Response of nuclear emulsions to ionizing radiations

A Passive Magnetoelastic Radiation Sensor

A passive gamma detection technology, consisting of a fielded sensor and a separate analysis system, is described. The sensor is a small cylinder, about 2.5 mm in diameter and 15 mm in length. It requires no onboard power sources or physical connections for power or data transfer, and retains its cumulative response to radiation. The sensor consists of an amorphous magnetoelastic wire held in a longitudinally-stressed state by a radiation-sensitive material. When the radiation-sensitive material is subjected to gamma radiation, it mechanically degrades, relaxing the stress on the wire and lowering the wire’s magnetic permeability. The changes in permeability are observed by switching the magnetic domains in the wire and measuring the reduction in the Faraday voltage as the stress is diminished. The analysis package is built around an excitation-detection coil set and can communicate wirelessly with the sensor through a metallic or nonmetallic barrier at distances up to about 25 mm. The sensor response is linear up to a dose of at least 7 kGy.

Tracks to therapy

Studies of the structure of particle tracks have led to models of track effects based on radial dose and radiobiological target theory that have been very successful in describing and predicting track effects in physical, chemical, and biological systems. For describing mammalian cellular inactivation two inactivation modes are required, called gamma-kill and ion-kill, the first due to synergistic effects of delta rays from adjacent ion paths thus resembling the effects from gamma rays, and the second to the effects of single ion transits through a cell nucleus. The ion-kill effect is more severe, where the fraction of cells experiencing ion kill is responsible for a decrease in the oxygen enhancement ratio, and an increase in relative biological effectiveness, but these are accompanied by loss of repair, hence to a reduction in the efficiency of fractionation in high LET therapy, as shown by our calculations for radiobiological effects in the "spread out Bragg Peak".

Radial distribution of dose

The radial distribution of dose about the path of a heavy ion, principally from delta rays, is one of the central contributions of atomic physics to the systematization of high LET radiation effects in condensed matter, whether the detection arises in chemical, physical, or biological systems. In addition to the radial distribution of dose, we require knowledge of the response of the system to X-rays or gamma-rays or to beams of energetic electrons such that the electron slowing-down spectra from these radiations can approximate the slowing-down spectra from delta rays even at different radial distances from the ion's path. A combination of these data enables us to calculate the action cross sections ion bombardments in all detectors for which this information is available. These cross sections are indispensable for the evaluation of effects caused by high LET radiations. In this paper we focus attention principally on the calculation and measurement of the radial distribution of dose and on their limitations.