Hanford Whole Body Counter 1980 Activities

Page 1

HANFORD WHOLE BODY COUNTER 1980 ACTIVITIES Personnel Dosimetry Section Occupational and Envi ronmen tal Protection Department Pacific Northwest Laboratories

Page 2

HANFORD WHOLE BODY COUNTER 1980 ACTIVITIES This report describes the routine whole body counting measurement program for the Hanford project personnel during 1980. and development work performed in conjunction with the whole body counting facilities are also described. Similar reports have been written since 1978 i n which the major facilities available for in vivo measurement were described. This report will discuss additions or changes i n these facilities. FACILITIES AND EQUIPMENT The mens shower and change facilities were reconstructed during 1980 which has alleviated previous crowded and sometime inefficient conditions where both men and women used the same facilities. The mobile whole body counter unit #l,which had not been used for several years, was reconstructed and placed into service. i s more useful than mobile unit B for making measurements at N Area because it has room for people t o change clothes. an extra trailer was necessary for a clothes change area. Mobile unit #1 is also temporarily being used for emergency preparedness and is being equipped with special radiation measurement instruments in addition to those existing for whole body counting facility. In previous years Two special detector holders were installed in the lead room for positioning detectors on any part of the body. time two phoswich detectors are mounted on them for use i n measuring special cases o f uranium, thorium, or transuranic elements inthe lungs or other organs ofthe body. These two holders are used i n conjunction with a third holder to position three detectors around the head for measuring bone seeking radio nuclides. has been shown t o be a reliable and sensitive method for measuring the total skeletal content of radio nuclides such as 241Am, 210Pb which have photon energies high enough to penetrate the bone. At the present The two 35% Ge(Li)detectors were installed in the shadow shield whole body counter and calibration studies have been comple ted for them. These have been especially useful in identifying

Page 3

and quantifying mixtures of radio nuclides in the body. soon replace the6 ” x ll?;”NaI(Ta) detector as the primary detector for who1 e body counting. A new Nova 4 Data General Computer was ordered and received and is presently being interfaced with our Whole Body Counter dual user capability. The greater storage capacity will allow all of our data files and programs t o remain on disc storage for rapid access. At the present time many of our files which are used less frequently are purged t o make room for routine results and then must be reloaded and recompiled when needed again. capability will allow plotting,printing, computing, or running other programs on one half of the computer while the other half is operating the routine counting program. Routine Counting of Project Personnel This computer has a much larger capacity and The dual user Figure1 shows the whole body and lung measurements made for The whole body section of the bargrapheach year since 1971. includes all types o f counts except lung counts. The total of 6,924 measurements reflect as light decrease in both whole body and lung counts over those made i n 1979. Table 1 shows the number and type of measurements made on the personnel o f each Hanford contractor, DOE, and the private industries, Exxon Nuclear, Nuclear Engineering Company, and Washington Pub1 i c Power Supply System. TABLE 1. --I n Vivo Measurements Made i n 1980 Contractor Whole Body Counts Lung Counts JAJ and Subcontractors 337 4

Page 4

The reduced number o f measurements i n 1980 marks the first time in more than 10 years that the number o f measurements did reduced the measurements on J.A. Jones Company employees to half that in 1979, tothe reduced summer hiring by all contractors, and to reduction in requests for measurements by private industries. The number o f measurements made for the four major users of the whole body counting facilities was 6% higher in 1980 than in 1979. This was due partly to the labor strike which I n Vivo Measurement of Incident Cases The number of Hanford project employees measured as a result of radioactive contamination incidents during 1980 was 73. a significant reduction over the 196 measured i n 1979 and slightly less than those i n 1978. Table 2 summarizes the type and contami nation level of these cases. TABLE 2. Incident Cases i n 1980 Internal Contamination Level Less Than ivtinimum Measurable But Greater Than Type o f Count Detectable Amount Less Than 10 nCi 10 nCi Whole Body Count 5 8 27 Several new operational procedures were adopted during 1980. A unit cost financing was started wherein each contractor is charged a fixed amount for each type of measurement. each contractor was billed for their fraction of the operating costs which was determined quarterly according to their past usage of the whole body counting facilities. From January through September 1980 the unit costs were $36 fora whole body count, $62 for a lung count, and $50 for all other types o f counts such as thyroid, head, wound, etc.At the beginning of FY-81 the rates were changed t o $40, $69, and $55 for the three classifications of counts.

