A non destructive high energy gamma photon activation technique has been developed for the determination of iodine in a wide
range of natural materials. Results are presented and compared with those obtained by independent analytical techniques. Studies
of the loss of iodine from soils on heating are also presented. The sensitivity and precision of the technique are discussed
and its practical aspects described.
An empirical study has been made of the potential of high energy γ photon activation and high resolution γ-ray spectrometry
for the survey analysis of trace elements in a variety of materials. Human blood, urine, bone ash, standard glass (NBS, SRM
612) and air particulates, along with synthetic multi-element standards, have been studied following irradiation with γ photons
of maximum energy 17–45 MeV. Elements found to be suited to determination by γ activation include Sb, As, Bi, Cd, Cs, Ca,
Ce, Cr, Fe, Au, Pb, Mg, Mo, Ni, Nb, Rb, Sr, Tl, Ti, Tm, Zn and Zr. γ spectra, elemental concentrations measured, and/or limits
of detection observed, for the matrices studied are given.
Anthropogenic radioactivity is being measured in near-real time by an international monitoring system designed to verify the
Comprehensive Nuclear Test Ban Treaty. Airborne radioactivity measurements are conducted in-situ by stations that are linked
to a central data processing and analysis facility. Aerosols are separated by high-volume air sampling with high-efficiency
particulate filters. Radio-xenon is separated from other gases through cryogenic methods. Gamma-spectrometry is performed
by high purity germanium detectors and the raw spectral data is immediately transmitted to the central facility via Internet,
satellite, or modem. These highly sensitive sensors, combined with the automated data processing at the central facility,
result in a system capable of measuring environmental radioactivity on the microbeequerel scale where the data is available
to scientists within minutes of the field measurement. During the past year, anthropogenic radioactivity has been measured
at approximately half of the stations in the current network. Sources of these measured radionuclides include nuclear power
plant emissions, Chernobyl resuspension, and isotope production facilities. The ability to thoroughly characterize site-specific
radionuclides, which contribute to the radioactivity of the ambient environment, will be necessary to reduce the number of
false positive events. This is especially true of anthropogenic radionuclides that could lead to ambiguous analysis.
A global radionuclide monitoring system is being engineered as part of a multi-technology verification system for the Comprehensive
Nuclear Test Ban Treaty. The system detects airborne radioactive aerosols and gases that can indicate nuclear weapons test
debris. The backbone of the system is a network of 80 remote detection stations that utilize high-volume air sampling and
high-resolution gamma spectrometry to provide in-situ assay and near-real time reporting. These stations are linked to the
International Data Centre, which is a central data processing hub where raw spectral data is automatically processed, analyzed,
and disseminated to the states parties. Measurements are categorized based on spectral content to determine which contain
anomalous anthropogenic radionuclides that require intensive radiochemical analysis at a certified laboratory. The resulting
system has the capability to measure microbecquerel concentrations of radionuclides and provide accessible data products within
minutes of field measurements. During the past year of international operations, the minimum detectable concentrations and
spectroscopy processing statistics were recorded as a function of geographical location and time. The results show that this
system is an effective tool for nuclear test monitoring, as well as other applications such as radiological emergency response,
public health monitoring, and scientific research.
The recent discovery of the migration of plutonium in groundwater away from underground nuclear tests at the Nevada Test Site has spawned considerable interest in the mechanisms by which plutonium may be released to the environment by a nuclear explosion. A suite of solid debris samples was collected during drilling through an expended test cavity and the overlying collapse chimney. Uranium and plutonium were analyzed for isotope ratios and concentrations using high precision magnetic sector inductively coupled mass spectrometry. The data unequivocally shows that plutonium may be dispersed throughout the cavity and chimney environment at the time of the detonation. The 239Pu/240Pu ratios are also fractionated relative to initial plutonium isotope ratio for the test device. Fractionation is the result of the volatilization of uranium and production of 239Pu by the reaction 238U(n,γ). We conclude that for the test under consideration plutonium was deposited outside of the confines of the cavity by dynamic processes in early-time and it is this plutonium that is most likely transferred to the groundwater regime.
