Question

c) (i) Briefly discuss the main principles of microdosimetry.
(ii)What is the difference between lineal energy transfer and linear energy transfer (iii) Explain what do you understand under microdosimetric spectra and how is it possible to derive it from a Multi-Channel Analyser (MCA) spectrum?

Answer 1

1)The field of microdosimetry is the study of those physical characteristics of energy transfers other than dose that produce variations in biological consequences of exposures to radiation.
Historically, this area developed primarily from a need to understand and quantify the differences in human responses to different types of radiation, in particular the variations in late complications for the same level of acute effects such as edema and vomiting or tumor control in radiation therapy, and further applications in radiation health.Ionizing radiations interact in a discontinuous form withmatter; dose and dose rate are statistical averages that disregard the inherent random fluctuations.

2)Linear Energy Transfer (LET) is the energy lost by an ionizing particle per unit pathlength
traversed by the particle.

The lineal energy, y, is defined as the ratio of G to the mean chord lengtb, l, in the volume of interest. The quantity y is restricted to individual events, i.e. to energy deposition in the volume due to a primary particle and/or its secondaries.

3)microdosimetric spectra themselves, discussdifferences in the results observed between different instruments and the additional information that may be drawn from the TEPC data.

The multichannel analyzer (MCA) operates like a conventional MCA, except that the input is already digitized. It detects the amplitude of the peak of the shaped pulse, using a digital peak detect circuit. If the selection logic indicates that the pulse is valid, then it increments the value stored at a memory location corresponding to the peak amplitude. The MCA supports 256,512,1024,2048,4096 or 8192 channels. The DPP allows 16.7 M counts per channel. Data transfers to the computer via USB, RS232 or Ethernet interface and occur
based on approximate real computer time. The Amptek‟s ADMCA software provides the access to all the required configurations parameters includes very simple analysis and the ability to save the data in suitable format.