Direct measurement of product of the electron mobility and mean free drift time of CdZnTe semiconductors using position sensitive single polarity charge sensing detectors

This article describes novel techniques to directly measure the electron mobility and mean free drift time product μeτeμeτe in semiconductor detectors. These methods are based on newly developed single polarity charge sensing and depth sensing techniques. Compared with conventional methods based on the Hecht relation, the new methods do not involve curve fitting, are less sensitive to the variation of pulse rise times, and allow the use of higher energy γ rays typical of many applications. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70289/2/JAPIAU-84-10-5566-1.pd

Measurement of the 171Tm isomeric lifetime as a teaching laboratory experiment

A teaching experiment is described in which two methods are applied to determine the lifetime of an isomeric state in 171mTm. One method, a single channel measurement, utilizes a delayed coincidence technique while the second, a multichannel measurement, employs time-to-pulse height conversion. Both serve to illustrate several principles of coincidence and timing measurements and can give results of good accuracy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32703/1/0000070.pd

Digital synthesis of pulse shapes in real time for high resolution radiation spectroscopy

Techniques have been developed for the synthesis of pulse shapes using fast digital schemes in place of the traditional analog methods of pulse shaping. Efficient recursive algorithms have been developed that allow real time implementation of a shaper that can produce either trapezoidal or triangular pulse shapes. Other recursive techniques are presented which allow a synthesis of finite cusp-like shapes. Preliminary experimental tests show potential advantages of using these techniques in high resolution, high count rate pulse spectroscopy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31506/1/0000428.pd

Calculated gamma ray response characteristics of semiconductor detectors

A Monte Carlo computer program has been used to calculate characteristics of the response of fully depleted silicon and germanium radiation detectors to monoenergetic gamma rays. Data for total absorption probability, intrinsic efficiency, escape peak efficiency and pulse height spectra are presented as functions of detector thickness and photon energy. Other parameters of interest in analysing detector response are also given. The results of a second Monte Carlo calculation of electron migration in silicon and germanium are employed to account for the leakage of secondary electrons from the detector volume. Bremsstrahlung energy loss by electrons is also simulated. The calculations are expected to be applicable in those cases in which secondary electron energies do not exceed 2 MeV. Comparison with experiment shows good agreement within this limitation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33414/1/0000815.pd

Fission cross-sections of 235U and 239Pu averaged over 252Cf neutron spectrum

A series of measurements have been carried out to derive values for the spectrum-averaged fission cross-section of 235U and 239Pu for 252Cf fission neutrons. Two nearly identical target foils were mounted on either side of a Cf source (107 neutron/sec) in a compensated beam geometry. Fission fragments passing through limited solid angle apertures were recorded from each foil by solid-state track-etch techniques. The Cf neutron source strength was calibrated in manganese bath relative to the standard source NBS-II. Values of 1.215 +/- 0.022 barn for 235U and 1.790 +/- 0.041 barn for 239Pu were obtained for the fission cross-sections, corresponding to a ratio value of 1.473 +/- 0.041.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22759/1/0000314.pd

An absolute determination of the 235U fission cross section at 964 keV

An absolute measurement of the 235U fission cross section has been carried out using a 24Na---Be photoneutron source with median neutron energy of 964 keV. A symmetric two-foil experiment was set up to measure the fission rate in a low-albedo laboratory, and variations in the source-to-foil spacing used to determine the room background. Fission fragments passing through a limited solid angle aperture were recorded from each foil by solid state tracketch techniques. The photoneutron source was calibrated after each run using the manganese bath method and the secondary national standard source NBS-II. A computed neutron source spectrum with 32 keV FWHM was derived by the Monte Carlo method and used in reducing the data to a cross section at 964 keV. The final value of 1.21 +/- 0.025 barns is absolute in that, except for small corrections, its determination was independent of any other cross section data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22187/1/0000618.pd

Evaluation and measurement of the experimental gamma-ray peak broadenings and recovery times in a gain stabilized system

Peak broadenings induced by gain wander in a gain stabilized system were measured and found to approximate values determined from prediction techniques and a system simulation. An equation is derived for the recovery time of the system; its predictions are validated by experimental measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31114/1/0000010.pd

Evaluation of p-terphenyl and 2,2" dimethyl-p-terphenyl as wavelength shifters for barium fluoride

p-Terphenyl (PTP) and 2,2" dimethyl-p-terphenyl (DMT) have been investigated for use as wavelength shifters (WLSs) for barium fluoride (BaF2) scintillation emission. These two organic fluors are attractive due to their high quantum efficiency, fast fluorescence decay time, and emissions above the wavelength cut-off of borosilicate glass. Measurements of these WLSs dissolved in cyclohexane are presented. Coincidence time spectra and fluorescence decay spectra measured with BaF2 as the pump source, are shown. The fluorescence decay time and the ratio of fast to slow intensities were determined from the fluorescence decay spectrum. The increase in signal resulting from using a WLS between the borosilicate end-window photomultiplier tube and the BaF2 crystal is measured. The motivation behind this work is the development of a gamma-ray spectrometer suitable for high count rate applications. We are also investigating the possibility of separating the fast and slow emissions of BaF2 using optical techniques. PTP and DMT both can spectrally separate BaFe2 emissions to a marginal extent.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30880/1/0000545.pd

Evaluation of wavelength shifters for spectral separation of barium fluoride emissions

Application of the barium fluoride (BaF2) scintillator for characterization of intense radiation fields has been pursued since the fast component was discovered in the early 1980's. Unfortunately, ~ 80% of the scintillator emissions have a slow ~ 600 ns decay time constant. The long decay time hampers the use of BaF2 at high count rates because the slow emissions appear as an afterglow which has an intensity that varies with the interaction rate in the crystal. The temporal separation of BaF2 emissions by spectral separation using wavelength shifting techniques has been explored in this work. Of the wavelength shifting techniques that were examined, the solvent excitation technique showed the greatest potential, but was insufficient by itself to suppress the slow emissions to the desired degree. All the wavelength shifting techniques yield an enhanced ratio of fast to slow photons, but a decreased fast photoelectron yield.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31384/1/0000297.pd