Maximum specific radioactivities

Most of the challenges associated with the handling of short-lived positron emitters are direct consequences of their physical properties, half-life and decay mode, from which also ensues very high maximum specific radioactivity and the associated practical minute amounts of material engaged in the radiosyntheses. 

In order to achieve maximum specific radioactivity, in target production of [ C]methane followed by iodination is the method of choice. Alkylation reactions on oxygen, nitrogen, phosphorus, and sulfur nucleophiles as well as on carbanions indeed cover a large variety of... 

The magnitude of the half-life of tritium implies a fairly high rate of nuclear disintegration the maximum specific radioactivity of monotritiated compounds is 29.15 Ci mmol , which is 1.078 TBq, where 1 Ci = 3.7 x 10 Bq (1 Bq is defined as 1 disintegration The only radiation emitted is soft 3"radiatloa... 

It is evident from Table 1 that certain limiting factors exist. For example, experiments with bromine-82 are limited to a duration of about one week because of the short half-life. At the other end of the scale, experiments with stable carbon-13 are limited to dilutions of less than x 500. Even with radioactive isotopes the maximum specific activity available may limit dilution though not to the same extent. Thus, chlorine-36 can stand dilutions up to x 107 but tritium can improve on this to a factor of x 1012. 

This complex reached a maximum of about 10% in the early stages of reduction and then decreased. Initially the relative specific radioactivity was 1.93 for methyl linoleate and zero for conjugated diene. Relative specific radioactivity in the products at 50% reduction was about equal in the monoene (1.0), stearate (0.96), and diene-Fe(CO)3 (1.0), but only minor in the free conjugated diene (0.14). Although the diene-Fe(CO)3 complex is a significant intermediate in the reduction of linoleate, the free conjugated diene is not. 

The term specific activity has several meanings. It may refer to any one of the following radioactivity per unit mass of an element, radioactivity per mass of labeled compound, or radioactivity per unit volume of a solution. The denominator of reference must be specified. In terms of radioactivity per unit mass, the maximum specific activity attainable for each radionuclide is that for the pure radionuclide. For example, pure C has a specific activity of 62Ci/mol or 4400Ci/kg. As usually available, is a tracer for compounds in which it represents only a small fraction of the total carbon, most of which is the natm-aUy occurring mixture of stable and stable C. If there is no stable element present, the radionucfide is said to be carrier free. 

Radionuclides of high specific activity are produced either through accelerator irradiation or through secondary reactions in the target ( 15.6) in a reactor. Maximum specific activity is obtained when the radioactive nuclide is the only isotope of the element. This is not possible to achieve in regular reactor irradiation through (n,y) capture processes. For example, reactor-produced Na may be obtained in specific activities of 2 X 10 Bq g while the specific activity of accelerator-produced Na may exceed 10 Bq g however, the total activities available are usually the inverse. 

Table 13.1 is merely a guide. Each laboratory should develop specific quantity limits. In some cases, the license under which the laboratory operates will specify the quantity limits. For instance, the NRC issues specific radioactive material licenses to facilities, and each license specifies the maximum quantity limit for a given radionuclide. At government owned and operated sites, the DOE facilities do... 

Radiopharmaceuticals of very high specific radioactivity are needed for "in vivo studies of specific receptor binding. The maximum specific activity achieved in the course of synthesis of various C-labelled compounds had been of the order of 1-2 Ci jumol after taking all precautions concerning pollution with atmospheric C02 at all stages of the synthesis . The maximum possible specific radioactivity of CH4 equals 8.38 x 10 Ci g or 76.1 Ci In a preliminary study it has been shown that CH4/ CH4,... 

When L-valine-l- C was added to suspensions of washed mycehum of the Cephalosporium sp. the specific radioactivity of extraceUular penicilhn N reached a maximum within a few minutes and then began to fall. The specific radioactivity of cephalosporin C continued to increase for some time while that of penicilhn N was fading, but the apparent specific radioactivities of the two antibiotics did not follow a course which could be interpreted in terms of a product-precursor relationship between them. However, some uncertainty attended the quantitative aspects of these experiments, in which the amounts of antibiotics were deduced from biological assay and their radioactivities from counts on paper after electrophoresis and chromatography (Warren et al., I967). Whether cephalosporin C is formed from penicilhn N is thus still an open question, although it would be difficult to reconcile this biosynthetic pathway with the apparent abihty of D-valine to depress selectively the production of penicilhn N. 

Urinary excretion of radioactivity was measured in human volunteers during and after a 3.5-hour period of dermal exposure to 0.11 or 0.22 g 32P-labeled TOCP (Hodge and Sterner 1943). The specific activity of the test substance was not reported. Radioactivity in urine was measured with a Geiger-Muller counter, but the limits of detection were not reported. Maximum estimated excretion rates, 10 and 43 pg TOCP/hour for the respective dosage levels, were measured within 24 hours of initiation of exposure. Radioactivity was not detected 48 or 72 hours after dosing ceased. Cumulative radioactivity detected in urine accounted for 0.13% and 0.36% of the dermally applied radioactivity. 

After maximum radioactivity incorporation the protein is denatured and generally subjected to HPLC or gel-electrophoresis. Those methods separate the proteins from the specific tissue by size and the radioactivity distribution can be determined among the protein components. The specifically labeled biopolymers are distinguished simply by a competition experiment performed by the addition of excess of non-labeled parent ligand. It eliminates the radioactivity incorporation. 

When using an HDCC accelerator, the required electric potential for having the same nuclear events is dramatically reduced. Note that for the maximum reaction rates for the D-D nuclear events, the maximum occurs at about 272 Volts (lower x-axis label). Some of the desired nuclear reactions to stabilize (transmute) specific highly radioactive species into stable elements will, of course, require that the combined HDCC be accelerated using potentials up to 70 keV. 

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