■MM ilMrafiiffinslllBnl TN295 mm mmm ■I mm m w No. 8888 MRS ■■ bum mm mm i 1 ii :«H HP ™ ■ 111' Iffiffi ill 1 - 1^ WBmi few BBSS w/aHHSS 9Hk 16* ^> •*T7^' .*^ L H°^ V4 # >v ^ .0 ..IV-. > v % .1^1 . . o • «0 1* .» • 6°* 0»»^ V- A* 6 o<.5tffc> >*\.S5to.V .A.aA ^..^:-X /^ %^s?t- 0^ \^^\/ v 3 ^"^ \^^y V* IC 8888 Bureau of Mines Information Circular/1982 Preliminary Testing of a Prototype Portable X-Ray Fluorescence Spectrometer By Lowell L. Patten, Neal B. Anderson, and John J. Stevenson UNITED STATES DEPARTMENT OF THE INTERIOR [(jjtcjjfrtu - / #*^V^*) > Information Circular 8888 M N Preliminary Testing of a Prototype Portable X-Ray Fluorescence Spectrometer By Lowell L. Patten, Neal B. Anderson, and John J. Stevenson UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES Robert C. Horton, Director afi K\0 % %** This publication has been cataloged as follows: Patten, Lowell L Preliminary testing of a prototype portable X-ray fluorescence spectrometer. (Bureau of Mines information circular ; 8888) Bibliography: p. 15-16. Supt. of Docs, no.: I 28.27:8888. 1. Spectrometer, 2. Fluorescence spectroscopy. 3. X-ray spec- troscopy. I. Anderson, N. B. (Neal B.). II. Stevenson, J. J. (John J.). III. Title. IV. Series: Information circular (United States. Bu- reau of Mines) ; 8888. TN295.U4 [QC373.S7] 622s [622'. 13] 82-600159 AACR2 / CONTENTS <\J Page Abstract 1 /K Introduction 2 History 2 Previous Bureau of Mines work 3 Acknowledgments 3 X-ray theory and its application to the portable spectrometer 3 Instrument design and description 4 Analytical procedures and results 6 Laboratory testing 7 Interference 9 Matrix effect 11 Summary of results 11 Field testing 12 Conclusions 14 Recommendations 15 Selected bibliography 15 Appendix A. — Selected sections of PXRFS operation and maintenance manual 17 Appendix B. — Tables of analytical results 24 Appendix C. — Nuclear Regulatory Commission (NRC) licensing information 33 ILLUSTRATIONS 1. Characteristics of X-ray fluorescence spectra 4 2. Portable X-ray fluorescence spectrometer (PXRFS) 5 3 . PXRFS as used in the field 6 4 . Periodic table of elements 8 5. Sensor-head rack and pulverized sample in petri dish 9 6. Spectra (CRT traces) of manganese ore and molybdenite 10 7. Spectra (CRT traces) of erythrite and mercury ore 10 8. Spectra (CRT traces) of samples containing iron, copper, calcium, and galena 10 9. Spectra (CRT traces) of samples containing lead, zinc, and ferberite 10 10. Spectra (CRT traces) illustrating interelement interference 11 11. Calibration curves of five element standards having granitic matrixes.... 12 12. High-impact plastic transport case for spectrometer 13 13. Spectrometer in use on a mine dump 13 14. Calibration spectrum of 109 Cd source under normal operating temperature and at 108° F 14 A-l. Front panel and controls of PXRFS 17 TABLES B-l. X-ray excitation capabilities of 55 Fe and 109 Cd for selected elements.... 24 B-2. Comparison of minus 200-mesh pulp sample analysis data with PXRFS test results 25 B-3. Comparison of USGS sample standards with PXRFS test results 31 B-4. PXRFS analysis of selected Bureau of Mines mineral display specimens 32 PRELIMINARY TESTING OF A PROTOTYPE PORTABLE X-RAY FLUORESCENCE SPECTROMETER By Lowell L. Patten, 1 Neal B. Anderson, 2 and John J. Stevenson ABSTRACT The Federal Bureau of Mines participated with the National Aeronautics and Space Administration and Martin Marietta Aerospace in developing, building, and testing a portable X-ray fluorescence spectrometer for use as an analyzer in mineral-resource investigative work. The prototype battery-powered spectrometer, measuring 11 by 12 by 5 inches and weigh- ing only about 15 pounds, was designed specifically for field use. The spectrometer has two gas-proportional counters and two radioactive sources, 109 Cd and 55 Fe. Preliminary field and laboratory tests on rock specimens and rock pulps have demonstrated the capability of the spec- trometer to detect 33 elements, to date. Characteristics of the sys- tem present some limitations, however, and further improvements are recommended. 'Mining engineer (retired). ^Geologist. All authors are with Intermountain Field Denver, Colo. Operations Center, Bureau of Mines, INTRODUCTION The principles of X-ray fluorescence spectrometry long have been known and studied intensively by numerous investi- gators (see bibliography). Laboratory model spectrometers have been available commercially for many years. The feasi- bility of a portable X-ray fluorescence spectrometer (PXRFS) was investigated in the 1960's, and several companies devel- oped portable analyzers, some using X-ray generators and others using radioactive isotope sources. In general, however, these analyzers were heavy, cumbersome, complex to use, and lacking in versatil- ity. Complications included the need to cool the X-ray generators, the use of filters to increase discrimination of the detectors, and the fact that most of these analyzers would detect only one or no more than a few elements at one time. An improved portable spectrometer would greatly facilitate the Federal Bureau of Mines mineral-land assessment work, would substantially assist mineral exploration work in general, and could benefit both Government and industry as an aid in min- eral identification and analysis. This report summarizes results of a twofold project to apply principles of X-ray fluorescence spectrometry to min- eral identification and element quantifi- cation. The first part of the project was to construct a portable, energy dis-> persive, X-ray fluorescence spectrometer. The second part was to test the prototype instrument in laboratory and field situa- tions to determine its operating charac- teristics, its response, and its useful- ness in mineral-resource investigative work. Instrument response was observed and recorded in the Planetary Geology Labora- tory of Martin Marietta Aerospace near Denver, Colo., in the Bureau's Inter- mountain Field Operations Center at the Denver (Colo.) Federal Center, in the mountains west of Denver, and near Tucson, Ariz. During testing, a limited effort was made to compare the PXRFS capabilities with those of emission spectrometers. The PXRFS can be used in conjunction with, but not as a substitute for, a laboratory emission spectrometer. History The idea of a spectrometer that could be carried easily in the field and could quickly identify and quantify many ele- ments with little or no sample prepara- tion only recently became technologically possible. In the 1970' s, Martin Marietta (MM), under contract with