Nuclear emulsions

The characteristic K line consists of a closely spaced doublet with a 2 1 intensity ratio between the K i and K 2 lines. This not a problem if a low spatial resolution recording medium, such as a fluorescent screen and image intensifier, is used but is a problem if high resolution nuclear emulsion plates are used. Then individual dislocation images are doubled because the diffracted beams from the two lines make different directiorrs in space, giving rise to a type... 

The observations are performed with a Leitz Ortholux polarizing microscope equipped with the ftOpak illuminator, lamps for reflected and transmitted light, immersion objectives, and verniers. Characteristics of the polished thin sections and of the nuclear emulsion plates are observed in transmitted light with the same immersion optics after removing the Berek prism. 

Polished sections and polished thin sections are prepared according to the usual techniques of coal petrography. They are mounted permanently on quadrangular pieces of transparent Lucite for location purposes. We have described elsewhere a graphical method of micro-surveying which allows an observer to locate any specific autoradiograph on nuclear emulsion plate of a given point in an opaque section (13). 

Nuclear emulsion plates are Ilford K 5-100 micron. They are processed as recommended by Bowie (I). 

The nuclear emulsion plates show that the bulk of the activity corresponds to discrete inclusions. The asphalt by itself shows very low activity (Figure 2e,h). 

The same instrument may be used for the microscopy of the sections and of the nuclear emulsion plates. In fact, the microscope builds a bridge between past and present distribution of radioactivity. 

Figure 17.1 Trails of ionization left by heavy charged particles (initial energy of 10 MeV/ nucleon) as they penetrate through a photographic plate (nuclear emulsion). The ions interact with the atomic electrons in the emulsion creating ion pairs to expose the emulsion and the hacks become visible after the Him is developed. Notice the straight-line tracks. (From Knoll, 2000.)...

Nuclear Emulsions The process involved here is a chemical one. Ionizing radiation from a sample interacts with the silver halide grains in a photographic emulsion to cause a chemical reaction. Subsequent development of the film produces an image and so permits a semiquantitative estimate of the radiation coming from the sample. 

Such search for experiments coincided with studies of the heavy element abundances in the cosmic radiation, carried out by exposure of particle track detectors - nuclear emulsions or plastic sheets - in balloon flights to high altitudes and analysis of the recorded tracks for atomic number and abundance. A survey [33] of all data obtained until 1970 showed one single... 

Photographic films with nuclear emulsions are used successfully in order to record very rare events induced by cosmic radiation. For this purpose, light-shielded packages of films have been carried by balloons to high altitudes. Some elementary particles, e.g. the positron and the n meson, have been detected by use of photographic emulsions. 

H. Yagoda, Radioactive Measurements with Nuclear Emulsions, Wiley, New York, 1949... 

A more common technique employs a nuclear emulsion to detect the radiation. The sample is irradiated in close proximity to a sensitive emulsion, which is subsequently developed, fixed, and examined under the microscope. In this way it is possible to distinguish tracks due to alpha particles, fission fragments, etc. Faraggi et al. 22) and Mayr 54) used this technique to determine boron by the B (n,a)Lr reaction down to a level of 2 X 10" gm. Lithium at the 10" -gm level was determined by Picciotto and van Styvendael 69) by the reaction Li (n.,a)H and Curie and Faraggi 18) studied the distribution of uranium in the surface of polished mineral specimens by the U (n,/) reaction. 

In one sorption experiment, the particle size distribution of the aqueous plutonium was determined by the centrifugation technique previously described (I). Simultaneously, a study was made of the size distribution of plutonium sorbed onto silica plates by an autoradiographic method (I, 2, 3). After the plutonium sorbed on the silica plates, the latter were dried and clamped for 2 to 4 days to glass plates coated with Kodak NTA nuclear emulsion. After developing the emulsion, the result-... 

The and decay-series methods are based on the fact that Th and Pa are generated in seawater by the decay of U isotopes. The isotopes are then carried to the sea floor on particles and incorporated into the nodules and crusts. The residence times for Th and Pa in seawater are short (less than 40 and 160 years respectively). The distribution of Th and Pa with depth in nodules or crusts can be measured by counting a particles after separation from the nodule material and plating on a planchet or more rapidly by a-track counting on nuclear emulsion plates. The growth rate of the nodule or crast can then be calculated from the formula... 

Photographic emulsions are sensitized by ionizing radiation resulting in darkening upon development. This is used in the film dosimeter for measurement of 0-, y-, or n-doses. In order to differentiate between various types of radiation, the film is siUTOunded by filters or transfer screens. Although any type of film may be used, special nuclear emulsions have been designed. The dose received is directly proportional to the optical daisity of the exposed film. Film dosimeters are useful in the same range as the pen dosimeter, and both are used for personnel measurements. While the pen dosimeter can be read directly, the film dosimeter requires development. 

In 1957 Russian scientists at the Joint Institute for Nuclear Research (JINR) at Dubna (now Flerov Laboratory for Nuclear Reactions, FLNR) claimed to have synthesized element 102 by irradiating Pu with ions, using nuclear emulsions for a-energy determination. 

Sensitive methods for analysis of plutonium in urine are particularly important for estimating occupational plutonium body burdens. Routinely available instrumentation, such as the alpha spectrometer, can readily detect these low concentrations. More sensitive methods are commonly required for urine samples in order to assess chronic exposures to plutonium. These low detection limits were first achieved in the past by nuclear emulsion track counting (see Table 6-1). In this method, the electrodeposited sample is exposed to nuclear track film, subsequent to the isolation of plutonium. The alpha-particle emitting isotopes of plutonium will leave tracks on the film which are counted to quantify the amount of plutonium. Nuclear emulsion track counting has been used in the past to measure plutonium concentrations in the urine of workers at a nuclear reactor plant (Nielsen and Beasley 1980). A type of scintillation counting has been used to measure plutonium-239 and americium-241 in animal tissues (NCRP 1985). 

After suitable autoradiographs have been generated (which may entail more than one exposure) the slides can be dipped in nuclear emulsion if quantification of probe binding at the single cell level is required (see Note 24). 

Lillie used an expansion chamber for studying the disintegrations of oxygen and nitrogen by 14 MeV neutrons this technique is well suited to a study of such reactions and gives detailed information about each event. These advantages are shared by the nuclear emulsion, although the number of elements which may be covered by both these techniques is rather limited. The exothermic reactions B (wa)Li and Li (n )He have been studied by both methods,... 

Allred et al., were derived by bombarding hydrogen with deuterons. The scattered particles were detected in a nuclear emulsion. 

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