nada92: an automated, user-friendly program for neutron activation data analysis

Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 180, No. 1 (1994) 55-63

Automated Data Handling

NADA92: AN AUTOMATED, USER-FRIENDLY PROGRAM FOR NEUTRON ACTIVATION DATA ANALYSIS

S. LANDSBERGER,* W. D. CIZEK,** R. H. CAMPBELL**

*Department of Nuclear Engineering, University of Illinois, 214 Nuclear Engineering Laboratory, 103 South Goodwin Avenue, Urbwna, Illinois, 61801 (USA) * *Department of Computer Science, University of Illinois,

1304 West Springfield Avenue, Urbana, Illinois, 61801 (USA)

(Received December 21, 1993)

We have developed a highly automated program for the analysis of data from neutron activation analysis (NAA). Spectral analysis is done using almost any common MCA employing regions of interest or peak-fitting routine of the user's choice. A wide variety of data entry possibilities is available, from fully mantml data entry to an automatic mode where the user enters all necessary data in a tabular format and the computer calculated the results. The resulting data can be automatically imported into a LOTUS 1-2-3 compatible spreadsheet for statistical analysis. All of the features of previous versions of NADA have been retained. These include a variety of methods for dead-time correction, correction of spectral and nuclear interferences, and a complete, concise hard-copy output. Future improvements include a routine which will automatically select regions-of-interest for spectra in ORTEC Maestro, thus reducing the processing time needed.

The application o f computers to scientific research has had t remendous effects, especially

since the advent o f powerful, low-cost personal computers. Using computers to perform the

rudimentary tasks o f data collection and calculations allows scientists to concentrate on problem

solving and research. This technology has been applied to N A A to aid researchers in every step o f

the procedure, from data collection with any of the many multichannel analyzer (MCA) systems

available; to peak-fitting with such programs as microSAMPO 1 or GAMANAL-PCZ; to producing

the final results with CINA 3, Q U A L C A N A L 4 or N A D A s and statistically analyzing these results in

a spreadsheet.

The process o f spectral peakfitting has been more intensely studied than that of handling the

resulting data or making the programs user friendly. Our program. Neutron Activation Data Analysis

(NADA92), was originally developed to simplify this process, by taking the data from a spectral

analysis program, and calculating the concentrations of the ~lements in question. As the program

developed, additional features were added, allowing spectral data to be automatically imported from

an M C A program, and accounting for various spectral and nuclear interferences, flux variations and

deadtime losses. Most recently, an implementation o f a hardware deadtime correction s and a more

aseful output format with detection limits for each individual element in the spectrum, have been

added.

Elsevier Science S. A., Lausanne Akad#miai Kiad6. Budapest

S. LANDSBERGER et al.: NADA92: AN AUTOMATED, USER-FRIENDLY

All of these additions have greatly improved the usefulness of the program, but they still

require the user to sit and enter all of the data while the program is running. This problem cannot

be totally e ~ a t e d - the data must be entered into the program in some form - but the method of

data entry can be streamlined to reduce the amount of time the user spends on this task.

As a result o f this, tke most recent update of NADA has been the addition of a new batch

mode, where the user enters all of the pertinent data into a single screen data entry form. The

program stores tiffs data and uses it to run any number of samples, either immediately or at a later

time. Some of the improvements necessitated by the batch mode have had the side effect of

improving the operation of the manual and automatic modes of NADA. This batch operation akso

a~lows NADA92 to be run from within most LOTUS i-2o3 compatible spreadsheets, with the resuit~

being automatically .;reported into the spreadsheet for any additio~ni analysis. This last feature is

crucial when dealing with very large data set,.

This update of NADA is writte~ in C to take advantage of the features of the language, such

as the data structures used in the program and the routines used for screen control and co,or coding

the program for improved user friendliness. For example, all important messages, such as error

messages, are colored yettow to attract the user's attention.

