**2. Radiation processing**

Radiation processing refers to the use of radiation to change the properties of materials on an industrial scale. The term 'ionizing radiation' relates to all radiation capable of producing ionization cascades in matter. The energy range characteristic of ionizing radiation begins at about 1000 eV and reaches its upper limit at about 30 MeV. To avoid induced radioactivity, which may appear if the gamma ray energy is higher than 5 MeV or the energy of the fast electrons exceeds 10 MeV, it is prohibited to use for sterilization radiation characterized by energy higher than these values. On the other hand, the application of lower energy radiation (below 0.2 MeV) is not rational. Commercial gamma ray irradiation facilities are typically loaded with 60Co of total activity from 0.3 to 3.0 MCi1, while commercial e-beam facilities are equipped with one or two electron accelerators generating high power (10– 100 kW) beams of 8–10 MeV electrons.

When radiation passes through materials it breaks chemical bonds. Radiation processing has been used commercially for almost forty years. Gamma radiation from 60Co, electron beams and x-rays, are all used to sterilize the medical devices used in operations and other healthcare treatments. Implants, artificial joints, syringes, blood-bags, gowns, bottle teats for premature baby units and dressings are all sterilized using radiation. The surgical gloves are sterilized using gamma radiation from 60Co. Other industries that benefit from radiation processing include the food, pharmaceutical, cosmetic, horticultural, and automotive industries. In the horticultural industry, growing-mats, fleeces and pots may be reused after irradiation-reducing waste and cost and saving the environment from unnecessary waste. Similarly, commercial egg trays may be recycled after irradiation without risk of proliferating salmonella.

Gamma rays are formed with the self disintegration of Cobalt-60 (60Co) or Cesium-137 (137Cs) sources. Among thousands of gamma emitters only 137Cs and 60Co are indicated for radiation processing. The energy of gamma rays, as electromagnetic quantum waves, is similar to light, but with higher photon energy and shorter wavelength. The 60Co radionuclide can be produced in a nuclear power reactor by the irradiation of 59Co (metal), with fast neutrons. The radioactive isotope is formed by neutron capture as showed equation 1 (Laughlin, 1989).

$$\text{zCo}^{59} + \text{ọn}^{1} \rightarrow \text{zCo}^{60} \tag{1}$$

The unstable nucleus of 60Co emits photons of 1.17 and 1.33 MeV, decaying with a half-life of 5.2714 years to stable 60Ni as shown the Figure 1 (Kaplan, 1955). The radioactive 60Co source is composed of small pellets of cobalt that are loaded into stainless steel or zirconium alloy sealed tubes (pencil arrays).

Radiation is the unique source of energy which can initiate chemical reactions at any temperature, including ambient, under any pressure, in any phase (gas, liquid or solid),

 1 Ci (currie)=3.7 x 1010 Bq (becquerel)

world. These factors facilitate to understand the relatively fast increase of the constitution of irradiation institutions. Thus, this chapter will discuss the use of sterilization by gamma

Radiation processing refers to the use of radiation to change the properties of materials on an industrial scale. The term 'ionizing radiation' relates to all radiation capable of producing ionization cascades in matter. The energy range characteristic of ionizing radiation begins at about 1000 eV and reaches its upper limit at about 30 MeV. To avoid induced radioactivity, which may appear if the gamma ray energy is higher than 5 MeV or the energy of the fast electrons exceeds 10 MeV, it is prohibited to use for sterilization radiation characterized by energy higher than these values. On the other hand, the application of lower energy radiation (below 0.2 MeV) is not rational. Commercial gamma ray irradiation facilities are typically loaded with 60Co of total activity from 0.3 to 3.0 MCi1, while commercial e-beam facilities are equipped with one or two electron accelerators generating high power (10– 100

When radiation passes through materials it breaks chemical bonds. Radiation processing has been used commercially for almost forty years. Gamma radiation from 60Co, electron beams and x-rays, are all used to sterilize the medical devices used in operations and other healthcare treatments. Implants, artificial joints, syringes, blood-bags, gowns, bottle teats for premature baby units and dressings are all sterilized using radiation. The surgical gloves are sterilized using gamma radiation from 60Co. Other industries that benefit from radiation processing include the food, pharmaceutical, cosmetic, horticultural, and automotive industries. In the horticultural industry, growing-mats, fleeces and pots may be reused after irradiation-reducing waste and cost and saving the environment from unnecessary waste. Similarly, commercial egg trays may be recycled after irradiation without risk of

Gamma rays are formed with the self disintegration of Cobalt-60 (60Co) or Cesium-137 (137Cs) sources. Among thousands of gamma emitters only 137Cs and 60Co are indicated for radiation processing. The energy of gamma rays, as electromagnetic quantum waves, is similar to light, but with higher photon energy and shorter wavelength. The 60Co radionuclide can be produced in a nuclear power reactor by the irradiation of 59Co (metal), with fast neutrons. The radioactive isotope is formed by neutron capture as showed

 27Co59 + 0n1 → 27Co60 (1) The unstable nucleus of 60Co emits photons of 1.17 and 1.33 MeV, decaying with a half-life of 5.2714 years to stable 60Ni as shown the Figure 1 (Kaplan, 1955). The radioactive 60Co source is composed of small pellets of cobalt that are loaded into stainless steel or zirconium

Radiation is the unique source of energy which can initiate chemical reactions at any temperature, including ambient, under any pressure, in any phase (gas, liquid or solid),

radiation.

**2. Radiation processing** 

kW) beams of 8–10 MeV electrons.

proliferating salmonella.

equation 1 (Laughlin, 1989).

alloy sealed tubes (pencil arrays).

1 Ci (currie)=3.7 x 1010 Bq (becquerel)

without use of catalysts. Thus, radiation processing uses highly penetrating gamma radiation from sealed radiation sources travelling at almost the speed of light, to bombard and kill bacteria in products sealed inside their final packaging. In this way the irradiated product remains sterile until the packaging is removed. The energy carried by the gamma radiation is transferred to the product being irradiated by collisions between the radiation and the atoms of the product. In these collisions atoms lose their bound electrons in a process called ionization. It is this process that results in irreparable damage to the life sustaining chemistry of living organisms and the initiation of crosslinking chemistry or main chair scission in polymeric materials.

Fig. 1. Disintegration of 60Co
