1. -Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements
Irradiation position: Rabbit system #2

2. -ray detection with semi-conductors  Pulse heigth spectrum+ -
n-Ge
p-Ge
-ray
-ray produces electrical charges in the semi-conductor. Total electric charge proportional to -ray energy.
 Pulse heigth spectrum
Energy (pulse heigth)

3. -Spektroscopy of 190mOs with I = 0, 2, 4,... (rigid rotator)
(n,)-reaction produces 190mOs. 190mOs → 190gOs + 
Low-level excited states correspond to rotational and vibrational excitation of the nucleus
Rotational energy as a function of total nuclear spin I:
with I = 0, 2, 4,... (rigid rotator)
Irradiation of natOs-sample: By (n,)-reactions production of 190mOs with T½ = 9.9 min
-Spektroscopy of irradiated sample after 2, 4, 6 ….20 min.
 Determination of T½ for 190mOs and moment of inertia  of the Os-nucleus for different I

4. Measured Rigid Rotator ( = const.)
Decay scheme of 190mOs
Measured Rigid Rotator ( = const.) k
E(In+2 → In) = k [In+2(In+2+1)] – k [In(In+1)]

5. β-Delayed Neutrons Fission of 235U:
Emission of 2.4 prompt Neutrons per fission event. Time scale: ca s
 Prompt neutrons cannot be detected outside the reactor
Fission products:
Emission of a neutron if excitation energy of a daughter nucleus resulting from preceeding ß-decay is sufficiently high. Time scale: ß-decay half-life of precursor  87/89Br, 94Rb, 135Sb, 137I …… (T½= s)

6. Properties of ß-Delayed Neutrons
0,009
0,027
-----
0,23 6
0,018
0,074
0,013
420
0,61 5
0,068
0,253
0,072
620
2,3 4
0,044
0,126
0,065
430
6,2 3
0,063
0,140
0,077
560 23 2
0,007
0,021
0,022
250 55 1
Yield for thermal fission [%]
233U U Pu
Energy
[keV]
T1/2 [s]
Gruppe

7. Detection of ß-Delayed Neutrons
DNAA: Delayed Neutron Activation Analysis
Cycle: 2 min. (100 kW) – 20 s cooling time – 1 min. Measuring time
Detection of ß-delayed neutrons with 3He counting tubes via the reaction 3He(n,p)3H
Irradiation and measurement of several U- and Th-samples with and without Cd-shield. Determination of the 235U- content in U-samples
Sample
3He-Counting tube
Boron-carbide
Wood
Cadmium PE
12 3He-Zählrohre:
Efficiency………..18 %
Background………4 cpm

8. Spectrum obtained with 3He-counting tube50
100
150
200
250
300 10 1 2 3 4 5 6 7
Counts/Channel
Channel
Delayed neutrons
-Back- ground

9. Calibration Curve for 235U
Without Cd shield
With Cd shield