Iodine-131 Activity Research Articles

Measurement of Iodine (I-131) Contamination in Staff Working in Nuclear Medicine Facilities

The increasing use of the radiopharmaceutical Iodine-131 (I-131) in nuclear medicine services has implications for the potential for internal radiation received by workers. I-131 has high volatility so it has the potential to become an air contaminant and be inhaled by nuclear medicine staff as internal radiation exposure. This study aims to estimate I-131 contamination in staff at a nuclear medicine facility using a gamma spectrometer. Measurements of I-131 activity in the thyroid were carried out on 38 staff including medical physicists, nuclear medicine specialists, radiographers, radio-pharmacists, nurses, house attendants, and cleaners. The I-131 activity value measured in the staff's thyroid had an activity value range of 13.1 – 238.2 Bq in 13 nuclear medicine staff. Meanwhile, for 25 other medical staff, the I-131 activity values ??measured in the thyroid had activity values ??below the detection limit of the device (14.2 ± 4.3 Bq for men and 11.8 ± 3.5 Bq for women). The highest internal dose rate measured in the thyroid of Pramu Husada nuclear medicine staff and radiopharmaceuticals was 0.1-0.5 mSv/year. This value is still below the dose limit value for internal radiation.

Gamma Ray Spectrum by Software Methods for Radioactive Waste

The requirements of NTD (Neglected Tropical Diseases) and technological regulations for the operation of NPP (Nuclear Power Plant) power units (NP-001-97 (OPB-88/97), NP-082-07) define the requirements for monitoring the specific activity of iodine-131 (the amount of iodine) in the NPP primary circuit coolants. The advantages of laboratory control include accuracy of measurement and the radionuclide composition of the primary coolant, measured using high-precision laboratory equipment. Instrumental spectra were obtained for the detection units BDKG-205m with various options for the placement of waste in a container, their composition, mass of waste, average density, and various activity levels of waste. The basic idea behind gamma-ray spectroscopy is to detect and analyze the energy of incident gamma rays. Gamma rays of varying energy and intensity are emitted from radioactive sources. The gamma-ray energy spectrum is produced when gamma rays are detected and examined using a spectroscopy instrument. The initial stage in gamma-ray spectroscopy is to detect gamma rays using a suitable detector. The detector captures and measures the energy of incoming gamma rays. Scintillation detectors, semiconductor detectors, and gas-filled detectors are among the detectors used in gamma-ray spectroscopy. The incoming gamma-ray energy is converted into electrical signals that can be processed and studied by these detectors. The spectroscopic system measures and records the energy of gamma rays when they are detected. The derived energy spectrum depicts the intensity distribution of gamma rays as a function of energy. The spectrum is a visual representation of the different energy levels found in gamma-ray emission.

SAT510 I-131 Therapy with Dosimetry for Advanced Thyroid Carcinoma: Recombinant TSH vs Thyroid Hormone Withdrawal

