Three-crystal Pair Spectrometer Research Articles

Studies of the gamma-strength function and low energy levels in 65Ga using the (p, γ) average resonance method

The 64Zn(p, γ) 65Ga reaction has been studied in the proton energy ranges E p = 2.0–2.9 and 3.3–4.3 MeV. Using a three-crystal pair spectrometer, gamma-ray spectra of primary transitions were measured throughout this proton energy interval in steps of about 20 keV. An average gamma ray spectrum for each energy region was formed by adding all the relevant individual spectra after adjustment due to the change of the proton energy. In the excitation energy range 0.0–3.7 MeV 50 levels, of which 20 are new, were observed. The gamma strength function was deduced from the average intensities of the primary gamma-rays. The absolute value of the strength function was found to be 5–10 times smaller than that expected from the extrapolation of the lorentzian shape of the El giant resonance.

A new facility for averaged resonance capture studies at the Omega West reactor

A facility has been developed at the Omega West reactor at Los Alamos to provide neutron beams of 2 and 24 keV average neutron energies. The neutron beam currents are comparable with those obtained at the Brookhaven high flux beam reactor. A three-crystal pair spectrometer has been developed to allow acquisition of high resolution primary neutron capture gamma ray spectra. This will be used for nuclear spectroscopy and structure studies.

Gamma-ray strength function measurement for 63Cu

The 62Ni(p, γ) 63Cu reaction has been studied in the proton energy range E p = 1.9–2.4 MeV. Using a three-crystal pair spectrometer, γ-ray spectra of primary transitions have been measured throughout this proton energy interval in steps of about 4 keV. An average γ-ray spectrum was formed by adding all the individual spectra after proper adjustment as a result of the alterations in proton energy. From the average intensities of the primary γ-rays the γ-ray strength function for energies between 5 and 8 MeV was deduced. It was found that the values of the γ-ray strength function, in the region investigated, display a much steeper slope than the giant dipole resonance predicts.

Investigation of the γ-ray strength function in 64, 66Zn by means of the average resonance method

The reactions 63 Cu( p, γ) 64 Zn and 65 Cu( p, γ) 66 Zn have been used to study the average intensities of primary γ-rays from compound nuclear states in a broad energy region just below the neutron binding energy in 64Zn and 66Zn. The γ-rays were detected with a three-crystal pair spectrometer for differences in the proton energies of 16–20 keV. Spectra obtained in this way were added to get one averaged spectrum for each of the two nuclei. Comparison of the relative intensities of the primary γ-ray transitions were made with the predictions of the compound nucleus statistical model. The E1 γ-ray strength functions for energies below 11 MeV have been deduced from the results.

Investigation of the γ-ray strength function in 51V by means of the average resonance method

A three-crystal pair spectrometer has been used to study the 50Ti(p, γ) 51V reaction for E p = 2.1–2.5MeV and2.6–3.1MeV The γ-ray spectra were measured throughout the proton energy interval in steps of about 15 keV. These spectra were added to get only one averaged spectrum. The intensities of high-energy γ-transitions populating the low-excited states of 51V have been determined. The intensities of the γ-rays to final states with known J π values were tested against theoretical calculations based on the Hauser-Feshbach theory with good results. The γ-ray strength function for energies lower than 11 MeV has been evaluated from the measured average intensities of primary γ-rays.

Investigation of65Cu by means of the average resonance proton capture method

The64Ni(p, γ)65Cu reaction has been studied in the proton energy rangeEp=2.05–2.55 MeV. The gamma-ray spectra were recorded with a three-crystal pair spectrometer at proton energy differences of 19 keV covering the proton energy range. An average gamma-ray spectrum was formed by adding all the individual spectra after proper adjustment as a result of the alterations in proton energy. The intensities of the gamma rays to final states with knownJπ-values were tested against theoretical calculations based on the Hauser-Feshbach theory. The gamma-ray strength function for energies lower than 9 MeV has been extracted from the experiment.

