RESUMEN
Tissue-equivalent proportional counters (TEPCs) have been used to measure energy deposition in simulated volumes of tissue ranging in diameter from 0.1 to 10 microm. There has been some concern that the wall used to define the volume of interest could influence energy deposition within the sensitive volume because it has a density significantly greater than that of the cavity gas. These effects become important for high-velocity heavy ions. Measurements of energy deposition were made for 1 GeV/nucleon iron particles in a TEPC simulating a 1-microm-diameter sphere of tissue. The TEPC was nested within a particle spectrometer that provided identification and flight path of individual particles. Energy deposition was studied as a function of pathlength through the TEPC. Approximately 30% of the energy transfer along trajectories through the center of the detector escapes the sensitive volume. The response of the TEPC, for trajectories through the detector, is always larger than calculations for energy loss in a homogeneous medium. This enhancement is greatest for trajectories near the cavity/wall interface. An integration of the response indicates that charged-particle equilibrium is essentially achieved for a wall thickness of 2.54 mm. However, estimates of the linear energy transfer for the incident particles are influenced by these wall effects.
Asunto(s)
Radiometría/instrumentación , Gases , Radioisótopos de Hierro , Transferencia Lineal de Energía , Radioquímica , Silicio , SincrotronesRESUMEN
This paper surveys some recent accelerator-based measurements of the nuclear fragmentation of high energy nuclei in shielding and tissue-equivalent materials. These data are needed to make accurate predictions of the radiation field produced at depth in spacecraft and planetary habitat shielding materials and in the human body by heavy charged particles in the galactic cosmic radiation. Projectile-target combinations include 1 GeV/nucleon 56Fe incident on aluminum and graphite and 600 MeV/nucleon 56Fe and 290 MeV/nucleon 12C on polyethylene. We present examples of the dependence of fragmentation on material type and thickness, of a comparison between data and a fragmentation model, and of multiple fragments produced along the beam axis.
Asunto(s)
Radiación Cósmica , Iones Pesados , Protección Radiológica/estadística & datos numéricos , Nave Espacial/instrumentación , Sincrotrones , Modelos Teóricos , Protección Radiológica/instrumentaciónRESUMEN
We have obtained charge-changing cross sections and partial cross sections for fragmentation of 1.05 GeV/nucleon Fe projectiles incident on H, C, Al, Cu, and Pb nuclei. The energy region covered by this experiment is critical for an understanding of galactic cosmic ray propagation and space radiation biophysics. Surviving primary beam particles and fragments with charges from 12 to 25 produced within a forward cone of half-angle 61 mrad were detected using a silicon detector telescope to identify their charge and the cross sections were calculated after correction of the measured yields for finite target thickness effects. The cross sections are compared to model calculations and to previous measurements. Cross sections for the production of fragments with even-numbered nuclear charges are seen to be enhanced in almost all cases.
Asunto(s)
Radiación Cósmica , Partículas Elementales , Hierro , Física Nuclear , Aluminio , Carbono , Cobre , Hidrógeno , Iones , Plomo , Modelos Teóricos , Polietilenos , Monitoreo de Radiación , SincrotronesRESUMEN
Numerous case reports of atypical and/or severe forms of syphilis in individuals coinfected with human immunodeficiency virus (HIV) have led many authorities to conclude that HIV exacerbates early syphilitic infection. Herein we report prominent osseous and unusual dermatologic manifestations of early syphilis in two individuals whose serostatuses for HIV infection were discordant. Our cases emphasize the need for caution before conclusions are drawn from anecdotal data about the interactions between HIV infection and syphilis.