Dose rate measurements of charged and neutral particles in the stratosphere

Transcription

1 Dose rate measurements of charged and neutral particles in the stratosphere Esther M. Dönsdorf1, Sönke Burmeister1, Stephan Böttcher1, Björn Schuster1, Eric Benton2, Bernd Heber1,Thomas Berger3 Institute for Experimental and Applied Physics, University of Kiel, Germany 2 Department of Physics, Oklahoma State University, USA 3 German Aerospace Center, Institute of Aerospace Medicine,Radiation Biology,Cologne, Germany 1 1

2 Outline The Balloon flight The Phoswich Detector Preliminary Results: Phoswich Detector Future Work and Summary 2

3 Stratospheric Balloon Flight Balloon flight near Stillwater/ Oklahoma: cutoff rigidity 4 GV Height ~ 30 km Duration ~ 2 hrs payload restricted to 3 kg total mass two instruments designed to measure dose rates Dosimetry telescope based on silicon diodes to measure charged particles Phoswich detector based on two different scintillators to measure neutrons and γ-rays O-12%20Post%20Flight.htm 3

4 The Instrumental Setup for the Balloon Flight Phoswich Detector Phoswich Detector Sensor head Electronics DOSTEL Dimensions: on top : 125 mm x 155 mm Battery pack at the bottom: 160 mm x 180 mm total height : 230 mm total weight : ~ 2 kg without insulation 4

5 The Scintillation Detector 5

6 Phoswich Detector: Sensor Head two dissimilar scintillators are optically coupled to one photomultiplier (PMT) inner plastic scintillator BC412 and anti-coincidence made of CsI(Na) read out by PMT BC-412 CsI(Na) n γ PMT n BC412 6

7 The Scintillators BC-412 based on polyvinyltoluene, density: g/cm3 tissue equivalent decay time 2.4 ns wavelength of max. emission: 434 nm CsI(Na) high density (4.51 g/cm3) and high atomic number high cross section for γ rays decay time 630 ns Wavelength of max. emission: 420 nm 7

8 Electronics for the Phoswich Detector ERENA Digital Board Phoswich Detector fast preamplifier, a fast ADC and an FPGA the signal goes differentially to the ADC the signals are further processed in the FPGA: two linear combinations are multiplied with the samples of the measured pulse data are stored on a SD card 8

9 Preliminary results 9

10 Measurements at the PTB: Calibration with Neutrons Red: 14.8 MeV primary neutron energy Green: 8 MeV primary neutron energy 10

11 Pulses from both Scintillators 11

12 Method for Pulse Shape Analysis bi ai si 12

13 Convolved Pulses A 0 B 0 13

14 B0/A0 Neutrons 14.8 MeV:mixed pulse A0 14

15 Red: neutrons Green: gammas B0/A MeV neutrons and Bi207 gammas A0 15

16 Red: neutrons Blue: gammas Green: muons B0/A MeV neutrons, Bi207 gammas and muons A0 16

17 Cut for the neutrons at B0/A = B0/A0 Cut for neutrons A0 17

18 8 MeV Neutrons Red: mixed signal, Blue: gamma events, Green: neutron events 8 MeV neutrons at 284 mv 18

19 14.8 MeV Neutrons Red: mixed signal Blue: gamma events Green: neutron signal 14.8 MeV neutrons at 585 mv 19

20 Quenching in Plastic Scintillators 8 MeV are quenched to 3 MeV, 14.8 MeV to 7.5 MeV The amplification has to be adopted to be able to detect 100 MeV neutrons 20

21 Future Work Improvement of the pulse shape analysis: use different linear combinations for the convolution to achieve the best separation for neutrons and gammas First atmospheric measurements: Measurement onboard an airplane: middle of September Balloon flight in Oklahoma: Beginning of November 21

22 Summary Silicon detector: has been built, tested and calibrated at HIMAC/NIRS with different heavy ions works well Phoswich detector: has been built and tested calibration results show that by pulse shape analysis a cut can be found that distinguishes between gammas and neutrons 22

23 Acknowledgements The calibration for the silicon based detector was performed at NIRS/ HIMAC therefore we would like to thank Yukio Uchihori and the ICCHIBAN working group The calibration for the scintillation based detector was performed at PTB/ Braunschweig. We would like to thank Frank Wissmann and Frank Langner 23