" 1 : | OF I ORNLP 2433 . : 6 i - : CEEFEEEE 11.1:25 | 1.4 11.6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS -1963 ORNL-P-2433 SEP 2 2 1966 Conf.667633 OROVI - REC - OfiiCiAL CMASTER LEGAL NOTICE The roport nus prepared as an account of Government spoasored work. Nellbar the wind Bustos, por the Commission, nor any pornoo uttag on behall of the Commiuloa: A. Makes way miraty or representation, expressed or implied, with respect to the accu- racy, compleans, or uchuldess of the lacormation contained in this report, or that the use of any taformation, apparatus, method, or process disclosed in this report may not latringo priniely owned rights; or B. Assumes may Habilities with respect was use of, or for damages resulting from the uw of any Irlormation, apparitu, method, or proces declosed in this report. As and in the above, "person acting on behall of the Commission" includes any en- plerus or coainctor of the Commission, or employee of such contractor, w tbe extent that euch employa or cuntractor of the Commissioa, or employce of such coatrucior proparca, disseminatos, or provides access to, any informatioa pursuant to dis employmeat or contract with the Commission, or his employment with such coatriclor. ORNL – AEC RELEASED FOR ANNCUNCEMENT IN NUCLEAR SCIENCE ABSTRACTS STANDARDIZATION OF MERCURY-197* CFSTI PRICES J. S. Eldridge Analytical Chemistry Division Oak Ridge National Laboratory Oak Ridge, Tennessee #01 LOS MN 52 C INTRODUCTIÖN Accurate standardizations of 197Hg have been diificult in the past due to inaccurate decay scheme information ană to a lack of isotopically pure 1978 scurces. Widespread medical applications of this nuclide (1) required better assay techniques as well as an enhancement in the quality of 197 Hg preparations. As part of a program to improve the isotopic purity of 197 Hg, we prepared it by several routes and studied various parameters affecting the assay of this nuclide. Mercury-197 has two isomers; (1) a 64-h state that decays entirely by electron capture to levels at 77 and 269 keV in 197Au, and (2) a 24-h isomer that decays 97% by isomeric transition to the 64-h state and 3% by electron capture to a level at 410 keV in 197Au. The decay scheme taken mainly from HELMER and MCISAAC (2) is shown in Fig. I. It can be seen from the decay scheme that gamma rays of 269 and 279 keV are emitted from tiie two isomers. In addition, 197Hg preparations made from natural mercury targets contain 20% Hg which emits a 279 keV gamma ray. To assay 197Hg preparations containing both 197 Hg isomers as well as 203Hg requires a knowledge of the gamnia-ray spectra of the individual species so that correc- tions may be applied for the 20% Hg and the 24 h 18 mmHg. Fig. 2 shows the gamma- ray spectrum obtained from a sample cf 197 Hg made by the irradiation of natural mercury for 61 hours iu che Low Intensity Test Reactor. The spectrum was made with a 3 in. x 3 in. NaI(TI) detector and a 9.3 cm sourcento-detector distance. Fig. 2 shows that the photopeak at channels 45-60 is made up of all three constituents (1971Hg, 197Hg, and 203Hg). The 203T1 X-ray from the 203Hg_decay fails within the energy range of the X-rays and 77 keV gamma ray from 197Hg and thus interferes with 197Hg determinations. ORNL - AEC - OFFICIAL *Research sponsored by the U. $. Atomic