National Aeronautic and Space Administration (NASA), devel- oped a miniature X-ray fluorescence spec- trometer, which employed 55 Fe and 109 Cd isotopes as X-ray sources, for use on the Viking Project Mars Lander. The senior author of this report sug- gested that the Mars Lander technology might be followed in developing a porta- ble spectrometer that could be useful as a field instrument in mineral explora- tion. Subsequently, Bureau personnel consulted with representatives of MM and NASA, and in 1975 a contract was negoti- ated for developing and constructing a portable X-ray fluorescence spectrometer. The work was funded mostly by the Bureau and it also provided a list of elements of interest in mineral exploration. Sug- gestions for design to facilitate field and laboratory use were contributed by both the Bureau and NASA. The PXRFS was completed in mid-1980; subsequently, several minor adjustments and microprocessor program modifications were made. A testing program began in late 1980 and continued intermittently until the spring of 1981. A Nuclear Reg- ulatory Commission (NRC) licensing (see appendix C for license requirements) problem delayed transfer of the spectrom- eter custody from the contractor to the Bureau until July 1981 when the Bureau's source license was modified to include the PXRFS and its radioactive isotopes. Previous Bureau of Mines Work The Bureau of Mines has done consid- erable work in laboratory and field applications of X-ray fluorescence as shown by citations in the bibliography. Most of this research advanced the general technology but was directed mainly toward special applications, and, in particular, toward high quantitative accuracy in the laboratory. ACKNOWLEDGMENTS Those who technically contributed the most to the current project were Benton C. Clark, senior research scien- tist, and Ludwig Wolfert, staff engineer, both of Martin Marietta. Also instru- mental in the development of the PXRFS were Warren C. Kelliher, contract mana- ger, and Charles R. Eastwood, manager, environmental projects, both from NASA, and Sheldon P. Wimpfen, chief mining engineer, and Lee R. Rice, geologist, of the Bureau of Mines. X-RAY THEORY AND ITS APPLICATION TO THE PORTABLE SPECTROMETER X-rays can be generated by electrical apparatus or originate as gamma rays dur- ing the decay of radioactive isotopes of elements. The origin of characteristic X-ray fluorescence can briefly be described as follows: When sufficient energy is introduced into the atom, by X-rays or gamma rays, an electron is dis- placed from one of the inner shells. The atom is then in an excited (ionized) state. The place of the missing electron is filled immediately by an electron from a neighboring outer shell whose place, in turn, is filled by an electron from the next outer shell. The electron from a high energy level (outer shell) enters a lower energy level (inner shell), emit- ting excess energy in the form of X-ray fluorescence. Each element has a characteristic emis- sion energy for each electron shell, referred to as K, L, and M spectra (K- alpha, K-beta, etc.), indicating from which electron shell the fluorescence originates. Figure 1 illustrates these phenomena by showing the characteristic K, L, and M spectra and their correspond- ing energies (in kiloelectron volts, keV). An X-ray fluorescence spectrometer, then, is used to record these character- istic spectra and their energies, thereby identifying and possibly quantifying the elements. Four functions, therefore, were required in the PXRFS to accomplish this: (1) generate X-rays, (2) transform fluorescent energies into electrical impulses, (3) process, interpret, and store these electrical impulses, and (4) display the interpreted data in a form the operator could use. ATOMIC NUMBER ELEMENT 20 ENERGY (keV) FIGURE 1#- Characteri sties of X-ray fluorescence spec- tra. (Copyright, ASTM, 1916 Race Street, Philadelphia, Pa. 19103. Reprinted/adapted, with permission.) INSTRUMENT DESIGN AND DESCRIPTION Design objectives were to obtain an optimum combination of available technol- ogy and commercially available compo- nents, considering the factors of weight, size, operator training, speed of analy- sis, accuracy, versatility, and durabil- ity under field conditions. Within this philosophy, the optimum spectrometer design became a unit containing two X-ray sources (radioisotopes), in order to excite X-ray response from a wide range of elements, coupled with gas- proportional counters (detectors) that would feed electrical impulses (trans- formed fluorescent energies) to a micro- processor for processing, interpretation, and storage in memory; in turn, the microprocessor would feed data to a cath- ode ray tube (CRT) display and a liquid crystal display (LCD). The PXRFS was designed for operators trained in mineral identification but lacking extensive technical knowledge of spectroscopy. The operator needs con- siderable experience in using the PXRFS before he/she fully understands the displays. The PXRFS (fig. 2) consists of an ana- lyzer unit, including a microprocessor, solid-state circuitry, batteries (power source ranges from 7 to 40 volts DC) and a control panel with a 1.3- by 1-inch CRT display, a 0.75- by 3.75-inch alpha- numeric LCD, and a variety of switches and dials (described in appendix A), all connected to a sensor head by a 6-foot, spring-coiled cable. The sensor head contains two radioisotopes, 100 milli- curies (mCi) of 55 Fe having a calibration target composed of sulfur and titanium, and 15 mCi of 109 Cd having a calibration target composed of titanium and zir- conium, two collimators, and two gas- proportional counters. When its cable is unplugged, the sensor head can be stored in the lid of the analyzer unit. Dimensions of the PXRFS, lid closed, are about 11 by 12 by 5 inches (sen- sor head is 10.5 by 2.5 by 1.5 inches). The complete spectrometer weighs about FIGURE 2. - Portable X-ray fluorescence spectrometer (PXRFS). A, Maimanalyzer unit; B, sensor head. 15 pounds and can be carried in the field by a shoulder harness (fig. 3) which allows the operator a good view of the displays and use of both hands trol manipulation. for con- ANALYTICAL PROCEDURES AND RESULTS Information gathered during the tests is preliminary and is presented here as a guide to prospective portable spectrom- eter users. Previous investigators (bibliography) have shown that factors having a signifi- cant influence on response include mois- ture, particle size, the geometric rela- tionship between the source, sample, and detector, and effects