez, 1987; Rebetez et al., 1988). Each of these three studiescan be conducted independently with ATOM. Lenfths and An~les S t u d y This option (found on the main menu) is used to input tracks and to study the statistics on track lengths and track orientations with regard to the user-defined referential axis. A new menu is then displayed on the screen (Fig. 3):
Characteristics Erase lengths Add a grain Statistics Referential axis File management Options Back to main menu
Last length Other length All lengths End Characteristics Load a file graph of lengths graph of orientations
Fig. 3. Some options in the sub-menus of "Lengths / angles Study"
This menu includes : * "Characteristics": Before any track data can be input, the measurement characteristics must be introduced: sample code, name of the experimenter, count number, figure fl0e, mineral type, objective enlargement, objective type and date. Most of this information is essenflai and directly related to the problem of measurement reproducibility. After their input (or default validation), the track input mode is automatically activated. Each length can then be input by placing the bitpad cursor on each end of the track. A beep and the representation of the track on the grid of the screen conf'n'm the input. The following information concerning the work session is displayed in the information window; total number of tracks input, number of the current grain, number of tracks in this grain, length of the shortest track and length of the longest track. * "Erase lengths": Input corrections can be made at any time (Fig. 3). Thus, the last length entered can be erased by clicking directly in the menu. Other track lengths can be erased after having been selected on the graph with the bitpad cursor. ,,F'm~ly, all .fl~,lengths entered in the current grain can be cancelled with one cortland. * The option Add a grain corresponds to a change of the field of view. A new blank grid is displayed on the screen. Before this, the "Referential axis" will have to have been input. * "Statistics": This menu (Fig. 3) is used to load a file, as it is directly accessible and independent of the inputs. It displays the charact~sfics and the graphs of the lengths and orientations. The graph of the lengths is drawn by classes half a micron wide between zero and twenty microns, but these limits can be modified. The typical statistical variables are displayed on the screen. A "Print-Screen" function is available. * "File management": This funcOon calls up the file selection box and can be used to save a file temporarily, or to reload a file in order to finish inpufing new tracks. Datin~ b y the P o n u l a t i o n M e t h o d
Remember that the population dating method consists in the successive determination, first of fossil track density, then of induced track density, on two mineral grain populations. This is why two quite similar menus are available (Fig. 4).
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM
PM fossil
tracks
PM induced tracks
Characteristics
Characteristics
Surface Input
Surface input
Erase a track
Erase a track
Start grain again
Start grain again
Add a grain
Add a grain
Induced tracks
.oad a fossil track file
Statistics
Statistics
Options
Options
Back to main menu
259
Back to main menu
Fig. 4. The options in the two "PM dating" menus.
Only the sixth line is different. When the input operation for fossil tracks is finished, the option "Induced Tracks" can be selected in order to begin the second part of the study. Reciprocally, the option "Load a fossil track file" loads fossil track data from the disk before beginning induced track counting. Certain of the other options, "Characteristics", "Erase a Track", "Start grm_n again", "Add a grain" and "Options" are self-explanatory or have previously been discussed. The option Surface input" is specific to the dating method for small grains or those having surface defects. In these cases, track counting on an area corresponding to the complete eyepiece grid is inadequate. This is why any smaller rectangular area can easily be selected with the cursor. This "Statistics" menu is different from the one in the "lengths / angles" menu. Its principal function is to determine the fission track age and its error. The experimenter must have already entered the thermal neutron flux received by the sample, the error on its determination, and the value of the decay constant for the fission of uranium 238 (which is still being debated) (Rcbetez, 1987; Chambaudet, 1988). DatinQ Dy the External Detector Method This method consists in d arlng each grain in a mineral sample individually. The fossil tracks in the mineral and the induced tracks on the corresponding area in the external detector must be counted. As previously seen, two similar menus are accessible (Fig. 5). Again there are the options "Characteristics", "Erase Track", "Count grain again" and "Options", which work in the same way as for the Population Method.