Average resonance spectroscopy in 93, 95, 97Tc

The (p, γ) reactions on the 92Mo, 94Mo and 96Mo isotopes were studied in the energy range E p = 2.4–3.0 MeV using a Ge(Li) detector incorporated into a three-crystal pair spectrometer and a Ge(Li) detector in coincidence with a NaI(Tl) detector. A three-crystal pair spectrometer was utilized to determine the average yield of γ-rays leading directly to the low-lying states in each of the three residual nuclei. These average yields were examined for a possible correlation between the intensity of high-energy γ-ray transitions and the J π of the final state. The data indicate that such a correlation exists. A two-dimensional coincidence experiment determined the decay scheme of the low-lying excited states in 93Tc 95Tc and 97Tc. The J π assignments inferred from these experiments are consistent with those for the states in 93Tc, 95Tc and 97Tc which have previously been obtained. For those states which were previously unassigned, the results of this experiment are as follows (all energies are in keV): 93 Tc-680 ( 7 2 +), 1193 ( 5 2 +), 1406 ( 1 2 −, 3 2 −), 1555 ( 1 2 −, 3 2 −), 2429 (≦ 5 2 ); 95Tc-1278 ( 3 2 +), 1619 ( 3 2 +, 5 2 −), 2556 (≧ 5 2 ); 97Tc-948 ( 1 2 −, 3 2 −), 1060 ( 5 2 ±, 7 2 +), 1138 ( 5 2 ±), 1366 ( 3 2 +), 1387 ( 3 2 +, 5 2 ∼), 1517 ( 1 2 −, 3 2 −), 1573( 3 2 +, 5 2 ±), 1676 ( 3 2 +, 5 2 ±) . The state at 2429 keV in 93Tc has not been reported previously.

A Theoretical and Laboratory Evaluation of Carbon Logging - Laboratory Evaluation

Abstract Results we presented from a laboratory experimental evaluation of a carbon well-logging tool based on the detection of the 4.43-MeV gamma rays produced by the inelastic scattering of 14-MeV neutrons. The success of a carbon logging tool is dependent primarily upon the gamma-ray detection scheme used, which in this investigation is a two-crystal pair spectrometer. Using such a device in a simulated reservoir with and without casing and a cement annulus, semiquantitative detection of carbon was accomplished for a fluid-filled packed sand of 35-percent porosity. Analysis of the spectral results show that the log would be sensitive to lithology, saturation and porosity as well as carbon. With the resolution of this particular gamma-ray detector scheme, the presence of the casing using seen, but did not interfere with the carbon signal. Likewise the 1-in. annulus of concrete had no effect on the carbon detection. Comparison of our results with those previously published show that the oxygen and silicon interference encountered i, other proposed logging schemes is eliminated by the two-crystal pair spectrometer. As presently envisaged, between 5 to 10 minutes per pay zone to be evaluated is required to per pay zone to be evaluated is required to accumulate raw data. However, the growth potential offered by the new Ge(Li) gamma-ray counters may well remove this restriction. Introduction Theoretical results presented in Ref. 1 have indicated that liquid hydrocarbons should be detectable in noncarbonaceous reservoirs. Although the interference problem posed by energy degraded gamma rays from omnipresent oxygen is severe, it is not severe enough to prohibit detection of hydrocarbons by nuclear means. The theoretical data also showed thermal neutron effects caused by energy degradation of gamma rays from thermal capture in silicon, chlorine and iron could be eliminated by proper choice of a neutron source gamma detector gating scheme. Indeed, this has been demonstrated experimentally. The crux of the hydrocarbon detection problem lies with finding a gamma detector system with sufficient resolution to pick out 4.43-MeV gamma rays (carbon) from the background provided by oxygen. Previous investigations have shown that single NaI(T1) crystal detectors did not have sufficient energy resolution to accomplish the task. However, energy resolution is not the whole answer when it comes to extracting a monoenergetic signal from a continuum background. In addition to the interfering gamma rays produced through Compton collisions external to the detector system, there is an in-crystal Compton background in single-crystal spectrometry. The second source of interference arises because gamma rays entering the crystal at energies higher than the discrete energy of interest will produce Compton collisions within the crystal generating electrons that have precisely the same energy as that of the "desired signal". This second source of interference significantly reduces the carbon sensitivity of a single-crystal detector. Hence, elimination of the in-crystal background from oxygen produced gamma rays would go far in improving the in-situ carbon detection picture. In searching for an acceptable detector system, this point was kept foremost in mind. It was known a three-crystal pair spectrometer would virtually eliminate the in-crystal Compton background, but limitations imposed by borehole tool size ruled out its use. However, from studying the working principle of this device the concept of the principle of this device the concept of the two-crystal pair spectrometer emerged. A description of such a device was later found in Ref. 4 although no evidence has been found that such a device has been used to record spectra in a borehole or simulated borehole environment. This report presents experimental results obtained with such a presents experimental results obtained with such a two-crystal spectrometer in various simulated reservoir conditions. SPEJ P. 129

