Hanford Whole Body Counter 1982 Activities

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HANFORD WHOLE BODY COUNTER 1982 ACTIVITIES Occupational and Environmental Protection Department Pacific Northwest Laboratories

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HANFORD WHOLE BODY COUNTER 1982 ACTIVITIES This report describes the routine whole body counting measurement program for the Hanford project personnel during 1982. development work performed in conjunction with the whole body counting facilities are also described. Similar reports have been written annually equipment atthe whole body counter, and subsequent reports have described additions or changes which have occurred since 1978. the activity and changes for 1982. brief to reduce the time needed for reading and preparation. manual for the whole body counting operations is planned qnd will be Special studies and The first report described all of the major facilities and This report describes These reports have been intentionally ROUTINE COUNTING OF DOE CONTRACTOR PERSONNEL Figure1 shows the --i nvivo measurements made atthe whole body counting facility since 1972. The total measurements for 1982 were 8113 which is only slightly higher than the 8081 performed i n 1981. section of each bar includes all types of measurements except lung counts. These totaled 6454 which was about 3% higher thar! the 6283 measurements i n 1981. The 1659 lung counts for 1982 i s about 8% lower than in 1981. Table 1 shows the number and type of measurements made on persoRne1 for each Hanford contractor, DOE, and private industries, which include Exxon flu clear, U.S. Ecology, the Washington Public Power Supply System and Allied Nuclear. work i s performed for private industry only when i t does not impact on the service to DOE Contractors. per year towards the support of the whole body counting services which i n turn reduces the cost to the DOE Contractors. The whole body counting This private work does contribute $20K t o $30K The requests for whole body counting service are usually heaviest in the summer, and 1982 was no exception. per month i n June and July as compared to approximately 500 per month i n October, November and December. We had monthly measurements of over 800

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TABLE 1. In Vivo Keasurements blade i n 1982 Thyroid Wound . Other Inthe 1982 routine counting program, 107 workers showed positive amounts o f gamma-emitting radio nuclides. and 19 were above this level.In addition,there were two cases where workers had received medically administered radio nuclides of 1311 o r were from previously known internal depositions. Eighty - eight were less than 10 nCi There were 25 positive lung counts for 239Pu arid 241Arn, but these 114 VIVO MEASUREMENT INCIDENT CASES The number o f Hanford DOE Contractor employees measured as a result of radioactive contamination in cider ? ts during 1982 was 81. Tzble2 shows a comparison ofthe number of incident measurements to that in previous years. TABLE 2. Number of Incidents Requiring --I n Vivo Measurements

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The types of measurements made a n d the magnitude of the internal contamination for the 1982 incidents i s shown i n Table 3. TABLE 3. 1982 Incident Cases Type o f Count Less than MOA* Whole body -- gamma ray 7 Lung -- Pu o r Am 36 * Minimum detectable amount FAC I1ITI ES AND EQU I PMENT New Intrinsic Germanium Detector - A major change i s being made i n the detector system for measuring low-energy gamma and x-ray emitters i n the lung. The 9.5-m-thick NaI(T1)and the phoswich detectors will be replaced by multiple 20 cmL by 13-mm-thick intrinsic germanium (IG) detectors. first set of three IG detectors were received in 1982 and were installed in the lead-shielded room for testing,calibration,and use on special incidents of internal contamination. The resolution o f the IG detection is about 650 eV full width at half maximum f o r the L x-rays emitted from 239Pu a n d the 59.5-keV gamma ray from 241Am. Although the total area of the three I G detectors is less than half that of a 5-in.-diameter NaI(T1) or phoswich detector, the much lower background under the narrow photopeak o f the I G detector provides better sensishows a one-hour measurement o f 236Pu accidentally inhaled by a radiatioti 43-keV gamma ray i s evident. i n Figure 3 shows the resolution o f the IG detectors more clearly. ratios of the L x-ray probe are very useful i n determining i f the distribution in the lung i s abnormal or i f some external activity exists on The resolution of the I G detector i s demonstrated i n Figure 2 which The L x-rays of 13.4, 17 and 20.4 keV are clearly resolved and the The summation of 13.9 hrs of measurements shown