Energy Commission under contract with the Union Cazibide Corporation. ORNI - AEC - OFFICIAL CHARACTERIZATION OF 197Hg ISOMERS A sample of the ground state isomer was prepared by the bombardment of a gold foil with alpha particles in the Oak Ridge Isochronous Cyclotron. The bombardment produced 19711 by the reaction: 197 Au(a,4n) 197T1. Sabsequent decay of the 2.8 h 197T1 produced the 64 h ground-state isomer. Solvent extraction separations were used to separate the 197Hg from the gold target and other nuciides produced in the bombardment. Fig. 3 shows the gamma-ray spectrum of the 64 h 19 Hg mede at a source-to-detector distance of 9.3 cm. The small photopeak at channel 30 was found to be due to coincident suming between X-rays and the 77 keV gamma rays. Samples of 197Hg rich in the 24 h isomer were prepared by proton bom- hardment of a gold foil stack in the Oak Ridge National Laboratory (ORNL) 86 in. cyclotron. By choosing the proper foils in the stack, we were able to select those where the (p,n) reaction had occurred. The 1971, 197 Hg produced by the (p,n) reaction showed the spectrum given in Fig. 4 with a source-to- detector distance of 9.3 cm. The contribution of the 64 h 197 Hg is shown by by the 64 h isomer since the conversion of the isomeric transitions in the 24 h isomer takes place in shells other than the K-sheli. Table I shows the result of six independent half-life determinations made on samples of the 64 h isomer. The four determinations marked (g) were made with the sample placed in a 2 in. x 2 in. NaI (Tl) well scintillation detector; the two determinations marked (s) were made with a 3 in. x 3 in. NaI(T1) spectrometer system. In general 20 days was the observed decay period for all determinations. The decay curve data were analyzed by a least squares program and the stated error is the standard deviation of the fit. All six values were then weighted to give the mean value of 64.14 + 0.05 n. The half-life of the 24 h isomer was determined by following the decay of either the 130- or 279 keV gamma ray with a 3 in. x 3 in. NaI(Tl) spectrometer system. Results of three independent determinations are given in Table II where the error statement and the weighted mean were determined as described for the 64 h isomer. FLATTOR PRODUCTION OF 197Hg Subsequent to the studies reported above, 196Hg in enrichment up to 45% became available due to an improved collection technique in the Oak Ridge electromagnetic isotope separators. Using an enrichment of 6.14% for the 196 Hg target, a greatly improved 197Hg product was obtained. Fig. 5 shows a comparison of the spectra obtained from a natural mercury target and from a 186Hg target enriched to 6%. Table III presents the comparison of the yields in the two production procedures. Thus, we have shown that 197Hg preparations can be made with negligible 203Hg contamination. Current production 07 197Hg is made with 22-46% 196Hg, yielding even less 20Hg contamination. STANDARDIZATION OF 197Hg HARRIS (3,4) presented a detailed analysis of the 197Hg decay scheme and calculated a value of 0.94 photons per disintegration in the energy range of 68.2' to 77.3 keV. These radiations make up the prominent photopeak in the 187 Pig gamma-ray spectrum and arise from Ky, K. and 77.3 keV gemma rays. Thus, the standardization of 197 Hg