Abstract Disclosure: D. Awad: None. J. Hamsa: None. A. Fingeret: None. C. Johnson: None. F. Rutar: None. C. Carson: None. A. Kotwal: None. A. Patel: None. A. Thornburg: None. W.S. Goldner: None. Background: Dosimetry can be used to calculate an optimal and safe dose of Iodine-131 (I-131) for treatment of advanced differentiated thyroid cancer (DTC). Thyroid hormone withdrawal (THW) is the preferred method of TSH elevation for I-131 therapy with dosimetry. At our institution, Recombinant TSH (RhTSH) is used in patients in whom prolonged hypothyroidism is deemed clinically unsafe or cannot tolerate THW. We aim to evaluate if RhTSH and THW are equivalent methods of preparation for I-131 therapy using dosimetry (I-131D). Methods: This is a single institution retrospective cohort study evaluating all patients who received I-131D from 2010-2022. Demographic, clinical variables were assessed and dosimetric calculations were obtained. Statistical analysis was performed with Mann Whitney U, Kruskal Wallis, Chi-squared and Fisher’s exact testing. Results: Fifty-one unique patients were included with a total of fifty-five I-131D treatments, with 55% being female. Median (IQR) age at time of treatment was 60.3 years (42.8-70.4), and BMI kg/m2 was 29.3 (24-33.8). Of these patients 13% were stage I, 18.5% stage II, and 68.5% stage III/IV AJCC 7th ed. Sixty percent underwent THW and 40% received RhTSH. Gamma camera and blood activity measurements, at several time points following the pre-therapeutic I-131 dose, were taken to calculate the residence times and effective half-lives in whole body and blood. All patients demonstrated a monophasic elimination of I-131 activity in both the whole body and blood. Patients receiving RhTSH exhibited a slower elimination of the I-131 in the whole body than THW patients (effective half-life of 22 hrs vs 17 hrs) resulting in a higher fraction of I-131 activity remaining in the whole body 48 hours post-dose (25% vs 16%, p= 0.025). The effective half-life in the blood was also higher in the RhTSH group (p=0.025) resulting in a higher amount of activity remaining in the blood. As a result, the median (IQR) RAI dose was lower for those who received RhTSH (187.5 mCi (167-198)) vs those who underwent THW (260 mCi (202-306)) (p<0.001). As expected, TSH at the time of treatment was higher in the RhTSH group (p=0.0038). Thyroglobulin was higher at the time of treatment in the RhTSH group (p=0.031), but thyroglobulin drop at three months was not statistically different (p=0.0682) between groups. Conclusion: RhTSH administration is non-inferior to THW as a method of TSH elevation and preparation for I-131D for patients with advanced DTC. RhTSH, in comparison to THW, results in a significantly longer half-life in the whole-body and blood resulting in a lower calculated RAI dose. More studies are needed to confirm these findings. Presentation Date: Saturday, June 17, 2023

Radiological study of a wastewater treatment plant associated with radioiodine therapy at a hospital in West Java, Indonesia

Nuclear medicine (NM) services in Indonesia have rapidly developed due to the increasing number of patients, and this growth has been supported by standardized regulations in the field, including the management of solid waste generated. However, multiple reports indicate that licensing control does not regulate liquid waste disposal from patient excretions to protect personnel and the community from radiopharmaceutical exposure. One of the radiopharmaceuticals commonly used in NM and having the longest half-life among the radiopharmaceuticals used in NM is iodine 131(I-131). Thus, this study used a high-purity germanium detector to measure iodine-131 (I-131) activity in liquid waste from decay tanks, temporary collection channels, the hospital’s wastewater treatment plant (WWTP) outlet, and six points around the NM service and liquid waste treatment unit. Concentration measurements in three decay tanks were carried out sequentially every 12 h for 3 d, corresponding to the therapy period. The results showed that the I-131 activity levels in the decay tanks and temporary collection channels, before being mixed with liquid waste from other units, were 95.9 × 106 ± 4.4 × 106 Bq m−3. At the point where the liquid waste from other units was mixed, the activity level decreased significantly to 472 680 ± 22 160 Bq m−3, which was below the clearance level of 107 Bq m−3. However, the recorded concentration exceeded the standard for environmental radioactivity at the hospital’s WWTP outlet, namely 37 670 ± 2040 Bq m−3. The measurement results for I-131 in the air in the open space for two nuclear buildings was above the standard at 1.3 ± 0.27 Bq m−3. According to the RESRAD simulation, based on the initial dose taken from the liquid waste treatment outlet point, the accumulation of doses and the risk of cancer among workers and the community decreased within 3 months after the maximum exposure.