Page 5

The reporting level of radio nuclides measured inthe body has been significantly reduced during the past two years. any routine measurement showing less than 100 nCi o f 6oCo (100 nCi i s 1% ofa MPBB under the old IC RPI1limits) was shown as at race and the actual value was not reported. that most of the long term retention 6oCo is in the lungs, and the fact that 6oCo i s an indicator of the presence of other radio nuclides such as 144Ce which are difficult to measure, the reporting level is now 2.6 nCi. This requires a much close revaluation of Whole Body Counter spectra, and background interferences from work related contamination on the skin,hair, and clothing has become a sign if - icant problem. Personnel from certain areas on the project are now required to change into clean coveralls.In addition radon daughter products originating from environmental radon in the air are strongly attracted to statically charged polyester clothing and this background interference becomes quite severe during atmosph eric inversions. It i s planned that all people will change into clean coveralls before their whole body counting measurement. This procedure will become effective during 1981. With new limits and evidence A new personnel decontamination procedure has been adopted. Personnel involved in contamination incidents who are found t o be externally contaminated during a preliminary survey upon arrival at the Whole Body Counter are now decontaminated atthe Emergency Decontamination Center rather than atthe whole body counting fac ili - ties.This is inconvenient,but it is the only way to effectively stop the spread of contamination into the low level background counting spaces. Although encouragement has been given to have all incident cases shower before arriving at the Whole Body Counter, this is not done very often and external contamination is frequently found i n these cases. RESEARCH AND DEVELOPMENT STUDIES As nuclear technology increases and work programs change on the Hanford project, new methods are needed for in vivo measurements and inthe case of the transuranic nuclides,there is a continuing need t o improve the sensitivity and accuracy of their measurement. The

Page 6

technology which exists and i s developed atthe whole body counting facilities is also applicable to other areas of nuclear energy. research and development studies associated with the Whole Body Counter are described on the following pages. Gas Scintillation Proportional Development Progress on the development o f gas scintillation proportional (GSP) counters was limited in 1980 by both time and funding. cant progress was made, however, inthe development of large photoionization detectors to replace photomultiplier tubes for detection ofthe xenon scintillation light emitted from the GSP counter. The photo ionization detector is a new type which is basically an Argon Methane gas proportional counter containing a few mm pressure of compound which is ionized by theU.V. xenon sc in t ll ation light. This type of photo ionization detector is superior to photomultiplier tubes for this application because of(1)a much more uniform response over the area of the detector since the sensitive material is in a uniform concentration rather than a vaporized photocathode, (2)better efficiency for detecting photons, (3)large area photo ionization detectors are easy to construct and therefore less expensive than photomultiplier tubes, and (4) they can be made with CaF2 o r MgF windows which transmit a high percentage ofthe xenon scintillation A prototype GSP counter using a photo ionization detector was constructed and tested during 1980. resolution.Parts were made for two GSP counters. One o f these i s 10" in diameter and will be used for lung counting the other is a 4" diameter phase 2prototype for a neutron spectrometer. are presently being assembled and will be completed and tested in 1981. If the lung counter is as successful as i t promises t o be it will significantly increase the sensitivity for measurement of plutonium and americium inthe body. The counter exhibited excellent

