Document Details


Title:
REALISTIC CALIBRATION OF WHOLE BODY COUNTERS FOR MEASURING PLUTONIUM
Author(s):
PARKINSON, W W [OAK RIDGE NATIONAL LABORATORY]; GOANS, R E [OAK RIDGE NATIONAL LABORATORY]; GOOD, W M [OAK RIDGE NATIONAL LABORATORY]
Subject Terms:
DOSIMETRY; CALCULATION METHODS; ACTINIDES; PHANTOMS; COMPARATIVE EVALUATIONS; RADIATION DETECTORS; DIAGRAMS; BODY BURDEN; LUNGS; CALIBRATION; PHOTONS; THEORETICAL DATA; ERRORS; SPATIAL DOSE DISTRIBUTIONS; SPECTRA; GRAPHS; STATISTICS; PERSONNEL DOSIMETRY; INTERNAL IRRADIATION; MATHEMATICAL MODELS; COMMENTARY; POTASSIUM 40; COUNTING TECHNIQUES; PLUTONIUM 239; DATA
Document Location:
Location - NNSA/NSO Nuclear Testing Archive Address - P.O. Box 98521 City - Las Vegas State - NV Zip - 89193-8521 Phone - (702)794-5106 Fax - (702)862-4240 Email - CIC@NV.DOE.GOV
Document Type:
REPORT
Publication Date:
1977 Dec 09
Declassification Status:
Never classified
Document Pages:
0022
Accession Number:
NV0062703
Document Number(s):
IAEASM22257
Originating Research Org.:
OAK RIDGE NATIONAL LABORATORY
OpenNet Entry Date:
1994 Aug 26
Description/Abstract:
THE LOW ENERGIES AND ABUNDANCE OF X-RAY PHOTONS FROM 239-PLUTONIUM MAK E ITS DETECTION IN VIVO ONE OF THE MOST DIFFICULT PROCEDURES IN LOW-LE VEL RADIOACTIVE COUNTING. STANDARD PRACTICE IS TO REDUCE BACKGROUND B Y THICK SHIELDING, CONTROLLED ATMOSPHERES AND ELECTRONIC PULSE SHAPE D ISCRIMINATION. THE NATURAL RADIOACTIVITY OF THE HUMAN SUBJECT, HOWEVE R, SETS A LOWER LIMIT ON THE QUANTITY OF PLUTONIUM WHICH CAN BE DETECT ED IN THE LUNGS AND CHEST. MONTE CARLO PHOTON TRANSPORT CALCULATIONS HAVE BEEN PERFORMED FOR THE 14, 17 AND 20 KEV L X-RAY PHOTONS FROM VAR IOUS DISTRIBUTIONS OF PLUTONIUM IN A SIMULATED HUMAN CHEST AND COMPARE D WITH MEASURED COUNTING RATES FROM A UNIFORM DISTRIBUTION AND A POINT SOURCE IN A RANDO PHANTOM. AGREEMENT IS REASONABLE FOR A 239 PLUTONIU M CALIBRATION FACTOR OF 6.5 NANO CURIES PER COUNTS/MIN. IN THE AVERAGE HUMAN CHEST (25 MM TISSUE) FOR THE PAIRED 127 MM PHOSWICH DETECTORS O F THE OAK RIDGE NATIONAL LABORATORY FACILITY. THE COUNTING RATE IN TH E PLUTONIUM REGION FOR THE AVERAGE HUMAN SUBJECT IS ABOUT 500 COUNTS I N 40 MINUTES, DUE LARGELY TO THE POTASSIUM-40 CONTENT OF NATURAL POTAS SIUM. THE MINIMUM DETECTAB;E ACTIVITY (MDA) OF PLUTONIUM-239, AT TWIC E THE STANDARD DEVIATION OF THIS COUNTING RATE, CORRESPONDS TO 6.6 NAN OCURIES. FURTHERMORE, UNLESS RECENT UNCONTAMINATED COUNTING DATA ON T HE SPECIFIC SUBJECT ARE AVAILABLE, IT IS NECESSARY TO ALLOW FOR THE NO RMAL POTASSIUM-40 RADIO-ACTIVITY BY DERIVING A RATIO OF THE COUNTS IN THE PLUTONIUM SPECTRAL REGION (14-25 KEV) TO SOME SPECTRAL REGION CHAR ACTERISTIC OF NORMAL HUMAN RADIOACTIVITY. THE TWO REGIONS UTILIZED FO R THIS PURPOSE AT ORNL HAVE BEEN THE 1.46 MEV POTASSIUM PHOTOPEAK AND THE 80-128 KEV UPPER END OF THE PHOSWICH SPECTRUM. FOR AN UNCONTAMINA TED, MALE POPULATION AT ORNL, THE RATIO OF THE PLUTONIUM 14-25 KEV BAN D TO THE 1.46 MEV POTASSIUM PHOTOPEAK HAS BEEN FOUND TO BE 0.022 AND T HAT OF THE PLUTONIUM TO THE 80-128 KEV VAND WAS 0.15 WITH STANDARD DEV IATIONS FOR THE POPULATION OF 23 PERCENT AND 17 PERCENT, RESPECTIVELY. WHEN THESE STANDARD DEVIATIONS AMONG THE NORMAL POPULATION ARE TAKEN INTO ACCOUNT, THE MDA FOR A HUMAN SUBJECT BECOMES 14 NCI OF PLUTONIUM- 239 AT THE 2 SIGMA LEVEL. IF COMMON RADIONUCLIDES SUCH AS THE FISSION PRODUCTS CESIUM-137 OR STRONTIUM-90 ARE PRESENT, THE MDA, EVEN WITH A CCURATE SPECTRAL STRIPING CAN EASILY BECOME 20-25 NANOCURIES, DEPENDIN G, OF COURSE, ON THE COUNTING RATE OF THESE ADDITIONAL CONTAMINANTS.


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