●o● specific activity diluted o molecules of compound of compound Figure 6.1 Diagrammatical representation of radiochemicals at low and high specific ctivity, and at high specific activity in a diluent. From Guide to the Self-decomposition of Radiochemicals, Amersham International, plc, 1992, Buckinghamshire, U.K. Reprinted by permission of Amersham Pharmacia Biotech Radionuclide, Energy, and Type of Emission(Alpha, Beta, Gamma, X ray, etc In most cases you won't have the choice. You will choose the adionuclide because of its elemental properties, and its reactivity in reference to the experiment, not its type of emission. Each radionuclide has its unique emission spectrum. The spectra are important in determining how you detect the radioactivity in your samples. This is discussed more fully later in the chapter. Specific Activity and Radioactive Concentration The highest specific activity and the highest radioactive con centration tend to be the best since it means that there will be the greatest number of radioactive molecules in a given mass and volume(Figure 6.1). But there are two caveats to this ideal. The first is that as you increase the specific activity, you decrease the molar concentration of your desired molecule. This molecule will become the limiting reagent and possibly slow down or halt the reaction. The second danger is that at high specific activities and/or radioactive concentrations, the rate of radiolytic decomposition will increase. These parameters are discussed in more detail in Chapter 14, Nucleic Acid Hybridization o take an example, a standard random priming labeling reaction requires 50 uCi (1.85 MBq)* of P dNTP(Feinberg *In the United States the unit of activity of"Curie"is still used The unit of common usage is the Becquerel(Bq). Whereas I Curie=3. 7 x 10 disintegrations per second(dps), the Bq=1 dps. For example, to convert picocuries(10 Curies)to Working Safely with Radioactive Materials 145Radionuclide, Energy, and Type of Emission (Alpha, Beta, Gamma, X ray, etc.) In most cases you won’t have the choice. You will choose the radionuclide because of its elemental properties, and its reactivity in reference to the experiment, not its type of emission. Each radionuclide has its unique emission spectrum. The spectra are important in determining how you detect the radioactivity in your samples. This is discussed more fully later in the chapter. Specific Activity and Radioactive Concentration The highest specific activity and the highest radioactive con￾centration tend to be the best since it means that there will be the greatest number of radioactive molecules in a given mass and volume (Figure 6.1). But there are two caveats to this ideal. The first is that as you increase the specific activity, you decrease the molar concentration of your desired molecule. This molecule will become the limiting reagent and possibly slow down or halt the reaction.The second danger is that at high specific activities and/or radioactive concentrations, the rate of radiolytic decomposition will increase. These parameters are discussed in more detail in Chapter 14, “Nucleic Acid Hybridization.” To take an example, a standard random priming labeling reaction requires 50mCi (1.85MBq)* of 32P dNTP (Feinberg Working Safely with Radioactive Materials 145 Figure 6.1 Diagrammatical representation of radiochemicals at low and high specific activity, and at high specific activity in a diluent. From Guide to the Self-decomposition of Radiochemicals, Amersham International, plc, 1992, Buckinghamshire, U.K. Reprinted by permission of Amersham Pharmacia Biotech. *In the United States the unit of activity of “Curie” is still used. The unit of common usage is the Becquerel (Bq). Whereas 1 Curie = 3.7 ¥ 1010 disintegrations per second (dps), the Bq = 1 dps. For example, to convert picocuries (10-12 Curies) to