EDM fossil tracks
EDM induced tracks
Characteristics Surface input
Characteristics
Erase a track
Erase a track
Start grain again
Start grain again
Induced tracks
Next grain
Statistics
Statistics
Options
Options
Back to main menu
Back to main menu
Fig. 5. The options in the two "EDM dating" menus. |9:1/4-J
260
M. REBETEZ et al.
The option "Input area" is only available in the fhst menu. Indeed, when the option "Induced Tracks" is selected, a "mirror image" of the corresponding area of the external detector is displayed on a new grid. The location of the image of the grain in the detector is thus facilitated. After entering the induced track countings, the option "Next grain" returns to the "EDM fossU tracks ~ menu. At the end of the analysis, the "Statistics ~ option, as previously seen, calculates the mineral age. Other statistical data such as the distribution of individual grain ages or radial plots (Galbralth, 1990) would be interesting and work on them is in progress. CONCLUSION So far, ATOM software development has taken approximately 500 hours. In its present version it is an excellent tool for the fission track analyst. It can be installed on very low-cost data processing equipment and fulfills rapidly and completely the majority of measurement and analysis requirements in the fission track field. It can also be developed. A more elaborate version which includes the control of a motorized stage for the optical microscope is in progress. The statistical menus could also be extended. Any and all expansion of the software is possible. For the present, however, we plan to concentrate on the developments possible within our self-imposed limit of 640 K of memory.
REFERENCES Chambaudet, A. (1988). Standardization of fission track dating methods.Nucl. Tracks. Radiat. Meas., 15, 665672. Chambaudet, A., D. Fellmann, M. Rebetez and P. Le Thanh (1984). Automatic track countings. Nucl. Tracks, 8, 207-210. Chambaudet, A., M. Mars, M. Rebetez and M. Rossy (1986a). Applications des traces de fission de l'uranium dans le domaine des Sciences de la Terre. Annales Sci. de l'Universit~ de Franche-Comt~ Besanfon, Geol., _4, 67-86. Chambandet, A., M. Mars and M. Rebetez (1986b). A comparison of different external detectors for fission track dating of apatite. Nuel. Tracks, 12, 859-862. Chambaudet, A., M. Mars, M. Rebetez and F. Theobald (1986c). Chemical etching and length disuibution of fission tracks: a model. Nucl. Tracks, J ~ 855-858. Dwivedi, K.K., A. Saxena, P. Crombach, E. Reichwein and G. Fiedler (1986). Track lengths of heavy ions in CR-39 and ZnP-Glass detectors. Nucl. Tracks, 12. 241-244. Galhraith, R.F. (1990). The radial plot: graphical assessment of spread in ages. Nucl. Tracks Radiat. Meas., 17, 207-214. Noll, A., G. Rusch, H. Rt~cher, L Dreute and W. Heinrich (1988). The Siegen automatic measuring system for nuclear track detectors: new developments. Nucl. Tracks Radiat. Meas., 15, 265-268. Rebetez, M. (1987). Modtlisation des distributions de longueurs de traces de fission de l'uranium clans le but de retracer l'histoire chronothermom~aique de mintraux. Tldse de Doctorat de l'Universit# de Franche-Comt~, mention Chimie Physique, 40, 283 p., Besan¢on. Rebetez, M., A. Chambaudet and M. Mars (1988). Theoretical etching effects on "Track in Track" and "Track in Cleavage" length distributions. Nucl. Tracks Radiat. Meas., 15, 69-72.
0735-245X/91 $3.00 + .00 Pergamon Press pie
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM F O R T H E ANALYSIS OF FISSION T R A C K C H A R A C T E R I S T I C S IN A N I S O T R O P I C MINERALS
M. REBETEZ, B. ZOPPIS, A. REBRAB, P. G R I L L O N , E. GENTINA and A. CHAMBAUDET Laboratoire de Mieroanalyses Nucl~.alres,U.F.R. Sciences et Techniques, 16 route de Gray, 25030 BESANCON Cedex, France
ABSTRACT We have developed a semiautomatic measuring system for the analysis of fission tracks in minerals. This system consists of an optical microscope equipped with a drawing tube which is connected to an IBM compatible computer equipped with a digitizer. ATOM is the software, developed using TURBO-PASCAL Version 4.0. It is presently used for performing data input operations of densities, lengths and orientations of tracks. It also coordinates the activities of storing and processing the data of measured tracks and it gives the results of the statistical analysis. In this way, the mineral age determination can be made either by the Population Method (I'M) or by the External Detector Method (EDM).The curves for fission track length distributions and orientations are drawn and may be printed out. This system's hardware and software are described in this paper.
