**4. Induced radiation effects on GFSA characteristics**

In order to test the performance of GFSA under the influence of n + γ radiation, the following variables were determined in a n + γ field: (1) the random variable "pulse breakdown voltage," (2) the random variable "DC breakdown voltage," and (3) the volt-second characteristic. The n + γ source was californium isotope 252Cf. This source was selected due to its neutron spectrum resemblance of a nuclear blast's neutron spectrum [20]. Since the nuclear cross section for capturing a neutron is large enough only for thermal and slow neutron capture and due to the structure of californium source fission spectrum, a relatively small part of neutrons takes part in the neutron activation of GFSA materials. GFSA was subjected to two neutron fluencies: 5.41 × 109 and 16.24 × 1011 n/cm2 . Along with the neutron component, emitted radiation also has a γ component. The latter influences the electric characteristics of GFSA only for the duration of the exposure to the radiation field. Also, the inelastic interaction cross section of the neutron component is larger than the corresponding γ component cross section [21]. This allows the observation of the effects of radiation resulting from the neutron fluency only. In the experiment, the type and pressure of gas varied in order to get a detailed insight into how the radiation influences the GFSA characteristics.

By measuring 1000 values, the influence on the "DC breakdown voltage" and "pulse breakdown voltage" random variables was tested. During the measurement series, discharge energy (current) was maintained constant. Results of the breakdown voltage obtained in the measurement series were divided into 10 groups of 50 successive values. Statistical tests were performed on each group of results by graphical visualization and chi-squared and Kolmogorov-Smirnov tests. Within each group of measurements, the measured values of breakdown voltage were tested with respect to the type of theoretical distributions (normal, exponential, double exponential, and Weibull's). U test was used to determine the groups of measurement series having the same random variable (with significance level α = 5%) [17, 22]. The area law was used to explore the effects on the pulse shape (volt-second) characteristic.

The experiments show that the standard deviation of the static breakdown voltage significantly decreased after the irradiation of the GFSA. The pulse voltage tests show that an irradiated GFSA reacts more readily and has somewhat narrower volt-second characteristic than unirradiated GFSA. Effectively, irradiation has improved GFSA's protective traits. GFSA DC breakdown voltage versus neutron fluency is presented in **Figure 2**. The GFSA volt-second characteristics before and after exposure to the radioactive source, respectively, is presented in **Figure 3A** and **B**.

**Figure 2.** *The GFSA DC breakdown voltage versus neutron fluency characteristic [7].*

**Figure 3.**

*The GFSA volt-second characteristic before (A) and after (B) radiation [7].*

Elevated concentration of free electrons in the inter-electrode gap, resulting from the ionization of the insulating gas, has enabled a faster response of an irradiated GFSA. This ionization was induced by radiation of the GFSA material as a consequence of neutron activation.

GFSA activation analysis diagrams before and immediately after the exposure to the radioactive source, respectively, are presented in **Figure 4A** and **B**. The radioactive isotopes are identified and recorded close to the expected energy peaks. The activity of these isotopes consists of both γ and β component. This induced radioactivity ionizes the gas, leading to the reduction the stochastic dissipation of a pulse breakdown voltage random variable. The improvement to the pulse shape characteristic due to neutron radiation is short lasting, disappearing quickly as the half-lives of induced activities vary from several hours to mere minutes. A diagram of the activation

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demonstrate:

*Influence of Gamma Radiation on Gas-Filled Surge Arresters*

analysis of irradiated GFSA that is taken 6 hours after radiation clearly confirms this effect (**Figure 4B**). In that time frame, most of the active isotopes have degraded to trivial activities, and the GFSA characteristics have returned to unirradiated state.

*Diagram of the GFSA activation analysis immediately (A) and 6 hours (B) after irradiation [7].*

An external γ ray source was used to test commercially available GFSA components to analyze the effect of γ radiation. The examination was carried out on the following commercial components (1) SIEMENS (type A) gas surge arresters (nominal voltage 230 V), (2) CITEL BB (type B) bipolar ceramic gas surge arresters (DC spark overvoltage 230 V). Тhе outer dimensions and shape of all components of the same type were the same. The effects of γ radiation on following GFSA

The scheme of the test cycle for investigating the radioactive resistance of GFSA

Examination of GFSA radioactive resistance was carried out in a gamma radiation field of 60Co at the Institute of Nuclear Sciences "Vinča." The average energy of the applied gamma quantum was 1.25 MeV. The dose rate in air was 87.5, 875, and 1750 cGy/h, respectively. The distance between the radioactive source and the examined overvoltage components was 272, 86, and 60 cm, respectively. All tests

Test specimens, consisting of 50 commercial components of a single manufacturer, having identical characteristics, have been used in the experiment. During the formation of experimental groups consisting of 50 components each, the nominal characteristics of the tested components have been measured. When the measured values for a particular component exhibited significant discrepancy with respect to the declared values, they were excluded from further testing in accor-

The GFSA prebreakdown current as a function of applied voltage without radiation and with γ radiation is shown in **Figure 6A** and **B**, respectively. The diagrams

**5. Radiation resistance of commercial GFSA components**

1.Prebreakdown current as function of applied voltage

2.Resistance as function of applied voltage

by a DC voltage is depicted in **Figure 5**.

were performed at room temperature, 20°C.

dance to the Sovene's criterion [2, 8].

characteristics were examined:

**Figure 4.**

*DOI: http://dx.doi.org/10.5772/intechopen.83371*

**Figure 4.**

*Use of Gamma Radiation Techniques in Peaceful Applications*

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**Figure 3.**

**Figure 2.**

*The GFSA volt-second characteristic before (A) and after (B) radiation [7].*

*The GFSA DC breakdown voltage versus neutron fluency characteristic [7].*

consequence of neutron activation.

Elevated concentration of free electrons in the inter-electrode gap, resulting from the ionization of the insulating gas, has enabled a faster response of an irradiated GFSA. This ionization was induced by radiation of the GFSA material as a

GFSA activation analysis diagrams before and immediately after the exposure to the radioactive source, respectively, are presented in **Figure 4A** and **B**. The radioactive isotopes are identified and recorded close to the expected energy peaks. The activity of these isotopes consists of both γ and β component. This induced radioactivity ionizes the gas, leading to the reduction the stochastic dissipation of a pulse breakdown voltage random variable. The improvement to the pulse shape characteristic due to neutron radiation is short lasting, disappearing quickly as the half-lives of induced activities vary from several hours to mere minutes. A diagram of the activation

*Diagram of the GFSA activation analysis immediately (A) and 6 hours (B) after irradiation [7].*

analysis of irradiated GFSA that is taken 6 hours after radiation clearly confirms this effect (**Figure 4B**). In that time frame, most of the active isotopes have degraded to trivial activities, and the GFSA characteristics have returned to unirradiated state.