Quantitative Iodine-123 single-photon emission computed tomography/computed tomography for Iodine-131 therapy of an autonomously functioning thyroid nodule

PurposeAutonomously functioning thyroid nodules (AFTNs) are treated with iodine-131 (I-131) therapy, which increases the risk of permanent hypothyroidism; however, the risk can be reduced by separately estimating the accumulated activity for the AFTN and extranodular thyroid tissue (ETT).MethodsA quantitative I-123 single-photon emission computed tomography (SPECT)/CT (5 mCi) was performed in one patient with unilateral AFTN and T3 thyrotoxicosis. The I-123 concentrations measured at 24 h were 12.26 µCi/mL and 0.11 µCi/mL in the AFTN and contralateral ETT, respectively. Thus, the I-131 concentrations and radioactive iodine uptake expected at 24 h by 5 mCi of I-131 were 38.59 µCi/mL and 0.31 for the AFTN and 0.34 µCi/mL and 0.007 for the contralateral ETT. The weight was calculated as CT-measured volume multiplied by 1.03.ResultsIn the AFTN patient with thyrotoxicosis, we administered 30 mCi of I-131, which would maximize the 24-h I-131 concentration in the AFTN (226.86 µCi/g) and maintain a tolerable concentration in the ETT (1.97 µCi/g). The percentage of I-131 uptake at 48 h post I-131 administration was 62.6%. The patient achieved a euthyroid state at 14 weeks and maintained the state until 2 years post I-131 administration with an AFTN volume reduction of 61.38%.ConclusionThe pre-therapeutic planning of quantitative I-123 SPECT/CT may enable a therapeutic window for I-131 therapy, which directs optimal I-131 activity to effectively treat AFTN while preserving the normal thyroid tissue.

RADIATION DOSE ASSESSMENT TO FAMILY MEMBERS TAKING CARE OF NON-CANCEROUS THYROID PATIENTS TREATED WITH I-131 THERAPY IN NUCLEAR MEDICINE DEPARTMENT.

This study aimed to determine the effective doses of caregivers taking care of non-cancerous patients treated with iodine-131 (I-131). Patients (administered 185-1110MBq of I-131) were given specific radiation safety instructions (RSI). Afterwards, caregivers were provided with thermoluminescent (TLD) dosimeter badges to be worn for 12-28days when taking care of the patients. At the end of this period, TLD measurements were obtained. Results showed that caregivers' mean effective dose was 0.15±0.15mSv, which is far less than the international recommendations of 5mSv. Furthermore, the effective doses had no significant correlation with administered I-131 activity to the patients, distance from the hospital, caregivers' age, educational level and mode of transport. Our study showed that radiation doses received by caregivers of non-cancerous patients are higher than that of cancerous patients, nevertheless their received doses were within the international limits, thereby indicating good compliance by the caregivers to RSI.

Evaluation of the physical and biological dosimetry methods in iodine-131-treated patients

The aim of the study was to compare physical and biological dosimetry methods in iodine-131 (I-131)-receiving patients. The present study comprised of 47 patients (mean age: 47.9 ± 15.8 years), treated with I-131. Group I consisted of 17 patients with hyperthyroidism and mean administered activity of this group was 432.9 ± 111 MBq. There were 15 follow-up patients of differentiated thyroid cancer (DTC) in Group II with mean administered activity of 185 ± 22.2 MBq, who were administered scanning dose of I-131. Group III comprised of 15 patients with DTC, ablated with high-dose of I-131, and this group's mean administered activity was 4347.5 ± 695.6 MBq. The whole-body absorbed doses were calculated in all patients both with the Medical Internal Radiation Dosimetry (MIRD) method using MIRDOSE3 software and cytokinesis-block micronucleus (MN) assay-based MN analysis and were compared. The whole-body absorbed dose, calculated by MIRD method, showed very good correlation with the administered I-131 activity (r = 0.89, P < 0.001), but it was moderate in the MN method (r = 0.52, P < 0.01). Absorbed dose estimations with MIRD method were 49.2 ± 20.8 mGy in Group I, 6.5 ± 1.6 mGy in Group II, and 154.3 ± 47.8 mGy in Group III; the differences were statistically significant (P < 0.001), as expected. Pre- and posttreatment MN frequencies differed significantly in all groups (P < 0.05). The whole-body absorbed doses, based on MN method, were 68.2 ± 17.5, 46.0 ± 11.4, and 90.5 ± 26.9 mGy in Groups I–III, respectively. The difference was significant between Group II and Group III (P < 0.01). The mean absorbed dose was 74.6 ± 27.9 mGy with MN versus 68.0 ± 67.1 mGy in MIRD method (P = 0.087) in the entire study population and the correlation was moderate (r = 0.73, P < 0.001). The whole-body absorbed doses, estimated by MN method, showed moderate correlation with administered radioiodine activities in low radioiodine doses and had significantly different and fluctuating values as compared to MIRD method in patients treated with I-131.

