Ge Gamma-ray Detectors Research Articles

Decay of 90Kr and 90Rb

The decay of 32 s 90Kr and 154 s 90Rb has been studied using NE102 beta detectors and NaI(Tl) and Ge(Li) gamma-ray detectors, singly and in coincidence. Thirteen excited states of 90Rb involving 35 transitions have been identified with excitation energies of 0.1064, 0.1215, 0.2419, 0.3557, 0.6144, 0.6610, 0.7408, 0.8375, 1.2402, 1.6740(1+), 1.7798(1+), 2.1261(1+), and 3.0937(1+) MeV. The 256 s isomeric state at an excitation of 0.1064 MeV (probably 4–) feeds high spin states of 90Sr at 2.2068, 2.4972, 2.5712, 2.9275, 3.5835, 4.1485, 4.3355, and 5.0397 MeV with a total intensity of 12%. The 154 s ground state of 90Rb feeds many low spin states in 90Sr, including the levels at 0.8315, 1.6555, 1.8921, 2.5271, 3.0385, 3.3833, 3.4497, 3.8985, 4.0325, 4.0360, 4.1360, 4.3660, 4.6466, 4.891, 4.921, 4.974, 5.070, 5.091, 5.163, 5.1876, 5.2540, 5.285, and 5.3336 MeV. Sixty-four transitions in 90Sr have been classified in this manner. The decay energy of 90Kr is 4.41 ± 0.03 MeV.

Estimation of the elapsed time after nuclear explosion by measuring activity ratio of 95Zr and 95Nb in the radioactive fall-out

A method for estimation of the elapsed time after nuclear explosion from a given radioactive fall-out has been developed wherein activities of 95Zr and 95Nb belonging to same decay chain in fission products are measured by the Ge(Li) gamma-ray detector, and the elapsed time is calculated from their activity ratio. The experimental results obtained from neutron irradiated uranium sample and from radioactive fall-out which had been found in Nagano City, Japan after the nuclear explosion experiment in China were good agreement with theoretical values. The method can be applied to estimation of history or origin on a given radioactive fall-out.

A Ge(Li) two crystal compton spectrometer

The performance of Compton spectrometers using two Ge(Li) gamma-ray detectors is demonstrated. Two different configurations of detectors have been used, together with on-line computer methods to show that a nearly-single-peak spectrum of good resolution can be obtained for a monochromatic gamma ray. Further, the peak is due to purely single Compton scattering of well determined scattering angle despite the large solid angles of the scattering and detecting crystals. These considerations make the device well suited to use as a gamma-ray polarimeter.

Lifetime measurements in mass-15 nuclei

The Doppler shift attenuation observed with a Ge(Li) gamma-ray detector was used to gain information on the electromagnetic decay rates of some bound levels of mass-15 nuclei. The values τ = 60±20 fs and τ = 700±150 fs were found for the mean life of the 7.563 MeV ( 15N) and 7.276 MeV ( 15O) levels, respectively. Upper lifetime limits were placed on the 15N levels at 6.323, 7.154, 7.300 and 8.312 MeV and on the 15O levels at 6.180, 6.789 and 6.857 MeV.

On the Origin of Leakage Current in Ge(Li) Gamma-Ray Detectors

Hole-electron pair generation in Ge(Li) γ-ray detectors due to thermal radiation from the cryostat outer casing is suggested as an often overlooked source of detector leakage current. Thermal-radiation-induced currents of the order of 10-9A are estimated for a typical large coaxial detector at 77°K when the cryostat outer casing is at 300°K.

Levels in the N = 82 nucleus 139La populated in 139Ba decay

The decay of 139Ba to levels in 139La was investigated using Ge(Li) gamma-ray detectors. On the basis of energy, intensity and coincidence measurements, a new decay scheme is proposed. In addition to well-known levels at 166 and 1420 keV, 12 new levels between 1200 and 2100 keV were observed. The results are compared with those for other odd-mass N = 82 isotones.

A risetime spectrometer for studying pulse shapes in Ge(Li) gamma-ray detectors

A risetime spectrometer has been developed to study the shape and distribution of shapes of γ-ray pulses from Ge(Li) detectors. This instrument employs a time to amplitude converter, a multichannel pulse height analyzer, and two discriminators to measure the distribution of times required for full-energy γ-ray pulses to reach a predetermined fraction of full pulse height. Using the risetime spectrometer and collimated beam techniques, pulse shapes from a planar and a coaxial detector were determined as a function of the position of irradiation in the detector. The measured pulse shapes were in close agreement with calculated pulse shapes.

Measurement of the ϵ/ β+ ratio in the decay of 22Na and 74As

The ϵ/ β + ratios of the transitions from 22Na and 74As to the first excited state of 22Ne and 74Ge were measured as 0.1042±0.0010 and 1.288±0.018, respectively. The coincidence method was applied, using a 4 π β-scintillation detector and NaI and Ge(Li) gamma-ray detectors.

