Cobalt-60 gamma irradiation

As for the relative suitability of an electron beam (EB) facility vis-a-vis a cobalt-60 gamma facility, a key point is that although the ultimate chemistry is nearly identical in both cases, there is a notable difference in the penetration of the radiations. Another point is that the large capacity and consequent cost of EB machines require a relatively large production rate to justify their use. On the other hand, the EB machine, not being a radioactive source, is completely safe when switched off. Overall, since the sixties, sterilization by irradiation has steadily increased. However, most of this is by cobalt-60 gamma irradiation, the EB machines accounting for about a fifth or sixth of the total number of facilities. 

IV. INDUSTRIAL-SCALE COBALT-60 GAMMA IRRADIATION STERILIZATION... 

There are broadly two types of product handling conveyors used in cobalt-60 gamma irradiators, conveyor bed designs and carrier designs. 

Oosimetry Dose delivery in industrial-scale cobalt-60 gamma irradiators is achieved through controlling the time of exposure of the product to the source. The initial relationship between source strength, product bulk density, time of exposure, and absorbed dose has to be determined empirically by dosimetry. 

Tn an earlier paper (13) p-nitrosodimethylaniline (RNO) was postu-lated to be an efficient scavenger of the OH radical at pH 9 in cobalt-60 gamma irradiated, air saturated, aqueous solutions. It was also postulated to be specific for the OH radical in these solutions since evidence was presented that neither HOL> nor 02 destroyed the chromophoric group at 440 n.m., the absorption maximum of RNO in the visible region of the spectrum for neutral and basic solutions. Relative rate constants for the reaction of OH with RNO and other molecules were reported to be in good relative agreement with those reported by others who used both the pulse radiolysis method and indirect competition techniques. 

Figure 2. Effect of 02 and RNO concentration on G(—RNO) yields calculated from spectroscopic changes at 350 n.m. in cobalt-60 gamma irradiated aqueous pH 2 (HCIO h) solutions of RNO , oxygen saturated solutions O, air saturated , Ar saturated...

Studies at pH 2. Cobalt-60 gamma irradiations were carried out at pH 2 to investigate the unusual effects reported previously (13) on the residual yields of RNO destruction upon the addition of ethyl alcohol and to establish the sensitivity of G( — RNO)350 to oxygen and RNO concentration so as to compare these results with those at pH 9. 

IAEA TECDOC-539 (1990) Guidelines for industrial radiation sterilization of disposable medical products (Cobalt-60 gamma irradiation). International Atomic Energy Agency, Vienna IAEA (1975) Radiation sterilization of medical products. 

Cobalt-60 gamma irradiation was performed at Studer AG Werk Hard in Daniken, Switzerland (Lot A). X-ray irradiations were performed at the laboratory of Professor Louis Rey in Lausanne, Switzerland (Lot A) and IBA, Edgewood, New York, U.S.A. (Lot B and Lot C). 

The effects of three different cobalt 60 gamma irradiation doses between 267 and 641 rad L on cryogenic (77°K) mechanical and thermal properties were measured. 

Samples of the polymers were evacuated with heating and sealed in high-purity quartz tubes. Cobalt-60 gamma-irradiation was carried out in liquid nitrogen (77 K) and at ambient temperature (300 K) at a dose rate of 1 kGy/h. 

Four cobalt polymers have been synthesized, three of which are very sensitive to gamma irradiation with resulting Gg values which exceed the analogous organic polymers. Furthermore, the cobalt is not released during the scission reactions. Films which adhere well enough for commercial use have not yet been obtained for the cobalt systems. Extension to chromium is in progress. 

TA-V installations that could potentially affect or be affected by the HCF include the Annular Core Research Reactor (ACRR), Gamma Irradiation Facility (GIF), Auxiliary Hot Cell Facility (AHCF), Radiation Metrology Laboratory (RML), and the Sandia Pulse Reactor III (SPR III). The GIF provides two cobalt cells for total dose irradiation environments. A new GIF is under construction in the northeast quadrant of TA-V. SPR III provides intense neutron bursts for effects testing of materials and electronics. The RML provides radiation measurement services to Sandia s reactors, isotopic sources, and accelerator facilities. The AHCF provides a capability to handle limited quantities of radioactive material in a shielded cell. These facilities have separate SARs that describe potential accidents. The most severe accidents for all of these facilities involve the release of radiological materials which could necessitate a site evacuation. No physical damage to the HCF could be induced by any of the postulated accidents, nor could any of the HCF accidents physically affect any of the other facilities. 

The R D department went to work and came up with a prototype gamma-irradiation machine. It was about the size of a jukebox and, like most cobalt-60 equipment, consisted primarily of lead shielding. A door through the shielding opened into a cylindrical chamber roughly six inches in diameter by eight inches high. When the door closed, the chamber descended to the level of a cobalt-60 source. A timer could be set to withdraw the material after it received the requisite exposure. 

Irradiation plants for sterilization continued to sell steadily in the late 1980s. In 1987-88, Nordion was completing installations in Japan and South Korea and made new sales in England, Pakistan, the United States, and West Germany. There were now some one hundred and forty-seven industrial gamma-irradiation plants in forty-three countries. More than half of them had been built by Nordion, but even those made by other companies required new and replacement sources. In 1989, Nordion shipped a record thirty-three million curies of cobalt-60. The investment it had made a few years earlier in an increased supply of cobalt-60 firom Hydro reactors was paying off handsomely. 

Also, since the practice of sterilization of biomedical devices by ethylene oxide is diminishing due to concerns for the environment, along with health and safety factors, it may also be necessaiy for future biomedical devices to be irradiation sterilizable (i.e., Cobalt/gamma, E-beam). From work at Ethicon on polymers with aromatic substituents in the backbone (4a, b), it is believed that aromatic groups lead to an enhancement in the radiation stability of a polymer. 

Even though no loss in physical properties was observed for aromatic poly(anhydride)s subjected to gamma irradiation, it is important to establish the polymers physical characteristics as a function of exposure time in-vitro. This is a necessary requirement, since past work has shown that absorbable polymers, and devices formed from them (PDS, Vicryl ), subjected to cobalt may indicate little change in physical properties, but when tested in-vitro rapidly lose strength. However, no difference is observed in in-vitro properties between coupons subjected to cobalt versus unirradiated coupons. In fact, yield strength as a function of weeks in-vitro appears to follow a linear decrease profile for annealed test coupons. However, unnanealed test coupons display an induction period (6 weeks) prior to the linear decrease in physical strength. 

The current system consists of cobalt chrome components with a titanium porous coating on the ulnar component and the distal half of the stem (Figure 10.17). The UHMWPE is direct compression molded and sterilized by gamma irradiation in argon. It may be used either cemented or uncemented. While the Kudo system has had high survival rates at some institutions, the rate of reported loosening of the humeral and ulnar components has been varied [18, 43, 46-53]. The Kudo Elbow System has been used extensively in Europe and Japan, but it is not currently marketed in the United States. 

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