from surrounding elements ("matrix effect and interelement interference") . The useful response from elements in certain combinations varied considerably; consequently, the success of these deter- minations varied widely, as indicated in table B-l. Analytical procedure consisted of plac- ing a sample as close as practical to the sensor-head port, opening the port by sliding the port-shutter control knob (as described in appendix A), thus irradiating the sample; then the operator recorded the lapsed time of irradiation, FIGURE 3. - PXRFS as used in the field. total counts, elements detected, and the ratio values. The operator determines the length of analysis time by either presetting the time on the control panel or releasing the port-shutter control knob when a significant spectrum is dis- played on the CRT. The spectrum is then studied and sometimes photographed by the operator. The ratio value is derived by the microprocessor, and is a ratio between the fluorescent intensity (counts) of the element being measured and the back- scatter (BS) peak intensity, a process intended to compensate automatically for sample grain size and the geometry of the source, sample, and detector. The BS peak is created by radioisotope X-rays that escape the fluorescence process, that is, reflected X-rays recorded by the detector and displayed as a peak at the high-energy end of the spectrum. Laboratory Testing Theoretically, 73 elements can be detected by the PXRFS tested by the Bureau (fig. 4A) . However, as of this writing, only 33 elements have been detected, as shown in figure 4B. This is attributable in part to a lack of speci- mens or standards that contain the other elements. Moreover, the precious metals were not detected, owing partly to the lack of spectrometer sensitivity to low concentrations of precious metals nor- mally found in natural occurrences and partly because the 109 Cd isotope decays to silver and does not cence from silver atoms. excite fluores- The PXRFS response (secondary X-ray emiss was investigated on 52 7 control standards Barton of the U.S. (USGS), Denver, Colo., display specimens, and pies previously analyz Indian-lands project through B-4) . to fluorescence ions) of elements samples including loaned by Harlan Geological Survey 13 Bureau mineral 32 pulverized sam- ed for a Bureau (see tables B-2 Pulverized samples were poured into plastic 35-mm-diameter by 10-mm-deep petri dishes. Each dish was filled to heaping, tamped lightly for compaction, and leveled with a knife or straightedge, which provided a smooth sample surface for X-ray analysis. The petri dish was placed in a sample receptable in the base of a sensor-head rack (fig. 5), which has corner uprights designed to support the sensor head at an optimum analysis dis- tance and position over the pulverized sample. Pulverized samples in standard kraft paper envelopes were analyzed without removal from the envelopes. The response from the 55 Fe source was not usable because the envelope blocked the second- ary, or perhaps, the primary X-rays; response from the 109 Cd source appeared normal. This rapid method of analysis may effectively identify the composition of pulverized samples without removing them from the envelopes. H Li Hi - Na Tt- Be Mg 30 Ca 21 Sc 32 Tl 23 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn B TC Al 31 Ga 14 Si 32 Ge N W 33 As 16 34 Se CI 35 Br He Tor 1 Ne if 1 - Ar 36 Kr [37 Rb 3T - Sr 39 40 41 Zr Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49~ In 50 - Sn 5T Sb 56 Ba 52 Te if*- Po w Xe 55 Ca La 72 Hf 73 Ta 74 w 75 Re 76 08 77 lr 7T~" Pt 7r~ Au 80 Hg 81 Tl 82 Pb w Bl 85 At 86— Rn [p - Fr ii — Ra Ac ** 58 Ce 90 Th 59 Pr 91 Pa 60 Nd 92 u 61 Pm 93 Np 62 Sm 94 Pu 63 Eu 95 Am 64 Gd 96 Cm 65 Tb 97 Bk 66 Dy 98 Cf 67 Ho 99 Es 68 Er 100 Fm 69 Tm 101 Md 70 Yb 102 No 71 Lu 103 Lr H Li [Tl Na w [37 Rb Be T5 Mg » — Ca Sr B 21 Sc 39 22 Tl 40 23 41 Nb 24 Cr 42 Mo 25 Mn ■11 43 Tc 26 Fe 44 Ru 27 Co 45 Rh 28 Ni 46 Pd 29 Cu 47 Ag 30 Zn 48 Cd B 13 Al 31 Ga VIA VII* 49 In 14 Si 32 Ge 50 Sn N 15 33 As 51 Sb 16 34 Se 52 Te IT - CI 35 Br 53 He 10 Ne Ar 36 Kr 54 Xe 55 Cs 56 Ba 57 * La 72 Hf 73 Ta 74 W 75 Re 76 77 Os lr 78 Pt 79 Au Hg 81 Tl 82 Pb 83 Bi 54 Po 85 At 86 Rn 87 Fr 88 Ra 89 ** Ac • 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu r* 90 Th 91 Pa 92 u 93 Np 94 Pu M— ■*■■ 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 102 No 103 Lr FIGURE 4. - Periodic table of elements. Shaded areas show A, elements theoretically detectable by PXRFS; B, elements actually detected in Bureau of Mines tests. FIGURE 5. - Sensor-head rack and pulverized sample in petri dish. Figures 6 through 9 are spectral traces from photographs of the CRT display. Each figure shows the response of certain elements or minerals. These spectral traces illustrate the fluorescent inten- sity (counts) plotted in relation to the element emission energies as interpreted by the PXRFS microprocessor. Shown are the element X-ray emission peaks and their spectral line classifications and the position of element emissions rela- tive to backscatter emissions. Interference Because X-ray emission energies (kilo- electron volts) of many elements (fig. 1) are close in value, and because the PXRFS uses a proportional counter as a detec- tor, fine resolution of the element emis- sion energies was difficult. The pro- blem was interference between elements, recorded as distortions of spectra. 10 Mn K-alpha BS Energy Energy FIGURE 6. - Spectra (CRT traces) of A, man- ganese ore and B, molybdenite (T°9Cd source). Co K-alpha \ At K-alpha BS Energy Hg L-alpha \ Hg L-beta Ca K-alpha /\ / Fe K-alpha Energy FIGURE 7. - Spectra (CRT traces) of A, erythrite and B, mercury ore (10'Cd source). Fe K-alpha BS I Energy Pb L-alpha Pb L-beta BS Energy FIGURE 8. - Spectra (CRT traces) of A, sam- ple containing iron, copper, and calcium, and B, galena ( 109 Cd source). , J ; Pb L-alpha / Zn K-alpha A p b L-beta i / \ BS i A nergy i W L-alpha 1 W L-beta 1 • „ Fe K-alpha / \ i /\J \ i / \ s J BS i 1 FIGURE 9. - Spectra (CRT traces) of A, sam- ple containing lead and zinc and B, fer- berite ( 109 Cd source). 