-Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements Irradiation position: Rabbit system #2 16.11.2018

-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) 16.11.2018

-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 190Os-nucleus for different I 16.11.2018

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)] 16.11.2018

β-Delayed Neutrons Fission of 235U: Emission of 2.4 prompt Neutrons per fission event. Time scale: ca. 10-15 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= 2 - 56 s) 16.11.2018

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 235U 239Pu Energy [keV] T1/2 [s] Gruppe 16.11.2018

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 16.11.2018

Spectrum obtained with 3He-counting tube 50 100 150 200 250 300 10 1 2 3 4 5 6 7 Counts/Channel Channel Delayed neutrons -Back- ground 16.11.2018

Calibration Curve for 235U Without Cd shield With Cd shield 16.11.2018