KEYWORDS semiautomatic measuring system; fission tracks; dating; lengths; orientations; densities; software; optical microscopy; bitpad digitizer, microcomputer. INTRODUCTION For many years now, the fission track dating method has provided much information for carrying out chronothermometric studies of minerals such as apatite, sphene and zircon (Chambaudet et al., 1986a). The increasing number of samples to be analysed and the difficulties involved in teaching the method to new experimenters have led us to develop a semiautomatic system for analysing fission track characteristics. The parameters to be studied include the projected length of confined or surface tracks, their orientation in comparison with the crystallographic axes and the densities of tracks used for mineral age calculation. The goals of developing such a system include: - having a tool for thorough and rapid processing, providing measurements which can be reproduced, - developing open-ended data processing software to be used with low-cost, standard computers. T H E SYSTEM
galaiameam Only a few years ago, the image analysis systems used for studying SSNTD's required high-cost data processing materials (Chambaudet et al., 1984). Given current microcomputer capabilities, it is now possible to develop such software on many commonly available systems, such as the IBM-PC (Noll et al., 1988). Figure l shows how the system is set up.
255
256
M. REBETEZ et al.
/
IM
drawing tube
RS 232 serial port cursor equipped with an LED
Microscope
\
/
Bitpad digitizer
IBM compatible
Fig. 1. Diagram of track measuring system components (inspired by Dwivedi et al., 1986)
Thus, the necessary equipment is : - a microscope with a drawing tube. We use an Olympus BH2 and normally work with a magnification of x1250 (dry objective xl00, eyepiece xl0, drawing tube magnification xl.25) ; - an IBM, XT or AT compatible microcomputer. An 8088 microprocessor will suffice, but at least 640K of RAM, and a monochrome monitor with either a Hercule or an EGA card are also needed. A hard disk drive is also recommended for greater speed and increased flexibility in the use of the ATOM software; - a Benson 6440-compatible bitpad digitizer (resolution of 0.02mm) connected to the serial port of the microcomputer;, - a graphic printer (Epson LX800, 80 columns); - the ATOM software. Software
The software was developed in Turbo Pascal 4.0 (Borland Inc.). This language has the advantages of being rather simple from a programming point of view, and offering a broad range of possibilities in terms of graphics and data management, all without sacrificing speed or performance for the final user. Because of the large number of ATOM functions and amount of storage space allotted by Pascal, ATOM had to be broken up into several modules according to the software requirements. The software is designed with 13 programs for a total of 4200 lines. The user, however, is completely unaware of this decomposition: he or she needs only the execution file ATOM.EXE (110 K) and a few graphics units (90 K) to get working. Each of the 13 programs correspond to either a utility (bitpad,_ management, menu management, window management, graphics mode management, etc.), or one of ATOM s main menus. After a brief presentation of the utilities, the menus "Lengths and Angles", "PM Dan'ng" and "EDM Dating" are described in detail. ATOM UTILITIES Semiautomatic analysis of fission tracks requires the use of an optical microscope. To reduce eye fatigue (and thus the chance of errors) the experimenter must be able to isolate himself from all outside diswactions. To help, great care went in the design of ATOM to make it user-friendly and ergonomic. Thus, for example, an audible beep highlights and confirms most inputs. The Screen The graphics screen is composed of du'¢¢ windows and an information line (Fig. 2)
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM
Information
257
line
ATOM Lon(:jths / Angles study PM DatJno EDM Da~ng Calibration Bitpad Options Quit
grid
Main menu
f
F.T. data display
&
Fig. 2. Layout of the A T O M
screen
The grid is where the tracks are shown. Exactly what is observed under the microscope can be reproduced. This is also where graphs are displayed when using the graphics menus. Display of the actual grid lines is optional. The information line indicates the current operation. The menu lists the various directly accessible options. Each option is organized into tree structures. Information about the grain number, the track length, the total number to tracks input, minimum and maximum lengths, etc., is displayed in the F.T. data display area. The Granhics Cursor When the bitpad is connected, a cross on the screen reproduces the movements of the bitpad cursor as well as the LED in the eyepiece. This cross (the graphics cursor) is used for all actions carried out on the screen, whether its measuring a uack, counting, erasing, or choosing an option from the menu. The bitpad can also be disconnected. This makes additional track input impossible, but file management and statistical functions can still be done on the keyboard. Warning, Boxes and File Selectioq
