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.
Low-Level Radiation Effects in Extrinsic Infrared Detectors
Experimental data are presented on the effect of gamma irradiation at low dose levels of 10 Rads or less on the responsivity of arsenic-doped extrinsic IR detectors under operating conditions at 4.3 to 12°K. The observed large changes in responsivity under irradiation, and the subsequent transient behavior during a period of less than 1 minute immediately after the radiation is turned off, are strongly dependent on temperature, bias voltage, and IR flux level. The net effect following irradiation is always a responsivity increase; however, under some conditions, the increase can be preceded by a decrease. The responsivity change relaxes slowly, requiring more than one day for complete recovery of the detector to its pre-irradiation condition. The effects anneal rapidly at temperatures over 20°K. The observed phenomena can be explained by radiation-induced changes in the charge state of the levels associated with the majority IR-active dopant and the compensating impurities. The complex dependence of the responsivity changes on the operating conditions is explained in terms of competing processes involved in capture, recombination, and sweepout of radiation-generated electrons and holes. The physical mechanisms and a qualitative model offering a possible explanation of the effect of temperature, bias, and IR flux level are discussed.
The Liverpool Cholera Epidemic of 1832 and Anatomical Dissection--Medical Mistrust and Civil Unrest
Asiatic cholera reached Britain for the first time in late 1831, with the main epidemic occurring during 1832. The disease caused profuse diarrhea, severe dehydration, collapse, and often death. There was widespread public fear, and the political and medical response to this new disease was variable and inadequate. In the summer of 1832, a series of "cholera riots" occurred in various towns and cities throughout Britain, frequently directed against the authorities, doctors, or both. The city of Liverpool, in the northwest of England, experienced more riots than elsewhere. Between 29 May and 10 June 1832, eight major street riots occurred, with several other minor disturbances. The object of the crowd's anger was the local medical fraternity. The public perception was that cholera victims were being removed to the hospital to be killed by doctors in order to use them for anatomical dissection. "Bring out the Burkers" was one cry of the Liverpool mobs, referring to the Burke and Hare scandal four years earlier, when two men had murdered people in Edinburgh in order to sell their bodies for dissection to the local anatomy school. This issue was of special concern to the Liverpool citizenry because in 1826, thirty-three bodies had been discovered on the Liverpool docks, about to be shipped to Scotland for dissection. Two years later a local surgeon, William Gill, was tried and found guilty of running an extensive local grave-robbing system to supply corpses for his dissection rooms. The widespread cholera rioting in Liverpool was thus as much related to local anatomical issues as it was to the national epidemic. The riots ended relatively abruptly, largely in response to an appeal by the Roman Catholic clergy read from church pulpits, and also published in the local press. In addition, a respected local doctor, James Collins, published a passionate appeal for calm. The Liverpool Cholera Riots of 1832 demonstrate the complex social responses to epidemic disease, as well as the fragile interface between the public and the medical profession.