11 Figure 10A is a spectral trace from a pulverized sample of a quartz vein in granite, which chemical analysis indi- cated to contain 23.7% As, 5.2% Cu, and 3.05% Pb. This spectral trace illus- trates the interference created when cop- per, iron, and arsenic occur together. The copper emissions were interpreted as having an additive effect to the area of the spectrum between the iron and arsenic emission peaks. Also, the arsenic emis- sions appear to mask the lead responses; however, lead emissions have an additive effect on the arsenic emission peak. Figure 10B, a spectral trace of a pulver- ized sample of galena in an igneous rock, which contains 1.32% Pb and 1.95% Zn, illustrates further the interference problem by showing the distortion of the predominant iron emission peak by the lead and zinc emissions. At K-alpha / Cu ? K-alpha Fe K-alpha BS I Energy 11 CRT overlap ->. JM Fa K-alpha 1 Zn K-alpha Ca K-alpha f W * ^ \ Pb L-alpha S S K-alpha / i \J \/ Pb L- beta BS Energy B FIGURE 10. - Spectra (CRT traces) illustrating inter- element interference. A, Sample containing As, Cu, Pb, and Fe; B, high-Fe sample containing Zn and Pb (lO'cd source). Iron was the most significant source of interference, owing to its natural abun- dance and strong X-ray emission response. Many elements of economic interest occur with iron; because iron interfered with the X-ray responses of these elements, iron interference became the major prob- lem. In tests on certain clays (ceramic raw materials) even minor amounts of iron impurities were detected; the PXRFS could be used for the selection of low-iron clays for industrial purposes. With experience, the PXRFS operator was able to recognize characteristic emission peaks of elements even though the peaks were modified by interference. Matrix Effect The matrix effect is a form of inter- ference simply defined as the effect matrix elements have on the X-ray response of other elements. Matrix effect is due to an interaction between the emission and absorption characteris- tics of the matrix elements and the emis- sion energies (or wavelengths) of the elements being analyzed. Rock-forming or gangue minerals (ma- trix) can have a significant effect on the X-ray responses from elements of possible economic interest. If rock com- position changes, the matrix effect also changes. That is, as the relative pro- portion of matrix elements changes, their effect on economic elements changes in the form of an increase or decrease in secondary radiations or emission absorptions. Summary of Results Positive identification and semiquanti- tative analyses of elements were possible for many of the samples tested. The lim- itations created by the detection system used in the PXRFS, however, precluded utilization of the instrument's full potential. Element identification was possible for most of the elements tested and was 12 affected only by the presence of inter- fering elements for element concentra- tions less than 0.10%. Quantitative analyses were hindered by both interelement interference and matrix effect, the matrix effect especially affecting the results when element con- centrations were low (generally less than 0.10%). Semiquantitative results proba- bly can be obtained by use of the PXRFS, but it will be necessary to use samples (standards) that have known but varying percentages of element concentration for comparison with samples of unknown com- position. Five element calibration curves (fig. 11), constructed from USGS standardized samples, are plots of ele- ment concentrations relative to the ratio values calculated by the PXRFS. Quanti- fication of elements in a sample of unknown composition can be estimated by using calibration curves if the composi- tion of the sample approximates that, of the standards used to make the calibra- tion curves. The overall quantification results, based on spectral emission data as com- pared to analyses of the samples, varied from useful to nearly useless, depending on the relative percentages of interfer- ing elements as well as the X-ray response characteristics of a particular element and those elements adjacent to it in the spectrum. Field Testing On short field trips to selected mining districts west of Denver, Colo. , and on a field trip to southwestern Arizona, the PXRFS was tested for its durability and its practicability in addition to its analytical accuracy and response capabilities. The PXRFS was transported in a four- wheel-drive vehicle to selected test sites over varying types of roads. Dur- ing transportation, the instrument was carried in a high-impact plastic case (fig. 12). Hand specimens collected from outcrops or mine dumps and outcrop faces were analyzed during the field tests (fig. 13). Some hand specimens and out- crop faces were difficult to analyze with the PXRFS because of their surface irreg- ularities. One-handed operation of the sensor head during field tests while climbing on rock outcrops proved to be difficult because of the sensor head shape and the tension on the port shutter control return spring. RATIO (element to backscatter) FIGURE 11.- Calibration curves of five element standards having granitic matrixes. 13 FIGURE 12. - High-impact plastic transport case for spectrometer. jff-i ; . • FIGURE 13. - Spectrometer in use on a mine dump. 14 The PXRFS response was compared with visual, physical, and chemical mineral-identification techniques; sider- ite, sphalerite, ferberite, and powellite were among the minerals identified during the field tests. The tests disclosed that air tempera- tures between 50° and 90° F had little effect on the PXRFS; however, the instru- ment did undergo a spectral shift toward the low-energy end of the spectrum at 108° F. Figure 14A shows the 1 ° 9 Cd cali- bration spectrum (trace) produced by the PXRFS within the operating temperature range; figure 14B^ illustrates the spec- tral shift that occurs to the same cali- bration spectrum at 108° F. At air tem- peratures less than 50° F, the spectrum appeared to shift slightly toward the high-energy end of the spectrum. The spectral shift phenomenon made element identification difficult and necessitated calibration adjustments in the sensor head that were time consuming and not always successful. Durability of the PXRFS was somewhat less than expected. A fuse holder attached to the chassis broke loose; wires in the sensor head broke twice from flexure; a beryllium window in the 109cd_ coupled detector shattered, which made the detector and the PXRFS inoperable; Calibration cursors Energy Calibration cursors Energy FIGURE 14. - Calibration spectrum of 109 Cd source. A, under normal operating temperature; B, at 108° F. and the analyzer unit lid hinges were sprung from the weight of the sensor head. CONCLUSIONS This project involved limited testing of the PXRFS for field use in mineral- resource investigative work, and results presented in this report should be con- sidered preliminary. Testing demon- strated a portion of the capabilities and limitations