In order to avoid any error in data handling and/or any information loss, warning boxes are superimposed on the screen. These special messages are designed to help the beginner learn how to use the software. These help menus can be disengaged at any time from the Option Menu. The F.T. data are recorded on the disk in files. File names are chosen by the user, following the same rules as for MS-DOS. There is afile selection box for choosing the disk unit, the directory and the file desired. The file selection and warning boxes can both be controlled with the bitpad cursor. This reduces the necessity of using the keyboard to a bare minimum. The Main Menu (Fie. 2)
The f'u'st three options are for the "Lengths and Angles", "PM Dating" and "EDM Dating" menus, and are described later. But before any track data can be input, the parameters must be entered and the bitpad must be calibrated. The "Bitpad" option is used to connect and disconnect the bitpad, and, above all, to correlate the screen grid with ~ient o f ~ e L m i ~ o l ~ e .. In .this way, all...wacks ap.p~. in the same p.lace on both grids. t.m,wrat.~.n" .opuon l~u.seo to.cml.t~'ate the bztpad using a rmcromeffic grid (5 successive measurements), or put me._c~l~'auon. coerncaent ¢In'ecuytrom the keyboard. The Opnons menu is used to change four program parameters by activing or deactivating them. The first two (display of the grid and the warning boxes) have already been discussed. The audible beeps and referential axis input are the last two parameters in the "Options" menu.
258
M. REBETEZ et aL
FISSION T R A C K ANALYSIS W I T H ATOM Fission tracks can be used to retrace the thermal history of a minerai. The history is obtained by a combination of dating - with one of the two most commonly-used methods, PM or EDM - (Chambaudet et al., 1986b) and analysis of the track length histogram (Chambaudet et al., 1986c; Rebetez, 1987; Rebetez et al., 1988). Each of these three studiescan be conducted independently with ATOM. Lenfths and An~les S t u d y This option (found on the main menu) is used to input tracks and to study the statistics on track lengths and track orientations with regard to the user-defined referential axis. A new menu is then displayed on the screen (Fig. 3):
Characteristics Erase lengths Add a grain Statistics Referential axis File management Options Back to main menu
Last length Other length All lengths End Characteristics Load a file graph of lengths graph of orientations
Fig. 3. Some options in the sub-menus of "Lengths / angles Study"
This menu includes : * "Characteristics": Before any track data can be input, the measurement characteristics must be introduced: sample code, name of the experimenter, count number, figure fl0e, mineral type, objective enlargement, objective type and date. Most of this information is essenflai and directly related to the problem of measurement reproducibility. After their input (or default validation), the track input mode is automatically activated. Each length can then be input by placing the bitpad cursor on each end of the track. A beep and the representation of the track on the grid of the screen conf'n'm the input. The following information concerning the work session is displayed in the information window; total number of tracks input, number of the current grain, number of tracks in this grain, length of the shortest track and length of the longest track. * "Erase lengths": Input corrections can be made at any time (Fig. 3). Thus, the last length entered can be erased by clicking directly in the menu. Other track lengths can be erased after having been selected on the graph with the bitpad cursor. ,,F'm~ly, all .fl~,lengths entered in the current grain can be cancelled with one cortland. * The option Add a grain corresponds to a change of the field of view. A new blank grid is displayed on the screen. Before this, the "Referential axis" will have to have been input. * "Statistics": This menu (Fig. 3) is used to load a file, as it is directly accessible and independent of the inputs. It displays the charact~sfics and the graphs of the lengths and orientations. The graph of the lengths is drawn by classes half a micron wide between zero and twenty microns, but these limits can be modified. The typical statistical variables are displayed on the screen. A "Print-Screen" function is available. * "File management": This funcOon calls up the file selection box and can be used to save a file temporarily, or to reload a file in order to finish inpufing new tracks. Datin~ b y the P o n u l a t i o n M e t h o d
Remember that the population dating method consists in the successive determination, first of fossil track density, then of induced track density, on two mineral grain populations. This is why two quite similar menus are available (Fig. 4).