Lifetimes in 32S

Lifetimes have been measured for five levels in 32S. The levels were populated by inelastic scattering of protons, and the gamma rays were detected at angles between 0° and 127° using a 40 cm3 Ge(Li) detector mounted inside a split annular NaI(Tl) crystal. The spectrometer was used simultaneously as both an escape-suppressed and a three-crystal pair spectrometer. Decay schemes and lifetimes have been determined using thick targets of PbS, MoS2, and sulfur cooled to 77 °K. Lifetime information was obtained both from analysis of the observed gamma-ray line shapes and from analysis of the Doppler shift attenuation in the different target materials. The two methods of analysis agree within the errors. A weak ground-state transition was observed from the J = 3 level at 5.012 MeV, establishing its parity as negative. Analysis of the line shape observed at 0° and the Doppler shift attenuation gave an average lifetime of 7.5 ± 0.5 × 10−13 s. The observed branching ratio (4 ± 0.4% to the ground state) implies an E3 enhancement of 20 ± 2.4 Weisskopf units (W.u.). A similar analysis gave a lifetime of 4.9 ± 0.9 × 10−13 s for the J = 1 level at 4.699 MeV, which implies that the dipole transition to the ground state is highly retarded. Lifetimes have also been measured for levels at 3.780 MeV [Formula: see text], 4.288 MeV (7.4 ± 0.6 × 10−14 s), and 5410 MeV (1.9 ± 0.2 × 10−13 s); the transition strengths are tabulated and discussed.

Sur la discrimination de forme, dans un spectrometre a coincidences, des impulsions livrees par un detecteur Au germanium

A simple and accurate pulse shape discrimination method is described for coincidence spectrometers using Ge(Li) detectors. Gamma ray pulses degraded by electron interaction in Ge(Li) detector's dead layers are rejected within 40% by delaying the Ge(Li) crossover signals. Spectra given by a Ge(Li)NaI(Tl) three-crystal pair spectrometer with and without rejection are shown. Results are compared with elaborated and much more expensive methods.

A Ge(Li)-Ge(Li)-NaI(Tl) coincidence spectrometer system for (n,γ) studies

A spectrometer system has been constructed to study 0.06–12 MeV neutron-capture γ-rays produced at the thermal-beam facility of the Livermore Pool Type Reactor. The system consists of two spectrometers, designed to cover the low-energy (0.06–2.5 MeV) and high-energy (2–12 MeV) portions of the spectrum. The low-energy system consists of a Ge(Li) detector surrounded by a NaI(Tl) anti-Compton shield, operated in anticoincidence. The high-energy system consists of a Ge(Li) detector flanked by two NaI(Tl) counters and operated in the coincidence mode as a “three-crystal pair spectrometer”. These systems are operated independently, or in coincidence. In the latter case, certain NaI(Tl) modes must be disengaged to obtain adequate coincidence efficiency. An automated pulser is used for linearity calibration and stabilization. Coincidence data is processed by a 4096-channel three-parameter pulse-height analyzer, buffered onto magnetic tape, and analyzed off-line by digital computers.

