When Should You order the materia? Analvsis Date Ideally you will want to schedule your experiments and your adiochemical shipments such that the material arrives at its maximum level of activity and lowest level of decomposition. This will tend to be when the product is newer, or nearer its analy date(the date on which the compound passes quality control tests and is diluted appropriately so that the radioactive concentration and specific activity will be as those stated on the reference date) Some isotopes and radiochemicals decompose slowly, so it is not always necessary to take this suggestion to the extreme. As you use a radiolabeled product, you' ll come to know how long you can use it in your work. AnI labeled ligand will not last as long as aC labeled sugar. An inorganic radiolabeled compound, such as Na I or sodium chromate, will decompose at the isotopes rate of decay, whereas a labeled organic compound, such as the tritiated thymidine alluded to earlier, will decompose at a much faster rate than the half-life of the isotope would indicate Manufacturers take this into account by having a terminal sale date The material will only be sold for so long before it is removed from its stores. Up until this date you will be able to purchase the material and still expect to use it over a reasonable period of time Reference Date The reference date is the day on which you will have the stated amount of material. If you purchased a 1 mCi vial of 3 P dCTP, yo will have greater than l mCi (37 MBq) prior to the reference date, l mCi on that date, and successively less beyond the reference date. (Note that since you will most likely receive your radioac tive material prior to reference, it is possible to exceed possession limits; consider this when determining limits on your radiation license ) In the case of longer-lived radioisotopes, such as H and C, the analysis date will also serve as the reference date How Do you calculate the amount of emaining Radiolabel? is to use the following exponential decay equation. For conve nience's sake, most manufacturers of radiochemicals provide decay charts in their catalogs for commonly used isotopes. This equation comes in handy for the less common isotopes. A= Aoe 0.693tT 148When Should You Order the Material? Analysis Date Ideally you will want to schedule your experiments and your radiochemical shipments such that the material arrives at its maximum level of activity and lowest level of decomposition. This will tend to be when the product is newer, or nearer its analysis date (the date on which the compound passes quality control tests and is diluted appropriately so that the radioactive concentration and specific activity will be as those stated on the reference date). Some isotopes and radiochemicals decompose slowly, so it is not always necessary to take this suggestion to the extreme. As you use a radiolabeled product, you’ll come to know how long you can use it in your work. An 125I labeled ligand will not last as long as a 14C labeled sugar. An inorganic radiolabeled compound, such as Na125I or sodium 51chromate, will decompose at the isotope’s rate of decay, whereas a labeled organic compound, such as the tritiated thymidine alluded to earlier, will decompose at a much faster rate than the half-life of the isotope would indicate. Manufacturers take this into account by having a terminal sale date.The material will only be sold for so long before it is removed from its stores. Up until this date you will be able to purchase the material and still expect to use it over a reasonable period of time. Reference Date The reference date is the day on which you will have the stated amount of material. If you purchased a 1 mCi vial of 32P dCTP, you will have greater than 1 mCi (37MBq) prior to the reference date, 1mCi on that date, and successively less beyond the reference date. (Note that since you will most likely receive your radioac￾tive material prior to reference, it is possible to exceed possession limits; consider this when determining limits on your radiation license.) In the case of longer-lived radioisotopes, such as 3 H and 14C, the analysis date will also serve as the reference date. How Do You Calculate the Amount of Remaining Radiolabel? The most straightforward way of calculating radioactive decay is to use the following exponential decay equation. For conve￾nience’s sake, most manufacturers of radiochemicals provide decay charts in their catalogs for commonly used isotopes. This equation comes in handy for the less common isotopes. A = A0e-0.693t/T 148 Volny Jr