Hanford Whole Body Counter 1981 Activities

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HANFORD WHOLE BODY COUtJTEP. 1981 ACTIVITIES Personnel Cosimetry Zection Occupational and Environmental Protection Department Pacific Northwest Laboratories

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HANFORG NHOLE BODY CC UK TER 1981 ACTIVITIES This report describes the routine whole body counting nieasureinent program for the tl an ford project persocnel during 1901. Special studies and development work performed i n conjunction with the whole body counting facilities are also described. Similar annual reports have been written since 1978 in which the ma,jor facilities available for in vivo measurement were described. This report w i l l discuss additions or changes in these facilities during 1981. FAC I L IT I ES AND EQUIPMENT New computer A new Nova 4 Data General computer a n d a new 8-track magnetic tape unit were p u t into operation during the year. computer has dual user capability a n d can operate the routine counting prosram while simultaneously providing plotting, printing, computing s n d operation of other programs. The larger storage capacity provides r a p i d access toall of our files and programs. retained f o r backup operation o f routine counting in case the Nova 4 The old Nova 2 computer wss New Calibration Phantom A major improvement in the accuracy o f measuring radioactivity in the lungs and l i v e r was made possible in 1981 by the purchase of a phantom which very closely simulates a human male torso. The phantom consists of2tissue equivalent polyurethane tcrso shell with a n imbedded bone equivalent rib cage. and liver organs are removable and can be obtained containing uniformly overlaid on the phantom t o simulate a range o f chest wall thickness from sufficient' t o give the same absorption of X and gamma ray radiation as human tissue for energies down to17 keV. lung sets containing FIBS certified standard amounts of 238Pu,239Pu, Tizsue equivalent lung Tissue equivalent chest plates can be The tissue equivalency o f the phantom parts i s Separate radioactivity tagged

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phantom. Radioactively tagged 1 iver organs were obtained with 2 3 8 P u , 239Pu,and241Am. We have made our own lung molds and have also made our own tagged lungs containing high energy gamma ray emitters. The phantom has been under development f o r the past several years a t Lawrence Livernore National Laboratory under t h e direction of an intercalibration committee consisting of representatives of the major DOE supported whole body counting facilities. body shell a n d organs were made from a cadaver. undergone extensive testing at many whole body counters andis expected to be certified as an international --in vivo calibration standard by the IAEA at the completion o f some further testing which i s described i n the research and development studies section of this report. Figure 1 shows some pictures of the phantom and organs. The use of this phantom in conjunction with the ultrasonic method of rneasuring chest wall thickness has very significantly improved our accuracy in estimating lung aRd liver burdens o f Plutonium, Americium, Uranium and many high energy gamma emitting radionuclides. The p hap tom molds for the The phantom has Array of Intrinsic Germanium Planar Detectors The experience a t the whole body counters a t the Rocky Flats Plant and OR NL with arrays of intrinsic germanium detectors has shown that they are more secs it ive than phoswich detectors for measuring 241Am in the lungs but less sensitive for determining the 235Pu directly by measuring the 1 7 keV purchasing an array since our sensitivity for measuring 241Am was Due t o the high cost o f these detectors we have delayed dosimetry for some of the low energy gamma emitters there isa need t o increase our lung counting sensitivity for radionuclides such as 144Ci and239Np as described in the Hanford Whole Body Count 1980 Activities With reduced limits a n d refinements in luna

