V. K. Mittal

Hydrogen loss under heavy ion irradiation in polymers

Abstract The hydrogen loss behavior in polymers under heavy ion irradiation is investigated for different electronic excitation energies. It is found that hydrogen loss under ion irradiation depends on the electronic energy deposition, and the type of bonds present in it. It is noticed that the hydrogen loss curve can be fitted with an equation contatining two exponential terms. The diminishing of hydrogen loss at higher fluences is discussed on the basis of overlapping of ion tracks.

Slowing down of MeV heavy ions with Z=6–29 in PEN (C7H5O2)

The stopping power for heavy ions with Z ¼ 6–29 in PEN (C7H5O2)foil has been measured in reflection geometry using the elastic recoil detection technique in the energy range � 0.2–3.0 MeV/u. These measurements have been carried out utilizing the 140 MeV Ag 13þ primary beam from the Pelletron accelerator facility at Nuclear Science Centre (NSC), New Delhi, India. All these stopping power measurements are new. The calculated stopping power values based on Lindhard, Scharff and Schiott (LSS)theory, Northcliffe and Schilling, Ziegler et al. (SRIM-2000.38 code)and extended Hubert et al. formulations have been compared with the experimental values. LSS theory agrees with the experimental data in the ion velocity range � 0:7v0Z 2=3

Stopping power of Mylar for heavy ions up to copper

Abstract The stopping powers of Mylar for several heavy ions covering Z =11 to 29 in the energy range ∼0.3 to 2.3 MeV/n have been measured using the elastic recoil detection technique and twin detector system. The technique provided a unique method to generate a variety of variable energy ion species utilizing a fixed energy 140 MeV Ag 13+ primary beam from the Pelletron accelerator facility at Nuclear Science Center, New Delhi, India. Most of these measurements are new. The experimentally measured stopping power values have been compared with those calculated using LSS theory, Ziegler et al. formulation and Northcliffe and Schilling tabulations. Merits and demerits of these formulations are highlighted. Stopping power calculations using the Hubert et al. formulation have been extended successfully beyond its recommended range of validity, i.e. 2.5–500 MeV/n down to energies as low as 0.5 MeV/n.

Modification of optical properties of polycarbonate by gamma irradiation

A detailed analysis of absorption, transmission, and reflection spectra of virgin and gamma-irradiated (50–800 kGy) polycarbonate polymer reveals that both indirect as well as direct band gap coexist in virgin and gamma-irradiated samples. The indirect band gap has been found to decrease from 3.00 eV (virgin sample) to 2.78 eV at a dose of 800 kGy. The emission behaviour of gamma-irradiated polycarbonate indicates a clear-cut emission peak in the visible region at –466 nm in the samples with a gamma dose of 400 kGy and above. The refractive index has a decreasing tendency as a result of the increasing gamma dose.

dE/dx measurements for heavy ions with Z = 6-29 in polycarbonate

Abstract d E /d x measurements for heavy ions with Z =6–29 in the polycarbonate (C 16 H 14 O 3 ) absorber in the energy range ∼0.3–3.0 MeV/u have been carried out utilizing the Pelletron accelerator facility at Nuclear Science Centre, New Delhi, India. The experimentally measured stopping power values have been compared with those calculated using Lindhard, Scharff and Schiott theory, Northcliffe and Schilling, Ziegler et al. (with and without bonding corrections) and extended Hubert et al. formulations. Merits and demerits of these formulations are highlighted.

γ-Ray modifications of optical/chemical properties of a PVC polymer

Polyvinyl chloride (PVC) films are subjected to high doses of γ -radiation up to 800 kGy. The modifications in the optical properties, the structural and chemical changes are investigated by recording the ultraviolet–visible (UV–VIS) and the Fourier transform infrared (FTIR) spectra of unirradiated and irradiated PVC films. The UV–VIS data show an increase in absorbance and shift of the absorption edge towards the visible region from the UV region with the increase in the γ -radiation dose. This may be attributed to the formation of conjugated system of bonds. The direct and the indirect optical energy band gaps are determined as a function of the γ -exposure dose. The results show that both the direct and the indirect energies of transitions decrease with the increasing γ -absorbed dose. Also the direct energy band gap has higher values when compared with the corresponding values of the indirect energy band gap. The intensity of the different infrared bands in the FTIR spectra of irradiated PVC indicates the presence of the hydroxyl group, release of volatile gases and polyene formation. A total destruction of the structure is observed at a very high γ -radiation dose.

Dependence of hydrogen released on the charge state of incident ions

The behavior of polymers under heavy ion bombardment is of great interest. In the present study, hydrogen released from polypropylene (PP) and polyethylene terephthalate (PET) was investigated as a function of charge state (11+, 14+, and 25+) for 130 MeV 107Ag ions. It was found that hydrogen released from the polymers varies as α q n , where n was found to be 2.98 and 1.94 for PP and PET, respectively, when compared with the value of ∼3.0 reported in the literature for different polymers and ion combinations. Radii of the damaged zones or ion track formed were deduced from the slope of the hydrogen released versus ion fluence curves. This radius was also found to depend upon the charge state of the incident ion. It varies as β q m , where m is 1.25 and 0.741 for PP and PET, respectively.

Study of secondary electron emission from various targets due to 100 MeV Si7+ beam

Abstract The total secondary electron yields Y were measured for 100 MeV Si 7+ ions on Be, Al, Si, Ni, Ag and Au as a function of the incident angle of projectile ranging from 0 ° to 65 °. In order to compare the angular dependence of the electron yield for Si 7+ ions using different targets, the experimental curves were fitted by the empirical relation of the form Y ( θ ) = Y (0)( cosθ ) − f , where θ is the angle of incidence, Y(0) is the yield at normal Incidence ( θ = 0 °) and f is a fitting parameter. The value of f varied from 0.69 to 1.52. The Z dependence of Y(0) for various targets ( Z = 4 to 79) were also observed.