FEASIBILITY STUDY FOR PRODUCTION OF IODINE-131 USING DIOXIDE OF TELLURIUM-130

Objective: Currently, nuclear medicine is becoming increasingly important, through the discovery of several medical radioisotopes, which are used in diagnosis, treatment, and medical imaging. Among the most important radionuclide which is commonly used is iodine-131, with a half-life of 8.02 d. Iodine-131 is one of the mainly essential elements in nuclear medicine. Since their first use, several studies have been conducted to meet the world need of hospital specialists in nuclear medicine. The purpose of this study was to participate in a lawsuit about the feasibility of producing 131I.Methods: using neutron activation of the dioxide of tellurium (TeO2) under a neutron flux which varies between 5 1011 and 1013 n/cm²s for 4, 6 and 8 hours** per irradiation cycle during 5 d, and used the Fortron90 Code to calculate the activity of iodine-131.Results: The result of the activity of iodine-131 found about 4,634 Curie with an irradiation of 4 hours** per day and 9.381 Curie with an activation of 8 hours** per day.Conclusion: Production of iodine-131 can be very effective if an acceptable capsule is used for different masses of tellurium and a neutron flux in a nuclear reactor.

An analysis of the intake of iodine-131 by a dairy herd post-Fukushima and the subsequent excretion in milk

This study focuses on iodine-131 detected in milk samples from the Dairy Science Unit at Cal Poly, San Luis Obispo, California following events at the Fukushima Dai-ichi Nuclear Power Plant in March of 2011. The milk samples, collected between March 21 and April 11, 2011, were part of the Diablo Canyon Nuclear Power Plant Radiological Environmental Monitoring Program. A correlation is made between the integrated activity of iodine-131 found in milk and the integrated activities of iodine-131 of rainwater, vegetation and air samples that were collected from March 19 to April 18, 2011. A comparison is then made to previous studies conducted on dairy cattle that were administered controlled amounts of iodine-131 through ingestion. The comparison shows good agreement to the model which states that generally 1 percent of the activity of iodine-131 ingested by dairy cattle will be detected in harvested milk. Considering the environmental factors and the uncertainties involved, these data and calculated results derived from a real world situation provide an excellent application and confirmation of studies done under controlled settings.

Monitoring rainwater and seaweed reveals the presence of 131I in southwest and central British Columbia, Canada following the Fukushima nuclear accident in Japan

Detailed analysis of 131I levels in rainwater and in three species of seaweed (Fucus distichus Linnaeus, Macrocystis pyrifera, and Pyropia fallax) collected in southwest British Columbia and Bella Bella, B.C., Canada was performed using gamma-ray spectroscopy following the Fukushima nuclear power plant accident on March 11, 2011. Maximum 131I activity was found to be 5.8(7) Bq/L in rainwater collected at the campus of Simon Fraser University in Burnaby, B.C. nine days after the accident. Concomitantly, maximum observed activity in the brown seaweed F. distichus Linnaeus was observed to be 130(7) Bq/kg dry weight in samples collected in North Vancouver 11 days following the accident and 67(6) Bq/kg dry weight in samples collected from the Bamfield Marine Sciences Centre on Vancouver Island 17 days following the accident. The 131I activity in seaweed samples collected in southwest B.C. following the Fukushima accident was an order of magnitude less than what was observed following Chernobyl. Iodine-131 activity in F. distichus Linnaeus remained detectable for 60 days following the accident and was detectable in each seaweed species collected. The Germanium Detector for Elemental Analysis and Radioactivity Studies (GEARS) was modeled using the Geant4 software package and developed as an analytical tool by the Nuclear Science group in the Simon Fraser University Department of Chemistry for the purpose of these measurements.