Small split NaI(Tl) annulus-Ge(Li) spectrometer for coincidence - anticoincidence with in-beam gammas

A small gamma-ray spectroscopy system useful for in-beam spectroscopy is described. The system consists of a small Ge(Li) central detector surrounded by a 12.7 cm o.d. by 2.5 cm i.d. by 14.0 cm long NaI(Tl) annulus split into quadrants. The system can be operated as an anti-Compton spectrometer, in which case the Compton continuum is reduced by a factor of 3 to 6. Approximate calculations of the expected Compton reduction factor were made and the results compared to experiment. In addition, the system can be used as a three-crystal pair spectrometer. Results are presented.

Inelastic Scattering of Monochromatic Photons from the 7.64-MeV Level ofNi62

The nuclear resonant scattering of the monochromatic iron capture gamma rays from natural nickel was studied with a single NaI crystal and a three-crystal pair spectrometer. The spectrum of the scattered photons exhibits three photon groups of 7.64, 6.47, and 5.38 MeV with relative intensities 0.69, 0.08, and 0.23, respectively. The spectrum of the low-energy cascade photons in coincidence with the scattered photons identifies these groups with the transitions from the 7.64-MeV resonant level to the ${0}^{+}$ ground state and the first (${2}^{+}$, 1.17 MeV) and second (${0}^{+}$, 2.05 MeV) vibrational levels in ${\mathrm{Ni}}^{62}$. Angular distribution measurements of the elastically scattered photons show that the 7.64-MeV level in ${\mathrm{Ni}}^{62}$ has angular momentum 1. The elastic-scattering cross section averaged over the incident gamma rays was determined to be $〈{\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}〉=190\ifmmode\pm\else\textpm\fi{}40$ mb.