appears to be simple enough, i.e., the deteraination of ORNL-AEC - OFFICIAL : ORNI - AEC - OFFICIA! ORMI - AEC - OFFICIAL the quantity of emitted gamma rays in the enurgy region 68.2 to 77.3 keV divided by 0.94. However, some radio-pharmaceutical manut'acturers experienced wide- spread discrepancies in the assay values of 187 Hg obtained from different primary suppliers. Accordingly, we arranged anter-laboratory comparison of two 15 Hg products. Samples for intercomparison were sent to thirteen labora- tories in the United States and three in Canada. Laboratories covered in the survey included most, if not all, of the primary and secondary suppliers of 18 Hg products in the United States. In addition, three primary standardization laboratories were included. Each participating laboratory received a sample of 18 Hg made from natural composition mercury and one made from 22.6% 18Hg. Both products were made from 61 h irradiations at a flux of ~2 x 1014 n/cm2 sec. Assay üime for the intercomparison was 58 hours after reactor discharge. Both solutions were prepared to contain a nominal 100 u Ci./mlitre in 2N HNOz: The enriched sample contained 0.6 ug Hg/mlitre while the natural sample contained ~150.448 Hg/mlitre. Results of the intercomparison for the two samples are shown in Table IV. At .ORNL, multiple samples were prepared for assay, more or less on a daily basis, as a check on solution stability, half-life, and purity of the inter- comparison samples for the period April 18 through May 2. The basic assay system consisted of a 3 in. x 3 in. NaI (Tl) spectrometer system with a 9.3 cm source-to-detector distance. Gamma-ray emision rates in the 67-80 keV energy range were determined with suitable corrections for iodine X-ray escape and attenuation. The branching ratio of 0.935 photons per disintegration was used for conversion to micorcuries. The ORNL result for the enriched sample was 122 $ 24Ci/mlitre where the error stated is l o for 18 determinations covering the period April 20 through April 30. The corresponding result for the natural target sample was 91.7 +1.0 and 3.90 + 0.06 u Ci/mlitre for the 257 Hg and 20% Hg content respectively. The stated error is 1 o for îl determinations for the period April 18 to May 2. Primary producers of 197Hg are those laboratories designated A,B,C,D,E,F, aira G. Radiopharmaceutical suppliers gave the results designated H, I,j-1,J-2, and K. Values designated L and M were from two U.$. government laboratories. There is a larger spread in values from the radiopharmaceutical manufacturers than from the primary producers for both products. Note also the spread of 3.58 to 5.5 uCi/mlitre in the 20% Hg content of the natural product. Each participant was asked to assay both solutions using whatever assay technique he was currently using for routine determinations of 18 Hg and to provide a description of the assay method with his report. Based on a critical inspection of the reports, certain techniques of counting and calibration of the detector system were rejected as being subject to larger uncertainties than the others. Thus, nine selected results wliere scintillation counting was used and calibrations were made with standards other than previous 197 Hg deter- minations gave a mean value and standard deviation of 119 + 9 ucimlitre for the enriched