Alpha Particle Absorption Research Articles

Calibration system for radon EEC measurements.

The measurement of radon equivalent equilibrium concentration (EECRn) is very simple and quick technique for the estimation of radon progeny level in dwellings or working places. The most typical methods of EECRn measurements are alpha radiometry or alpha spectrometry. In such technique, the influence of alpha particle absorption in filters and filter effectiveness should be taken into account. In the authors' work, it is demonstrated that more precise and less complicated calibration of EECRn-measuring equipment can be conducted by the use of the gamma spectrometer as a reference measuring device. It was demonstrated that for this calibration technique systematic error does not exceed 3 %. The random error of (214)Bi activity measurements is in the range 3-6 %. In general, both these errors can be decreased. The measurements of EECRn by gamma spectrometry and improved alpha radiometry are in good agreement, but the systematic shift between average values can be observed.

Near single-crystal electrical properties of polycrystalline HgI/sub 2/ produced by physical vapor deposition

Polycrystalline films of HgI/sub 2/ prepared by physical vapor deposition (PVD) were found to have electrical charge transport properties similar to those of single crystals. Transient charge transport (TCT) measurements were used to evaluate the electrical conduction properties of the samples. The mobility /spl mu/, trapping time /spl tau/, and surface recombination velocity s of electrons or holes were determined by analyses of transient voltages developed across the sample in response to a drift of the corresponding charge carriers created by alpha particle absorption near one of the electrodes. Typical electron and hole mobilities were /spl mu//sub n/=88 cm/sup 2//V/spl middot/s and /spl mu//sub p/=4.1 cm/sup 2//V/spl middot/s, respectively; trapping times were /spl tau//sub n/>16 /spl mu/s and /spl tau//sub p/<3.5 /spl mu/s, and surface recombination velocities s/sub n//spl cong/1.4/spl times/10/sup 5/ cm/s and s/sub p//spl cong/3.7/spl times/10/sup 3/ cm/s. All parameters depend to a large extent on the material deposition technology. The effect of carriers being first generated in near-surface traps and then gradually released is observed.

Re-evaluation of ITER ion cyclotron operating scenarios

Various ICRH scenarios for ITER-FEAT are evaluated. Awave propagation and damping study confirms the potential of thesecond harmonic tritium heating scenario for both heating and current drive purposes. The fundamental deuterium heating schemeis dominated by beryllium and alpha particle absorption. Owingto the reduced ITER size, the low frequency current drive windowis lost in practice. A 3He minority greatly enhances theperformance. In the early stage of the discharge, the powerabsorbed by the 3He is transferred to the background ions but,later on, the power of the fast particles (from both the 3Heand the tritium tails) is roughly equally distributed betweenelectrons and ions. Using the experimentally establishedexpression for the L to H mode threshold, it is found that the Hmode regime can always be reached using RF heating. To achieveQ = 10, high density operation is required. Minority currentdrive competes with heating and with electron current drive. Thescenarios foreseen for the non-activated ITER-FEAT phase arealso discussed.

New method to measure the Schottky barrier potential

A relatively simple technique to measure the Schottky barrier potential is described. The method is based on the alpha particle absorption impinging on a silicon surface barrier detector (SSBD). The measured potentials are compared with those given by commercially available detectors. The experimental values and its relative error for the barrier height measurement obtained are as accurate as those obtained by more complex methods.

Effect of Energetic Particle Absorption on Fast-Wave Current Drive

Fast-wave current drive presents a promising scheme for steady-state operation of reactor tokamaks. This scheme is being studied for application in the International Thermonuclear Experimental Reactor (ITER), the Joint European Torus (JET), and the Doublet III-D reactor (DIII-D). There are two regimes that appear to be promising, the low-frequency range 0 {lt} {omega} {lt} 2{Omega}{sub D} and the lower hybrid frequency range {Omega}{sub D} {much lt} {omega} {lt} {omega}{sub LH}. In the latter scheme, the wavelength of the fast wave becomes much shorter than the alpha particle gyroradius and alpha-particle absorption can become significant. An analytic formula for alpha-particle absorption of fast waves for the standard slowing down distribution has been derived and compared with electron absorption at ITER parameters. It has been found that at t{sub D} {gt} 30 keV and n{sub e} {approximately} 10{sup 14} cm{sup {minus}3}, the alpha-particle absorption is large and can greatly decrease the current drive efficiency. However, without sacrificing the fusion reactivity rate, by increasing the density and decreasing the temperature 15 keV {lt} T{sub D} {lt} 25 keV, the alpha-particle absorption can become small at a sufficiently high frequency. In this paper is suggested that a simulation of the alpha-particle absorption effect onmore » fast-wave current drive can be made in DIII-D by using a lower frequency source ({approximately}30 MHz) to create a minority tail and a high-frequency source (200 MHz) to drive the current. Results of minority absorption are presented. Effects that can improve current drive efficiency are discussed.« less