of the spectrometer in min- eral identifications and quantitative determinations. The advantages of the PXRFS are (1) it is portable and can be carried in the field with little difficulty, (2) it has repeat analysis capabilities, (3) analy- sis time is generally less than 1 minute (if the radioisotopes have not undergone a decay of one half-life), (4) all data are available instantly on the displays, (5) no sample preparation is necessary in the field, and (6) it is relatively main- tenance free. Limitations of the PXRFS are (1) poor resolution of emission data owing to use of a gas-proportional detector that causes interference problems, (2) short half-life ( 109 Cd = 1.2 years, and 55 Fe = 2.6 years) of the radioisotopes results in periodic replacement expense, (3) dur- ability is somewhat less than expected, (4) the calibration adjustment screws, located in one end of the sensor head, are relatively inaccessible, (5) spectral shifts occur when the PXRFS is operated in air temperatures less than 50° F or more than 90° F, (6) the CRT display is 15 hard to read because of its miniature size, or because of bright daylight in the field, and (7) one-handed operation of the sensor head is difficult because of its shape and port shutter control spring tension. At this time the PXRFS falls short in achieving the desired objective of reliable quantitative analytical results. RECOMMENDATIONS Recommendations for modification of the PXRFS mainly involve the detectors and the radioactive sources. In order to improve spectral resolution and reduce operating expenses of the PXRFS, the fol- lowing modifications are suggested: 1. Replace the gas-proportional coun- ters with a single mercuric iodide detec- tor to enhance spectral resolution. 2. Replace the 1 ° 9 Cd and 55 Fe radio- isotopes with an americium ( 24 1 Am) source, thereby increasing the element excitation range and reducing isotope replacement costs (the 241 Am source has a half-life of 458 years). A miniature X-ray generator may be an alternative to radioactive isotopes as an X-radiation source. Other modifications to the special-use purposes (such trol sampling) and to further and complexity, might include ing: Use only one radioact test a weaker radioactive lower cost); eliminate the use a three- or four-digit manual element selector (cu in present PXRFS) with a me readout. PXRFS, for as ore con- reduce cost the follow- ive source; source (at CRT display; LCD and a rsor control ter (analog) SELECTED BIBLIOGRAPHY 1. Bearden, J. A. X-Ray Wavelengths and X-Ray Atomic Energy Levels. National Bureau of Standards Reference Data Series No. 14, 1967, 66 pp. 2. Bertin, E. P. Principles and Prac- tice of X-Ray Spectrometric Analysis. Plenum Press, New York, 2d ed. , 1975, 1079 pp. 3. Birks, L. S. X-Ray Spectrochemical Analysis. Wiley Interscience, New York, 2d ed. , 1969, 143 pp. 4. Burkhalter, P. G. , and W. J. Camp- bell. Comparison of Detectors for Iso- topic X-Ray Analyzers. Proc. 2d Symp. Low Energy X- and Gamma Sources and Applications, University of Texas, Aus- tin, Tex., Mar. 27-29, 1967, ORNL-IIC-10, pp. 393-423. 5. Campbell, W. J. Application of Radioisotopes in X-Ray Spectrography. Ch. in Radiation Engineering in the Academic Curriculum. International Atomic Energy pp. 225-258. Agency, Vienna, 1975, 6. Campbell, W. J. Energy Dispersion X-Ray Analysis Using Radioactive Sources. In X-Ray and Electron Methods of Analy- sis, ed. by H. Van Olphen and W. Parrish (Progress in Analytical Chemistry Series: v. 1). Plenum Press, New York, March 1968, pp. 36-54. 7. Campbell, W. J., and J. V. Gilfrich. X-Ray Absorption and Emission. Anal. Chem. Ann. Rev., v. 42, No. 5, April 1970, pp. 248R-268R. 8. Clark, B. C, and A. K. Baird. Martian Regolith X-Ray Analyzer: Test Results of Geochemical Performance. Geology, v. 1, No. 1, September 1973, pp. 15-17. 9. Hurlbut, C. S., Jr. Dana's Manual of Mineralogy. John Wiley & Sons, Inc., New York, 17th ed. , 1959, 609 pp. lo 10. Jenkins, R., and J. L. DeVries. Practical X-Ray Spectrometry. Springer- Verlag, New York, 2d ed. , 1969, 180 pp. 11. Muller, R. 0. Spectrochemical Analysis by X-Ray Fluorescence. Plenum Press, New York, 1972, 326 pp. Electron Probe Analysis. ASTM Special Tech. Pub. 485, 1971, 285 pp. 14. Thatcher, J. W. , and W. J. Camp- bell. Fluorescent X-Ray Spectrographic Probe — Design and Applications. BuMines RI 5500, 1959, 23 pp. 12. Nuffield, E. W. X-Ray Diffraction Methods. John Wiley & Sons, New York, 1966, 406 pp. 13. Russ, J. C. (coordinator). Energy Dispersion X-Ray Analysis: X-Ray and 15. Instrumentation for Pri- mary and Secondary Excitation of Low Energy X-Ray Spectral Lines. BuMines RI 6689, 1965, 29 pp. 17 APPENDIX A.— SELECTED SECTIONS OF PXRFS OPERATION AND MAINTENANCE MANUAL 1 Figure A-l provides a display of the front panel and controls of the PXRFS as a reference for the instructions contained in this section. CRT display^ Calibration switch^ /Memory switch /Liquid crystal display 'CRT intensity control 'Cursor potentiometer FIGURE A-l. - Front panel and controls of PXRFS. Count range switch Element-count- ratio switch iMartin Marietta Corp., rev. July 11, 1980. 18 OPERATING INSTRUCTIONS 1 . Power on A. Connect sensor head to instrument by pushing the sensor head cable connector onto the face panel connector (aline before plugging in) and then turning clockwise for approximately one-third turn. B. Turn the COUNT RANGE switch to any of its numbered positions (typically to the 250 position). C. Set the SECONDS switch to 30. D. The liquid crystal display (LCD) shows the results of the instrument auto- matic self-test. It will display either "SELF TEST PASSED" or a combination of warning messages. E. The next message is the name and revision level of the software program stored in the PXRFS microcomputer. F. The LCD will now continuously repeat "WAITING FOR OPEN SHUTTER OR CAL SWITCH" until one or the other of these actions is taken. 2. Sleep Mode A. If no switch positions are changed for approximately 2 minutes, the unit will switch to a low-power mode, and the LCD will display "ASLEEP." The CRT and other high power circuits are powered off. Memory data are retained. B. To resume operation, toggle the ELEMENT-COUNT-RATIO switch. The unit will wake up with the same status as when it went to sleep. 