A knock-on deuteron imager for measurements of fuel and hotspot asymmetry in direct-drive inertial confinement fusion implosions (invited)

A knock-on deuteron imager (KoDI) has been implemented to measure the fuel and hotspot asymmetry of cryogenic inertial confinement fusion implosions on OMEGA. Energetic neutrons produced by D-T fusion elastically scatter ("knock on") deuterons from the fuel layer with a probability that depends on ρR. Deuterons above 10 MeV are produced by near-forward scattering, and imaging them is equivalent to time-integrated neutron imaging of the hotspot. Deuterons below 6 MeV are produced by a combination of side scattering and ranging in the fuel, and encode information about the spatial distribution of the dense fuel. The KoDI instrument consists of a multi-penumbral aperture positioned 10-20 cm from the implosion using a ten-inch manipulator and a detector pack at 350 cm from the implosion to record penumbral images with magnification of up to 35×. Range filters and the intrinsic properties of CR-39 are used to distinguish different charged-particle images by energy along the same line of sight. Image plates fielded behind the CR-39 record a 10 keV x-ray image using the same aperture. A maximum-likelihood reconstruction algorithm has been implemented to infer the source from the projected penumbral images. The effects of scattering and aperture charging on the instrument point-spread function are assessed. Synthetic data are used to validate the reconstruction algorithm and assess an appropriate termination criterion. Significant aperture charging has been observed in the initial experimental dataset, and increases with aperture distance from the implosion, consistent with a simple model of charging by laser-driven EMP.

Characteristics of eighth-grade students who initiate self-care in elementary and junior high school

The purpose of this paper is to examine whether children who care for themselves for longer periods of time are at increased risk of poor grades, truancy, anger, family conflict, stress, risk-taking, and peer influences (in addition to the increased risk of substance use previously reported). Demographic characteristics of eighth-grade students who initiate self-care in junior high school are compared with those initiating self-care in elementary school. Further, increased risks for those initiating self-care in elementary school are examined. Over two thirds of the respondents (67.8%) cared for themselves after school without adult supervision at some time during the week; 23.5% for 1 to 4 hours per week, 15.7% for 5 to 10 hours per week, and 28.6% for 11 or more hours per week. Of those in self-care, 48.5% initiated self-care during elementary school and 51.5% during junior high school. Students who were in the highest category of self-care (greater than or equal to 11 hours per week) vs those in self-care zero hours per week were 1.5 to 2 times as likely to score high on risk-taking, anger, family conflict, and stress, to be more likely to see their friends as their major source of influence, and to attend more parties. The self-reports of academic grades did not differ. The grade of initiation of self-care (elementary vs junior high school) conferred additional risk for drinking alcohol (odds ratio = 1.4), risk-taking tendencies (odds ratio = 1.5), and attending parties (odds ratio = 1.6).

Substance use among eighth-grade students who take care of themselves after school

This investigation focused on substance use among children who regularly care for themselves after school (latchkey children). The data, collected from 4932 eighth-grade students, indicated that self-care is an important risk factor for alcohol, tobacco, and marijuana use. Data collected from 2185 parents validated these findings. Eighth-grade students, who took care of themselves for 11 or more hours a week, were at twice the risk of substance use as those who did not take care of themselves at all. This relationship held at all levels of sociodemographic status, extracurricular activities, sources of social influence, and stress. Of the 186 stratified tests of the relationship, 90% were significant; even those not found to be significant were in the direction expected. Path analyses suggest that risk-taking, having friends who smoke, and being offered cigarettes may partially explain the relationship between self-care and substance use. Those eighth-grade students who select friends who smoke and place themselves in situations in which they are offered cigarettes may be manifesting a desire to display their sense of maturity and independence. The fact that the increase in substance use occurred among almost all strata tested and the fact that mediation was not complete suggest that more than one mechanism may account for the associated increase in substance use. It is also possible that more time in self-care results in more unnoticed solitary trials of substances, as well as trials motivated by peer offers or peer pressure to use substances.