Studies of Electromagnetic Transitions inN15andO15

Electromagnetic transitions in ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ have been investigated through the reactions induced (a) by ${\mathrm{He}}^{3}$ bombardment of ${\mathrm{Be}}^{9}$ targets and (b) by deuteron bombardment of ${\mathrm{B}}^{10}$ targets employing bombarding energies ranging from 2.0 to 3.5 MeV. Branching ratios for the decay of the bound levels of ${\mathrm{B}}^{11}$ populated in (a) and (b) by the ${\mathrm{Be}}^{9}({\mathrm{He}}^{3}, p){\mathrm{B}}^{11*}$ and ${\mathrm{B}}^{10}(d, p){\mathrm{B}}^{11*}$ reactions were determined through measurements of proton-gamma coincidence spectra. The ratios of radiative width to total width for the unbound 9.19- and 8.92-MeV levels of ${\mathrm{B}}^{11}$ were obtained as $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}(9.19)}={{0.1}_{\ensuremath{-}0.05}}^{+0.2}$ and $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}(8.92)}=1.08\ifmmode\pm\else\textpm\fi{}0.12$. Additional measurements of the direct gamma spectra employing a three-crystal Nal(Tl) pair spectrometer, and of the internal pair transitions using an intermediate-image magnetic spectrometer, complement the above results and provide information on the decay of those bound levels of ${\mathrm{C}}^{11}$ populated by the ${\mathrm{Be}}^{9}({\mathrm{He}}^{3}, n){\mathrm{C}}^{11*}$ and ${\mathrm{B}}^{10}(d, n){\mathrm{C}}^{11*}$ reactions. The angular distributions of gamma rays from the four listed reactions were measured with the three-crystal pair spectrometer, and indicate significant anisotropies for those gamma rays arising from decay of the 8.92- and 7.99-MeV levels of ${\mathrm{B}}^{11}$ and the 7.50-MeV level of ${\mathrm{C}}^{11}$ formed in the ${\mathrm{Be}}^{9}$+${\mathrm{He}}^{3}$ bombardment. From the Doppler shifts apparent in the angular-distribution data an upper limit of $\ensuremath{\tau}l5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ sec was extracted for the mean lifetime of all bound levels of ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ except the 6.81-MeV level of ${\mathrm{B}}^{11}$, which could not be studied in this manner. The intermediate-image spectrometer was used to determine the multipolarity of those internal pair transitions in ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ having transition energies greater than 4 MeV. These results show that the 7.99- and 7.30-MeV levels of ${\mathrm{B}}^{11}$ and the 7.50-, 6.90-, and 6.35-MeV levels of ${\mathrm{C}}^{11}$ decay by $E1$ ground-state transitions and hence have even parity, while the 8.92- and 6.76-MeV levels of ${\mathrm{B}}^{11}$ and 6.49-MeV level of ${\mathrm{C}}^{11}$ decay by $M1$ and/or $E2$ ground-state transitions, and hence have odd parity. Combining these results with previously available information leads to spin-parity assignments of ${\frac{5}{2}}^{\ensuremath{-}}$ and ${\frac{3}{2}}^{+}$ for the 8.92- and 7.99-MeV levels of ${\mathrm{B}}^{11}$, respectively, and strongly suggests the assignment ${\frac{3}{2}}^{+}$ for the 7.50-MeV level of ${\mathrm{C}}^{11}$. The odd-parity assignment to the 2.14-MeV level of ${\mathrm{B}}^{11}$ is confirmed while the parity of the ${\mathrm{C}}^{11}$ 2.00-MeV level is fixed as odd. For the remaining levels the measurements serve to further restrict the range of possible spin-parity assignments. In addition the parities of the ${\mathrm{Be}}^{11}$ ground state and ${\mathrm{B}}^{11}$ 6.81-MeV level are determined to be even since the beta decay of ${\mathrm{Be}}^{11}$ to the ${\mathrm{B}}^{11}$ ${\frac{3}{2}}^{+}$ 7.99-MeV level and the 6.81-MeV level are known to be allowed. The level schemes of ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ as deduced from the present results are discussed in terms of the predictions of the intermediate-coupling shell model and the weak-coupling scheme.

High-energy transitions in the decay of 132I

A study of the high-energy gamma rays of 132I with a three-crystal pair spectrometer has disclosed the presence of several new transitions. In addition, it has permitted more precise energy assignments for the previously observed gamma rays. Gamma rays having energies greater than the pair production threshold were found at 1.141±0.009, 1.22±0.02, 1.282±0.008, 1.359±0.012, 1.393±0.008, 1.439±0.014, 1.716±0.017, 1.767±0.012, 1.914±0.009, 1.988±0.009, 2.076±0.016, 2.162±0.016, 2.222±0.016, 2.394±0.012, 2.55±0.04 and 2.68±0.04 MeV. The electron spectrum has been examined with a six-gap iron beta-ray spectrometer covering the energy range of 100–2200 keV. Electron lines were observed corresponding to transitions at 147.4±0.9, 263.0±0.9, 285.5±1.1, 523.0±1.2, 631.5±1.4, 669.0±1.2 (complex), 728.8±1.7, 773.8±1.6, 954.9±1.9 and 1395±8 keV. A careful study of the end-point region of the beta spectrum has shown thet the maximum energy beta ray of 132I is at 2118±15 keV.