3. Calibration Mode A. Calibration should be performed before starting a new series of analyses. B. After the power-on step, with the LCD repeating the "WAITING..." message, set the SECONDS switch to either COUNTS or to one of the numbered seconds positions. C. Set COUNT RANGE switch to desired scale (typically 250 for calibration). D. Verify sensor head shutter is closed. E. Toggle CAL switch momentarily to LO. LCD displays "Fe-55" for 2 seconds, then begins displaying elapsed analysis time as the spectrum is accumulated. F. The unit is now analyzing the Fe-55 calibration sample (sulfur and titanium target) built into the sensor head. G. Adjust CRT focus and intensity knobs for best viewing of the spectrum. H. When analysis is complete the LCD will display "CAL," and the CRT display will be continuous with two flashing cursors. The left cursor marks where the sulfur peak should appear, and the right cursor where the titanium peak should appear. 19 NOTE: At any time during or after analysis the COUNT RANGE switch may be used as desired to adjust the vertical expansion of the spectrum on the CRT display. I. If the cursors are not on the two peaks, adjust the LO trimpot on the sensor head and repeat the analysis as necessary. After adjusting the poten- tiometer, restart the spectrum by operating the CAL switch again. J. After the Fe-55 channel is calibrated, repeat the above procedure for Cd-109. Substitute CAL HI for CAL LO and use the HI trimpot on the sensor head. For Cd-109 the left cursor marks titanium and the right cursor marks zirconium. 4. Normal Operation A. After power-on and calibration steps, the unit is ready to analyze samples. B. To analyze, adjust the SECONDS and COUNT RANGE switches for the desired type of analysis. Set the MEMORY switch to either A or B, depending upon which half of memory the spectrum is to be stored. Use the A and B setting only if there is no need to compare two different spectra. C. Place the sensor head port against the sample of interest. If this is not possible, place the port as close to the sample as possible (see "Safety" section at the end of the appendix) . D. Using an index finger, press and hold the shutter control either forward for a Cd-109 analysis, or backward for an Fe-55 analysis. The LCD will first identify which radiation source is in use and then the elapsed analysis time (in seconds). The beeper in the sensor head will sound to warn that a radio- active source is exposed through the open shutter. NOTE: If the beeper doesn't sound when the shutter is opened, notify the instrument manufacturer. E. While waiting for the analysis to complete, observe the spectrum building up on the CRT. When sufficient data have been taken, release the shutter con- trol. Verify that the alinement circle is properly centered in the port win- dow, indicating the spring-loaded shutter is in the fully closed position. F. The COUNT RANGE switch may be used to expand the CRT display as desired. CAUTION: Do not turn the COUNT RANGE switch to the 9 o'clock position, or the unit will be powered off and special data lost.) G. To identify a peak, use the CURSOR knob to adjust the bright dot to the top of the peak of interest. When the cursor is adjusted to an element channel, it will flash once per second, and with the ELEMENT-COUNT-RATIO switch set to ELEMENT, the LCD will display the element's chemical symbol. H. For a hard-copy record of the spectrum, connect the plot or tape output wires to a chart recorder or tape recorder, respectively. These wires are availa- ble from the connector at the front panel end of the sensor cable. 20 1. For a plot, set the SECONDS switch to PLOT. The LCD will display "PLOT REQUESTED" and "PLOT." When the "PLOT" message appears the unit will begin outputting 0- to -5-volt analog signals of spectral data at eight channels per second. The spectrum will repeat as long as the SECONDS switch is left on plot. Switching off the PLOT position at any time will terminate the output and return the spectrometer to the previous mode. 2. For recording the spectrum onto magnetic tape, connect the tape output plug to the auxiliary or microphone input of a recorder. NOTE: It may be necessary to adjust the drive circuit output impedance to match the recorder input impedance. Turning the TAPE trimpot, on the INTERFACE printed circuit board, clockwise will increase the impedance to 60 kilohms maximum; turning counter-clockwise will decrease it to its 10-kilohm minimum. Set the COUNT RANGE switch to TAPE and then put the recorded in the record mode. . The LCD will display "TAPE DUMP REQUESTED" and "RECORD" (signals start of dump). The spectrum will be dumped only once, and the dump is not interruptable (takes approximately 2 minutes). I. To perform more analyses, either leave the MEMORY switch in the same position it was, or change from A to B or from B to A to save the last spectrum taken. Repeat the steps under section 4. 5. Charging the Batteries A. Be sure the COUNT RANGE switch is in the power-off position. B. Unplug sensor head cable by twisting counter-clockwise for approximately one- third turn and pulling to disengage. C. Plug in cable from the charging unit to the front panel connector. D. Place the CHARGE switch on the charging unit to one of its three positions. Under standard conditions, the unit contains nickel-cadmium batteries, but lead-acid may also be installed. Use L0 RATE for nickel-cadmium batteries if the time available for charging is 16 hours or more; if a fast charge is needed, or if the unit is to be operated during charging, use the HI RATE setting. E. Connect the appropriate terminals to either the 110-volt-ac source, or auto- motive battery (12 volts dc). ROUTINE MAINTENANCE 1. Changing Sensor Heads A. Place the COUNT RANGE switch in the power-off position. B. Unplug sensor head at the front panel connector of the main unit by twisting counter-clockwise for one-third turn and pulling off. C. Plug in new sensor by alining connector, pushing to mate pins, and rotating connector clockwise to snap into locking position. 