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The IG detectors have been very useful in identifying a n d quantifying they are put into routine use i n 1983, they will also be useful i n measuring 300 keV and have some limited usefulness a t higher energies. The second s e t o f detectors will be delivered i n the early part of 1982. At that time, the NaI(T1) and phoswich lung counters will be replaced by the two IG systems. Design o f New Shielded Facilities - The capacity o f the present shielded facilities in the 747A Building i s presently being exceeded, and the overflow i s being handled in the mobile whole body counters located across the parking lot. The 747A building was originally designed t o accommodate a second neering study report a n d the cost estimates have been compJeted. w i l l be fabricated with an inner layer of pre-World War I 1 steel plate ( 2 - 1 / 2 inches thick),a layer of lead brick ( 4 inches thick) and a n outer shell of carbon steel (1/2 inch thick) utilizing all welded construction. The steel i s available from the Nevada test site operations for just the shipping A shielded rom has been designed a n d the preliminary engiThe total cost of the shielded fi ici lit y has been estimated a t The justification for this facility has been written and included a survey of information from whole body counting operations a t other DOE laboratories throughout the United States. Table 4 shows that the labor, facilities and overall costs per measurement are significantly lower a t the PNL facilities because of the lsrge number of measurements. A source of funding and priority for this shielded room has not been established, and i t may be a few years before i t can be built. A summary of this survey in To zvoid routine whole body counting in the mobile counters u n t i l the new shielded room can be built,a shielded facility was also designed that can be economically constructed with materials a n d equipment available a t the whole body counter. would contain five large NaI(T1) detectors having a thickness of 4 inches and ranging in diameter from 9-3/8 t o 11-1/2 inches. employee in this counter would give a count rate from a radionuclide i n the body that would be 2.6 times that for the person in a 10-minute count i n the routine shadow shield counter. This facility would be a mall walk - i n maze-type and A two-minute count of an

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This new counter would not quantify the radionuclide content as accuThe short counting time of two or three minutes would allow a l l rate ly,butit would have greater sensi ti vii y for detecting radioactivity in people t o be measured in the counter and eliminate the need for people t o walk across the parking l o t t o the mobile counters. Those few people who show positive internal radionuclide content would then be measured on the standard shadow shield counter foran accurate determination of amount facility for several years. will be constructed by July 1983. Improved Data Processing for the Mobile Counter - A n Apple I 1 computer This facility would postpone the need fora large shielded room I f approved, this walk - i n maze-type facility was purchased f o r each of the two, mobile, whole body counter units. computers replace the function of the paper tape punches, which were old, Lvorn out and exhibiting a high rate of malfunction. spectra on magnetic (floppy) discs and are programmed t o calculate and print the results immediately after the count. A t the present time, the spectra and computations are transferred to the Nova 4 main whole body computer from the floppy disc which i s carried t o the whole body counter a t the end of each channel analyzer and t o the Nova 4 computer by moden transmission. The computers store Work i s continuing i n interfacing the Apple I 1 computer t o the multiFor 17-keV x-rays, the transmission through fat is significantly different than through muscle, in the average chest wall thickness will result in a 27% increase in the transmission of a 17-keV x-ray. The percent fatis an important parametct- i n estimating the content of P u or U in the lungs. thickness mezsurements, the ultrasound instrumentation i s adjusted t o optimize the definition of the chestwall-lung interface. However, the instrumentation response can be tuned t o give mare detail near the skin surface. When this is done, a n image of the fat-muscle interface near the chest wall can be made made. (see Figure 5 ) . The thickness of the f a t layer is easily seen as the space between the chest surface and the fat-muscle inter - face a n d can be determined a n d expressed as a percentage of the chest wall A change in fat composition from 20% t o 33% During regular chest wall