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An array of three 20 cm2 by1 cni thick intrinsic germanium were ordered i n 1981. This array will only be large enough t o measure one lung. Additional arrays will be purchased as funding permits until ' we have 4 arrays so that two people can be monitored simultaneously in both lungs for uranium, transuranic radionuclides, and low energy gama - ray Lung counting a t the Emergency Decontamination Center The shadow shield whole body counter was modified so that lung counting for 2'r1Am could be done in emergency situations where a person might be externally contaminated ata level which would not be allowed a t the main whole body counter facilities. The modification included additional shielding and remodeling t o allow phoswich detectors and the intrinsic germanium array to be mounted into the counter. Gamma Camera Installation at the Emergency Decontamination Center A medical gamma camera was donated t o the University o f CJashington School of Medicine which has assigned it to Bat tell e through a professional staff relationship which exists between the two decontamination center isfor emergency use in imaging and localizing internal contamination associated with radiation contamination accidents. Gama cameras borrowed from nearby medical institutions have been useful in past accident cases. The main purpose of its location a t the emergency New Shielded Room Facilities A new shielded room facility is needed t o keep abreast of the increasing whole body counting needs of the Hanford Site.A room made from 2 f " thick World War I battleship s t e e l surrounded by 4 inches o f lead has been designed during 1981. The steel i s available free from Reynolds Electrical and Engineering Company a t the Nevada Test Site. This room will be constructed as funding

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ROUTINE COURTING OF DOE CONTRACTOR PERSONNEL body a n d lung measurements made t o r each year since 1 9 7 1 . body section o f the bargraph includes all types of counts except lung counts. . The total of 8081 measurements reflect a significant increase i n whole body counts over those made in a l l previous years. of lung counts has remained about the same over the past 4 years. 1 shows the number a n d Lype o f measurements made on the personnel of Figure 2 shows the whole Exxon Nuclear, Nuclear Engineering Company, a n d hashington Public Power TABLE 1 . --I n Vivo Measurements Made in 1981 Contractor Body Counts Counts Thyroid klound JAJ and Subcontractors IN VIVO MEASUREMENT O F INCIDENT CASES The number o f Hanford DOE Contractor employees measured as a result of radioactive contamination incidents during 1981 was 90. This is slightly higher than the 7 3 measured for this purpose in 1980 and significantly less than the 196 of these cases. Table 2 summarizes the type a n d contamination level

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Internal Contamination Level Less Than IIinimuni But Less Greater Than Type of Count Detectable Amount Than 10 nCi 10 nCi Glhole Body Count NEN PROCEDURES There were no significant changes i n methods o r procedures o f whole body counting during 1981. in the routine gamma ray measureniert i s anticipated i n 1922 and much study and consideration was given to this in 1981. t o discuss this forthcoming change and its need and justification in However, a major change I t has been demonstrated from recent intakes of activated corrcsion and fission product radionuclides that inany of these have long retention interest has increased in lower levels of internally deposited radionuclides in the Hanford personnel over the past few years. To attain the necessary sensitivity a change in the routine whole body counting procedure i s needed. This change will result in greater sensitivity and reliability for measuring gama emitting radionuclides in the lung and still provide adequate measurement of the whole body t w o 35% Ge(Li) detectors will replace the present procedure which provides a 10-minute scan over the er,tire length of the bcdy with a Thus with the lung a s the limiting organ, In this change a stationary 10 minute count over the lung with

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The lung i s the limiting organ for most o f the fission and actAivated corrosion products comnlonly associated with reactor sites. stationary count over the chest with the h i g h resolution detectors will provide the sensitivity to detect lung burdens we1 1 below the required level for almost all gamma emitting radionuclides. Since body tissues of lung, muscle, bone and f a t a l l occur in the chest region, any radionuclide having a distribution throughout the body will also be If a stationary lung count exceeds a reporting level f o r any gamma enlitter, other measurements will be made t o determine the major location o f the radionuclides in the body and the appropriate calculation will be done t o provide the quantity of a radionuclide present in the organ or total body. If a radionuclide i s identified but is less than the reporting level itis reported as a trace witha " less than " value. The stationary chest count will provide sensitivity for radionuclides in the thyroid, gastrointestinal tract,or skeleton which i s as good or better than the presently used scanning whole body This new procedure will still require all people t o change into coveralls before counting. due t o the interference of radon daughter products which accumulate on polyester type personal clothing. the reporting level i n the whole body count, the person will be recounted after showering and washing the hair. This has been necessary for the past year If radioactivity i s found t o be above This new procedure will be used until the new shielded room described i n the facilities and equipment section of this report isin systenis which can each provide a whole body gama ray scan, agama ray lung count, a plutonium americium lung count, a n d a thyroid count in one With this new shielded room we will then be able t o have two