Methods

Our work is primarily in the field of airborne particulate matter. Spectra from this type of

sample contain few overlapping peaks, which would imply that a sophisticated peak-fitting routine

would work very well. The neutron activated samples, however, usually contain important small peaks,

which an automated peak fitting routine often may not identify or fit, such as peaks with 4 to 6

channels. For this reason ORTEC MAESTRO is used for spectral analysis, although NADA92 can

be modified to allow the use of almost any MCA or peak-fitting program. The user analyzes the first

spectrum, selecting regions-of-interest (ROI) for each element of interest, as well as for a small area

on either side of the peak for background correction. These ROt are then used to analyze the rest

o f the spectra. A report file is made from each spectrum, with the necessary data from each ROI.

as well as the time of the start o f count, real time, and live time.

NADA92 has three modes of data entry: 1) the manual mode, in which all of the data i~

entered interactively by the user, 2) the automatic mode, where the spectral information is handled

by the computer and the other information is entered by the user interactively, and 3) the batch

mode, where the spectral information is handled by the computer and all o f the other information

is entered into a spreadsheet style data entry screen by the user before the samples are processed.

Despite the variance in the method of data entry, the basic calculations performed on the data remain

the sarqe. The peak areas are first corrected for any spectral interferences. Next, the deadtime and

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flux corrections are applied and the samples are normalized to the standards in relation to weight and

irradiation, decay and counting time. Finally, the actual concentrations of the requested elements are

calculated, along with the specific detection limits, based on Currie's method 7, necessary for

multivariate statistical analysis. At this point, if all of the data for the samples is complete, uranium

and thorium interferences on samarium 8, as well as uranium fission interferences 9, are accounted

for.

The data necessary for the analys~s is organized in two general categories: the standards data

and the sample data. The standards data is stored in a disk file as a standards library. It is a table

of the results of analyzing known elemental concentrations, either from primary standards or

reference materials. Sho~a in table 1, this file contains the actual concentration and measured count

value for each element, as well as a correction for any variances in the weight o f the sample or the

irradiation, decay or counting time. This standards fibrary is made fxom within NADA92 using either

of the manual or automatic modes.

The other data category is the sample data, consisting of the spectral information in the form

of the peak and background areas of the elements in question, the irradiation, decay and counting

Table 1 Standards library. The correction factor is use to account for variances in the weight and other parameters of the standards and the samples. Different isotopes of the same element are denoted by the A and B suWaxes.

Element Units Given Error Counts Error Correction Name Cone. Factor

CE-141 PPM 1005.000 10.050 6267.823 84.948 .58285E-08 CELIQ C8-134 PPM i000.000 I0,000 10627.450 104.650 ,11937E-10 CSLIQ CR-51 PPM i000,000 i0.000 10382.060 101.889 .34686E-07 CRLIQ CO-60A PPM 1005.000 10.050 11770.620 113.924 .35123E-11 COLIQ CO-60B PPM 1005.000 10.050 10581.340 103.848 .35123E-II COLIQ EU-152 PPM 995.000 9.950 10539.600 104.620 .26447E-12 EULIQ GD-153 PPM i005,000 10.050 14753.540 134.512 .13034E-08 GDLIQ HF-181 PPM 985.000 9.850 57821.820 242.751 .96354E-08 HFLIQ FE-59A PPM 1005.000 10.050 14151.750 129.311 .28858E-05 FELIQ LU-177B PPM I000.000 i0,000 78060.440 287.897 .39277E-I0 LULIQ HG-197 PPM i000,000 i0.O00 55156.770 254.512 .20822E-06 HGLIQ HG-203 PPM 1000.000 i0.000 10632.100 104.869 .37834E-08 HGLIQ

time. the sample weight, a flux correction, and the name of the detector used to count the sample.

The spectral information is either read in from a MAESTRO report file, or is entered by the user.

This gives novice users an in-depth experience with the process of the analysis, while allowing the

experienced users to bypass this step and reduce the chance of errors by letting the computer handle

the data. The rest of the data is entered in one of two forms. [n the manual and automatic modes

the user enters this data as the program is running, while in the batch mode this data is entered into

a spreadsheet style screen as shown in table 2.

