Neutron Damage Mechanisms in Silicon at 10°k
Neutron-irradiation effects on the photoconductivity and electrical properties of arsenic-doped silicon were measured at 10K so that the degradation mechanisms in infrared detectors fabricated from doped silicon could be examined. The measurements were performed at reduced optical background so that both thermal and optical generation were minimized as they are in the conditions under which the detectors are operated. The primary effects of the neutrons on the measured properties were (l) the introduction of acceptors (at a rate to 16 cm-1) which decreased the electron (majority-carrier) lifetime and thus the optical response, and (2) the production of bandtailing, which may be associated with cluster damage. The bandtailing diminished significantly, or even disappeared, with annealing up to 100K, but all the other effects remained essentially unchanged with annealing as high as 673K. The possibility of the bandtailing remaining after 100K annealing appeared to be related to the amount of damage present. It was hypothesized that a certain defect concentration and/or cluster size was required for the bandtailing to be observed.
Numerical analysis of transient photoconductivity in insulators
The nonlinear partial differential equations which describe transient photoconductivity in insulators are solved numerically. Trapping and recombination are included which allows photoconduction to be studied in the presence of large space charge. Use of methods for ‘‘stiff’’ differential equations insures stable time dependent solutions even for problems which have widely different time constants. The program is applied to a thin film (1000 A) of silicon dioxide to illustrate the salient features of the numerical solutions and the capabilities of the program.
CATARACT: A HISTORICAL PERSPECTIVE.
The earliest extant description of a surgical operation for the cure of cataract is that of Celsus, toho practiced medicine in Rome at the beginning of the Christian era. In his text De Meclicina he described in detail his method of couching, by which he inserted a bronze needle into the eye at the equator on the lateral side of ihe globe and depressed the cataract downward into the lower part of the vitreous where the surgeon hoped it would remain out of the way of vision. The same method had been employed by the Greeks and Hindus for at least several hundred years earlier and ivas to continue as the only operation available until the middle of the eighteenth century when Daviel of Paris described extraction of the lens through the cornea. The early couchers worked on the premise that the crystallin humor we know as the lens was the receptor for vision, and that in certain conditions of disease a suffusion flowed doivn in front of the crystallin humor where it solidified and formed a dense curtain. The purpose of couching was to press the hardened corrupt humor out of the way of the lens. That cataract was opaque material within the lens itself was not recognized until after the middle of ihe seventeenth century. Until then ihe surgeons were not even aware that it was the lens they were dislocating.