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The tissue equivalent torso phantom has three sets of chest plates of different fat composition. i n the phantom with the various chest wall compositions, a family of curves can be generated so that a calibration factor can be obtained fora person with any chest wall thickness and any percent fat value. The three compositions are 1) all muscle, 2 ) 50% By measuring standard 239Pu lungs RESEARCH AND DEVELOPMENT ACTIVITIES gas scintillation proportional (GSP) counter witha "Kapton" plastic window was tested t o determine i f the xenon gas would remain pure enough t o maintain good resolution. By using ahot calcium purifier with convection gas flow, the counter was operated in the laboratory for six months with only as light degradation of the resolution. The Teflon construction material i s essentially free from radioactivity and does not contribute t o the background of the Further development was made on the photoionization chamber which i s used as a scintillation light detector. anode sections which can be independently adjusted f o r gain. chamber significantly improved the resolution for broad beam radiation, but the resolution was not as good as that for a collimated beam of radioactivity. Further work i s needed on this uniform light-collection problem. The chamber h a s multiple concentric This type of Our experience this past year with the new IG detector described in5 previous section has shown t h a t the performance of these detectors is superior to that expected from the GSP counter i n every way except that of large areas. However, our experience w i t h the 238Pu inhalation case, which was described previously in this report, indicates that large area detectors are not as advantageous as previously thought. Therefore, itis doubtful that the GSP counter would provide a sensitivity that would be lower thari the IG detectors,, and further expenditure of time and money cannot be justified from the whole body counting programs. The GSP counter is still very attractive for improved neutron spzctroscopy a n d environmental monitoring, and i t will be developed for these purposes as outside funding becomes available.

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Inter laboratory Comparison o f 92mNb inthe Lungs o f Humans and in Tissue Equivalent Torso Phantom - hork was completed on the certification of the tissue equivalent torso phantom as an international standard for lung ca libra - tion for adult male humans. eight male adults who inhaled small quantities of 92mNb on one-micron-size microspheres. The 92Nb emits a 15.8-keV x - ray which is similar in energy t o thex - rays from 239Pu and it also emits a 934-keV gamma-ray which allows the quantity in the lung to be easily determined. lung a calibration factor can be determined for the measurement ofthe 15.8-keV the 92mNb in the lung,these subjects were measured a t ' several whole body cou fit ing laboratories in the United States and Great Britain. activity was also uniformly incorporated in the lungs ofthe phantom and measured with several different chest wii ll thicknesses.the calibration factors obtained from the human subjects for the 15.8-keV x-rays are shown i n Figure5along with the calibration factors obtained from the phantom. Since the human subjects had varying amounts of fat in their chest wall thickness, all the factors of both human subjects and the phantom were normalized to ri ing ing from 13% t o 100% muscle equivalency. subjects and the phantom is quite good and demonstrates that atleast for one-micron particle size,the activity uv i for n ly distributed in the phantom lung gives the same detector response as that normally distributed in human inhale 92mNb t o determine the effects of thicker chest walls. This work was sponsored by the IAEA and involved B y knowing the amount inthe The inhalation was done a tHar well,England. ' After stabilization of This was pcs sib l efron data obtained using phantom chest plates The agreement between t h e human Further studies are planned i n which several female subjects will Llhole Body Counting Staff H. E. Palmer Staff Scientist and Technical Leader 6. W.Perkins Electronic Technician(assigned from Craft, and Operation

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PRESENTATIONS AND PUBLICATIONS DURING 1982 Counter." Presented a t the 1982 Nuclear Science Symposium, Washington,

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- EFFICIENCIES FOR BOTH PHANTOM AND HUMANS HAVE EQUIVALENT CHEST WALL - BEEN CORRECTED TO THAT FOR A 100% MUSCLE CHEST WALL THICKNESS (cm) PNL TWIN PHOSWICH LUNG COUNTER DETECTOR EFFICIENCY FOR 92mi4b