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S. LANI)SBt. R(iI!R et al.: NADA92: AN AUTOMATED, USER-FRIENDLY

Table 2 Spreadsheet style data entry screen for NADA92's batch mode. On screen the rows of data are alternately colored white and green to aid in identification of a particular 1 () ~ .

Ent<~ data for the individual runs as shown, Enter "done" for Vial Number when finished.

Vial ~ Sample Name Weight Ti End of Irradiation Flux Detector Pos (gm) (sec) date time Corr.

pl[ Egyptian Pot 0.23251 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 p12 Egyptian Pot 0.17514 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 p]3 Egyptian Pot 0.18537 2960.0 03-feb-92 17:10:00 l. OOO00 mcbl 5 p]4 Egyptian Pot 0.16852 2960.0 03-feb-92 17:10:00 l. O00f)O mcbl 5 p]5 Egyptian Pot 0.14350 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 p16 Egyptian Pot 0.20081 2960.0 03-feb-92 17:10:00 1.04000 mcbl 5 p17 Egyptian Pot 0.14199 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 p]8 Egyptian Pot 0.19343 2960.0 03-feb-92 17:10:00 1.04000 mcbl 5 p19 Egyptian Pot 0.13923 2960.0 03-feb-92 17:10:00 1.000(I0 mcbl 5

pll0 Egyptian Pot 0.14949 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 plllb Egyptian Pot 0.22734 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 pllla Egyptian Pot 0.12300 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 pl12 Egyptian Pot 0.18264 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5 pl13 Egyptian Pot 0.12404 2960.0 03-feb-92 17:10:00 1.04000 mcbl 5 pl14 Egyptian Pot 0.17360 2960.0 03-feb-92 17:10:00 1.00000 mcbl 5

T a b l e 3

Detector selection in NADA92. Detector MCBI is linked with library nsfl2, and MCB4 is being linked with library nsf08. The values P1 and P2 correspond to the hardware deadtime correction [see reference 6].

Select the detectors which were used in these run~::

DETECTOR PI P2 LIBRARY

> i, MCBI 0.4688 -0.2865 o:\nsfl2.stf 2. MCB2 0.2450 0.0000 3. MCB3 0.1340 0.00OO

> 4. MCB4 0,0355 -0.1320 5. MCB5 0.1535 0.0000

Enter the detector to change, {enter} when finished :4 Enter library to be used with the detector :c:\nsfOS.stf

In all three modes of use, the standards libraries :m: !inked to the detector name as shown

in table 3, so simply selecting the proper detector will aura natically select the proper standards

library. This eliminates some of the repetitive data entry' si~,.,:, ti,r any group of samples, each

detector will use one set standards library. This method ot linking the libraries to the detectors is

optional for the manual and automatic modes, primarily m give the bcgimaing user the chance to

5~


learn more about the process and how it works. In batch mode the user is required to link the

libraries with the detectors due to the nature of the processing.

The other data to be entered in the manual and automatic modes, such as irradiation time,

decay time, sample weight and flux correction, are prompted for by the program. When this data is

Table 4 Hardcopy and screen data output from NADA92.

Sample Title Vial number Weight Irradiation Time Delay Time

End of irradiation Start of count

Real Time Live Time Percent Dead Time Flux Factor Detector P factors Standards Library

Element

i. SM-153A 2. NP-239 3. LA-140A 4. AS-76 5. SB-122 6. NA-24A

Net Counts Concentration Det Lim

209942 • 570 7.6 • 0.7 PPM 0.04 4759 • 248 4.14 • 0.25 PPM 0.7

47457 • 264 43 • 4 PPM 0.4 2612 • 153 7.4 • 0.9 PPM 1.3 5989 • 169 1.67 i 0.ii PPM 0.14

56342 i 259 11200 i 700 PPM 70

Egyptian Pottery pti

0. 23251 gm 12960.0 sec 671538 sec

03-FEB-92 17:10:00 II-FEB-92 11:42:18

3600.0 see 3347.1 sec

7.03 i. 00000

mcbl O. 134000 O. 000000 a:pt. stf

Error

0.27 % 5.22 0.56 5.86 2.82 0.46

entered it is displayed for the user to check for accuracy, after which the calculations are performed

and the output is displayed, both to the screen and to the printer, in the format shown in table 4.

