B.K. Sinha

Performance of extrapolated leading edge timing for fast coincidence with a large-volume HPGe detector

Abstract The performance of the extrapolated leading edge type of time pickoff used with a large HPGe coaxial detector is studied. The time resolution using such a type of time pickoff has been found to be comparable with that obtained by employing the commonly used amplitude and rise-time compensation technique. For a BaF2−HPGe (27% efficiency) coincidence setup, the values of FWHM and FWTM are 3.2 and 7.0 ns, respectively, when 60Co photopeaks are selected.

Neutron-gamma discrimination based on leading edge shape measurement

A neutron-gamma discriminator using a NE213 liquid scintillator and an amplitude independent pulse risetime measurement technique is presented. A separation index S has been proposed in place of the figure of merit M to evaluate the performance. Performance of the n−γ discriminator has been studied with a 30 mCi Am-Be source in the light of S and other possible performance indices. A good performance in an in-beam experiment has been obtained for a dynamic range of 20 keV to 10 MeV electron equivalent energy.

Risetime measurement of HPGe detector pulses

Abstract A new method of measuring the risetime and its distribution of HPGe detector pulses using only one fast comparator, a delay line shorted at one end and a few discrete components is described. Setting 10% and 90% of the pulse height is easier and definite. The calibration procedure is also simple. Pulses from two HPGe detectors of different sizes detecting gamma rays of different energies are studied.

Studies on a pulse shaping system for fast coincidence with very large volume HPGe detectors

Abstract A variant of the leading edge timing (LET) has been proposed which compensates the “walk” due to risetime spread in very large volume (∼ 100 cm3) HPGe detectors. The method - shape compensated leading edge timing (SCLET) — can be used over a wide dynamic range of energies with 100% efficiency and has been compared with the LET and ARC methods. A time resolution of 10 ns fwhm and 21 ns fwtm has been obtained with 22Na gamma rays and two HPGe detectors of 96 and 114 cm3 volume. This circuit is easy to duplicate and use and can be a low cost alternative to commercial circuits in experiments requiring a large number of detectors.

Measurement of quadrupole moment of the 134 keV level in 131Cs

Abstract: The time differential as well as time integral perturbed angular correlations of the 486-134 keV cascade in 131Cs have been studied in a polycrystalline BaSO4 powder source using a HPGe-BaF2 detector system. The fundamental quadrupole frequency for the 134 keV level has been found to be ω0= (4.4 ± 0.4) × 107 rad/s. From a comparison of the quadrupole frequencies of this level and that of the 81 keV level in 133Cs, measured earlier in the same crystalline environment of the source, the absolute value of the quadrupole moment of the 134 keV level in 131Cs has been found to be 0.022 ± 0.002 b. This value of the quadrupole moment is reported for the first time and compared with the value predicted theoretically within the unified nuclear model with intermediate coupling.

0+ analogue state in118Sb from117Sn(p,nγ) reaction

The analogue of the 0+ ground state in118Sn has been observed in the compound nucleus118Sb through117Sn(p,nγ)117Sb reaction. The neutron decays of this analogue resonance have been studied from the deexcitingγ-rays of the residual nucleus117Sb. From off resonance excitation functions, spin assignments have been made to states in117Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.

Hrynkiewicz's third relation and its application in the measurement of magnetic moments

Abstract The magnetic moment of the 87 keV level of 160 Dy is measured using the third relation of Hrynkiewicz for a two angle variant of the differential perturbed angular correlation method. The advantage of using this method is also indicated.

Pulse shaping for fast coincidence with NaI(Tl) detectors

Abstract The effect of multiple limiting of the anode pulses of the photomultiplier tubes on the resolving time of an NaI(Tl)-NaI(Tl) fast coincidence set up is investigated with the help of a simple transistorised limiter circuit. The performance of the set up for different energy ranges selected in the side channels is also investigated.

Lifetimes of the 321, 636 and 642 keV levels of125Te

SummaryThe lifetimes of the 321, 636 and 642 keV levels of125Te have been reported from delayed coincidence measurements using BaF2 and plastic scintillation detectors. The values of half-life are measured to be (647±8) ps for the 321 keV level and ⩽70 ps for the 636 and 642 keV levels.

Time-differential angular correlation of the 208-113keV cascade of177Hf at subnanosecond time resolution

SummaryMeasurements of time-differential angular correlation on the 208-113keV cascade of177Hf have been performed, for the first time, in liquid chloride and nitrate sources at a time resolution of 620ps. The results obtained are:A2(0)=−0.162±0.004, λ2=(6.4±2.6)·107 s−1 in the LuCl3 source andA2(0)=−0.165±0.006, λ2=(7.5±4.0)·107 s−1 in the Lu(NO3)3 source. From the average value ofA2(0) in chloride and nitrate sources the mixing ratio of the 113keV γ-transition is found to beδ=−4.85±0.05.