Nuclear TracksNuclear Tracks
Sup. P.J.ApelSup. P.J.Apel
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A solid-state nuclear track detector or SSNTD (also known as an etched track detector or a dielectric track detector, DTD) is a sample of a solid material (photographic emulsion, crystal, glass or plastic) exposed to nuclear radiation (neutrons or charged particles, occasionally also gamma rays), etched, and examined microscopically.
Solid-state nuclear track detector
Solid-state nuclear track detector
The tracks of nuclear particles are etched faster than the bulk material, and the size and shape of these tracks yield information about the mass, charge, energy and direction of motion of the particles.
If the particles enter the surface at normal incidence, the pits are circular; otherwise the ellipticity and orientation of the elliptical pit mouth indicate the direction of incidence.
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Charged particles which penetrate a solid, can lose their energy via
various interaction types, such as
• Excitation and ionization of target electrons (electronic energy loss)
• Projectile excitation and ionization
• Electron capture
• Elastic collisions with target atoms (nuclear energy loss)
• Electromagnetic radiation(Bremsstrahlung, Cherenkov effect)
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The energy loss depending on the specific energy of the incoming
ion is displayed in fig. (1) for a uranium ion passing through
polyimide, calculated using the SRIMo3 code.
It is a characteristic of fast ions that the maximum of the irradiated
electronic energy loss occurs shortly before the particle is stopped,
because their interaction cross section for these processes increases
with decreasing velocity.
a b4/4/2010 4
The electronic energy loss can be described by the Bethe-Bloch formula
wheree elementary chargeZeff effective charge of the projectileZt atomic numberN number of target atoms per unit volumeme electron massv velocity of the ionI ionization energyβ v/cδ relativistic correctionU correction taking in to account screening of inner electrons
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The reasons for the widespread use of SSNTD include:
The basic simplicity of its methodology The low cost of its materials The great versatility of its possible applications The small geometry of the detectors Their ability in certain cases to preserve their track
record for almost infinite length of time Their rigidness
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The basic principles of SSNTD technique
When heavy charged particles [proton upward] traverse
a dielectric medium, they are able to leave long lived
trials of damage that may be observed either directly by
transmission electron microscope [TEM] provided that
the detector is thick enough, viz. some m across or
under ordinary optical microscope after suitable
enlargement by etching the medium.
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They fall in two distinct categories:1)Polymetric or plastic detectors: These are widely used not only for radiation monitoring
and measurement, but also in may other fields involving nuclear physics and radioactivity .
2) Natural minerals crystals (and glasses): That have imprinted within them, a record of their
radiation (and thermal) history over the icons. These find their greatest application in fields such as geology, planetary sciences [especially lunar and meteoritic samples], oil exploration etc.
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Figure: Chemical Etching of SSNTD4/4/2010 10
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Track Evaluation Methods:
1) Manual (Ocular) Counting:
Manual [or more accurately, ocular: eye] counting denotes
non-automatic counting of etched tracks generally using an optical
microscope, with a moving stage, and two eye pieces
Figure: Track analysis of charged particle on SSNTD after chemical etching4/4/2010 13
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Measurements and Applications:
1.Earth and Planetary Sciences
Radon Measurements:
Radon measurements are one of the most widely
used application of SSNTDs today. Radon is
naturally occurring radioactive gas that constitutes
both a hazard e.g. Lung Cancer, and a helpful
resource – e.g. means for uranium exploration and
tentatively for earthquake prediction.
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Figure: Measurements of radon exhalation rate from granites using SSNTD with sealed vessel.
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2. Fission Track Dating
3. Planetary Science
b) Meteoritic Samples:
a) Lunar Samples
1) Age determination
2) Cooling-down of the early solar system
3) Determination of pre-atmospheric size of meteorites
4) Cosmic Ray Measurements: Particle Identification
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