The most often used mode of NADA92 is batch mode, simply because of the great time

savings it affords the user. Aside from the simple spreadsheet look of the data entry screen, various

additional features have been implemented to both decrease the amount of time spent entering data,

and to increase the accuracy of the data entered. The data input screen uses color coded lines,

alternating green and white, to aid the user in identifying the current line. This is especially helpful

in editing the data after an entire screen has been entered. As can be seen in table 2. the amount

of similar data on the screen reqmres some type of aid in remembering where the current line is.

Other features have been made possible by some simplifying assumptions on the use of the program.

First, the values of certain parameters may be constant for groups of samples. For this

reason, most parameters default to the value from the previous sample. The two most common

examples of this are a constant irradiation time and end of irradiation time for medium and long lived

NAPL ff no values are constant between samples, then the user need not use these defaults, and no

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loss o t pertOrmanee is experienced. A related case occurs when samples are counted on two different

detectors and therefore require two different standards libraries, or when two different flux

eorrectiom are needed for a group of samples. Both of these cases generally have an even-odd

pattern, such that the first, third, fifth.., sample uses one detector and flux correction, and the second,

fourth, sixth.., sample uses the other detector and flux correction. Since this case can happen quite

often, it has been accounted for in the data entry routine. The default values for the detector and

flux correction are taken from the sample before the previous sample, so when the four th sample is

being processed, the default values for the detector and the flux correction are from the second

sample. In this situation, since the default detector alternates, the standards library to be used with

the sample also alternates, the end result being that the proper standards library is used with the

corresponding samples. It should be noted that this system also works for constant values for the

detector or flux correction, since in this case the previous two values are identical.

The second assumption concerns the vial numbers. Partially because an automatic sample

changer is used, our report files are named in a format such as f'de110.rpt, where the number

distinguishes the individual samples within in the group. This prompts the user with the next vial

number, based on the assumption that if file110 is being run now, then file111 should be next. The

number can be changed if necessary, retaining total control for the user.

Third. since the user must pre-select the detectors to be used in the analysis run, the program

can ensure that an incorrect detector is not entered. If only one detector has been selected for use.

then the program will simply skip the entry of the detector name. since the choice has already been

made by the user.

At the completion of each screen of data, the user is given the chance to either correct or

delete any entries. T hen a run file is created, containing all of the sample data and the information

concerning the detectors and libraries. This data can be immediately run, or saved and run at a later

time. In either case the run file is saved and can b e re-used if some or all of the samples must be

run again. Because o f this, two people may work at the same time. one analyzing the spectra with

the ROI and the other entering the data, if the analysis must be done quickly.

In order to account for any corrections and to ensure that the correct data set is being used,

the user must guide NADA92 through the first sample in batch mode. The data read from the first

report file is displayed on screen and the user has the option of removing one o r more of the peaks

selected for analysis. Any peaks removed from this sample are subsequently removed from the other

samples. Any spectral interferences found are displayed and corrected at this point.

Next, the program reads in the standards library and displays it on the screen for the user 's

information. Finally, the program calculates and displays the final results and generates a hard-copy

of the results.

For the rest of the samples, the program displays nothing except a notation on the screen

telling which report file is currently being run. At the finish of the batch run any uranium or thorium

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M C A P r o g r a m

NADA92 F E r r ~

Fil0s/ 1 - 2 - 3

Figure 1 Data flow through the NADA92 system.

interferences on samarium or uranium fission interferences are corrected, and if NADA92 was started

from LOTUS 1-2-3, the results are automatically imported into the current spreadsheet.

In the ease o f an error occurring during the batch run, a message is written to a special error

file, and the next sample is processed. At the end of the batch run, NADA92 will alert the user to

the number o f errors and generate a printout if requested. These errors can arise because of a

nonexistent report file, er roneous data in the report file, or an element not being identified in one

of the samples. This error file allows the user to re-run a subset of the samples, since the absence

of any report files will simply generate a message in the error file and will not adversely effect the

program.

