الفهرس 
Solid State Nuclear Track DetectorsOnly 14 pages are availabe for public view
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Abstract
CR-39 plastic nuclear track detector has been used to measure ionizing
radiation since its discovery in 1978. This detector is passive, integrating,
lightweight, cheap and compact therefore it has been adopted to be used in many
radiation fields such as nuclear chemistry, nuclear physics, biomedical and
environmental studies, health effects, low activity radon and space radiation field.
Due to the widespread use of CR-39 detector, its properties have been intensively
investigated to reach the best response for this detector.
The aim of the present work is to investigate the bulk etch rate of PADC
CR-39 at a wide possible concentration range of NaOH from 2 to 30 mol/l where
etching at extreme etching conditions (low as well as high concentrations) was
covered. Studying the effect of adding different ethanol volumes of 0, 1, 2 and 3
ml to the different NaOH concentrations were also studied. The optimum etching
condition for the production of thick nuclear track membranes from thick CR-39
track detectors irradiated to swift heavy ions was determined. Nuclear track
membranes for Si, Fe, Ni and Au tracks of different diameters and geometry were
produced.
CR-39 detector sheet from American Acrylics of thickness 650 µm was cut
into small pieces of area 1 cm2. Preserved samples were exposed to 252Cf source
one by one for 30 min. Exposed CR-39 detectors were chemically etched to reveal
fission fragment tracks. Fresh NaOH aqueous solution was prepared with
concentrations from 2 to 30 N. Samples were etched in 8 ml NaOH aqueous
solutions (2-30 N) with 0, 1, 2 and 3 ml ethanol. Etching temperature was kept at
70°C and maximum variation in it was up to 1°C.
Variation in bulk and track etch rate with deep depth of Poly allyl diglycol
carbonate (PADC) CR-39 polymer SSNTDs of thickness ≈ 650 µm from American
Acrylics were studied. High energy ions of normal incidence (90°) of 7 GeV Si,
17.48 GeV Ni, 46.48 GeV Fe, and 98 GeV Au were investigated. Each piece was
etched in strong etching solution (8 ml of 18 N NaOH + 1ml of ethanol) and the
water bath was mounted at 70°C.
The obtained experimental data for bulk etch rate at different etchant
concentrations is really complicated data and has many trends. As ethanol volume
increases as the bulk etch rate increases and the deviation between data increases
by increasing the NaOH concentration. Adding ethanol in NaOH/H2O solution of
CR-39 detectors is a simple way to speed up the chemical etching process and to
shorten the etching time. In such extended concentration range and different
ethanol volumes, different reaction and bulk etch rates were observed. This adds
more complexity to the process of chemical etching. Three regimes of CR-39 bulk
etching have been identified. Regime I spans from 2 to 12N concentrations of the
etchant. This is concentration-limited regime. Regime II is very important in
operational perspective. It spans from 12 and 25N concentrations. We call it
dynamic bulk etching regime. Regime III is beyond 25N concentration. We call
this regime as diffusion-limited regime. In such regimes, Arrhenius as well as
Multi-hit model are no longer holding to describe the chemical reaction rate and
the corresponding bulk etch rate. For this, new equations were proposed and
discussed from statistical as well as chemical point of view. The Origin software
offer the non-linear fit for such equations and one can judge the goodness of fitting
using the residual, χ2 and R2 (adj). It was found that Slogistic, Rational and
Exponential equations give good fitting as well as good data manipulation of the
different growing rate.
Deep depth properties of PADC CR-39 detectors of sensitivity, V, bulk, Vb
and track etch rates, Vt were intensively investigated by measuring the track
opening as well as the track cone length. Fe and Si ions show an interesting and
newly observed track profile for the first time. Their profiles geometry is quite
different than Ni and Au profiles that show normal geometry. Fe and Si profiles
need further study to establish its new geometry. Microphotographs for the
developed track profile for each ion were shown.
Thick nuclear track membranes, TMs were produced from PADC CR-39
SSNTDs of thickness ≈ 650 µm irradiated to swift heavy ions and processed in the
suggested strong etchant solution of NaOH mixed with ethanol. TMs for Au, Ni, Si
and Fe were produced with different open channel diameters starting from ≈ 5µm
pore diameter. Thick membranes are needed for higher stress duties and therefore
can be used in many applications. Different pore sizes and shapes were obtained
and can be controlled further by different etching conditions as well. I-V
characteristics for the newly formed membranes are under investigations