Characterization of n_TOF fission samples

Rosa Vlastou

National Technical University of Athens, Department of Physics, Athens, Greece

 FIC0 2003 targets description                

Position in the beam

Position from U5 Flight path Isotope Label Mass Diameter

Front End channel

DAQ channel

TDC channel FADC.channel

1 -0.03 185.36 Dummy - - - 1 7 7(<66) OSC2.2

2 -0.02 185.37 Th-232 1,2 38.2 80 24 1 1 FADC4.2

3 -0.01 185.38 Th-232 3,4 37.6 80 25 9 9 FADC4.3

4 0 185.39 U-235 9,10 35.6 80 23 2 2 FADC1.3

5 0.01 185.4 U-236 16,17 11.15 80 21 3 3 FADC3.2

6 0.021 185.411 U-236 18,19 10 .20 80 19 5 5 FADC3.1

7 0.031 185.421 U-238 20,21 23.3 80 17 6 6 FADC2.3

8 0.042 185.432 U-238 22,23 25.4 80 16 8 8 FADC2.2

9 0.052 185.442 Np-237 28,29 12.82 80 15 4 4 FADC3.3

10 0.077 185.467 U-234 7 5 50 14 - - -

11 0.087 185.477 U-234 6 5.17 50 13 - - -

12 0.098 185.488 U-234 5 5.17 50 12 10 10 OSC2.1

13 0.108 185.498 U-234 4 5.46 50 11 11 11 OSC1.4

14 0.119 185.509 U-234 3 5.28 50 10 12 12 OSC1.3

15 0.129 185.519 U-234 2 5.4 50 9 13 13 OSC1.2

16 0.14 185.53 U-235 13,14 12.79 50 7 16 16 FADC1.2

17 0.15 185.54 U-235 78 5 * 50 5 14 14 FADC1.1

18 0.161 185.551 U-238 209,210 20* 50 3 15 15 FADC2.1

BG - - Cf-252 10   7 20 - - -

1. Homogeneity Using CR-39 plastic track detectors

2. Mass – ContaminationUsing alpha-spectroscopy and Rutherford Back Scattering

The targets were thin layers of 100% enriched isotopes depοsited on 100μm thick Al backing using the painting technique

Characterization

1. Homogeneity

K.Ioannidis & K.Stamoulis : University of Ioannina

CR-39 track plastic detectors, placed on top of the samples for a few seconds to a few hours, depending on the activity of the sample, in order to achieve a

surface tracks’ concentration of at least 200 tracks/mm2.

237Np: activity 1.3x10 5 Bq 4 min exposure time

234U : activity 2x10 6 Bq 16 sec exposure time

238U : activity 360 Bq 24 hours exposure time

The detectors were etched in a 6 N aqueous NaOH solution, maintained at 75 °C in a water bath with a temperature control better than 1°C. Then a number of

images of the detectors’ surfaces were captured with the use of a microscope - video camera - frame grabber - computer recording arrangement.

234U 237Np

8 cm diameter5.2 cm diameter

To construct the following diagrams, images were captured every 5 mm.

Then the images were automatically analyzed using the TRIAC II software to count the number of tracks per 5x5 mm2

Homogeneous distribution within 7-9%

2. Mass – ContaminationM.Diakaki , R.Vlastou

Using alpha-spectroscopy, in a scattering chamber at a vacuum ~10-2 Torr 80mm2 Si Surface Barrier detector with a Ta mask of 4mm diameter and a calibrated

241Am α-source with various masks and at various distances from the detectorMCNP simulations to define the effective solid angle for each case

234U (4a)

From the two sides of 324U (4a and 4b) the Total Mass was estimated as 5.38+- 0.26 mg , while the nominal Total Mass was 5.46 mg

234U (2.5x105y)

232U (69y)

232U 228Th 224Ra 212Bi 220Rn 216Po 212Po

232U contamination : 0.03 %

232U contamination

Contamination of the scattering chamber

4000sec

80.000sec

Cleaning the contaminated parts of the chamber reduced the contamination by ~50%

237Np (28) measured in the air out of the chamber

From one side of 327Np (28 ) the Mass was estimated as 6.36+- 0.26 mg , while the nominal Total Mass from both sides was 12.82 mg

241Am contamination : 0.02 %

237Np

241Am

In order to do RBS measurements the external beam system will be used to avoid further contamination of the chamber

Work in progress