Levels in the 89-neutron nucleus 153Gd

The electron-capture of 57 h 153Tb has been studied with isotope-separated sources by means of direct and coincidence spectrometry with a six-gap beta-ray spectrometer and Ge(Li) gamma-ray detectors. New levels in 153Gd were established at 315.1 and 1103 keV. New relative parity assignments were made for levels at 183.5, 249.6, 315.1, 368.6, 448, 549, 946 and 1103 keV.

Effects produced by fast neutron bombardment of Ge(Li) gamma ray detectors

The effects of fast neutron bombardment on Ge(Li) gamma-ray detectors have been investigated at neutron energies of 1.10, 5.75 and 16.49 MeV. Measurements were made of reverse leakage current, capacitance, rise-time, energy resolution, and pulse-height decrease as a function of neutron dose. A degradation of energy resolution was the most notable effect and occurred for each energy after approximately 10 10 n/cm 2. Experiments with a collimated gamma-ray source show that the degradation in energy resolution is due primarily to hole trapping. Calculations were made of the total number of defects produced by the bombardment of 1.2×10 11 n/cm 2 at 1.10 MeV and a value of 1.3×10 13 defects/cm 3 is estimated. Some rougher estimates were made at the other energies. Procedures and results obtained in processing two detectors after irradiation are described. The detector irradiated at 16.49 MeV was restored by redrifting at ∼30°C.

An empirical method for determining the relative efficiency of a Ge(Li) gamma-ray detector

An empirical method for determining the full-energy peak efficiency between 0.2 and 3.0 MeV and the two-escape peak efficiency between 2 and 9 MeV of a Ge(Li) gamma-ray detector is described. The full-energy peak efficiency is determined with the use of several nuclides which emit gamma rays with accurately known intensity ratios and a linear least-squares fitting procedure. With the full-energy peak efficiency determined, a number of high and low energy thermal neutron capture gamma ray cascades with known relative intensities are then utilized in the determination of the two-escape peak efficiency.

Contribution à l'étude du doublet de niveaux à 6.88 MeV de 28Si

Using a Ge(Li) gamma-ray detector and a magnetic pair spectrometer changed into a “multipole meter”, we have studied gamma-rays from 28Si. Our results show that in the doublet at 6.88 MeV the excitation energy of the level 6.88 a MeV, which decays primarily to the ground state, is lower than that of the other level 6.88 b MeV which decays essentially to the 1.78 MeV first excited state. The study with the “multipole meter” of the 6.88 a MeV → 0 transition shows that this transition is probably E3. Consequently this level has probably J π = 3 −.

Measurement of the Energy Loss of Germanium Atoms to Electrons in Germanium at Energies below 100 keV. II

The amount of energy lost in the production of hole-electron pairs by germanium atoms stopping in a germanium crystal has been measured at energies of 56.2 and 102.9 keV. Inelastic neutron scattering in a Ge(Li) gamma-ray detector was used to produce the 690-keV ${\mathrm{Ge}}^{72}$ state and the 596-keV ${\mathrm{Ge}}^{74}$ state. The lines corresponding to the de-excitation of these states were broadened by summing with the hole-electron pairs produced by the recoiling Ge atom. A particular recoil energy was selected by requiring a coincidence with the outgoing inelastically scattered neutron, which was detected by a stilbene recoil counter placed at either 90\ifmmode^\circ\else\textdegree\fi{} or 150\ifmmode^\circ\else\textdegree\fi{} to the incident neutron beam. The results of the present experiment confirm a previous investigation by Chasman, Jones, and Ristinen and do not agree with the published results of Sattler, Vook, and Palms.

Decay ofAg103

Natural palladium foil was irradiated with 18-MeV protons to produce 1.1-h ${\mathrm{Ag}}^{103}$ by ($p,xn$) reactions. The target foil was placed directly into the ion source of the Princeton isotope separator, and the silver isotopes were volatilized, dispersed, and collected. Spectroscopic data were obtained using Ge(Li) gamma-ray detectors, an orange-type electron spectrometer, and permanent magnet spectrographs. Transitions were observed at 118.66, 148.26, 244.5, 266.9, 532.2, (555.9), 578.8, 741.9, 940.6, 1007.1, 1030.3, 1155.8, 1183.6, and 1274.6 keV. (Energies of doubtful transitions are mentioned in parentheses.) Gamma-ray spectra in coincidence with several conversion-electron lines, taken with a NaI(Tl) detector in conjunction with the orange spectrometer, gave evidence for levels in ${\mathrm{Pd}}^{103}$ at 0, 118.7, 244.5, 266.9, (532), (823), (1184), and 1274.4 keV.

