Y emitters

Table 11.5 Approximate half-thickness values for a selection of shield materials and y-emitters...

There is, however, a temperature range in which the y emission is a function of temperature. In this range, the anisotropy of y emission can be used as thermometric property. The advantage of using y emitters is that the detection can be done from outside the cryostat (no wiring necessary inside the cryostat). 

Actinium decays via a series of short-lived isotopes, eventually ending with stable lead. The presence of these radioactive daughters, particularly Th (which is a strong y-emitter), necessitates the use of lead-lined gloved boxes and remote control manipulators. Consequently, the metallurgy of actinium has been little studied and, due to the great expense and trouble involved, probably will not be studied extensively in the future. 

An allied application of radiolabelled anti-tumour monoclonal antibodies is that of diagnostic imaging (immunoscintigraphy). In this case, the radioisotope employed must be a y-emitter (such that the radioactivity can penetrate outward through the body for detection purposes). Although various radioisotopes of iodine have been evaluated, (technetium) is the one... 

Applications. The —y coincidence method can be used to determine trace amounts of a -emitting isotope in the presence of large quantities of a y emitter with no coincident beta. The application of this technique is illustrated by the spectrum of a separated cesium sample... 

The fi-y coincidence spectrometry technique has been used for low level 131I measurements in various environmental samples. The presence of other y emitters in the samples and the sample bulk have often required... 

The contribution of the y-spectra to knowledge about radionuclide fractionation is limited pure and nearly pure f3 emitters (e.g., 89Sr, 90Sr, and 91Y) are not detectable by y-spectrometry only relative magnitudes of the y-emitters can be determined from the spectra. Quantitative information on the radiochemical composition was obtained by radiochemical analyses performed by Tracerlab, Division of Laboratory for Electronics, Inc., Richmond, Calif. 

A few radioisotopes of biochemical significance are y emitters. Emission of a y ray (a photon of electromagnetic radiation) is often a secondary process occurring after the initial decay by /3 emission. The disintegration of the isotope 131I is an example of this multistep process. 

The properties of several radioisotopes that are important in biochemical research are listed in Table 6.1. Note that many of the isotopes are /3 emitters however, a few are y emitters. 

The first responsibility of the student is to become knowledgeable about the properties and hazards of the radioactive substances to be used. You must know which radioisotopes are to be handled and the form, gas, liquid or solid, of the material. It is also important to know whether the isotope is a /3 and/or y emitter and whether it is weak or strong. 3H and 14C are considered weak j8 emitters and 32P is a strong /3 emitter. 

Why is an a emitter more hazardous to an organism internally than externally, whereas a y emitter is equally hazardous internally and externally ... 

II The radioactive isotopes of iodine, by contrast, are both y emitters, providing a... 

Knapp calculated that Cfonax) would have been in the range 0.7-2.6 [xd 1 1(0.026-0.10 MBq l-1) at St George, a range of values which is consistent with measurements near Windscale (Dunster et al., 1958 Booker, 1958). Knapp calculated further that an infant drinking 11 of milk per day (perhaps more than is usual) would have received a thyroid dose of 120-440 rad (1.2-4.4 Gy). Since the iodine isotopes are (3, y emitters, the dose equivalent in Sv is the same as the dose in Gy. 

When designing a radiopharmaceutical one should have in mind the potential hazard the product may have to the patient. The goal must be to have maximum amounts of photons with a minimum radiation exposure of the patient. For use in therapy, P emitters and a emitters are particularly useful. For diagnostic purposes, y emitters are most widely used. In general, those y emitters with a short physical half-life and with a y energy between 100 and 300 keV are most widely used in medical application, since these can easily be detected by standard y cameras. 

Pure p emitters are not as easy to check as the y emitters. However, they may be checked for purity with a p spectrometer or a liquid scintillation counter. 

The relative advantages of using a p-emitter ( H and " C), rather than a y-emitter are ... 

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