21 2. Changing the Desiccant Tube A. Replace or rejuvenate desiccant whenever the 60% sector changes from its nor- mal blue color to either pale pink or white. B. Remove the cartridge from the front panel by unscrewing it with fingers or a suitable straightedge. C. Screw in new unit, or rejuvenate removed cartridge by baking in an oven at 125° C (257° F) for 2 hours or more. 3. Replacing the Batteries The unit is powered by seven D-size batteries. Either rechargeable batteries (for example, nickel-cadmium or lead-acid cells) or nonrechargeable cells (for exam- ple, carbon-zinc, mercury, or lithium types) may be used. Standard rechargeable bat- teries are of the nickel-cadmium type, but the lead-acid type is preferred for opera- tion in very cold weather. A. Turn power off and unplug the sensor head. Remove the hinged lid (optional). B. Unscrew and remove the four mounting feet at the base of the instrument. C. Carefully place the unit on the side where the four mounts were removed (front panel facing up). D. Lift up on the front panel to pull the unit slowly out of the housing (assistance from a second person will be helpful and is a sensible precaution) . E. Set the unit down on a smooth surface. F. Note the battery orientations. All cells are alined in the same direction, with negative terminals closer to the CRT than the positive terminals. G. Remove batteries from holders by pushing end clips toward each other, and re- leasing tiedown clip with a slight twisting motion. H. Place new battery in proper direction and again press end clips inward to facilitate installing the tiedown clip in its original orientation. I. Replace one or more batteries as required. J. Carefully place unit in housing, aline holes at bottom with ports, and screw in mounting feet. TROUBLESHOOTING The first thing to suspect in the event of improper operation of the unit is a weak or dead battery. Even when the unit is powered by an external electrical source, a malfunctioning cell can prevent proper operation. Therefore, first try changing the batteries (see step 3 of the "Routine Maintenance" section) to verify that is not the problem. During this operation, check for any obvious internal problems: a printed circuit board that is not seated into its connector, a broken wire, dirt or other contamination in critical locations, charred or burned spots, etc. :: If this does not solve the problem, and the unit is known to have been exposed to high humidity or low temperatures, remove the desiccant tube and place the entire unit in a dry, warm environment to remove condensation. Replace the tube with a fresh or rejuvenated desiccant. In the case that the calibration peaks do not line up properly and cannot be adjusted into position with the appropriate potentiometer, the unit will require resetting by the manufacturer. However, it is possible to make temporary use of the instrument for field purposes by using the calibration targets built into the lid to note the channel numbers into which the elements of interest fall. With this approach, the operator must disregard the element symbols given on the LCD since these peaks will now occur slightly upscale or downscale from the normal position. SAFETY The PXRFS instrument has been engineered with every consideration for safety. A number of special features are designed to minimize the possible risks to the opera- tor and bystanders. It is extremely important, however, that all persons who are using, or have plans to use this instrument, read this section very carefully. THIS UNIT CONTAINS RADIOACTIVE MATERIALS and although these sources emit relatively low energy X-rays, and are carefully shielded, there is the possibility of unnecessary radiation exposure whenever the shutter is opened without the sensor head being placed flush against a suitable thick sample. 1 . Radiation Hazard The standard sensor head contains two radioactive materials: approximately 100 mCi of iron-55 isotope and 15 mCi of cadmium-109. These sources are electroplated onto a substrate and then hermetically sealed into a rugged holder. The possibility of leakage of radioactive material is extremely remote. The sources are in turn mounted in shielded collimators. When in the neutral closed position the safety shutter pro- vides additional shielding to prevent any radiation from penetrating outside the sen- sor head. There is no hazard associated with handling or being near the sensor head when the shutter is closed (that is, when neither source is exposed). Of course, the sensor head should be kept secured from access by casual bystanders at all times. During acquisition of a spectrum, one or, the other of the two sources must neces- sarily be positioned to irradiate the samples with X-rays. To prevent unnecessary exposure to the operator and for maximum safety, the following rules must be followed: A. Always place the sensor head analysis port up against the sample before opening the shutter. B. If the sample surface is irregular or it is impractical to place the sen- sor head totally against the sample, be sure to position your hands, limbs, and body such that they are behind the sensor head. C. Never look at or handle the port window, except when the shutter is fully closed. D. If the warning beeper fails to operate when the shutter is opened, return the unit to the manufacturer. 23 E. Never attempt to repair or disassemble the sensor head. The only exception is simple replacement of the plastic film port window using a pre-prepared window kit. Make sure the shutter is in the neutral closed position before making this change. F. Insure that the radiation sources are leak checked at required intervals (typi- cally, every 6 months). G. Have available a thin-window Geiger counter or other radiation monitoring device. Periodically check the radiation level during normal operation to make sure unsafe procedures are not being followed. 2. Shock Hazard All circuits within the PXRFS sensor head operate at low voltages, with the excep- tion of the detector bias supply. This supply provides 1,000 to 1,500 volts for operation of the proportional counters. Because this supply is potted, shielded by a metal housing, and contains a current-limiting resistor, the possibility of a malfunction causing serious shock is minimal. In the event of any indications of electronic problems within the sensor head, the unit should be returned to the manufacturer. An additional high voltage circuit is located within the main unit to provide the electron beam accelerating voltage for CRT operation. Because of this supply, it is recommended the unit never be turned to power-on condition when removed from its housing — for example, during a battery change-out operation. :4 APPENDIX B. —TABLES OF ANALYTICAL RESULTS TABLE B-l. - X-ray excitation capabilities of 5 ^¥e and 1 09 Cd for selected elements Element X-ray source used in analysis 55 Fe 55 F e 55Fe and 109 C d 55Fe and !09cd 109 C d 109 Gd 109 Cd 109 C d 55pe 109 Cd 109 C d 109 Cd 10? Cd 109 C d 55 Fe and 109 Cd 55Fe and 109 Cd 5 5Fe and 109cd. ... 