F. Wagner

Correction for Phosphor Backscattering in Electron Scintillation Spectrometry

An iterative numerical integration procedure has been developed to correct both beta spectra and differential beta‐gamma directional correlations for the effects of finite instrument energy resolution including the effect of backscattering from a scintillation detector.The method has been tested and found to reproduce the true spectral shape in the cases of Re186, Au198, Tl204, and to allow separation of composite beta spectra as in the case of W187. Application of the method is limited to maximum beta energies exceeding 200 kev.

Response of NaI, anthracene and plastic scintillators to electrons and the problems of detecting low energy electrons with scintillation counters☆

Abstract The electron response of NaI(Tl) has been measured with magnetic-spectrometer-energy-selected electrons incident on cleaved crystal surfaces, in the energy range 5–1000 keV. The light output/keV (≡ response) shows a maximum in the neighborhood of 15–20 keV which is some 20% larger than that at 1 MeV; below 15 keV the response falls sharply reaching 80% of the peak value at ∼ 5 keV. The electron response of anthracene and a plastic scintillator (Pilot B) were measured under the same experimental conditions for comparison. Both anthracene and Pilot B show nonproportional response in the low energy region. At 500 keV the ratio of the responses NaI(Tl)/anthracene/Pilot B are 1.6/1.0/0.38; at 20 keV the ratios are 2.5/1.0/0.41. Decay curve analysis yields for some of the long lived states (excited by incident electrons) in NaI(Tl), 200–300 μsec, 7–9 msec, 40–80 msec, 4 sec, 1 min and 12 min; for anthracene 36 μsec, 120 μsec and 570 μsec. Relatively intense long lived states and more backscattering make NaI(Tl) not generally useful as a low energy electron detector. Uncovered anthracene mounted directly on a photomultiplier and the combination cooled to prevent sublimation of the phosphor in the high vacuum of the beta spectrometer provides a counter which has efficiencies measurable from the pulse height distributions down to ∼6 keV. At backgrounds of 300–500 cpm it has usable efficiencies down to 1 keV.

A simple cooled Si(Li) electron spectrometer

Abstract The construction of an electron spectrometer using a 80 mm 2 × × 3 mm cooled Si(Li) detector has been described. The system resolutions (fwhm) for 115, 194 and 624 keV electrons were found to be 0.88, 1.06 and 1.50 keV, respectively. The resolution (fwhm) for 5.8 MeV α-particles was found to be 12.0 keV. The Si(Li) detector did not show any deterioration in performance after several warming and cooling cycles over a period of two years. The thickness of the Si dead layer on the detector face was estimated from the energy loss of low-energy electrons and was found to be 0.6 μm. The spectrometer described here can be used for the measurement of electron lines above 20 keV energy. Also because of its simple design the spectrometer can be used for α−e − and γ−e − coincidence experiments.

Absorption spectra of NpCl3 and NpBr3

Low temperature absorption spectra are reported for NpCl3 and NpBr3 in the range 3300–40 000 cm−1. Term assignments are made to a number of excited levels not previously identified, and the data are interpreted in terms of a refined free‐ion model. Some of the parameters associated with this model are found to have similar values for both 3+ actinide and lanthanide chlorides. The values determined for other of the parameters are in good agreement with those calculated independently using Hartree‐Fock methods. The similar crystal‐field quantum number ordering of levels in the ground states of actinide trichlorides and analogous lanthanides doped into LaCl3 is noted and discussed.

Absorption spectrum of CfCl3

The absorption spectrum of thin films of CfCl3 was measured at 298, 77, and 4°K in the range 6000–46 000 cm−1. Interpretation of the results was based on systematic variation of energy level parameters over the actinide series. Electrostatic, spin‐orbit, and configuration interaction terms were calculated by diagonalization of the complete interaction matrices and a least squares fitting process involving 27‐level assignments. Compared to the energies of the first f→ d transitions observed in lighter actinide trichlorides, the corresponding band in CfCl3 appears to occur at an anomalously low energy.

Fluorescence from the TbCl3‐AlCl3 vapor complex system: A potential new gas‐phase laser

We report the first fluorescence spectrum of a lanthanide chloride–aluminum chloride vapor complex and discuss the temperature dependence of the fluorescence lifetime.

Internal conversion coefficients with relativistic hartree-fock atomic model: comparison with 67Zn

Abstract Improved agreement of measured internal conversion coefficients for 67Zn with new calculations based on a relativistic Hartree-Fock treatment with the inclusion of finite nuclear size effects was obtained, in comparison to the earlier internal conversion coefficient tabulation.

Large Volume Degausser with Gradient Compensation

A solution is presented to the practical problem of adapting known theoretical multicoil magnetic field generators for compensation of slightly inhomogeneous fields. Three concentric orthogonal sets of coils are used as uniform field generators. The two sets used to compensate the strong field components are each an array of four parallel, equal‐size square coils, separated by ⅓ of a side length, i.e., uniformly spaced on the surface of a cube. Each of these sets generates a magnetic field uniform to 2×10−4 within the central sphere of diameter equal to 0.2 of the side length of a coil. The outer pair of coils (22 turns each) and the inner pair (13 turns each) are series connected to a single current supply. By shunting small fractions of the current from one‐half of two of the three coil sets, and by appropriate location of two pairs of small coils near the main degausser coils (also series connected), field gradients that result in variations of the order of 2×10−3 of the uncompensated field over the ce...

Absorption spectrum of BkCl3

The absorption spectrum of thin films of BkCl3 was measured in the region ∞ 3800–48 000 cm−1 at 298°, 77°, and 4°K. The absence of transitions from the ground state to excited J=0 and J=1 states, together with the number of crystal field components observed in several isolated groups, suggested that the ground level BkCl3 is characterized by the crystal quantum number μ=0, as is the case in LaCl3:Tb3+. Assignments were made based in part on a predicted energy level scheme which assumed a systematic variation in energy level parameters over the actinide series. The free‐ion electrostatic, spin orbit, and configuration interaction parameters for Bk3+ were calculated by a least squares fitting process involving 23 level assignments.

Half-life of the longest-lived einsteinium isotope-252Es

Abstract The half-life of the nuclide 252 Es has been measured by following the decay of the 785.1 keV γ-ray associated with its electron capture decay. The 252 Es sample used in this study was produced by 249 Bk(α, n ) reaction. The γ-ray spectrum of a chemically purified 252 Es sample was measured with a high-resolution 25 cm 3 Ge(Li) spectrometer. 137 Cs activity, fixed to the 252 Es sample, was used as an internal calibration source to correct for variations in the source-detector geometry. The decay of the γ-ray spectrum was followed for three years. A least-squares fit to the areas of the 785.1 keV photopeaks gave a half-life of 471.7±1.9 d for 252 Es decay. This half-life indicates that 252 Es is the longest-lived einsteinium isotope.