An accurate measurement of the neutron lifetime requires a determination of neutron fluence rate to an accuracy of a few tenths of a percent. The10B(n,)7 Li reaction offers the possibility of achieving this uncertainty. The thermal cross section is large and its departure from 1/v behavior is about 3 parts in 10000. The principal alpha branch is to the first excited state of7Li which then decays by emission of a 478 keV gamma ray. The measurement of the gamma branch can be made with boron samples that totally absorb thermal neutrons, allowing greater sensitivity and eliminating the uncertainty of target thickness. The absolute efficiency of the gamma detector can be determined by an alpha-gamma coincidence technique. Preliminary investigations of this method are presented with a discussion of the problems that must be overcome to achieve the desired uncertainty.
Authors:D. Williams, J. Hislop, A. Mead, T. Sanders, and D. Wood
A sensitive activation technique for the determination of trace levels of oxygen in a wide range of materials is described
with particular emphasis on the γ-irradiation facilities at AERE Harwell and experience of the use of the technique over a
number of years. Procedures for removing surface oxygen contamination prior to determination of bulk oxygen concentrations
are given, together with details of the radiochemical separation procedures used for a wide range of materials, and examples
of the results obtained.
Authors:W. Grant, C. Christodoulides, D. Pogarides, and J. Williams
Rutherford backscattering provides a simple experimental technique for investigating the thermal oxidation of silicon containing
heavy impurity species. The technique provides both mass and depth analysis of para-surface layers. Using conventional apparatus,
typical depth resolution is 250Å N. This paper describes a simple method of improving the resolution to ∼25 Å. The method
is then illustrated with data on the analysis of thin (<300Å) layers of thermally oxidised silicon containing ion-implanted
impurities. The effect of the type and dose of implanted ions on oxidation rate has been measured. The re-distribution of
implanted ions during thermal oxidation is also investigated.
Authors:M. Ginic-Markovic, N. Choudhury, J. Matisons, and D. Williams
A two-pack polyurethane coating was analyzed using thermoanalytical techniques. The curing reaction, monitored using pressure differential calorimetry (PDSC), rheometry and dynamic mechanical analysis (DMA) shows the temperature dependency of activation energy and hence rate of curing. In-situ ATR-FTIR shows the formation of urethane linkage over time. The decomposition behavior carried out under non-isothermal mode using thermogravimetric analysis (TGA) shows bimodal behavior. The activation energies of the initial step (10% decomposition) from both iso and non-isothermal experiments are in very good agreement with each other. The use of dynamic mechanical analysis (DMA) shows the difference in glass transition behavior (Tg) and elastic modulus (E') due to the different state of cure. Also the coating exhibits a very broad loss modulus peak (E'') indicating higher energy dissipation with deformation.
Authors:D. Thompson, S. Parry, R. Benzing, J. Williams, and K. Jarvis
The use of paint as a coating for toys intended for sale on the European market is controlled by a European Standard (EN 71-3:
1994-European Standard for the Safety of Toys, Part 3—Migration of Elements). This work is the result of a preliminary study
organised by the European Commission to produce a new paint reference material which can be used to validate the test methods
given in the European Standard. The migration of elements from painted panels and comminuted paint produced by the Laboratory
of the Government Chemist, (U.K.) was studied. Several methods were used in this certification exercise and this work reports
the recults of neutron activation analysis and inductively coupled plasma mass spectrometry to determine the migration of
As, Ba, Cd, Cr, Hg, Pb, Se and Sb into a simulated stomach environment. Replicate extracts obtained from paint samples gave
a precision of within 10% for most elements by both analytical techniques for the paint panels and for the comminuted paint
sample. This preliminary study has shown that the standard method can provide reproducible results for each of the paint materials
studied and indicates that the study should be continued to produce a fully certified paint reference material.