The Response Of An Hyperpure Germanium Detector To Ionizing Radiation

A basic understanding of the response of semiconductor detectors to ionizing radiation is important for their proper usage and their further development. Such devices may also be used to explore the energy deposition process in semiconductors.;The detailed response of an HPGe detector ({dollar}\sim{dollar}1 cm{dollar}\sp3{dollar} hyperpure Ge with an ion-implanted front contact) to ionizing radiation has been studied with regard to the radiation ionization energy ratio, {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar}, using radioactive {dollar}\alpha{dollar} and {dollar}\gamma{dollar} sources and accelerated ion beams ({dollar}\sp1{dollar}H, {dollar}\sp{lcub}3,4{rcub}{dollar}He, {dollar}\sp7{dollar}Li). The data span the energy range of a few hundred keV to a few MeV. Effects of temperature and bias voltage variation have been investigated. The response to charged particles and {dollar}\gamma{dollar}-rays have been measured simultaneously by using {dollar}\sp{lcub}152{rcub}{dollar}Eu, {dollar}\sp{lcub}60{rcub}{dollar}Co, and {dollar}\sp{lcub}137{rcub}{dollar}Cs {dollar}\gamma{dollar}-ray sources.;Analysis of the results reveals: (1) Contrary to earlier conclusions, a difference of {dollar}\sim{dollar}1% between {dollar}\varepsilon\sb0{dollar} and {dollar}\varepsilon\sb{lcub}\rm\alpha\ or\ p{rcub}{dollar} has been found in Ge, often showing {dollar}\varepsilon\sb{lcub}\rm\alpha,p{rcub}\u3c\varepsilon\sb0{dollar}--results that are qualitatively in accord with the observed behaviour for Si semiconductor detectors; these observations cannot be explained by trapping or recombination effects during the stopping of the ion in the sensitive volume. (2) The functional behaviour of {dollar}\varepsilon\sb\alpha{dollar}/{dollar}\varepsilon\sb0{dollar} and {dollar}\varepsilon\sb{lcub}\rm p{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} exhibits a non-linear response of the Ge detector as a function of ion energy for a given projectile, which is similar to results observed for Si detectors; the ratios approach unity as the particle energy increases--a result that is to be expected from fundamental considerations. (3) Where comparisons can be made with earlier works, the present results for {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} are in good quantitative agreement when similar assumptions are included, e.g. the apparent window thickness of the Ge detector is assumed to be independent of ion energy. (4) The energy loss in the window of the Ge detector is found to vary with the energy of the incident particle in a manner that does not agree with the stopping power curve. The apparent thickness of this window region is observed to decrease dramatically with increasing detector temperature ({dollar}\sim{dollar}30% decrease as T increases from 80K to 175K). This observation suggests that the surface layer of the Ge detector does not consist of a simple passive dead layer. The reasons for this behaviour are not presently understood. (5) Pronounced channeling effects are evident in the pulse height spectra as the incidence angle of the ions is rotated with respect to the detector surface normal. These features arise from ion channeling effects in the ion-implanted entrance window region. Monte Carlo calculations of the projectile energy loss under channeling conditions are in qualitative agreement with experimental observations. However, such channeling effects do not account for the deviations of {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} from unity

Development and formative evaluation of an instructional simulation of adiabatic processes

The purpose of this research was to develop a computer-based instructional simulation of adiabatic processes and to study the effects of selected characteristics of the simulation on students conceptual development, problem solving and transfer. To study these issues the related literature was reviewed, a simulation was developed and a two-pronged research study was employed. From the review of literature and constructivist theory, a simulation to facilitate active and situated learning was developed. It included the features of multiple representations, interaction, and authentic tasks;The subjects for the study were students enrolled in a beginning meteorology course at Iowa State University. An experimental study was conducted comparing achievement measures of two groups who used different versions of the simulation and a control group who did not use the simulation. In addition, selected students were interviewed to gain a deeper understanding of their use of the simulation. The performances of the groups were compared on scores from a posttest and weather forecasts. As expected, since the simulation was not integrated into classroom activities, there were no statistically significant differences between the groups;Interview data supported the design and future use of the simulation. Four of the five students saw the task as being authentic. The multiple representations were used by the students to construct knowledge across representations and to choose their own mode of representation for exploring the simulation. Of the five students interviewed, only one had used an effective problem solving strategy. This student also demonstrated a better understanding of how to transfer newly-gained knowledge to weather forecast exercises. Two other students were poised for improvement of their problem solving strategies, having the basic strategy but needing refinement, and the other two were in need of basic instruction and guiDance;;This study clearly revealed a serious weakness in student\u27s problem-solving skills as well as the value of the simulated environment for revealing those weaknesses. It is recommended the simulation be used in future studies which address the issues of integrating simulations into classroom activities so that optimal learning of the concepts and optimal development of problem-solving strategies will occur