Intercomparison of phosphorus-32, technetium-99m and iodine-131 activity measurement in Pakistani nuclear medical centers and supplier

Technetium-99m and iodine-131 are the leading isotopes used in diagnosis and radiotherapy, respectively in Pakistani nuclear medical centers. Both radionuclides are regularly supplied by Isotope Production Division (IPD), PINSTECH to nuclear medical centers in Pakistan. The packages of 32P, 99Mo → 99mTc generators, and 131I, are prepared at IPD and dispatched by air, rail or road according to the desired activity at reference day to nuclear medical centers. An accurate determination of the activity to be administered to the patient plays key role on the quality of the clinical result of a medical investigation. Activity meters are employed for quantification of radioactivity of radionuclides at supplier site as well as by the users. In order to investigate the performance on the quality of activity measurements and elution efficiency of PAKGEN 99mTc generators, a pilot program of intercomparison was organized between the supplier and the users. The results of intercomparison of the activity measurements showed a maximum difference of ±13 % between supplier and nuclear medical centers.

Traitement de l’hyperthyroïdie par l’iode 131 : à propos de 280 cas

We report through this work the experience of nuclear medicine department at Ibn-Sina hospital (Rabat), in the treatment of hyperthyroidism with iodine-131. We retrospectively studied a cohort of 280 patients with hyperthyroidism, from several regions of Morocco between January 2001 and January 2010. A clinical examination and a serum assessment of TSHus, FT4 and FT3 have been made at baseline and at 3, 6, 12 and 24 months after radioiodine therapy. The activity of iodine-131 administered ranged from 296 to 740MBq and depended on the pathology being treated, age, thyroid volume, intensity of clinical and biological hyperthyroidism and socioeconomic situation. Radioiodine therapy has often been proposed as a treatment for second or third intention, 71 patients were initially treated with iodine-131, while 209 patients had received iodine-131 after failure of medical treatment and/or recurrence after surgical treatment. Graves’ disease was the most common etiology (60%), followed by toxic adenoma (20%), and multinodular toxic goiter (13%). The therapeutic efficacy of a single dose of radioiodine evaluated after a 6-months follow-up was 92% in Graves’ disease, 98% in toxic adenomas and 97% in toxic multinodular goiter. No acute complication was observed. Taking into account our socioeconomic context, radioiodine therapy remains the preferred treatment of hyperthyroidism in our country with good value vs. price and excellent tolerance.

CANCER RISK FROM IN UTERO EXPOSURE TO CHERNOBYL FALLOUT IN UKRAINE

Background and Aims: - Iodine-131 (I-131), the major component of Chernobyl fallout and an isotope readily absorbed by the thyroid gland, has been clearly linked to a subsequent increase in thyroid cancer among those exposed in early childhood. The embryo/fetus could also be vulnerable given the small size of the gland, the proliferative activity of fetal thyroid cells, and the high rate of radioiodine accumulation from the maternal circulation after 12 weeks gestation. We evaluated risk of thyroid cancer from in utero exposure to I-131 and also explored the incidence of non-thyroid cancers. Methods: We identified 2,582 mother-child pairs from the northern region of Ukraine in which the mother was pregnant at the time of the Chernobyl accident or the two months following when I-131 fallout was still present. Individual fetal thyroid I-131 doses were estimated from I-131 activity in the mother’s thyroid (mean dose=72 mGy; range 0-3,230 mGy). From 2003-2006, the in utero cohort was screened using an in-depth, standardized clinical examination. To evaluate incidence of other cancers, we linked the cohort to the Ukrainian National Cancer Registry (UNCR) for the period 1997 (the earliest year for which electronic records were available throughout the study area) and 2008, and estimated the standardized incidence ratio (SIR). Results:Seven cases of thyroid carcinoma and one case of Hurthle cell neoplasm were identified at the time of screening. The estimated excess odds ratio per Gray for thyroid carcinoma was markedly elevated (EOR/Gy=11.9) although not significantly so (P=0.12). Preliminary results of record linkage with the UNCR identified 6 cases of non-thyroid cancer, including 2 brain gliomas, 3 cases of Hodgkin disease, and 1 choriocarcinoma. The SIRs were 0.9 for males (95% confidence interval (CI): 0.11, 3.28) and 1.8 for females (95% CI: 0.49, 4.66). A subsequent linkage is currently underway. Conclusions : The data suggest that in utero exposure to I-131 in Ukraine may have increased the risk of thyroid carcinoma 20 years after the Chernobyl accident. Given the young age of the cohort, the results for cancer incidence at other sites are based on small numbers and should be interpreted cautiously.