sample. Further selection of laboratories based on stated uncertainties and callibration procedures narrowed the group to five laboratories that resulted in the best value" of 122 + 3 HCi/mlitre for the enriched sample using a branching ratio of 0.935 for the combined photopeak at 68-77 keV. ABSOLUTE DETERMINATIONS OF 197Hg ORNI - AEC - OFFICIAL Three laboratories reported results for the enriched sample that were independent of calibration standards and only slightly dependent on decay ORNI - AEC - OFFICIAL EA ORNI - AEC - OFFICIAL ORNI - AEC - OFFICIAL scheme parameters. Two of the results were obtained using Yoy coincidence counting with single and dual detectors respectively. The third result was based on a "B"- coincidence technique using a pressurized 41 proportional counter for detecting Auger-electron-photon cascades. The results from these triree determinations are given in Table V. The average value and standard deviation obtained from these three results is 1ll + 3 uCi/mlitre. Since the best value" from singles courting based on a branching ratio of 0.935 is 122 + 3 «Ci/mlitre and the average value from "absolute" determinations is 111 + 3 u Ci/mlitre, it is apparent that the branching ratio of 0.935 calculated from decay scheme parameters is in error and that the branching ratio is probably 1.03 photons of 68-77 keV per disintegration. PRACTICAL STANDARDIZATION OF 197Hg ..For routine 197Hg standardizations, the technique of absolute gamma-ray spectrometry using a branching ratio of 1.03 photons (68-77 keV) per disin- tegration will yield absolute disintegration rates with an accuracy better than 5% if sufficient care is exercised. Difficulties may be encountered due to coincident surming effects it high-geometry NaI(TI) detectors are used. Fig. 6 gives a comparison of 13 Hg spectra made with the same detector at two different geometries: (1) inside a 3 in. x 3 in. crystal and (2) at 10 cm from the crystal face. The spectra are normalized at the major photopeak. It is evident from this comparison that large inaccuracies may be introduced in 19. Hg assays if coincident suming effects are not accounted for. Corrections ior iodine X-ray escape and attenuation of the gamma rays must be applied. Other difficulties may be encour.vered with this auclide due to volatili- zation or adsorption effects. At specific activities of >200 Ci/g and con- centrations < l ug/mlitre, mercury will adsord on many surfaces; therefore, it is advisable to pre-coraition glassware or add mercury carrier to the solutions. Volatilization effects may be overcome by courcing small liquid samples sealed in thin polythene containers. CONCLUSIONS Several experimental difficulties accompany the accurate standardization Hg samples. The use of enriched 1Hg targets effectively eliminates 203Hg contamination Techniques of X-% coincidence counting or "singles" counting using a branching ratio of 1:03 photons (68-77 keV) per disintegra- tion can yield absolute disintegration rates with accuracies »St. Half-life determinations yieided values of 23.8 + 0.1 and 64.14 + 0.05 hours for the two 197Hg isomers. ORNI – AEC - OFFICIAL ORNI - AEC - OFFICIAL ORNI - AEC - OFFICIAL REFERENCES [1] RHOTON, A. L., EICHLING, J., TOP-POGOSSIAN, M. M., "Comparative study of mercury-197 chlorm.erodrin and mercury-203 