Correlation measurements of ionizing radiation induced phonons in silicon using superconducting tunneling junctions

Nonthermal phonons produced by X-ray and alpha particle absorption in silicon were detected with superconducting Sn/SnO x/Sn tunneling junctions. The correlation of signals induced by phonons from the substrate in two closely spaced junctions shows structures indicative of an anisotropic propagation of the non-thermal phonons. Taking into account the geometrical collection efficiency of the small-area junctions, more than 60% of the energy deposited in the crystal is converted into excess quasiparticles.

Anomalously fast charge collection in partially depleted p +n −n + silicon detectors for alpha-particle absorption through the high-low junction

A new mechanism of excess charge transport from quasi-neutral silicon is proposed to account for the fast collection of charges generated in the field-free region of partially depleted p +n −n + detectors. The new mechanism is based on the action of the n − junction and satisfactorily explains the small ballistic deficits observed from field-free layers of ca 100 μm across. The literature on field-free transport is critically reviewed. Field funnelling into the main space-charge layer of alpha-generated charge is probably important in quasi-neutral layers less than 50μm across.

A new method for assessing counting efficiency with LR115 Kodak track detectors

Abstract The alpha track detection efficiency of the solid state track detector LR115 Kodak applied to alpha dosimetry depends strongly on the residual thickness of the cellulose nitrate film after etching. In this paper, we present a new method for assessing this efficiency. It is based on the measurement of the absorption of alpha particles by the etched and stripped detector. This method can be used for any kind of thin plastic film. It is particularly well adapted for alphacounting in the field of thermoluminescent (TL) dating, because the same TL apparatus can be directly used with only simple accessories.

Determination of Dew-Point by the Use of a Radioactive α Source

A new device was made to determine the dew-point from the varintion in ionization current due to the absorption of alpha particles by the dews. The construction of the hygrometer is shown.

Elastic and Inelastic Scattering of 18-Mev Alpha Particles from Neon, Argon, and Xenon

The scattering of 18-Mev alpha particles from neon, argon, and xenon was studied with a multiplate reaction chamber. The scattered particles were defined within an rms angular width of 0.45\ifmmode^\circ\else\textdegree\fi{} by a system of slit pairs, spaced every 2\textonehalf{}\ifmmode^\circ\else\textdegree\fi{} from 10\ifmmode^\circ\else\textdegree\fi{} to 170\ifmmode^\circ\else\textdegree\fi{}. The elastic scattering from neon and argon show the pronounced maxima and minima characteristic of diffraction scattering but are equidistant in $\ensuremath{\varphi}$, not $sin(\frac{\ensuremath{\varphi}}{2})$. The ratio to Rutherford scattering varies as much as 25-fold between successive maxima and minima in the case of neon, the well-defined structure indicating a small mean free path for absorption of alpha particles in the nucleus. Nuclear interaction radii calculated by the formula $2kR\ensuremath{\Delta}[sin(\frac{\ensuremath{\varphi}}{2})]=\ensuremath{\pi}$ were found to be 6.36\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for neon and 6.95\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for argon. Xenon, investigated chiefly for control purposes, showed no definite deviation from Rutherford scattering up to 50\ifmmode^\circ\else\textdegree\fi{}. Groups corresponding to the excitation of the 1.63-, 4.25-, 4.97-, 5.81(5.63)-, and 7.2-Mev levels of ${\mathrm{Ne}}^{20}$ and the 1.46-Mev level of ${\mathrm{A}}^{40}$ were observed. No excited states were observed in xenon. Notably absent was excitation of the 6.74-Mev ${(0}^{+}$) level in ${\mathrm{Ne}}^{20}$. As predicted by direct-interaction theories, the cross sections for inelastic scattering leading to the first excited ${(2}^{+}$) states of neon and argon could be approximated by the squares of spherical Bessel functions of the second order with interaction radii of 6.71\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for neon and 6.60\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for argon. These cross sections do not tend toward small values in the forward direction, which is interpreted as evidence for distortion of the incident and scattered waves. No fit was possible for any of the other excited states.