109 C d 109 Cd 55Fe and 109cd 109 Cd 109 Cd Source excitation capabilities Fair Good Fair Good Good Good Good Good Fair Good Fair Good Good Fair Fair Fair Good Good Fair Fair Good Good Most likely interfering elements Aluminum. . . Arsenic. . . , Calcium. . . . Chromium. . , Cobalt Copper. Iron , Lead Magnesium. , Manganese. . Mercury. . . , Molybdenum, Nickel. Niobium. . . , Silicon. . . , Sulfur...., Titanium. . , Tungsten. . , Uranium. . . Vanadium. . Zinc Zirconium. , Mg, Pb, K Fe, Mn, Fe, Cr, As Na, Cr, As, Nb, Cu, Th, Al K Ca, Cu, Mo, Ti, Cu, Th, Si Se, Hg V, Mn Fe, Ni, Cu Co. Ni, Zn Mn, Co, Ni, Cu Al Fe Pb U Co, Fe U V Zn Th, Sr, Nb Cr, Mn W Nb 25 3 3 O -3 ■ •H 4-> ■H 4-> •H 4J CO 3 CO ■H •H -a CO -a CO CU CU CO M l-i 0) U 4-1 CU U § on 3 CO on 1 o •H 3 o o 1— o •— • U CU fa ^r CO o CO co o 4-1 H a) CO 3 o CU u • CU CO CU o 3 1 fa CO 1 cfl CO o CO 3 o i-l 01 W vD 0) M CO w CO UO o CM CM CM fa CNI fain m CM r^ cm fa CO O > r-. m i-H -X) , — , < -< < CM r^ , — l CO >x> s 4-1 •H H co r-~ 00 m 00 3 oo 2 . — , CO CO r-H m rH 4-1 CO • • • • • • fa 3 pS CO r^ O m 00 CM r> CO co CM ON a r- P r^ a> i — l cm m 4-> fa CO 3 CN LO CO CO 2 r^ 2 CO 00 CO r-» r~- co 4-> fl 4-> 3 1 — 1 1 — 1 CM O 4J CO o o a CO O fa H O r-H X) CO CO V A •H CO CO < < < CD i-l 2 2 2 2 00 2 o 2 2 O >, rH CO o O , — i ■ — 1 o o H >, o. >,s-s o o i — i o 00 m CO X> >H 3 CO cO ~H 1 4J s •H 0) 3 cO T3 r-l CD cfl 3 CU X> • 3 cO 3 CU XI • •H 3 CO CO 4-1 W S U o fa fa CO NI c_> U fa fa CO H CM fa T-t s • CO HH 3 3 3 (U CO o fa o o O •H CO 1 u CU Lj cd 4-1 4-1 X! 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CN O O O o oooo o o o Or~.ro ro O O CO cfl O U 3 CU -3 CU N >> <-l Cfl 3 cfl 4-1 o Z < Z • U cu 4J § o M 4-1 O cu a- CO CO CO 1 XI CO •H CO >■> rH Cfl 3 cfl H cfl 3 •H 00 •H M O > ■-I O 3 • 3 3 ^ O S-i ro ■H O 4-1 0.-3 • u CU IO O 4J O CO CJ CM xi cu 3 3 4-1 Cn cu CJ X) CO tu 3 o o XI 4-1 Z 3 3 N >, >>p iH X3 z 3 3 CO < •H . CN CO cu >,rH H X> • 3 3 O 3 CJ 3 3 -H CJ H H 3- CO 3 a, 3 3 3 •H XI 00 4J 3 H O N (-4 Z >» O tH 3 a, 3 < < < < 2 31 TABLE B-3. - Comparison of USGS sample standards 1 with PXRFS test results (Ratio value: Total counts divided by backscatter) Sample analysis, PXRFS test results 2 Element Sample analysis, PXRFS test results 2 Element Total Ratio Total Ratio % counts % counts Copper. . . 0.01 21 0.125 Rubidium. 0.010 6 0.062 .01 25 .125 .021 16 .062 .05 30 .125 .046 18 .187 .10 25 .187 .100 31 .250 .20 54 .312 .215 73 .625 .50 92 .625 .464 116 1.187 1.00 130 1.000 2.00 301 2.312 Strontium .001 10 5.00 945 9.062 .010 .021 13 12 .062 .046 18 .062 .046 13 .125 .100 20 .125 .100 16 .250 .220 17 .125 .215 83 .625 .460 37 .250 1.000 267 2.812 1.000 52 .437 2.150 104 1.000 .01 27 .125 4.640 288 2.375 .02 22 .125 10.000 781 8.250 .05 .10 24 26 .125 .187 .01 10 .062 .20 62 .375 .02 14 .062 .50 111 .750 .05 16 .125 1.00 182 1.437 .10 30 .125 2.00 419 3.125 .20 28 .187 5.00 1,371 14.750 .50 54 .437 1.00 89 .750 2.00 163 1.625 5.00 348 4.687 Manganese .010 .022 .046 .100 .215 .464 1.000 376 384 406 404 361 444 434 3.812 3.875 4.250 3.937 4.187 4.375 5.750 'These element standards have a granitic matrix. 2 120-sec I09cd irradiation. 32 TABLE B-4. - PXRFS ( 109 Cd) analysis of selected Bureau of Mines mineral display specimens Sample and Elements Element to composition (9) detected Counts backscatter Comments by PXRFS ratio Carnotite in sandstone; K 77 1.687 30-sec irradiation. K 2 (U0 2 ) 2 (V0 4 ) 2 tiH 2 0. Ca 66 1.437 Cu 45 1.375 U 213 4.750 Cinnabar and antimony ' . . . Hg 123 2.312 60-sec irradiation. Sb not S 39 .250 detectable with this Ca 51 .812 instrument. Fe 23 .437 Cupro-tungstate; CuO and Cu 265 9.375 60-sec irradiation. W re- wo 3 . 1 Fe 170 5.625 sponse is masked by intense Co 185 6.312 Cu response combined with Ni 282 9.187 Ni and Co responses. Pb 535 17.312 Ca 50 1.875 Erythrite; 37.5% CoO, Co 189 ( 2 ) 30-sec irradiation. Overflow 38.4% As 2 5 , 24.1% H 2 0. As 184 ( 2 ) indicates a ratio is not possible because backscatter is nonexistent. Ferberite; 23.7% FeO and Fe 94 (2) Do. 76.3% W0 3 . W 175 (2) Galena; 86.6% Pb and Pb 580 56.562 60-sec irradiation. 13.4% S. S 42 3.500 Ca 35 4.500 Fe 62 5.625 Garnierite; (Ni,Mg)Si0 3 K 38 3.375 30-sec irradiation. •nH 2 0. Ni 710 57.000 Ca Fe 115 24 3.437 .875 60— sec irradiation. Double peak could be from Hg or Pb Au 138 4.500 response as well as Au. Niccolite; 43.9% Ni and Ni 156 26.000 30-sec irradiation. 56.1% As. As 84 12.562 Ca 60 8.000 Rhodonite; 54.1% MnO and Mn 671 31.437 45-sec irradiation. 45.9% Si0 2 . Scheelite in granite; Ca 93 2.187 60-sec irradiation. 19.4% CaO and 80.6% W0 3 . W 84 1.500 Fe 54 .812 Rb 4 .250 Scheelite and pyrite; Ca 48 1.062 Do. 19.4% CaO, 80.6% W0 3 , W 78 1.375 46.6% Fe, 53.4% S. Fe 120 2.312 Uranium in sedimentary U 106 .875 Do. rock. ' Ca 42 .312 Fe 123 1.062 1 Exact comDosition percent not knowi l. 2n V srf low. 33 APPENDIX C— NUCLEAR REGULATORY COMMISSION (NRC) LICENSING INFORMATION All manmade radioactive materials are strictly controlled by the NRC, and it has issued comprehensive regulations for controlling and licensing radioactive isotope sources (called "byproducts" because of their origin in a nuclear reactor). Briefly, the NRC regulations require the following relative to the PXRFS: 1. The licensing of any company or individual (including Government agencies) that uses isotopes of the strength required in portable X-ray fluorescence spectrometers. 2. The isotopes be under the control of a trained and qualified person at all times. 3. The material be kept reasonably secure against theft or loss by accident. 4. Safety precautions be adequate to protect the user and others in the vicinity from radiation. 5. An authorized individual user be present and directly supervise the use of the spectrometer at any temporary job site. 6. User qualifications include, as a minimum, the completion of the instrument manufacturer's training course. 7. Training by companies is permissible, but the NRC must approve the training course. 8. If multiple users are listed on the license, a radiation protection officer must be named. "A Guide for Preparation of Byproduct Material Application for the Use of Sealed Sources in Portable and Semiportable Gauging Devices" can be obtained by writing: Materials Licensing Branch, Division of Fuel Cycle and Material Safety, Nuclear Regu- latory Commission, Washington, D.C. 20555. fcU.S. GOVERNMENT PRINTING OFFICE: 1982 - 505 - 002/65 INT.-BU.OF MINES, PGH., PA. 26244 amm mmama ^o 1 ■5°.* - )* •!*•- V^ f >* v^V V^V v :£&■* \/ .'^fe: V** -MBS''. %/ •**«*• **-♦* ••*•* ^-«* VV V .^ ■■ 0°* •* **b **» A> <*. raS'^ • J"\. •« ^^' ■"IB'- ** :'iM£"- * u ,5,^ :*Hgal^r 4 v** »W J" "V. ••!•?.•". ♦♦"*♦. °-?W-" J" *+ VHR-' ♦*""** --««w-- ^>- "•• *o -^, X +1* urn LIBRARY OF CONGRESS I llll Ill III Hill llllllll mi mn i 002 959833 2 ' ■ ! : f InafSHsr