Energy levels in 132Xe

The energy levels in 132Xe populated by the decay of 132I have been analysed in the light of recent internal conversion electron and three-crystal pair spectrometer studies. All previous information on the decay of 132I as well as that on the decay of 132Cs has also been considered. The energies in keV and the spins and parities of the following excited levels in 132Xe are observed in the decay of 132I: 667.8±0.3,2 +; 1298.1±0.4,2 +; 1440.7±0.4,4 +; 1805.9±0.7, (2,3) +; 1963.7±0.7 (3, 4) +; 2110.4±0.5, (2–5) +; 2112.2±0.5 (2–5) +; 2395.6±0.5, (3–5) +; 2584.3±0.8, (3 −); 2658±2, (2, 3); 2762.4±0.5, (3, 4); and 2839.5±0.5, (3) +. Thirty-three transitions have been assigned as depopulating these levels. The states at 667.8, 1298.1, 1440.7 and 1805.9 keV as well as one at 1987.8±2.5 keV are observed in the decay of 132Cs to 132Xe.

Studies of Electromagnetic Transitions inB11andC11

Electromagnetic transitions in ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ have been investigated through the reactions induced (a) by ${\mathrm{He}}^{3}$ bombardment of ${\mathrm{Be}}^{9}$ targets and (b) by deuteron bombardment of ${\mathrm{B}}^{10}$ targets employing bombarding energies ranging from 2.0 to 3.5 MeV. Branching ratios for the decay of the bound levels of ${\mathrm{B}}^{11}$ populated in (a) and (b) by the ${\mathrm{Be}}^{9}({\mathrm{He}}^{3}, p){\mathrm{B}}^{11*}$ and ${\mathrm{B}}^{10}(d, p){\mathrm{B}}^{11*}$ reactions were determined through measurements of proton-gamma coincidence spectra. The ratios of radiative width to total width for the unbound 9.19- and 8.92-MeV levels of ${\mathrm{B}}^{11}$ were obtained as $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}(9.19)}={{0.1}_{\ensuremath{-}0.05}}^{+0.2}$ and $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}(8.92)}=1.08\ifmmode\pm\else\textpm\fi{}0.12$. Additional measurements of the direct gamma spectra employing a three-crystal Nal(Tl) pair spectrometer, and of the internal pair transitions using an intermediate-image magnetic spectrometer, complement the above results and provide information on the decay of those bound levels of ${\mathrm{C}}^{11}$ populated by the ${\mathrm{Be}}^{9}({\mathrm{He}}^{3}, n){\mathrm{C}}^{11*}$ and ${\mathrm{B}}^{10}(d, n){\mathrm{C}}^{11*}$ reactions. The angular distributions of gamma rays from the four listed reactions were measured with the three-crystal pair spectrometer, and indicate significant anisotropies for those gamma rays arising from decay of the 8.92- and 7.99-MeV levels of ${\mathrm{B}}^{11}$ and the 7.50-MeV level of ${\mathrm{C}}^{11}$ formed in the ${\mathrm{Be}}^{9}$+${\mathrm{He}}^{3}$ bombardment. From the Doppler shifts apparent in the angular-distribution data an upper limit of $\ensuremath{\tau}l5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ sec was extracted for the mean lifetime of all bound levels of ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ except the 6.81-MeV level of ${\mathrm{B}}^{11}$, which could not be studied in this manner. The intermediate-image spectrometer was used to determine the multipolarity of those internal pair transitions in ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ having transition energies greater than 4 MeV. These results show that the 7.99- and 7.30-MeV levels of ${\mathrm{B}}^{11}$ and the 7.50-, 6.90-, and 6.35-MeV levels of ${\mathrm{C}}^{11}$ decay by $E1$ ground-state transitions and hence have even parity, while the 8.92- and 6.76-MeV levels of ${\mathrm{B}}^{11}$ and 6.49-MeV level of ${\mathrm{C}}^{11}$ decay by $M1$ and/or $E2$ ground-state transitions, and hence have odd parity. Combining these results with previously available information leads to spin-parity assignments of ${\frac{5}{2}}^{\ensuremath{-}}$ and ${\frac{3}{2}}^{+}$ for the 8.92- and 7.99-MeV levels of ${\mathrm{B}}^{11}$, respectively, and strongly suggests the assignment ${\frac{3}{2}}^{+}$ for the 7.50-MeV level of ${\mathrm{C}}^{11}$. The odd-parity assignment to the 2.14-MeV level of ${\mathrm{B}}^{11}$ is confirmed while the parity of the ${\mathrm{C}}^{11}$ 2.00-MeV level is fixed as odd. For the remaining levels the measurements serve to further restrict the range of possible spin-parity assignments. In addition the parities of the ${\mathrm{Be}}^{11}$ ground state and ${\mathrm{B}}^{11}$ 6.81-MeV level are determined to be even since the beta decay of ${\mathrm{Be}}^{11}$ to the ${\mathrm{B}}^{11}$ ${\frac{3}{2}}^{+}$ 7.99-MeV level and the 6.81-MeV level are known to be allowed. The level schemes of ${\mathrm{B}}^{11}$ and ${\mathrm{C}}^{11}$ as deduced from the present results are discussed in terms of the predictions of the intermediate-coupling shell model and the weak-coupling scheme.

