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-Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements

-Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements. Irradiation position: Rabbit system #2. + + + +. - - - -. n-Ge. p-Ge. -ray. -ray detection with semi-conductors.

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-Spectroscopy of Os-Isotopes ß-Delayed Neutron Measurements

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

  2. + + + + - - - - n-Ge p-Ge -ray -ray detection with semi-conductors -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 • (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

  4. 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. 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)

  6. Gruppe T1/2 [s] Energy [keV] Yield for thermal fission [%] 233U 235U 239Pu 1 55 250 0,022 0,021 0,007 2 23 560 0,077 0,140 0,063 3 6,2 430 0,065 0,126 0,044 4 2,3 620 0,072 0,253 0,068 5 0,61 420 0,013 0,074 0,018 6 0,23 ----- 0,009 0,027 0,009 Properties of ß-Delayed Neutrons

  7. Sample PE 3He-Counting tube Boron-carbide Cadmium Wood 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 12 3He-Zählrohre: Efficiency………..18 % Background………4 cpm

  8. 7 10 6 10 5 10 4 10 Counts/Channel 3 10 2 10 1 10 0 10 0 50 100 150 200 250 300 Channel Spectrum obtained with 3He-counting tube Delayed neutrons -Back-ground

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

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