Properties of Excited States inC14

The 6.59-, 6.72-, 6.89-, and 7.34-MeV levels of ${\mathrm{C}}^{14}$, formed in the ${\mathrm{C}}^{13}(d, p){\mathrm{C}}^{14}$ reaction, have been studied by means of proton-gamma and gamma-gamma coincidence techniques, magnetic-pair spectrometer measurements, and observations with a Ge(Li) gamma-ray detector. Transition branches from the 6.59-MeV level are 6.59 \ensuremath{\rightarrow} 6.09 [(99.0\ifmmode\pm\else\textpm\fi{}0.4)%] and 6.59 \ensuremath{\rightarrow} 0[(1.0\ifmmode\pm\else\textpm\fi{}0.4)%]. Gamma-ray branches determined for the 6.72-MeV level are 6.72 \ensuremath{\rightarrow} 6.09 [(7\ifmmode\pm\else\textpm\fi{}2)%] and 6.72 \ensuremath{\rightarrow} 0[(93\ifmmode\pm\else\textpm\fi{}2)%]. For the 7.34-MeV level the gamma-ray branches are 7.34 \ensuremath{\rightarrow} 6.72 [(35\ifmmode\pm\else\textpm\fi{}7)%], 7.34 \ensuremath{\rightarrow} 6.09 [(47\ifmmode\pm\else\textpm\fi{}4)%], and 7.34 \ensuremath{\rightarrow} 0[(18\ifmmode\pm\else\textpm\fi{}4)%]. Multipolarity measurements with the magnetic pair spectrometer have shown that the 6.72-MeV transition is almost certainly $E3$ and that the 7.34-MeV transition is not $E1$. Gamma rays observed with the Ge(Li) detector from the 6.72 \ensuremath{\rightarrow} 0 and 6.59 \ensuremath{\rightarrow} 6.09 transitions are neither Doppler-broadened nor Doppler-shifted, whereas the gamma rays from the 7.34 \ensuremath{\rightarrow} 0, 7.34 \ensuremath{\rightarrow} 6.09, and 6.89 \ensuremath{\rightarrow} 6.09 transitions exhibit Doppler effects. Accurate gamma-ray energies were measured for some of the cascade transitions. By combining the various observations with previous work, it is concluded that the 6.72-MeV level is ${J}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ and the 7.34-MeV level is ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$. Theoretical calculations have been made for the various transition rates in ${\mathrm{C}}^{14}$ and are compared with the experimental results. An incidental experimental result is a value of 495.33\ifmmode\pm\else\textpm\fi{}0.10 keV for the energy of the first excited state of ${\mathrm{F}}^{17}$.

The accurate measurement of the relative efficiency of Ge(Li) gamma-ray detectors in the energy range 500 to 1500 keV

A method is discussed for obtaining empirically the relative total-energy-peak efficiency, ε, over the gamma-ray energy range 500 to 1500 keV, for any given Ge(Li) detector in a specific geometry. Use is made of sources for which the relative emission rates of pairs of gamma rays are precisely known. An accuracy of about 1% in the relative efficiency curve is obtainable by use of the semi-empirical formula ε α ⊥ + σA exp (− BE), where ⊥ and σ are photoelectric and Compton absorption coefficients respectively, E is the gamma-ray energy and A and B are constants determined from the gamma-ray measurements.

The accurate measurement of the relative efficiency of Ge(Li) gamma-ray detectors in the energy range 500 to 1500 keV

A method is discussed for obtaining empirically the relative total-energy-peak efficiency, ϵ, over the gamma-ray energy range 500 to 1500 keV, for any given Ge(Li) detector in a specific geometry. Use is made of sources for which the relative emission rates of pairs of gamma rays are precisely known. An accuracy of about 1% in the relative efficiency curve is obtainable by use of the semi-empirical formula ϵ ∝ τ + σ A exp (− BE), where τ and σ are photoelectric and Compton absorption coefficients respectively, E is the gamma-ray energy and A and B are constants determined from the gamma-ray measurements.

LIFETIMES OF THE 16O 6.13-MeV LEVEL AND THE 17O 0.871-MeV LEVEL

The mean lifetimes of the 0.871-MeV state of 17O(E2) and the 6.13-MeV state of 16O(E3) have been measured by a new recoil method using a Ge(Li) gamma-ray detector. The data yield mean lifetimes of (2.33 ± 0.27) × 10−10 and (2.5 ± 0.2) × 10−11 sec for the states in 17O and 16O respectively. The recoil method is generally applicable to the measurement of lifetimes greater than about 5 × 10−12 sec and provides a technique for a region of time where neither direct electronic timing nor Doppler-shift attenuation methods are accurate.