Page 7

Inter laboratory Comparison o f Lung Measurements of Transuranic Bat tell e is a major contributor and a member ofthe DOE sponsored Inter - Cal ib ration Committee for Low Energy Photon Measurements and also is one of three U.S. laboratories which participates in an IAEA inter laboratory comparison o f measurements made on subjects who have inhaled known quantities of radio nuclides which emit low energy photons. The inhalation of these low level radio nuclides is done i n England. In the current IAEA sponsored study,subjects containing 92Nb are measured. Two o f these subjects were extensively studied atthe Whole Body Counter during 1980. Niobium-92m emits a 16 KeV content of 92mNb in the lung to be accurately deter dined by standard whole body counting methods which allow the number o f 16 KeV photons emitted to be calculated.External measurements o f 16 KeV photons give the counting efficiency and calibration factor and by using subjects cf different chest wall thickness the change in calibration factor as a function of chest wall thickness can be determined. The main purpose of this study is to confirm the accuracy of the tissue - equivalent torso phantom which was developed and tested by the Inter - Calibration Committee for Low Energy Photon Measurements. When this confirmation is complete this phantom will become an international The Measurement o f Low Energy Gamma-Rays in the Lung Studies were conducted on the detection of radio nuclides in the lung which have low energy gamma-ray energies in the range o f 80 t o 200 KeV inthe presence of other high energy gamma emitters. was done in regards to the current interest in measuring 239Np which emits gamma and X-rays o f 106 and 104 KeV respectively and l4lCe and 144Ce with gamma-rays o f 145 and 134 KeV respectively. Tests were made with three types of detectors on a mixed radio nuclide standard placed in our lung phantom. This approximates the situation where we are trying to measure 239Np and Ce isotopes in the presence o f large quantities of high energy gamma emitters such as 6oCo, 54Mn,

Page 8

These studies clearly show thata planar intrinsic Ge detector isfar superior for measuring gamma-rays in the energy region of 80 t o 200 KeV. This i s due toits excellent resolution o f 400 eV a s compared t o 2600 eV for the Ge(Li) detector and about 11,000 ev for the NaI(Ta) detector fora 100 KeV gamma-ray. To effectively measure these lower energy gamma-rays in a reasonable length o f time, one o r two arrays of the planar intrinsic Ge need t o be procured a t a cost of $40,000 each. Whole Body Counting Staff and Operation Services Department) Presentations and Publications During 1980 and 241Am to Study Shallow Depositions in Body Surfaces. Health

Page 10

HANFORD WHOLE BODY COUNTEP. 1981 ACTIVITIES Personnel Cosimctry Section Occupational and Environmental Protection Department Pacific Northwest Laboratories

Page 11

HANFORC \#/HOLE BODY CCURTER 1981 ACTIVITIES IN TROO UC TION This report describes the routine whole body counting nieasureinent program for the Ilarrford project personnel during 1981. Special studies and development work performed in conjunction with the whole body counting facilities are also described.Similar annunl reports have been written since 1978 in which the major facilities available for in vivo nieasurement were described.This report will discuss additions or changes in these facilities during 1981. magnetic tape unit were put into operation during the year. computer has dual user capability and can operate the routine counting program while simultaneously providing plotting,printing, computing and operation of other programs. The larger storage capacity provides rapid access to all of our files and programs. The old Nova 2 computer wss retained for backup operation of routine counting in case the Nova 4 A new Nova 4 Data General computer and a new 8 - track New Calibration Phantom A major improvement inthe accuracy o f measuring radioactivity in the lungs and liver was made possible in 1981 by the purchase ofa phantom which very closely simulates a human male torso. The phantom consists of a tissue equivalent polyurethane t cr so shell with an imbedded bone equivalent rib cage. and liver organs are removable and can be obtained containing uniformly distributed radio nuclides. overlaid on the phantom to simulate a range of chest wall thickness from sufficient to give the same absorption of X and gamma ray radi a tic n as human tissue for energies down t o 17 keV. lung sets containing FIBS certified standard amounts of23 * Pu, 239Pu, Tissue equivalent lung Tissue equivalent chest plates can be The tissue equivalency of the phantom ps.rtsis Separate radioactivity tagged

Page 12

phantom. Radioactively tagged 1iver organs were obtained with 23aPu, 239Pu, and 241Am. 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 develcpment for %he past several years a t Lawrence Liver nore National Laboratory under the direction of an inter calibration committee consisting of representatives of the major DOE supported whole body counting facilities. body shell and organs were niade froma cadaver. undergone extensive testing at many whole body counters and i s expected t o be certified as an international --i n vivo cd lib ration standard by the IAEA at the completion of some further testing which is described in the research and development studies section of this rep dr t.Figure1 shows some pictures of the phantom and organs. conjunction with the ultrasonic method of neas u ring chest wall thickness has very significantly improved our accuracy in estimating lung and 1iver burdens of Plutonium, Americium, Uranium and many high eriergy gamma emitting radio nuclides. The phar?tom molds for the The phantom has The use of this phantom i n Array of Intrinsic Germanium …