We present the details of a new linear array dosimeter consisting of a chain of semiconductors mounted on an ultra-thin (50 m thick) flexible substrate and housed in an intracavitary catheter. The semiconductors, manufactured by NMRC Cork, have not been packaging and incorporate a passivation layer that allows them to be mounted on the substrate using flip-chip-bonding. This paper reports, for the first time, the construction of a multiple (ten) detector array suited to in vivo dosimetry in the rectum, esophagus and vagina during external beam radiotherapy, as well as being adaptable to in vivo dosimetry during brachytherapy and diagnostic radiology.

The feasibility of large-geometry Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices has been assessed for both active and passive neutron dosimetry and use in radiotherapy environments. Neutron sensitivity has been enhanced with the use of polymeric cement surrounding the gate region. Neutron activation via nuclear interaction processes is a potential problem with conventionally packaged and fabricated devices. To overcome this problem, a unique low-activation device design is described. Standard Dual in-Line devices, modified with polymeric cement and boron loaded cement have been exposed to gamma rays (60Co) and neutrons (gamma-ray shielded 252Cf) to provide neutron sensitivity estimates. The results show that the neutron sensitivity can be increased by a factor of approximately three by the use of a thin layer of polymeric cement over the gate region. Essentially zero activation is observed in the activation-reduced design compared with 1000 cps in the conventional design MOSFET when both are exposed under identical conditions to a neutron field from a gamma-ray shielded 252Cf isotopic source.

The dependence of radiation-induced charge neutralization ͑RICN͒ has been studied in metal-oxide-semiconductor field-effect transistor ͑MOSFET͒ dosimeters. These devices were first exposed to x rays under positive bias and then to further dose increments at a selection of reverse bias levels. A nonlinear empirical trend has been established that is consistent with that identified in the data obtained in this work. Estimates for the reverse bias level corresponding to the maximum rate of RICN have been extracted from the data. These optimum bias levels appear to be independent of the level of initial absorbed dose under positive bias. The established models for threshold voltage change have been considered and indicate a related nonlinear trend for neutralization cross section N as a function of oxide field. These data are discussed in the context of dose measurement with MOSFETs and within the framework of statistical mechanics associated with neutral traps and their field dependence.

The results of a recent study on the limiting uncertainties in the measurement of photon radiation dose with MOSFET dosimeters are reported. The statistical uncertainty in dose measurement from a single device has been measured before and after irradiation. The resulting increase in 1/f noise with radiation dose has been investigated via various analytical models. The limit of uncertainty in the ubiquitous linear trend of threshold voltage with dose has been measured and compared to two nonlinear models. Inter-device uncertainty has been investigated in a group of 40 devices, and preliminary evidence for kurtosis and skewness in the distributions for devices without external bias has been observed.

This paper compares and contrasts the use of MOSFET dosimeters and extended rem counters for neutron detection in cosmic radiation fields. These technologies have been exposed to a reference field and data are presented that demonstrate the contrasting sensitivities of these approaches. The MOSFETs are observed to be insensitive to dose levels associated with cosmic fields whilst the extended rem counters give a good response, demonstrating that copper has potential as a replacement for lead in these systems. ).Publisher Item Identifier S 0018-9499(00)11181-5.Authorized licensed use limited to: Lancaster University Library. Downloaded on December 23, 2008 at 04:46 from IEEE Xplore. Restrictions apply.