Gamma Rays from Lithium Bombardment ofBe9,B10,B11, andC12

Relative intensities of gamma rays produced in the bombardment of ${\mathrm{Be}}^{9}$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, and ${\mathrm{C}}^{12}$ targets by ${\mathrm{Li}}^{6}$ and ${\mathrm{Li}}^{7}$ beams have been obtained with a three-crystal pair spectrometer and with a single NaI(Tl) crystal. Gamma rays have been observed from excited states in the residual nuclei ${\mathrm{Li}}^{7}$, ${\mathrm{Be}}^{10}$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{B}}^{12}$, ${\mathrm{C}}^{12}$, ${\mathrm{C}}^{13}$, ${\mathrm{C}}^{14}$, ${\mathrm{N}}^{14}$, ${\mathrm{N}}^{15}$, ${\mathrm{O}}^{15}$, ${\mathrm{O}}^{16}$, and ${\mathrm{O}}^{17}$. Some of these gamma rays have not been observed previously. Relative populations deduced from the data are discussed.

Coincidence Studies of the Thermal Neutron Capture Gamma Rays of Chromium

The gamma-ray cascades which follow thermal neutron capture in chromium have been investigated by means of the measurement of coincidences between gamma rays detected by a three-crystal pair spectrometer and a single NaI crystal. Samples of normal chromium and chromium enriched in ${\mathrm{Cr}}^{50}$ and ${\mathrm{Cr}}^{53}$ were used. The following assignments of gamma rays to individual isotopes have been made. ${\mathrm{Cr}}^{51}$: 8.499, 7.36, 6.34, 6.12, 5.46, and 5.18 Mev; ${\mathrm{Cr}}^{53}$: 7.929, 7.36, 5.61, and 5.26 Mev; ${\mathrm{Cr}}^{54}$: 9.716, 8.881, 7.097, 6.872, 6.644, 6.31, 6.00, and 4.83 Mev. A number of features of the de-excitation of the energy levels populated by these transitions are established.

Thermal Neutron Capture Gamma Rays in Iron

The gamma rays of ${\mathrm{Fe}}^{57}$ emitted following thermal neutron capture in ${\mathrm{Fe}}^{56}$ have been investigated by the measurement of coincidences between a three-crystal pair spectrometer and a single NaI(Tl) crystal. These data have been combined with information about the levels of ${\mathrm{Fe}}^{57}$ derived from the decay of ${\mathrm{Co}}^{57}$, which has been re-examined here, the decay of ${\mathrm{Mn}}^{57}$, and nuclear reaction data in order to determine the properties of several of the low-lying levels in ${\mathrm{Fe}}^{57}$. The spins, parities, and decay characteristics of the first four excited states in ${\mathrm{Fe}}^{57}$ now appear to be established as well as the main features of the decay of the levels at 1.266, 1.630, and 1.728 Mev.