Measurement americium

There are two common approaches for measuring americium in the environment. Americium can either be measured directly in the field (in situ) using portable survey instruments or samples can be procured from the field and returned to the laboratory for quantification of americium. 

Only five transuranic elements exist or are anticipated to be produced in amounts which could lead to significant environmental concentrations. These are neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), and californium (Cf). Of these five, only two, plutonium and americium, have been detected and measured already in the marine environment as a result of global fallout of nuclear testing debris. The procedures described below were developed specifically to measure plutonium and americium. However, as will be expanded later, the techniques for measuring americium are also able to detect curium and californium should they be present in significant amounts in the future. 

For the neutron porosity measurement, fast neutrons are emitted from a 7.5-curie (Ci) americium-beryllium (Am-Be) source. The quantities of hydrogen in the formation, in the form of water or oil-filled porosity as well as crystallization water in the rock if any, primarily control the rate at which the neutrons slow down to epithermal and thermal energies. Neutrons are detected in near- and far-spacing detectors, located laterally above the source. Ratio processing is used for borehole compensation. 

Quantities of americium, as well as other radioactive elements, are measured in units of mass (grams) or radioactivity (curies or becquerels). The becquerel (Bq) is a new international unit and... 

Discharge water and emission from facilities that make americium smoke detectors or gauges or produce plutonium for nuclear weapons may contain americium. These operations are strictly regulated, but you can check local health advisories before consuming fish or other seafood from these waters. Nuclear reactors are not expected to discharge measurable amounts of americium. 

Most physicians do not test for americium in their offices, but they can collect samples and send them to special laboratories. Since americium is radioactive, it is normally measured by its radiation emissions. These emissions are used to tell the amount of americium (in curies or Becquerels) and the radiation dose it gives to your body (in Sieverts or rem). Radiation detectors measure the radiation that is released from objects or materials, including the whole body. If... 

Various cases of internal exposure to americium have been reported in which the exposures resulted from skin punctures with materials also containing plutonium. Information on the distribution of americium in these cases has been derived from the analysis of autopsy tissues. In most cases, the largest fraction of the 241 Am activity measured in the body was associated with tissues near the puncture wound. In one case,... 

A large degree of variation is apparent in retention rates for americium in the liver among various animal species (Durbin 1973), as indicated by measured or estimated liver clearance half-times of approximately 5-16 days in rats, 152 days in baboons, 1-10 years in dogs, and 10 years in Chinese hamsters. A liver clearance half-time of 2 years has been estimated for humans (Griffith et al. 1983). Refer to Section 3.5.1 for information regarding toxicokinetic mechanisms that may play a role in interspecies differences in liver retention of americium. 

Information on the excretion of americium after dermal exposure in humans or animals is extremely limited. Some qualitative information is available from an accidental exposure in which a worker received facial wounds from projectile debris and nitric acid during an explosion of a vessel containing 241 Am (McMurray 1983). The subject also inhaled 241Am released to the air as dust and nitric acid aerosols, which was evident from external chest measurements of internal radioactivity thus, excretion estimates reflect combined inhalation, dermal, and wound penetration exposures (Palmer et al. 1983). Measurements of cumulative fecal and urinary excretion of241 Am during the first years after the accident, and periodic measurements made from day 10 to 11 years post accident indicated a fecal urine excretion ratio of approximately 0.2-0.3, although the ratio was approximately 1 on day 3 post accident (Breitenstein and... 

The ICRP (1994b, 1995) developed a Human Respiratory Tract Model for Radiological Protection, which contains respiratory tract deposition and clearance compartmental models for inhalation exposure that may be applied to particulate aerosols of americium compounds. The ICRP (1986, 1989) has a biokinetic model for human oral exposure that applies to americium. The National Council on Radiation Protection and Measurement (NCRP) has also developed a respiratory tract model for inhaled radionuclides (NCRP 1997). At this time, the NCRP recommends the use of the ICRP model for calculating exposures for radiation workers and the general public. Readers interested in this topic are referred to NCRP Report No. 125 Deposition, Retention and Dosimetry of Inhaled Radioactive Substances (NCRP 1997). In the appendix to the report, NCRP provides the animal testing clearance data and equations fitting the data that supported the development of the human mode for americium. 

The USTUR proposed modifications to the ICRP americium model, based on post-mortem americium measurements in human exposure cases (Kathren 1994). The major modifications are 1) the initial deposition fraction is assumed to be skeleton 45%, liver 25%, muscle 20%, other tissues 10% 2) the half-... 

Mclnroy et al. 1985). Americium radioactivity can be measured in the teeth of rats, where it accumulates in the dental pulp of developing teeth and eventually is incorporated into the mineralized dentin (Hammerstrom and Nilsson 1970). 

Epidemiological and Human Dosimetry Studies. Epidemiological studies of radiation dose typically involve estimates of exposure that are based on whole-body measurements of internally-deposited americium. A need remains for epidemiological data that can provide quantitative human dose-response information while supplying additional information on the health effects of exposure to ionizing radiation and americium in particular, for cases of known internal exposure. 

Time series measurements on seaweeds and winkles show that the americium levels peaked in the early 1980s and then declined by 1989, levels were the lowest they had been in 12 years. In comparison,... 

Exposure Levels in Humans. Although some data on the levels of americium in human tissues exposed to natural background levels (food, water, and air) are available, few measurements have been made on the americium content in human tissues. The principal source of information about occupationally exposed individuals is the U.S. Transuranium and Uranium Registries (USTUR) Tissue Program and database, established to document levels and distribution of uranium and transuranium isotopes in human tissues for occupationally exposed workers (USTUR 1999). Several major database files are available. 

The purpose of this chapter is to describe the analytical methods that are available for detecting, measuring, and/or monitoring americium, its metabolites, and other biomarkers of exposure and effect to americium. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). Additionally, analytical methods are included that modify previously used methods to obtain lower detection limits and/or to improve accuracy and precision. 

In assessing initial exposure, whole body counting techniques measure amounts of americium that have been deposited within organs or tissues and have not been excreted. In cases of accidental ingestion, some of the americium may have been excreted in the urine or through the feces, before exposure is assessed. In... 

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