Detection and activity of iodine-131 in brown algae collected in the Japanese coastal areas

Iodine-131 (physical half-life: 8.04 days) was detected in brown algae collected off the Japanese coast. Brown algae have been extensively used as bioindicators for radioiodine because of their ability to accumulate radionuclides in high concentration factors. The maximum measured specific activity of 131I in brown algae was 0.37 ± 0.010 Bq/kg-wet. Cesium-137 was also detected in all brown algal samples used in this study. There was no correlation between specific activities of 131I and 137Cs in these seaweeds. The specific activity of 137Cs ranged from 0.0034 ± 0.00075 to 0.090 ± 0.014 Bq/kg-wet. Low specific activity and minimal variability of 137Cs in brown algae indicated that past nuclear weapon tests were the source of 137Cs. Although nuclear power stations and nuclear fuel reprocessing plants are known to be pollution sources of 131I, there was no relationship between the sites where 131I was detected and the locations of nuclear power facilities. Most of the sites where 131I was detected were near big cities with large populations. Iodine-131 is frequently used in diagnostic and therapeutic nuclear medicine. On the basis of the results, we suggest that the likely pollution source of 131I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.

Dosimetrie bei Radioiodtherapie benigner Schilddrüsenerkrankungen – Hintergrund und Durchführung

Radioiodine therapy of benign thyroid diseases (focal = [toxic adenoma], multifocal, disseminated autonomy, Grave's disease or clinical relevant goitre) needs to be and can be performed individually for each patient. Most frequently a radioiodine test is performed applying a small activity of iodine-131 ( 131 I). The paper discusses some protocols for pre- or posttherapeutic dosimetry and discusses their advantages and disadvantages. All are based on the volumetry of the target tissue as well as the radioiodine kinetics in the target volume what may be represented by maximum uptake and half life of iodine retention in the thyroid. Possible disturbances and measuring uncertainties of these parameters are presented and discussed. In spite of the discussed uncertainties in dosimetry, due to its high therapeutic width radioiodine therapy is a very successful procedure to cure hyperthyroidism or to reduce goitre volume with only little side effects.

Contamination of the home environment by patients treated with Iodine-131: initial results.

We have employed twin sodium iodide radiation detectors to analyze iodine-131 transfer from thyroid patients to their families. Unlike previous studies of this problem, we measured thyroid radioiodine activity directly and are able to detect as little as 92 pCi of iodine 131 in adult thyroids. As in previous studies, we have also measured direct radiation exposures of family members with wristband thermoluminescent dosimeters. Thus far, we have studied seven families with 17 persons. Eleven of these are children under age 16. Direct radiation exposure of family persons from proximity of these radioactive patients ranged from 0.17 to 126 mR per day (natural background radiation amounts to approximately 0.35 mR per day). The maximum activity of iodine-131 in family thyroids ranged from less than 92 pCi to as high as 110,000 pCi and resulted in thyroid dose equivalents of 4 to 1330 mrem. Based on recent estimates of thyroid cancer, the latter dose equivalent could possibly double the risk of thyroid malignancy in children over what is expected normally. Such a risk implies the addition of 10 induced cases to the 10 naturally occurring cases per million people per year.

