7 Application of CR-39 Solid State Nuclear Track Detectors …
135
100 keV/µm in the material). On the other hand, CR-39 produced with purified allyl
diglycol carbonate monomer can detect protons of a few MeV. In addition, a more
sensitive type of CR-39 detector was developed in Japan. For example, HARZLAS
(TD-1) and HARZLAS (TNF-1), which are copolymers with N-isopropylacrylamide
(NIPAAm), can detect protons up to 20 and 27 MeV (stopping power below 10
keV/µm), respectively [19–21].
The following sections explain the etch pit growth behaviour and analysis of the
SSNTDs, including the CR-39, which has been studied by pioneering researchers
[8, 22, 23].
7.2.2 Etch Pit Growth Behaviour
When an energetic ion enters the SSNTD, the ion transfers kinetic energy to the
material and loses energy. Primary ionization by the incident particles and ionization
by secondary electrons, which are called δ-rays, mainly occurs in the process of
losing energy. Based on these processes, the damaged region, which is called the ion
track, is formed with a size of a few nm in the radial direction. The ion track region is
preferentially etched by chemical etching compared to the pristine region, and then
the etch pit is created. After chemical etching by alkaline solutions, the damaged
region can be recognized as an etch pit with an optical microscope. Each etch pit
shows that the unique growth behaviour depends on the stopping power along the
ion track, which allows us to predict the ion species and the incident energy.
The sensitivity of an SSNTD for a charged particle is defined as the ratio of the
track etching speed V t to the bulk etching speed V b as described in (7.1).
S ≡
V t
V b
,
(7.1)
where S is the sensitivity of the SSNTD. V t and V b are the etching speeds along the
ion track and its unirradiated area, respectively. A schematic cross-sectional view of
an etch pit after t hours of etching is shown in Fig. 7.2. The surface of the SSNTD is
etched in accordance with V t and V b ; therefore, the track length L and the thickness
of layer removed G are given by V t t and V b t, respectively. In the case of V t being
constant, the etch pit wall has a perfect conical shape. The relation between the etch
pit tip angle δ and the sensitivity is shown in (7.2).
sin δ =
V b
V t
=
1
S
(7.2)
From (7.2), the etch pit tip angle can determine the sensitivity S directly, but the
tip angle cannot be obtained by optical microscopy from the surface of the SSNTD.
135
100 keV/µm in the material). On the other hand, CR-39 produced with purified allyl
diglycol carbonate monomer can detect protons of a few MeV. In addition, a more
sensitive type of CR-39 detector was developed in Japan. For example, HARZLAS
(TD-1) and HARZLAS (TNF-1), which are copolymers with N-isopropylacrylamide
(NIPAAm), can detect protons up to 20 and 27 MeV (stopping power below 10
keV/µm), respectively [19–21].
The following sections explain the etch pit growth behaviour and analysis of the
SSNTDs, including the CR-39, which has been studied by pioneering researchers
[8, 22, 23].
7.2.2 Etch Pit Growth Behaviour
When an energetic ion enters the SSNTD, the ion transfers kinetic energy to the
material and loses energy. Primary ionization by the incident particles and ionization
by secondary electrons, which are called δ-rays, mainly occurs in the process of
losing energy. Based on these processes, the damaged region, which is called the ion
track, is formed with a size of a few nm in the radial direction. The ion track region is
preferentially etched by chemical etching compared to the pristine region, and then
the etch pit is created. After chemical etching by alkaline solutions, the damaged
region can be recognized as an etch pit with an optical microscope. Each etch pit
shows that the unique growth behaviour depends on the stopping power along the
ion track, which allows us to predict the ion species and the incident energy.
The sensitivity of an SSNTD for a charged particle is defined as the ratio of the
track etching speed V t to the bulk etching speed V b as described in (7.1).
S ≡
V t
V b
,
(7.1)
where S is the sensitivity of the SSNTD. V t and V b are the etching speeds along the
ion track and its unirradiated area, respectively. A schematic cross-sectional view of
an etch pit after t hours of etching is shown in Fig. 7.2. The surface of the SSNTD is
etched in accordance with V t and V b ; therefore, the track length L and the thickness
of layer removed G are given by V t t and V b t, respectively. In the case of V t being
constant, the etch pit wall has a perfect conical shape. The relation between the etch
pit tip angle δ and the sensitivity is shown in (7.2).
sin δ =
V b
V t
=
1
S
(7.2)
From (7.2), the etch pit tip angle can determine the sensitivity S directly, but the
tip angle cannot be obtained by optical microscopy from the surface of the SSNTD.