ATOM: A SEMIAUTOMATIC MEASURING SYSTEM
PM fossil
tracks
PM induced tracks
Characteristics
Characteristics
Surface Input
Surface input
Erase a track
Erase a track
Start grain again
Start grain again
Add a grain
Add a grain
Induced tracks
.oad a fossil track file
Statistics
Statistics
Options
Options
Back to main menu
259
Back to main menu
Fig. 4. The options in the two "PM dating" menus.
Only the sixth line is different. When the input operation for fossil tracks is finished, the option "Induced Tracks" can be selected in order to begin the second part of the study. Reciprocally, the option "Load a fossil track file" loads fossil track data from the disk before beginning induced track counting. Certain of the other options, "Characteristics", "Erase a Track", "Start grm_n again", "Add a grain" and "Options" are self-explanatory or have previously been discussed. The option Surface input" is specific to the dating method for small grains or those having surface defects. In these cases, track counting on an area corresponding to the complete eyepiece grid is inadequate. This is why any smaller rectangular area can easily be selected with the cursor. This "Statistics" menu is different from the one in the "lengths / angles" menu. Its principal function is to determine the fission track age and its error. The experimenter must have already entered the thermal neutron flux received by the sample, the error on its determination, and the value of the decay constant for the fission of uranium 238 (which is still being debated) (Rcbetez, 1987; Chambaudet, 1988). DatinQ Dy the External Detector Method This method consists in d arlng each grain in a mineral sample individually. The fossil tracks in the mineral and the induced tracks on the corresponding area in the external detector must be counted. As previously seen, two similar menus are accessible (Fig. 5). Again there are the options "Characteristics", "Erase Track", "Count grain again" and "Options", which work in the same way as for the Population Method.
EDM fossil tracks
EDM induced tracks
Characteristics Surface input
Characteristics
Erase a track
Erase a track
Start grain again
Start grain again
Induced tracks
Next grain
Statistics
Statistics
Options
Options
Back to main menu
Back to main menu
Fig. 5. The options in the two "EDM dating" menus. |9:1/4-J
260
M. REBETEZ et al.
The option "Input area" is only available in the fhst menu. Indeed, when the option "Induced Tracks" is selected, a "mirror image" of the corresponding area of the external detector is displayed on a new grid. The location of the image of the grain in the detector is thus facilitated. After entering the induced track countings, the option "Next grain" returns to the "EDM fossU tracks ~ menu. At the end of the analysis, the "Statistics ~ option, as previously seen, calculates the mineral age. Other statistical data such as the distribution of individual grain ages or radial plots (Galbralth, 1990) would be interesting and work on them is in progress. CONCLUSION So far, ATOM software development has taken approximately 500 hours. In its present version it is an excellent tool for the fission track analyst. It can be installed on very low-cost data processing equipment and fulfills rapidly and completely the majority of measurement and analysis requirements in the fission track field. It can also be developed. A more elaborate version which includes the control of a motorized stage for the optical microscope is in progress. The statistical menus could also be extended. Any and all expansion of the software is possible. For the present, however, we plan to concentrate on the developments possible within our self-imposed limit of 640 K of memory.
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