An-Najah National University New Campus, Nablus, Palestine Second Palestinian International Conference on Material Science and Nanotechnology (PICNM2016) March 23-24, 2016 An-Najah National University New Campus, Nablus, Palestine Development of Alpha Spectroscopy Method with Solid State Nuclear Track Detector Using Aluminum Thin Films N. Dwaikat, Physics Department King Fahad University of Petroleum & Minerals Prof. Ghassan Saffarani Physics Department, An-Najah National University

Contents Objective Basic Principle of Solid state nuclear track detectors (SSNTDs) Applications of SSNTDs Advantages and disadvantages of using SSNTDs Calculation of alpha radiation range in Aluminum Samples Irradiation Chemical etching Etch pits counting Results and discussion Conclusion

Objective All reported methods for alpha spectroscopy with SSNTDs need a calibration of energy versus alpha tracks diameter . This research aims to develop a method for alpha spectroscopy with SSNTDs that does not need energy calibration versus alpha tracks diameter.

Basic Principle of Solid state nuclear track detectors (SSNTDs) When charged particles incident on the surface of SSNTDs, they induce latent tracks along their trajectories. Chemical etching fix these tracks and makes them visible under optical microscope.

Applications of SSNTDs CR-39 is a solid state nuclear track detector (SSNDs) and is extensively used in various experiments: Radiation detection –radon concentration measurements. The technique of track etch is widely applied in Europe for measuring the total indoor radon level Space sciences – measurement of cosmic rays Nuclear science – fission and fusion research Identification of the nature of nuclear particles.

Disadvantages The main drawback of using SNTDs in radiation measurement is limited to counting the number of alpha particles. It is difficult to distinguish between the tracks of alpha particles of different energies produced in SSNTDs. It needs a calibration of alpha energy versus tracks diameter.

Advantages Cheap It is passive detector – it needs no power in the sampling process- natural diffusion Permanent record An integrated detector gives the average value over long time (three months) Can be used any where

Alpha radiation range in Aluminum SRIM -2013 was used to calculate the range of alpha particles in Aluminum thin Films Alpha particle energy (MeV) Rang of alpha particles in aluminum (mm) 5.11 22.00 3.86 14.91 2.7 9.37

Samples Preparation CR-39 detector (1 cm x 1 cm) of thickness (1 mm) (Fukuvi chemical industry C., Ltd., Japan) was used in this study. Three sets of samples, each of five, were mounted on thick copper substrates to block the exposure from backside. On front side, two sets of samples were covered with aluminum films of thickness (15 mm and 10 mm) and the third one was kept uncovered.

The first film (15 mm) will block out the lower two particles (3 The first film (15 mm) will block out the lower two particles (3.86 MeV and 2.7 MeV) and alpha particles at energy of 5.11 MeV are able to penetrate the film and produce tracks on CR-39 detector. The second film (10 mm) will range out alpha particles at 2.7 MeV and the other alpha particles at energies 5.11 MeV and 3.86 MeV will produce tracks. For uncovered detector all alpha particles at different energies can produce tracks on the detector.

Samples Irradiation Each sample was irradiated for 5 seconds with alpha particles using Cf-252 standard source at energies of 5.11 MeV, 3.86 MeV and 2.70 MeV, which were produced by changing the distance between the detector and standard source. The irradiation process was done in air and a manual shutter was used to close the opening window between the source and the detector.

Etch pits counting Chemical etching The detectors were etched in 6.25 N NaOH chemical solution at 70 for 6 hours. After etching, CR-39 detectors thoroughly washed with distilled water and dried in the open air. Etch pits counting The tracks number was counted using optical microscope fitted with digital camera and connected to PC. Fifteen field of views were taken for each sample and the average number of tracks was calculated.

Calculation The tracks on the first set of detectors (covered with 22 mm Al) are only due to alpha particles at energy of 5.11 MeV. The tracks on the second set (covered with 14.91 mm Al) are produced by alpha particles with energy of 5.11 MeV and 3.86 MeV. The difference between the tracks number on the first set and the tracks on the second set of detectors is due to alpha particles at energy of 3.86 MeV. By subtracting the tracks number on the second set of detectors from the tracks number on the third set detectors (uncovered), we can find the tracks number due to alpha particles at energy of 2.7 MeV.

Results and discussion Figures 1 through 3 show the results of alpha measurement with SSNTD using aluminum film of various thickness. It can be noticed that the number of tracks on figure 1 half of that on figure 2 and one third of that tracks on figure 3. Fig. 1: Tracks produced by alpha particles at energy of 5.11 MeV. The detector covered with 15 mm aluminum film. Fig. 2 : Tracks produced by alpha particles at energies of 5.11 MeV and 3.86 MeV. The detector covered with 10 mm aluminum film. Fig. 3: Tracks produced by alpha particles at energies of 5.11 MeV, 3.86 MeV and 2.70 eV. The detector was uncovered.

Results and discussion Fig. 1 shows the results of alpha particles measurement with detector covered with 15 mm aluminum film. Only alpha particles at energy of 5.11 MeV able to penetrate and produce tracks on detector and the other two ranged out thin film. It can be seen that the number of tracks is seven. For the second detector covered with 10 mm aluminum film, alpha particles at energies of 5.11 and 3.86 will reach the detector and produce tacks. As it is expected, the number of tracks is double of that one on the first (see fig.2). For third one (uncovered) all particles are able to produce tracks on the detector.

Results and discussion Detector Number Thickness of aluminum film (mm) Average number of tracks 1 15 8.80 ± 1.30 2 10 16.85 ± 2.75 3 Uncovered 21.83 ± 3.81 Table 2 shows the average number of tracks for fifteen fields of view take for each detector. There is a slightly difference between expected number of tracks and the experimental values. This difference is due error in irradiation time because a manual shutter was used to close the opening window between the detector and standard source.

Conclusion The aluminum filter was used as energy window for alpha particles measurement with SSNTD. The counting and calculation process of tracks was developed and effectively used to discriminate between alpha particles at different energies. The resolution of this method is high and does not need calibration of track diameter versus alpha energy. It may provide researcher and radiation protection officer with a cheap and powerful tool for measurement of alpha radiation.

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