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Objective of experiment:
In this experiment we need to study etching characteristics of SSNTD. We observe effect of duration of etching on tracks formed on detector Radioactive elements emit different kinds of radiations. These radiations may be alpha particles, beta particles or electromagnetic gamma rays. Solidstate nuclear track detector is also used to detect nuclear radiations. . Solid state nuclear track detector (SSNTD): Fast moving charged particles are known to produce trails of atomic disorder in an immense variety of dielectric solids and some other materials. These dielectric solids include crystals, glasses, and high polymers, and other materials used, include intermetallics, certain metals and amorphous metals, oxide conductors and superconductors. Tracks produced by radiations from nucleus are known as nuclear tracks. Nuclear tracks have found many applications in different branches of science. A solid-state nuclear track detector or SSNTD is also known as an etched track detector or a dielectric track detector DTD. When it is uncovered to nuclear radiation i.e. neutrons or charged particles, intermittently as well gamma rays , is etched, and inspected microscopically which give information about the radiation
WORKING: When a heavily ionized particle falls on SSNTD, it penetrates inside it. During the process particle strikes with the atoms of lattice of SSNTD and may knock out them from their lattice sites. Depending on particle’s energy, it may penetrate deep inside SSNTD and having some decrease in energy. Therefore track continuous inside the detector also in form of cone. These tracks are used to extract valuable information about the radiation incident on detector. SSNTDs fall in two distinct categories:
- Polymeric or plastic detectors: These are widely used for radiation monitoring
- Natural minerals crystals (and glasses): This kind of SSNTD has greatest application in fields such as geology, planetary sciences [especially lunar and meteoritic samples], oil exploration etc.
The most widely used SSNTDs today are plastic, which unlike mineral crystal do not require special preparation such as grinding and polishing. They are also much more sensitive than crystals and glasses. Tracks visualization: Due to irradiation of radiation tracks are formed on SSNTD. These tracks are of very small size and of order of 10nm. To make these tracks visible, they are passed through a process called etching. In etching 6 Molar solution of NaOH is used and SSNTD is placed in it for irradiation. This process make the tracks formed by radiation larger in size and after some time their size become of the order of micrometer .Size of tracks depends on duration of etching. In this experiment we study etching characteristics of SSNTD detector. Tracks evaluations: Many methods are used to evaluate tracks so that valuable information about the radiation is obtained.
- Manual (Ocular) Counting: Manual or more accurately, ocular (with eye)counting denotes non- automatic counting of etched tracks generally using an optical microscope, with a moving stage, and two eye pieces. But there is a problem with this method that some of tacks may be repeated in counting and some may be left. 2.There are also spark counting and automatic track evaluation. By these methods we can also count tracks of pits. From data taken track density is found. Track densities are expressed either in relative terms or in absolute terms which is converted after calibrating into a dose or radon concentration by dividing by the time of exposure.
MATERIALS AND METHODS:
In this experiment we used SSNTD strips which were already passed through the process of etching and irradiation from two different radiation sources and microscope. Procedure:
Fig1. Calibrationof microscope. Measuring size of tracks: Now to get data about size of tracks, we placed different strips of SSNTD which were irradiated from different sources and were etched for different time durations. First of all we used strips irradiated with Americium 242 source which is an alpha emitter. We used strips etched for different time duration.Using slide attached with stage, strip of SSNTD could be moved in back and forth direction and also in right and left direction. Using this facility, different pits i.e. tracks of radiation were brought on scale of eyepiece from where it size were found. Many readings were taken for each strip. Similar procedure was repeated for cf 252 which is an alpha emitter and also fission fragments come out from this source due to spontaneous fission so we took different readings for alpha particles and for fission fragments . Figure 2. Measuring size or diameter of tracks of radiation on SSNTD. Observations:
First we took reading for Americium 242 element. Ten different tracks/pits were selected and diameter of those pits was measured for five different strips. Data is given below. For each case we can see that etching or diameter of tracks of alpha particles and fission fragments are increasing with time.
Table of data taken for alpha particles emitted from Americium 242 , scale is in micrometer Diameter measured ten different times All readings are taken in μm
Etching time :12hrs
10hrs 8hrs 6hrs 4hrs
Avg= 8.2μm =7.9μm 6.6μm 4.7μm 3.6μm
Table of data taken for Fission fragments particles emitted from Californium 252 , scale is in micrometer
Etching time 10.5hrs
8.5 hrs 6.5hrs 4.5hrs 2.5hrs
16.3μm 12.1μm 10.1μm 7.9μm 11.9μm
Diameter of tracks measured for ten different tracks randomly in micrometer
Table of data taken for alpha particles emitted from Californium 252 , scale is in micrometer
Diameter measured in micrometer For ten different tracks for each track
Etching time 10.5hrs
8.5 hrs 6.5hrs 4.5hrs 2.5hrs
