1. Radiation Characteristics of the FN-II Plasma Focus Device Julio Herrera 1, Fermín Castillo 1, Guillermo Espinosa 2, Isabel Gamboa 1, José Ignacio Golzarri 2, José Rangel Gutiérrez 1 Instituto de Ciencias Nucleares Instituto de Física Universidad Nacional Autónoma de México

2. Outline Description of thel FN-II device and its diagnostics Soft X rays observed with pinhole camera and PIN diode. Measurement of the hard X-rays angular distribution by means of TLD-100 dosimeters. Use of needle point electrode for contrast radiography. Dosimetry using TLD-200 dosimeters. Hard X-rays and neutron detection using scintillator- photomultiplier arrays. Conclusions

3. Sketch of the FN-II Dense Plasma Focus Device

5. Main parameters (F. Castillo et al., Brazilian J. Phys. 32 (2002) 3) Inner electrode:length 40 mm (oxygen-free copper)diam.50 mm Outer electrode:squirrel cage type (12 bars) (oxygen-free copper) diam.100 mm Insulator (Pyrex ® )length19 mm diam.50 mm Usual operating voltage:36 kV Stored energy:4.8 kJ Current350 kA

6. Main diagnostics Current (Rogowski coil) Neutrons 2 Silver activation counters CR 39 nuclear track detectors 5 BC-400 Scintillator-photomultiplier systems X-rays Pinhole cameras PIN diodes TLD-100 and TLD-200 dosimeters 5 BC-400 Scintillator-photomultiplier systems

7. Cámara de agujero

8. Soft X-rays – Hollow electrode

9. Rogowski and PIN in Hydrogen

10. Bored electrode after several hundreds of shots

11. Electrode with a 2 mm INOX-304 inserted needle

12. Pin-hole image of a discharge with a needle

13. Worn out 2 mm needle point after a few shots

14. Worn out 1 mm needle point after a few shots

15. Erosion of the needle

25. TLD-100 dosimetry (1) 60 shots for the hollow electrode. Number of counts at 20 o /90º for the activation detectors is 68774/65312 → 4.12  10 8 / 6.13  10 8 neutrons/steradian 54 TLD-100 dosimeters were placed 1 m away from the focus, measurenments were made of four groups of 9 dosimeters: 1. 9 Unfiltered 2. 18 Filtered by 0.5 mm Al 3. 18 Filtered by 1.0 mm Al A dose estimate is made using the Unfiltered group, using their TL response and the calibration factor previously obtained by means of 60 Co irradiation.

26. TLD-100 dosimetry (2) 79 shots for the needle electrode. Number of counts at 20 o /90º for the activation detectors is 63448/58478 → 3.81  10 8 /5.49  10 8 neutrons per steradian. 63 TLD-100 dosimeters were placed 1 m away from the focus, measurenments were made of four groups of dosimeters: 1. 9 Unfiltered 2. 18 Filtered by 0.5 mm Al 3. 18 Filtered by 1.0 mm Al 4. 18 Filtered by 2.0 mm Al A dose estimate is made using the Unfiltered group, using their TL response and the calibration factor previously obtained by means of 60 Co irradiation.

27. Attenuation of the thermoluminiscent (TL) response of filtered TLD-100 dosimeters placed at 1m from the focus.

28. TLD-100 dosimetry (3) Hollow electrode: 60 shots. 4.12  10 8 / 6.13  10 8 neutrons/steradian at silver activation detectors 4.6 ± 0.5 mGy → 0.077 ± 0.006 mGy Needle electrode: 79 shots. 3.81  10 8 /5.49  10 8 neutrons per steradian. at silver activation detectors 8.5 ± 0.5 mGy → 0.11 ± 0.01 mGy (Environmental daily dose ~ 0.01 mGy)

29. Sketch of the FN-II Dense Plasma Focus Device

30. Angular distribution of X-rays measured with TLD-200 dosimeters Sensibilty peaked at ~ 30keV

31. Tracks at upper detectors (400X)

32. Tracks at lower detectors (400X)

33. Angular distribution of protrons

34. Angular distribution of neutrons at upper detectors

35. Angular distribution for neutrons at lower detectors

36. Isotropic and Anisotropic Contributions

37. Comparisson Between Both Samples I BHσKA1A1 A2A2 AIso.Aniso. Neutrons up 4.6848.85532.420.288158.8616.0374.890.78600.2140 Neutrons down 20.4417.2044.340.4925256.953.22310.10.82840.1716

38. Comparisson Between Both Samples II  10 6 Y Iso  10 6 Y Aniso  10 6 Y Total  10 6 Iso % Aniso % Neutrons up 0.370  0.178 21.78  10.48 5.93  2.85 27.7178.621.4 Neutrons down 0.103  0.0 51 26.46  13. 10 5.48  2.71 31.9482.817.2

39. Scintillator-Photomultiplier systems

40. Rogowski and PIN in Deuterium

41. Shielding on scintillators

43. No. de detectorShielding (Pb cm)Channel 1(PMT only)5Osc. 1-Ch.2 223 (water)Osc. 2-Ch.2 35Osc. 2-Ch.3 410Osc. 1-Ch.4 510Osc. 1-Ch.3

44. Shielding on scintillators Shot 7735-Low performance

45. Shielding on scintillators Shot 7726-High performance

46. Response of the neutron detectors

47. Conclusions (1) The signals from the pin-hole camera show that the plasma column is around 3 cm long and 3 mm diam. The PIN signals are peaked at the moment of the dip in the B-dot signal, and then show a platform which lasts about 1μm. By placing a needle at the tip of the elecrode, the hard X- rays can be well localised, and the dosimetry shows that the yield is doubled. Further work needs to be done in order to estimate the spectrum. The better concentration of the x-ray bright-spot allows their use for high contrast radiography. Some of the hard X rays are highly energetic (gamma rays?) In “high performance” shots the rate and production of gamma rays is highly increased, masking the neutron signal (scattering of gamma rays?).

48. Conclusions (2) The angular distribution of neutrons shows an isotropic and an anisotropic component. The latter usually contributes less than 30%. The angular distribution of protons is aligned to the axis and falls rapidly for angles greater than  40 º, implying the existence of strong magnetic field. The X-rays show a bimodal angular distribution. While the needle slightly increases the X-ray emission, the hollow electrode is best for neutron generation.

49. References [1] F. Castillo, J.J.E. Herrera, J. Rangel, A. Alfaro, M.A. Maza y V. Sakaguchi "Neutron Anisotropy and X-Ray Production of the FN-II Dense Plasma Focus" Brazilian Journal of Physics 32, 3-12(2002). [2] F. Castillo, J.J.E. Herrera, J. Rangel, J.I. Golzarri y G. Espinosa "Neutron Angular Distribution in a Plasma Focus Obtained Through Nuclear Track Detectors", Radiation Protection Dosimetry 101, 557-560(2002). [3] F. Castillo, J.J.E. Herrera, J. Rangel, M. Milanese, R.Moroso, J. Pouzo, J.I. Golzarri y G. Espinosa "Isotropic and Anisotropic Components of the Neutron Emissions at the FN-II and PACO Dense Plasma Focus Devices” Plasma Physics and Controlled Fusion 45, 289-300 (2003). [4] F. Castillo, J.J.E. Herrera, J. Rangel, I. Gamboa, G. Espinosa y J.I. Golzarri “Angular Distribution of fusion products and X-rays emitted by a small dense plasma focus machine” Journal of Applied Physics 101 013303-1-7 (2007).