When finished, if NADA92 was run from within LOTUS 1-2-3, the user is left with all of the

data imported into the current spreadsheet. This data can be easily used to create a graph or

analyzed in other ways. A summary of the data flow throught NADA92 is shown in figure 1.

Error Analysis

Final errors for elemental concentrations are calculated by combining in quadrature the

statistical photopeak error o f the standard, the error of the concentration, and the statistical

photopeak error of the unknown. If one uses a photopeak of an arsenic standard, which has 10,000

61


+ 200 counts, with a precision of 10.0 + 0.2 ppm, and the unknown photopeak has a statistical error

o f 3,500 + 500 counts, then the final error is 0.23, as calculated by the follow/rig equation:

i , 200 ,2 , 0 .2 ,2 , 500 ,z

Deadtime Correctior~

As stated before, deadtime corrections can be calculated in three differentways: by taking the

live time directly from the MCA, by using the pulser method, or by using a pileup-factor based ori

the standard two source method.

Discussion

The most important part of an interactive program is the interface between the computer and

the user. This is especially important in the general scientific community, where the users usually

have some knowledge about computers, but are not experts. A completely automated analysis routine

may be the fastest way of obtaining results, but if it is difficult to learn and understand, particularly

for the novice user, its usefulness is diminished. Simplifying the interface allows the user to

concentrate on the task of performing the analysis instead of remembering how to use the program.

Allowing the user to enter all of the pertinent data at one time, as opposed to while the

program is running, reduces the amount of time spent on this analysis task. The data is stored to

eliminate the need for re-entry if the samples need to be re-run, and two people can work at the

same time, one doing spectral analysis and the other entering the data for NADA92, to greatly reduce

the amount of time needed for analysis in any time critical situation. The creation of the error file

ensures that ff any problem occurs during the anaylsis, the user will be alerted to it and will have a

clear record to help determine what the actual cause of the error was.

The greatest problem now is the amount of time spent using the M C A program to analyze

the individual spectra. A future addition to NADA92 is a routine to work with the M C A program

to allow the user to specify the ROI on the first spectrum file. Then the program would inspect the.

spectrum files to adjust the ROI on an individual basis. This would not be a full-fledged peak search

routine, since the user would be required to enter the ROI for the first spectrum, but instead would

be an automatic method of fine-tuning the ROI for the individual spectra. No small peaks would be

lost because if the program could not accurately detect the edges of a peak, the ROI would remain

unchanged. Other planned developments include the implementation of self absorption corrections

which are crucial for high Z material.

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References

1. P. A. AARNIO, J. T. ROUTII, J. V. SANDBERG, J. Radioanal. Nucl. Chem., 124 (1988) 457. 2. M. HEIMLICH, P. A. BEELEY, J. A. PAGE, J. Radioanal. Nucl. Chem., 132 (1989) 281. 3. G. W. NELSON, J. Radi0anal. Nucl. Chem., 114 (1987) 231. 4. P. A. BEELEY, M. S. HEIMLICH, J. B. EDWARD, L. G. I. BENNETT, J. A. PAGE, A New Microcomputer

Program for Processing Data in Neutron Activation Analysis, 8th Conf. in Modern Trends in Activation Analysis, Vienna, Austria, 1991, to b e published in J. Radioanal. Nuct. Chem.

5. S. LANDSBERGER, W. D. CIZEK, NADA: A Versatile PC Based Program for Neutron Activation Data Analysis, Methods and Applications in Radioanalytical Chemistry II, Kona, Hawaii, 1991, to be published in J. Radioanal. Nucl. Chem.

6. R. M. LINDSTROMJ, R. F. FLEMING, Accuracy in Activation Analysis: Count Rate Effects, Proc. 4th Intern. Conf. Nuclear Methods in Environmental and Energy Research, 1980, p. 25.

7. L. A. CUqtRIE, Anal Chem., 40 (1968) 586. 8. S. LANDSBERGER, A. SIMSONS, Chem. Geol., 62 (1987) 223. 9. S. LANDSBERGER, Chem. Geol., 77 (1989) 65.

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nada92: an automated, user-friendly program for neutron activation data analysis

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