Page 8 - PR 2014 2016 03 Applications of Ionizing Radiations

50 Application of Ionizing Radiations | Progress Report

Figure 6. MCz and Epitaxial silicon diodes on a ceramic base and the PMMA probes.

small megavoltage fields (Fig 7). directly coupled with a digital electrometer
in a short circuit mode to record real-time
Radiation Processing: The rising demand for currents and, consequently, dose rates. The
applications in the field of radiation process- dose delivered to the product can be obtained
ing with very high doses has pushed research- offline via integration of the current signals as
es to develop dosimetry systems to withstand a function of the exposure time. As expected,
harsh radiation environment. In this context, it was observed a negligible current sensi-
to improve quality assurance in electron beam tivity decay for accumulated doses less than
processing of many products, active semicon- 1.5 MGy. For higher doses, damage effects
ductor dosimeters were designed based on on electrical properties of the diodes rose up
radiation-hard diodes processed on n-type the dark currents with the accumulated dos-
Magnetic Czochralski (MCz) silicon substrate. es and the sensitivity decay reached almost
The main application envisaged was to mon- 10%. As a consequence, the correspondent
itor 1.5 MeV electron beam processing cover- dose-response curves were not linear being
ing the dose range from 10 kGy to 2 MGy and fitted by a second order polynomial function.
dose rates up to 8 kGy/s. During the electron So far, the results evidenced that MCz diodes
irradiation, the diodes were unbiased and are substantially tolerant to radiation damage
assuring their potential
use for high-dose pro-
cessing dosimetry. It still
remains to be dwindled
the damage produced
on both the entrance
window and the walls
of the dosimetric probe.
Researches on this mat-
ter are under way.

Figure 7.Miniature FZ diode in a waterproof protection and its connection to a coaxial cable.

Instituto de Pesquisas Energéticas e Nucleares