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RESEARCH AND DEVELOPMENT STUDIES As nuclear technology increases and work programs change on the Hanford site, new methods are needed for --in vivo measurements and in the case of the transuranic nuclides, there i s a continuing need t o improve the sensitivity and accuracy of their measurement. exists and is developed a t the whole body counting facilities is also applicable t o other areas of nuclear energy. development studies associated with the Whole Body Counter are described on the following pages. The technology which Gas Scintillation Proportional Counters Progress o f the development of gas scintillation proportional (GSP) counters was again quite limited in 1981 due t o manpower availability and funding. type o f detector still has promise of providing a more sensitive detector for measuring plutonium and americium in the lung than other detectors presently available. The main advantage o f the detector i s its resolution and large size. Other details are presented i n previous reports on Hanford Nhole Body Counter activities. The remaining problem of the GSP counter is that of finding a non-conducting material with low vapor pressure and outgassing properties which is free from radioactivity. Excellent, stable counters have been constructed using AL203 ceramic materials f o r the body of the counter and beryllium for the window. Both o f these materials have t o o much natural radioactivity in them f o r low background counting purposes. During 1981 a large 10-inch diameter GSP counter was constructed using Teflon for the body anda double window made from thin sheets of outgassing properties and are free from radioactivity but testing of the counter, which i s currently i n progress, will determine whether the xenon gas will remain pure enough when contained in these materials. Both of these materials have reasonably low

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Several prototypes of photo ionization chambers for detecting the scintillation light from GSP counters were constructed and tested. The latest prototype zppears t o be adequate for use with the 10 inch The development work on GSP coufiters i s t o be Interlaboratory Comparison of Lucg Measurements o f Trsnsuranic Radionuclides (See 1980 report for details.) Three more subjects who had inhaled 92mNb a t the Atomic Energy Research Establishment, Harwell , England were measured and studied a t the whole body counting facilities. The total number o f subjects measured in this study is6 ana there will be one more in June of 1982. A known amount o f 92mNb was also placed in the lungs of our t i s s u e equivalent torso phantom and measured with various chest wall thicknesses. The increased absorption of the 16 keV x-ray with increased chest wall thickness in the phantom agrees well with that measured i n the subjects whose chest wall thickness ranged from 2 . 2 t o 3.4 cm. This study may be continued f o r another year so t h a t several female subjects can also be studied. Skeletal Distribution of 241Am Studies on the distribution of 2 4 1 A m in the skeleton were completed on a cadaver (SRG) containing a skeletal burden of 2"lArn. studies by the U.S Transuranium Registry. made over the total 'length of the body. 12.7-cm-diameter Phoswich detectors over aslot collimator with an aperture 5 cm wide and 40 cm long. other and centered over the collimator which runs perpendicular t o the length of the body. collimator t o the body was adjusted so that it just cleared the nose. Measurements were made a t 2-inch intervals starting with the center of the collimator over the top of the head. (See report Hanford Whole Body Counter 1979 This whole body donation was made available t o us for Linear scan mezsurements w r e This w a s done by placing two These detectors contained a The two detectors were placed beside each The distance from the lower surfaces of the

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Figures 3 a n d 4 show the profile o f radioactivity over the length of the body which was obtained by the coll imated n;easureiuents. profile is very similar t o those obtained by other investigators from other people who have skeletal burdens of241Am with peak levels over the joints and head and lower values i n the bone mid-shaft regions. This agrees with the analysis o f the 241P.m content of the defleshed long bones were cut into several sections and analyzed, the area under the curve corresponding t o various parts o f the body can be compared with the actual measurement of 241Arn in that part of the body. shows the comparison of the curve area with the 2 4 1 A m content i n body sections divided a t the joints. sections divided a t points of low activity. gGOG agreement between the area under the curve and the 241Arn content w h e n considering the variable thickriess of the …