**21. References**

Albuquerque, J.E. de, L.H.C. Mattoso, R.M. Faria, J.G. Masters and A.G. MacDiarmid. 2004. Study of the interconversion of polyaniline oxidation states by optical absorption spectroscopy. *Synthetic Metals* 146, (1): 1-10.

hydrochloric acid were about 100 to 150 nm for PVA/PANI nanocomposites (Cho *et al*., 2004) and 40 nm for PVP/PANI nanocomposites (Dispenza *et al*., 2006). This suggests that

Fig. 26. Shows SEM image of PANI nanoparticles polymerized by 50-kGy Co-60 -rays for

The formed pallets of pure PANI-HCl (Fig. 1) were characterized with Voltmeter and LCRmeter. It is conductivity was obviously higher than that of PVA\PANI-HCl, which is ascribed to the presence of PVA within the composites, the conductivity was 1 S/m and it is

The ionizing -radiation could be used successfully to obtain the polymerization of monomers such as aniline hydrochloride AniHCl and the induced properties for the new product could be controlled by adjusting the amount of monomers and the applied

Albuquerque, J.E. de, L.H.C. Mattoso, R.M. Faria, J.G. Masters and A.G. MacDiarmid. 2004.

Study of the interconversion of polyaniline oxidation states by optical absorption

UV-spectrum was peaked at 790 nm which is same as in PANI\PVA composites.

radiation dose with consideration to technical aspects.

spectroscopy. *Synthetic Metals* 146, (1): 1-10.

28.6 wt% monomer.

**20. Conclusion** 

**21. References** 

the type of binder determined the diameter of spherical nanoparticles.


**Part 4** 

**Radiation Biology** 


**Part 4** 

**Radiation Biology** 

146 Gamma Radiation

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**8** 

Madhu Bala

*India* 

*Brig. S K Mazumdar Marg, Delhi,* 

**Radiation Induced Radioresistance** 

**– Role of DNA Repair and Mitochondria** 

*Radiation Biology Department, Institute of Nuclear Medicine and Allied Sciences* 

The bio-positive effects of exposure to small doses of environmental stressors such as radiation, chemicals and mutagens have been reported since long. A number of studies and reviews (Bala & Mathew, 2000; Luckey, 2008; Pandey et al., 2006; Sasaki et al., 2002) document that exposure to small doses of ionizing radiation enhanced the tolerance towards the detrimental effects of lethal doses of ionizing radiation given subsequently. Such phenomenon was observed in prokaryotes as well as in eukaryotes. Some of the laboratory studies with human lymphocytes are summarized in Table 1. The information on beneficial effects of low dose irradiation also poured in from the epidemiological studies (reviewed by Bala & Mathew, 2000; Dasu & Denekamp, 2000; Luckey, 2008). The populations exposed to high background radiation showed long term beneficial effects such as increased life span, enhanced immune system, decreased cancer mortality and cancer risk (Calabrese et al., 2001; Cohen, 1999; Nambi & Soman, 1987, UNSCEAR, 2000). Among the A-bomb survivors from Hiroshima and Nagasaki, those, who received doses lower than 200 mSv, showed no increase in cancer deaths. Further, the population which received doses below 100 mSv, showed decrease in the mortality caused by leukemia in comparison to the age-matched

Often in epidemiological studies the exposure to low levels of radiation was for longer duration, while in laboratory studies the exposure to low level radiation was for a shorter duration (sometimes even a pulse exposure). Nonetheless, beneficial effects were observed in short as well as in prolonged exposures. This strongly suggested that the low dose radiobiological studies could have bearing in diverse and important applications such as radiation protection, risk assessment and radiotherapy. It was, therefore, considered important to initiate investigations for understanding more about the mechanisms of radioprotective effects caused by pre-exposure to low doses of radiation. It was reported that the resistance to lethal doses of ionizing radiation could be induced not only by low doses of radiation but also by variety of agents other than radiation, *viz.* heat, pH, nutrients, UV rays, though, the genes and the molecular pathways affected in these cases differed with the inducing agent. (Bala & Goel 2007; Boreham & Mitchel, 1991; 1994; Boreham et al.,2000). Further, it was believed that the induced resistance to lethal doses of radiation by short term pre-exposure to low doses of radiation was transient in nature and the radiation doses

**1. Introduction** 

control cohorts (UNSCEAR, 1994).
