Common terms of irradiation sterilization

• 1) Cobalt-60: isotope of cobalt 59 with a half-life of about 5.27 years.

• 2) Half life: the time required for the number of radioactive nuclei to decay to half the initial value.

• 3) Radioactivity: the nuclear decay variable of a certain amount of radionuclide occurring in a certain time interval divided by the time interval is called radioactivity. In the international system of units, the unit of radioactivity is Becquerel, abbreviated as Becquerel, the symbol is BQ, 1BQ is equal to the radioactive nuclide has one nuclear decay in one second, that is, 1BQ = 1 decay / second. The unit of activity in the early stage is known as the unit of activity (CI) of 1011 C.

• 4) Absorbed dose: the amount of radiant energy transmitted to the unit mass of a substance. The unit of measurement of absorbed dose is gray, and 1gray is the energy absorbed by one kilogram of material. The unit used to measure absorbed dose was rad (RAD), named "radiation absorbed dose". 1 gray = 100 rad.

• 5) Sterility assurance level (SAL): the probability of microorganisms on the unit product after sterilization. For example, Sal of 10-6 means that one product in a million products is contaminated.

• 6) D-10 value: the irradiation dose (kGy) required to kill 90% of the total number of homologous microorganisms.

• 7) Non uniformity: the ratio of the maximum absorbed dose and the minimum absorbed dose of the same batch of products in the irradiation container, i.e. u = Dmax / Dmin, also known as dose uniformity.

• 8) Minimum radiation absorbed dose: in the irradiation container, the radiation energy transmitted to the unit mass of the material at the lowest dose position.

• 9) Maximum radiation absorbed dose: the radiation energy transmitted to the unit mass of the substance at the highest dose position in the irradiation container.

• 10) Bioburden: the total number of live microorganisms on a product.

• 11) Dosimeter: a device or system that has a repeatable, measurable response to radiation and can be used to measure the absorbed dose in a given material.

• 12) Microbial limit standard: specific quantitative standard specified by relevant laws and regulations or production process standards. The microbial load of qualified products shall not be higher than the microbial limit standard within the shelf life.

• 13) Initial microbiological index: microbial load of the product before sterilization (sterilization).

• 14) On or off label: a sticker label that changes color when receiving enough gamma rays to distinguish the irradiated product from the non irradiated product. Whether or not the label is divided into two ranges (sensitivity): 4-10kgy, the color changes from green to purple after irradiation; when it is greater than 10kGy, the color changes from yellow to red after irradiation.

• 15) Disinfection: the process of killing or eliminating pathogenic microorganisms on the product to make it harmless.

• 16) Sterilization: the processing of confirmed products without living microorganisms. (in the process of sterilization, the death law of microorganism is expressed by exponential function. Therefore, the presence of microorganisms on any single product can be expressed by probability. The probability can be reduced to a very low number, but not to 0. The probability can be expressed as the sterility guarantee level SAL)

Radiation principle and characteristics

• energy conservation.
• Sterilization is complete, no pollution. Because gamma ray has a strong penetrating power, it can kill all kinds of bacteria and microorganisms (including viruses) in a certain dose. Therefore, radiation sterilization is a very effective sterilization method.
• Radiation sterilization is a "cold disinfection" method, which can be sterilized at room temperature. It is especially suitable for some heat sensitive materials, such as plastic products, nylon, chemical fiber products, biological products, etc.
• It can be sterilized after packaging. As long as the packaging materials used are impermeable to bacteria, the sterilized medical supplies can be preserved for a long time.
• It has the advantages of fast sterilization, simple operation and continuous operation, which is conducive to the realization of industrial production.

This is because radiation sterilization has the following advantages:

• (1) irradiation sterilization is complete without pollution and residue.
• (2) irradiation sterilization does not need heating, which is a "cold disinfection" method.
• (3) the gamma ray penetrating power is strong, and the product package is not needed to be opened during processing. The operation is simple and fast, continuous operation and easy process control.
• (4) the sterilized products can be stored for a long time under sealed condition.