chlormerodrin for brain scanning", J. nucl. Med. 7!1966)50. [2] HELMER, R. G., McISAAC, L. D., "Level structure in 187 Au from the decay of 197MH3,197 H8, and 187 Pt", Prys. Rev. 137(1965)B223. SMITH, E. M., HARRIS, C. C., ROHRER, R. H., "Calculation of local energy deposition due to electron capture and internal conversion", J. nucl. Med. I(1966)23. (5] HEATH, R. L., Scinüillation Spectrometry, Gamma-ray Spectrum Catalogue, ORNI - AEC - OFFICIAL K ORNI - AEC - OFFICIAL E TABLE I ORNL - AEC - OFFICIAL R HALF-LIFE DETERMINATIONS FOR 64 H 197 Hg S SN SAMPLE PRODUCTION METHOD DETECTION SYSTEM / *HALF-israin) , .- * - Р - 0 - (pin) (pin) (pin) * * . . OR OC OR OR na = ..** (n,r) 64.127.10 64.234.44 63.986.17 64.194.20 63.94.14 64.204.08 64.14.05 . * *. - - О\U (a,4n) (a,4n) - - ... - - weighted mean - - *- : * . * * - - - s'refers to a gamma-ray spectrometer measurement, g refers to an integral scintillation detector. - E AS S. --. - ORNI - AEC - OFFICIAL OKNL - AEC - OFFICIAL ORNI - AEC - OFFICIAL TABLE II HALF-LIFE DETERMINATIONS FOR 24 H 197mHg USING GAMMA-RAY SPECTROMETER SAIPLE MEASURED Y-RAY(keV) HALF-LIFE(h) 130 23.727.08 24.135.24 279 279 23.993:27 23.8 t.l weighted mean ORNL - AEC - OFFICIAL TA . ORNI - AEC - OFFICIAL ORH; - nic - OFFICIAL TABLE III COMPARISON OF 197HG PRODUCTS MADE FROM NATURAL AND ENRICHED MERCURY TARGETS SAIPLE Natural (0.15%) 6.1% 196H8 RATIO 197HgR03H8 21/0.5 52/0.04 % 203H8 2.3 .08 197 H8 Ci/8 1.1 790 ORNL - AEC - OFFICIAL TABLE IV ORAL - AEC - OFFICIAL INTERLABORATORY COMPARISON OF 197 Hg SAMPLES DISTRIBUTED BY OAK RIDGE NATIONAL LABORATORY 20 APRIL 1966 LAB ASSAY METHOD AND STANDARDS") 197 Hg (uci/mlitre) Enriched Natural + 200Hg IDO-7366242 AM 91.8 VAR 86.7 84.0 103 128 139 ce 92.8 75 9.3 cm, 3x3 in. Na I 120 10 cm, 2x2 in. NaI 108.6 20 cm, 2x2 in. NaI 209ca, 197Hg 99.5 10 cm, 3x3 in. NaI IDO-16880 20 cm, 3x3 in. NaI 210 Pb. 203Hg. 57Co. 117.8 3x3 in. NaI 191 keV 0.009/dis 1.6cm Ge (Li) 191 keV y 0.009/ais 2x2 in. NaI-well 121 2x2 in. NaI-well 108 ION CHAMBER, 2x2 in. we12237Hg 101 4 cm, 2x2 in. NaI (c) 2x2 in. NaI 127.3 2x2 in. Nal-well 65.83 10 cm, 3x3 in. NaI IDO-16890 133 20 cm, 3x3 in. NaI 203Hg, 5700 109 93.3 OCH heart önnt mit eiwitt*** o o 20378, 197 Het 100 20471 99918 137CS, 2100D 118 105 85.4 94.3 71.7 102.2 87.6 ITOT BRU "Source to detector distance and detector size for y-ray spectrometry. IDO-16880 refers to technique according to Heath (5). "Indicates no information for this item. ORNL - AEC - OFFICIAL ORNL - AEC - OFFICIAL ORNI - AEC - OFFICIAL TABLE V ABSOLUTE DETERMINATIONS OF 197 HG IN THE ENRICHED INTERCOMPARISON SAMPLE OF 20 APRIL 1966 - - - - LAB - METHOD 197Hg uci/mlitre - - - - - ORNI 114 - - - - - 3 in. * 3 in. NaI X-y coincidence 2--0.025 in. x 2 in. NaI X.y coincidence 4773-, coincidence 211.4 - - - - - 108.4 - - - - - - ORNL - AEC - OFFICIAL 0?111AC - OFFICIAL Figure Captions Fig. i Decay scheme of 107H8 isoners 518. 2 Gamma-ray spectrum of 197Hg nade from a natural mercury target Fig. 3 Gamma-ray spectrum of 64n 107Hg; source at 9.3 cm from 3 in. x 3 in. NaI(T1) detector Fig. 4 Gamma-ray spectrum of 197 HE produced by the (pin) reaction Fig. 5 Gamma-ray spectra of 197 Hg products made from a natural target (left) and from 6.14% enriched 198Hg (right) Fig. 6 Normalized gamma-ray spectra of 197 Hg made with the source inside a 3 in. x 3 in. NaI(Ti) and at 10 cm from the crystal face ORNI – AEC - OFFICIAL ORNL - AEC - OFFICIAL ORNI - AEC - OFFICIAL Fig. 1 Decay scheme of 197 Hg isomers ORNL – AEC - OFFICIAL ORNI-AE-OU!"