**7.2 Positive charge accumulation in PI irradiated by a proton**

In this section, the space charge distribution in PI irradiated by a proton is explained [12]. **Figure 14** shows space charge distribution in PI irradiated by a proton with several irradiation energy. PA and PB shows the polyimide materials, and the differential between PA and PB is the fabrication company. The irradiation condition is 1.0–2.0 MeV for energy with 0.3–30 nA/cm2 under 1 × 10−5 Pa, and those irradiation times is 30 min. The space charge measurement was carried out with each 30 s for the irradiation and 10 min relaxation following from the above irradiation. The irradiation was carried out using 3 MeV tandem type ion accelerator facility of Takasaki Advanced Radiation Research Institute of National Institutes for Quantum and Radiological Science and Technology (QST), 3.75 MV Van de Graff of High Fluence Irradiation Facility at the University of Tokyo and the space environment examination facility at Japan Aerospace Exploration Agency (JAXA).

From **Figure 14**, those space chare distributions show the only maximum charge accumulation during irradiation with the 30 nA/cm2 current density. In the figure, the irradiation direction is described on the right side of the figure. From the figure, it is found that positive charges are accumulated in the bulks under all irradiation condition. The charge accumulated position is moved become from the bulk near the irradiation side to middle of the bulk with irradiation energy progress. The

**Figure 14.** *Positive charge accumulation in PI under proton irradiation.*

**Figure 15.** *Total positive charge amount in the bulk of PI under And after proton irradiation.*

ideal penetration depths calculated by the SRIM code are shown with broken line in the bulk on the figure. From these results, we found that the calculated penetration depth has a good correlation with charge accumulated position. Therefore, it is considered that the irradiated proton is the origin of those positive accumulated charges in the bulk.

**Figure 15** shows the time dependence of the amount of accumulated positive charges in those bulks irradiated by 2.0 MeV proton. Those are obtained by integration calculation of the charge distributions shown in **Figure 14**. From the figure, concerning accumulation behavior, the increases of the amounts of charges saturate within 3 minutes from the start of irradiation. The accumulated positive charges saturated for a brief time with the current density increasing. After the saturations, the amounts of charges decreased with irradiation time progress.

Furthermore, while we also observed that those accumulated positive charges remained after irradiation with low current density 0.3 nA/cm<sup>2</sup> , no charge was observed immediate after irradiation with high current density irradiation.

From the above charge accumulation penonena, we considered that the origin of those phenomena was produced due to the generation of radiation induced conductivity (RIC). Form the previous research, we could find that conducitibity κ of the PI irradiated a proton with an energy of 2 and 1.5 MeV is 103 and 102 higher than non-treated sample, respectively. It is though that the strength of activation is depended on the irradiation energy. Furthermore, the charge accumulation phenomena may be strongly affected by proton dose. The origin of the RIC is considered activation of material, sission of molecular chain, ionization, and vacancy [13]. Furthemore, after the irraidaion, we could confirm the condirctivity was 104 times larger than prisitn sample's. It is one of evidence about molecule chain modification such as mentioned above.
