P. Venugopala Rao

An ultra-high resolution Ge(Li) spectrometer for singles and coincidence x-ray and gamma-ray studies☆

Abstract This paper describes the characteristics of a small (8 mm dia., depletion depth 4 mm) ultra high resolution (fwhm-450 eV at 14 keV and 1.7 keV at 1332 keV) Ge(Li) spectrometer. In particular the following were studied: resolution versus energy, the Fano factor for Ge, the full energy and K X-ray escape efficiency, and the detector linearity. Besides being used to measure singles spectra over the energy region from 6 keV to 2 MeV, the detector was used simultaneously with a high resolution Si(Li) detector to measure coincidences between Kα1, Kα2 and L X-rays.

Si(Li) spectrometers for electrons and low-energy photons

Abstract The determination of the photopeak efficiency is described for a Si(Li) spectrometer over an energy range of 5 keV to 170 keV using calibrated radioactive sources. The nature of the silicon dead layer and the active detector volume are investigated. The probability of Si K-X-ray escape from the front surface of the detector is measured as a function of energy and compared to theory. A simple design for converting a Si(Li) photon detector to an efficient and good-resolution electron detector suitable for singles and coincidence spectrometry is described.

Levels in 72Ge populated by 72Ga

Abstract The radioactive decay of 72 Ga has been investigated by means of Ge(Li) and Si(Li) detectors. The energies and intensities of 71 γ-rays have been determined from the γ-ray singles spectrum. Extensive γγ coincidence experiments were performed with two Ge(Li) detectors coupled to a two-parameter analyser. Internal conversion electron measurements were performed with a Si(Li) detector system. The electron-γ delayed coincidence experiments were carried out with an anthracene crystal and a 35 cm 3 Ge(Li) detector. These extensive coincidence relationships were used to identify the levels of 72 Ge populated by 72 Ga with excited states at 691.2, 834.02, 1463.88, 1728.24, 2064.80, 2402.0, 2463.74, 2514.65, 2583.5, 2754.1, 2943.45, 3035.41, 3094.7, 3324.92, 3341.68, 3439.3, 3455.2, 3566.0, 3678.1, 3707.1, 3758.6 and 3815.4 keV. The β − feedings and the log ƒt values were calculated from the relative γ-ray intensities.

Precision determination of high-Z K-shell fluorescence yields from195Au,207Bi, and235Np decays

A new method utilizing a cooled, high resolution, windowless Si(Li) x-ray and Auger electron detector has been developed for the accurate measurement of high-Z K-shell fluorescence yields. With this method, values of theK-fluorescence yield ωk have been determined with high accuracy atZ=78, 82, and 92 from the radioactive decay of carrier-free195Au,207Bi, and235Np, respectively. The values of ωk are 0.968±0.008, 0.972±0.008, and 0.970±0.005, respectively where the error limits represent 95% confidence. In addition, relativeK-Auger electron group intensities atZ=92 were measured and found to be(K-LL)∶(K-LX)∶(K-XY)=100∶(65.2±6.0)∶ (8.1±0.8). The experimental results for ωk are compared with the relativistic calculations of Bhalla, Ramsdale and, Rosner, and satisfactory agreement is found.

Gamma radiation in the decay of249Cf

Gamma radiation following alpha decay of249Cf was investigated with high resolution Ge(Li) detectors in singles and coincidence arrangements. Nine new γ-rays were identified and placed in the previously-known decay scheme. Their energies in keV and intensities relative to the 388 keV (100) γ-ray are: 37.5±0.1 (0.026), 65.87±0.1 (0.017), 121.5±0.4 (0.070), 229.2±0.2 (0.072), 255.7±0.2 (0.065), 390.5±0.2 (0.025), 405.9±0.1 (0.014), 588.8±0.1 (0.003), and 643.5±0.1 (0.007). Coincidence measurements revealed that the intensity of the 54.7 keV γ-ray is shared by three intraband transitions and that the 121.5 keV crossover transition is present in the ground-state band.

Note on the gamma ray spectrum from the 47Ca decay

Abstract Gamma rays of energy 41.06±0.05 and 1878.0±0.5 keV from the decay of 47 Ca are studied with high resolution Ge(Li) spectrometers using singles and coincidence methods.

A Fano factor measurement for silicon using low energy photons

Abstract The Fano factor in silicon at liquid nitrogen temperature is measured to be F = 0.143±0.006 using photons from 6.40 to 74.97 keV. No energy dependence of the value of F is found in the range of the present measurements. Extreme care was taken to eliminate possible errors caused by electronic pulse shaping, electronic gain stability and pile-up effects.

L1 subshell yields atZ=73 from the electron capture decay of181W

The TaL x ray spectrum from the electron capture decay of181W is analyzed into components characteristic of the threeL-subshells and theL1 subshell yields atZ=73 are determined to beΩ1=0.15±0.02,f12=0.23±0.05 andf13=0.32±0.02. A revised decay scheme for the decay of181W is proposed from measurements of x-ray and gamma intensities. A value of 0.97±0.08 for theK-conversion coefficient of the 153 keV transition is obtained and itsE2/M1 multipolarity mixing ratio,δ2(0.25) is deduced.

K-electron capture probabilities in the decays of Gd151 and Dy159

TheK-electron capture probability,PK, in the allowed and non-unique first-forbidden transitions is measured by observing coincidences betweenK x rays and γ rays. The following results are obtained. In Gd151 decayPK to the 349.8 keV level is 0.713 ± 0.015 andPK to the 307.4 keV level is 0.813 ± 0.020. It is also deduced that the decay energyQEC is 491−9+14 keV and the spin of the 307.4 keV level is 7/2. In Dy159 decayPK to the 58.0 keV level is found to be 0.803 ± 0.032.

Electron capture decay of181W: L subshell fluorescence and Coster-Kronig yields in Ta

The TaL x-ray spectrum from the 140 d electron capture decay of181W was studied with high resolution semiconductor detectors and fast coincidence techniques. Measurement ofL x-ray-K x-ray andL x-ray—γ-ray coincidence rates yielded the followingL shell fluorescence and Coster-Kronig yields and radiative decay branching ratios: ω2=0.250±0.013, ω3=0.228±0.013 (corrected for angular correlation effects),f23=0.180±0.007,v1=O.218±0.016,s3=0.205+-0.010,s2=0.215+-0.010,f13+f12f23=0.36+-0.02, and ω1+f12ω2=0.14±0.02, from which upper limits were obtained off13<0.36 and ω1<0.14.