Track Volume Research Articles

Detection of Neutron-Induced Heavy Charged Particle Tracks in RPL Glasses

Tracks of heavy charged particles (HCP, with Z,A(1) in solids are characterised by a strongly localised dose distribution around the path of the HCP. A method for the detection of these HCP-induced high-dose ‘spots’ in radiophotoluminescent (RPL) phosphate glasses is proposed. The relative HCP/gamma luminescence efficiency of a single HCP track is calculated within the scope of simple model, based on an analytical dose distribution formula and an adjusted gamma response function. The relative luminescence output from a single HCP track depends on the ratio of the ‘track volume’ to the glass volume illuminated by the excitation light. Thus experimental detection of HCP tracks requires a small ‘excitation volume’ which may be achieved by using a focused laser beam and flat RPL glasses. In neutron dosimetry heavy charged particles mainly arise as recoils from elastic scattering by fast neutrons. The application of the proposed method to fast neutron detection is discussed.

Track characteristics and detection in borate glasses doped with fissionable material

Fission fragment tracks were registered on the surface of alumino-borate glass using natural uranium foil as external radiator followed by chemical etching in hydrofluoric acid. In another glasses, of the same base composition to which uranium atoms (as internal radiators) were added, neutrons were applied directly on its surface and the tracks were detected. The track densities in both cases were found to be a function of neutron doses. However, in the former case, the relative volume of the track was found to increase with increasing etching time, while that of the second case seems to increase an the initial stages of etching and then hardly changes in a certain region, after which it increases again. The relative volume of the tracks in the second case is smaller when compared with that in the former case, however, application of gamma radiation seems to increase again the relative track volume. The results are discussed on the basis of structural changes that may occur during the interaction of neutron and gamma radiation with glass.

Nuclear tracks in iron garnet films

Epitaxial iron garnet films of composition ${\mathrm{Y}}_{3}$${\mathrm{Fe}}_{5}$${\mathrm{O}}_{12}$, ${\mathrm{Gd}}_{3}$${\mathrm{Fe}}_{5}$${\mathrm{O}}_{12}$, and ${(\mathrm{G}\mathrm{d},\mathrm{B}\mathrm{i})}_{3}$${(\mathrm{F}\mathrm{e},\mathrm{G}\mathrm{a})}_{5}$${\mathrm{O}}_{12}$, irradiated with xenon or uranium ions of energies 1.4 and 6 MeV per nucleon exhibit nuclear tracks of lengths between 10 and 30 \ensuremath{\mu}m. These tracks were studied by saturation magnetization measurements and conversion electron M\"ossbauer spectroscopy elucidating a strong crystallographic disorder and a paramagnetic behavior in the track volume. The track diameter depends on mass and energy of the ions used for irradiation and was found to range between 15 and 20 nm for the energies investigated.

Pinning of 180° Bloch walls at etched nuclear tracks in LPE-grown iron garnet films

For increasing the magnetic-wall coercivity Hwc in liquid-phase epitaxial (LPE) ferrimagnetic garnet films of composition (Gd,Bi)3(Fe,Al,Ga)5O12, magnetic-wall ’’traps’’ are formed via bombardment by xenon ions with 180-MeV/ion energy and doses between 106 and 108 cm−2. For efficient wall pinning, the width of the nuclear damage tracks associated with the ion trajectories in the film have been enlarged to about the wall width by using a selective (chemical) etchant that makes use of the drastically increased etching rate in the damaged track volume. Therefore, channels of cylindrical or prismatic cross section are created having a width of a few 102 to about 103 Å and a length of more than 10 μm at the given etching conditions. The pinning capability of such channels can be further enhanced in films that are grown under planar compressive or tensile misfit strain. Then, strain relaxation occurs in the vicinity of these channels which results in steep gradients of the magnetic-wall energy via magnetostriction. These strain halos extend sufficiently beyond the channels so that efficient wall pinning is observed, even if the channel cross section is small compared with the wall width. Thermomagnetic compensation-point writing in LPE garnet film, that were treated accordingly, yield a pattern of stable magnetic domains of down to 8 μm in diameter in 3-μm-thick layers. The effect of etched nuclear tracks on the magnetic-wall coercivity can be interpreted satisfactorily with present models on Hwc.

Directional effects in track-etch imaging

A detailed mathematical-physical model of the track-etch imaging process for a central converter imaging system is formulated. The model involves a neutron induced reaction density in the converter and a corresponding track volume density in the recorder. Optimum converter thicknesses are found for the 6L(n, α)T reaction suggesting the existence of a nuclear track conversion efficiency maximum.

Ionic Processes in γ-Irradiated Organic Solids: Positive-Hole Migration in 3-Methylpentane

The yields of positive and negative species trapped in γ-irradiated organic glasses at −196° have been measured as a function of glass composition. Increased yields of solvent-trapped electrons (e−) and biphenyl anions (φ2−), as well as decreased yields of various solute cations (A+), were noted when additives capable of undergoing charge-transfer or proton-transfer reactions were present in small amounts (<2 mole %) in 3-methylpentane (3MP). All results can be understood qualitatively in terms of the mobile positive hole being transferred from 3MP to these additives and trapped. A simple scheme of competition for the total available number of positive holes accounts for the decrease in A+ when a second solute (B) is added and relative cross sections to form A+ and B+ can be determined. Additives affect the optical absorption spectrum of (e−) in 3MP. The spectra of the biphenyl positive and negative ions are similar but displaced, while the anion and cation from benzene are anomalous in 3MP glass. The rates of decay of N,N,N′,N′-tetramethyl-phenylenediamine cation and of (e−) are compared following γ irradiation and photoionization of the amine in 3MP. Very efficient attachment of photoelectrons by φ2 indicates an average track volume >10−18 cc.