Performance of Silver Zeolite in a Radioiodine Monitor

Measurement were made of the interaction of 8Kr, 133Xe, CH3I (131I) and I2 (131I) with various silver zeolites and activated charcoals under varying relative humidities and temperatures. Results show silver zeolite has significantly less interaction with noble gases and high adsorption efficiencies for CH3I making it superior to charcoal for airborne radioiodine monitoring. The penetration of airborne iodine activity into the silver zeolite filter bed was also examined. CH3I penetrated slightly deeper than I2 at the same air flow velocity; however, at 17.4 feet per minute, no more than 5% of the iodine activity in either form penetrated deeper than 1 cm into the filter bed. The sensitivity of the iodine-131 activity detection system was found to be approximately 2.5% (1% = 2.22 x 104 counts per minute/μCi) at the 364 Kev photopeak with a 100 Kev energy window width.

DETERMINATION OF SMALL AMOUNTS OF CARBON-14 IN THE PRESENCE OF LARGE IODINE-131 ACTIVITIES, AND AN EXPERIMENTAL ESTIMATION OF THE SPECIFIC ACTIVITIES OF (131-I)-IODOTYROSINES.

IN the examination of mechanisms of chemical reactions, and particularly in biochemical studies of this nature, radioactive tracer substances of high specific activity are needed. In many cases it is desirable to use doubly labelled tracers containing carbon-14 or tritium as well as iodine-131. Recently, in an investigation of thyroid hormones (131I)-iodotyrosines of very high specific activity were prepared by Reith and Tampion1. As the specific activity of these compounds could only be calculated from uncertain values, it was necessary to attempt an experimental determination using 14C-tyrosine in the iodination procedure. However, even using a carbon-14 substance of the highest obtainable specific activity, the iodine-131 activity is so much higher that their simultaneous counting becomes an extremely difficult if not an impossible task. Taking the specific activity of carbon-14 tyrosine as 20 mc./m.mole, an average iodination would give a relation of 0.01 µc. carbon-14 for 500 µc. iodine-131; that is, a ratio of activities of approximately 1 : 50,000 on liquid scintillation counting. So it was necessary to find a method of eliminating as much of the iodine-131 as possible prior to scintillation counting of the carbon-14. The following method allows the elimination of more than 99.9 per cent of the counts of iodine-131, making it possible to count even small amounts of 14CO2 in a multichannel liquid scintillation spectrometer. The method can easily be used in serial determinations of several dozen experiments per day.

Increase in background gamma-radiation and its correlation with iodine-131 in milk.

Measurements were made of the gamma -ray dose rate over a lawn and a house in Leeds during Aug. and Sept. 1957, and were repeated on Oct. 19, 1957 following the Windscale Reactor accident of Oct. 10. Small increases in dose rate were observed. The measurements were continued for several months. Data are tabulated. The relation of the radioactivity to the iodine-131 activity in milk from the area is discussed. (C.H.)

Radioactivity in Animal Thyroid Glands

Iodine-131 activity was readily found in thyroid glands from grazing animals in Arizona, Pennsylvania, Ohio, and Oregon within 2 weeks following the start of the 1956 US Pacific atomic weapons tests. A progressive increase was noted in the proportion of samples which were active from mid-May to mid-October, at which time the study was terminated. Based on the Arizona and Ohio data, the average weekly dosages from mid-May to mid-October to cattle and sheep were 35 and 120 milli-roentgen equivalent physical, respectively, apparently harmless to the health of animals. It is suggested that the average cattle /sup 131/I level found in this study is approximately the average continuously existing in US cattle during the past 2 or 3 years. Theoretical considerations indicate that with the levels of /sup 131/I found in cattle thyroids, detectable amounts of /sup 131/I would have been secreted with the fresh milk produced in these areas.