! S . -* s 4:5 9 -- - - -- ORNL-DWG 66-7335 ORNI-AE-nos!"!! ORNI - AEC - OFFICIAL 197 m Ha (24 hr) 165 3396 134 197H9 (6411) 230 130 4,2% * ----B-- 420 1 191 98.8% 268 279- 279 7 ORNL - AEC - OFFICIAL BioTAU ORNL - AEC - OFFICIAL . ORNI - AEC - OFFICIAL - - - - - -- . . - - - - - - - - - - - -- - - Fig. 2 Gamma-ray spectrum of 197 Hg made from a natural mercury target ORNI - AEC - OFFICIAL ON! - AS, Me!:-. ORNL-DWG 65-6094R o ORNI - AEC - OFFICIAL No X-RAY + 77 ''HE PRODUCT FROM NATURAL HO... 61 hr IN LITR, 9 hr DECAY 5 kev/channel No . I li 197 mHg counts/unit time 203 Ha + 197 Hg No o N ORNL-MEC -- OFFICIAL 5x100 o 20 40 60 80 100 CHANNEL NUMBER 120 140 ORNL - AEC - OFFICIAL -. - . . - - ORNI - AEC - OFFICIAL 4 - IN - - .-.- . -. - - - - --. -. A n . AV I - - * - - - .. . - - . - - .. . * a * :+2V AC. NaI(ri) detector Fig. 3 Gamma-ray spectrum of 64n 197Hg; source at 9.3 cm from 3 in. x 3 in. ORNL - AEC - OFFICIAL ORNI - AEC - OFFICIAL - . . . - E TUSIVR Y _ S = > > . -- in = - = - = - = =-- liinin ORNL-DWG 66 - 7334 lid viivad ORNI - AEC - OFFICIAL no 2 - X-RAY + 77- 4 - - do 64 hr 197493 3x3-in. Nol (TI) + ENERGY SCALE: 5 kev/ch a Jon a no counts/unit time ou a 1 - - - no = .+ ho a o n 5x100 OPNL - AEC - OFFICIAL o 20 40 60 80 100 120 140 CHANNEL NUMBER ORNL - AEC - OFFICIAL ORNI - AEC - OFFICIAL ORNI - AEC - OFFICIAL --- --- --- A L V IN VW*FYW Fig. 4 Gamma-ray spectrum of 197Hg produced by the (p,n) reaction ORNL - AEC - OFFICIAL ORNL - AEC - OFFICIAL + O - A . .- - - . . - - Er+LAVA ORNL-DWG 65-6092R 17101310 - 138 - INEO X-RAY + 77-- ORNI LAIN-OLECAM 24 hr 197mHg + 64 hr 197H9 - 3x3-in. Nal (TI) ENERGY SCALE: 5 kev/ch FILEEE -- counts/unit time 1 1 -- - ORNL - AEC - OFFICIAL LIIT 0 20 40 60 80 100 120 CHANNEL NUMBER: 140 ORNL - AEC - OFFICIAL -- ORNI - AEC - OFFICIAL ORNI - AEC - OFFICIAL ORNI - AEC - OFFICIAL Fig. 5 Gamma-ray spectra of 197 g products made from a natural target (left) and from 6.2 enriched 196Hg (right) ORNL - AEC - OFFICIAL ORNL-DWG 65-6091 OPNL - AEC - OFFICIAL . X-RAY + 77 . X-RAY + 77 197 HG PRODUCT FROM NATURAL Hg 61 hr IN LITR, 9 hr DECAY 5 kev/channei: S'HE PRODUCT FROM 6.14%** 139 hr IN ORR 28 hr DECAY - 5 kev/channel HILL Silk ig7mHg counts/unit time in 203 Ha + "9' Hg 268 + 279 . . . - O 20 40 60 80 100 CHANNEL NUMBER 120 140 0 20 40 60 80 100 CHANNEL NUMBER 120 ORNL - AEC - OFFICIAL 140 ORNL – AEC - OFFICIAL ORNL - AEC - OFFICIAL -. - . . . . . . . . . - - ... - - - . . . 3 in. x 3 in. NaI(Tl) and at 10 cm from the crystal face Fig. 6 Normalized Camma-ray spectra oſ 197Hg made with the source inside & ORNI - AEC - OFFICIAL . . 4 r. CE IV ri ORNL-DWG 65-6090 s . TX-PAY + 77 . !! U... EE . 197-ig In 3x3 in. WELL CRYSTAL 197Hg 10 cm FROM 3x3 in. WELI CRYSTAL 5 kev/channel E INMI --SUM .. ITS ; . . . 22 - counts/unit time 70 the – !!!1 BY S. A. AN entre helyett -HAHH #EEE . LR IYIDIO) - 334. 11:20 o 20 40 60 80 100 CHANNEL NUMBER 120 140 119 4 - til 1 4 . .. ... AN INIMUM W A . . " " 7. Ca ) a . T 4.2 ide SUV PAH W 4. " 1-10; NYA END DATE FILMED 10/25 /66 .. "Non ' Munk: Myw TV , . M WWWWWWWWWWW'. www.W W , A AW NO - WS IM myyy. M