Gamma-gamma Coincidence Measurements Research Articles

The decay scheme of 112Ag

The γ-radiations following the decay of 112Ag have been studied with Ge(Li) detectors. The 112Ag half-life has been measured as 3.16±0.02 h; twenty gamma radiations ranging in energy from 606.7 keV to 2829.6 keV have been observed. Gamma-gamma coincidence measurements have been performed with Ge(Li) and NaI(Tl) detectors. A decay scheme consistent with the present data is proposed.

Excited states in 178Hf from resonance neutron-capture gamma-ray studies

A total of 16 excited states up to 1818 keV in the deformed doubly even nucleus 178Hf was located from observation of the primary gamma rays produced in the reaction 177 Hf( n, γ) 178 Hf . Gamma-ray spectra were obtained at neutron resonances with energies of 1.1, 2.4, 5.9, 6.6 and 8.8 eV. Since the angular momenta of these resonance states are known, the angular momentum quantum numbers of the resulting states were limited to two or at most three values. The level at 1268 keV was studied in a gamma-gamma coincidence measurement and was assigned as a K, I π = 2, 3 + state. Other members of this K = 2 band appear to be at 1174 keV (2, 2 +) and at 1385 keV (2, 4 +). The neutron separation energy of 178Hf was found to be 7625 ± 1 keV.

Étude de la région de 3 MeV d'excitation de 27Al

The region of the 3 MeV doublet of 27Al has been subjected to precision investigation via broad-range magnetic analysis, gamma-ray spectroscopy and gamma-gamma coincidence measurements. The excitation function for the 27Al(p, p′) 27Al reaction has been measured for E p = 4.32–4.43, 4.81–4.90 and 5.70–5.80 MeV. No evidence has been found for a third level at 3 MeV excitation in 27Al, which had been suggested by the discrepancies in reported measurements in this excitation region. The present results support the assignment 9 2 + to the 3.002 MeV state; branching ratio data are in accord with earlier measurements. It is not possible to reproduce all the static and dynamic properties of the low levels of 27Al with either strong- or weak-coupling models, although features of both are present; this is consistent with the assumption that 27Al lies in a transition region between regions of positive and negative static deformation.

The excited states of 193Ir populated by the beta decay of 193Os

Gamma-gamma coincidence measurements were used to establish the decay level scheme of 193Ir, which is populated by the beta decay of 193Os. Angular correlation measurements were carried out for seven cascades utilizing a Ge(Li) detector and a NaI(Tl) scintillator. A comparison between the gamma singles spectra and the electron conversion lines yielded the conversion coefficients for the most prominent transitions. From these angular correlation measurements and the conversion coefficient results, the spin assignment for the 180, 361 and 712 keV states was determined as 3 2 + . The most prominent transitions were found to be predominantly M1 with a small E2 admixture. The sequence of levels in 193Ir and their mode of de-excitation were found to resemble very closely those of 197Au.

The decay of 56Co and 56Mn

Gamma radiations following the radioactive decay of 56Co and 56Mn have been measured with Ge(Li) detectors. From 56Co, previously unobserved gamma rays of energies 2213.0 and 3598.7 keV have been identified while those of energies 1810.9, 1963.4 and 2112.8 keV are confirmed. Gamma-gamma coincidence measurements have been carried out with Ge(Li) and NaI(Tl) detectors. Gamma spectra in coincidence with the 846.6, 1037.6 and 1238.0 keV gamma rays have been measured, and a number of gamma-gamma cascades identified. From 56Mn, a previously unreported gamma ray of energy 3119.3 keV has been observed. A revised decay scheme is presented together with a discussion of the information that the new data provide on level energies, spins and parities.

Decay of 144Pr to levels in 144Nd

The γ-rays from 144Pr have been measured with a 6 cm 3 Ge(Li) detector. Nine γ-rays were observed. Gamma-gamma coincidence and angular correlation measurements were performed with the Ge(Li) detector and a NaI(Tl) scintillation detector. It is proposed that 144Pr decay populates levels in 144Nd at 1510, 1560 and 2085 keV in addition to the previously known levels at 0, 696.3 and 2185.6 keV. Angular correlation measurements show that the spin of the 2085 level is 0. The half-life of 144Pr is 17.3±0.1 min.

Decay of 139Pr

The decay of 139Pr has been investigated by means of NaI(Tl) and high-resolution Ge(Li) spectrometers. Accurate energy and relative intensity determinations of the gamma rays have been performed. Levels of 139Ce at 255.15, 1320.0, 1346.8, 1595.6, 1630.7, 1729.8, 1818.0, 1907.0 and 2015.0 keV have been deduced. The existence of the 255.15 keV level was confirmed by gamma-gamma coincidence measurements. Spin and parity assignments for all observed levels have been given from electron capture and positon disintegration considerations and gamma branches.

Study of theCo59(n,γ)Co60Reaction and the Level Structure ofCo60

The level structure of the odd-odd $^{60}\mathrm{Co}$ nucleus has been studied using the thermal-neutron capture reaction $^{59}\mathrm{Co}(n,\ensuremath{\gamma})^{60}\mathrm{Co}$. The gamma-ray spectrum from this reaction in the energy intervals 50-1850 keV and 4500-7500 keV has been studied with a Li-drifted Ge spectrometer system. A number of new transitions are reported. The observed levels are compared with those excited by the $^{59}\mathrm{Co}(d,p)$ reaction. Gamma-gamma coincidence measurements using Ge(Li) and NaI detectors have been made, which provide considerable information about the low---energy-level structure. In these measurements a primary high-energy transition, selected by the Ge(Li) detectors, defines a particular low-lying level. The decay of this level, isolated by the coincidence requirement from extraneous background, is observed with a NaI detector. Spins and parities of the excited states below about 1 MeV are deduced from the observed gamma-ray branches. The low-lying excited states are interpreted in terms of the $\ensuremath{\pi}{({f}_{\frac{7}{2}})}^{\ensuremath{-}1}\ensuremath{\nu}{({p}_{\frac{3}{2}})}^{\ensuremath{-}1}$, $\ensuremath{\pi}{({f}_{\frac{7}{2}})}^{\ensuremath{-}1}\ensuremath{\nu}{({f}_{\frac{5}{2}})}^{1}$, and $\ensuremath{\pi}{({f}_{\frac{7}{2}})}^{\ensuremath{-}1}\ensuremath{\nu}{({p}_{\frac{1}{2}})}^{1}$ proton-neutron configurations. The spectra of these configurations, calculated using a zero-range central force for the residual interaction, are compared with the observed levels.

Level Scheme ofGa69

The gamma-ray spectrum from the decay of ${\mathrm{Ga}}^{69}$ has been studied with the aid of a lithium-drifted germanium detector. Gamma rays of energy 2023, 1922, 1893, 1576, 1525, 1349, 1335, 1206, 1107.2, 1052, 871.8, 788, 763, 587, 573.4, 553, 532, 511, 320, and 237 keV have been observed. A new level scheme consistent with gamma-gamma coincidence measurements is presented for ${\mathrm{Ga}}^{69}$. The experimental results are compared with a calculation of the energy levels in ${\mathrm{Ga}}^{69}$ based on the intermediate-coupling model.

Excited energy levels in U235

The transitions and levels in U235 populated by Pu239 alpha decay have been studied by alpha fine-structure investigations, alpha-gamma and gamma-gamma coincidence measurements. The spectra revealed the existence of at least 17 alpha groups and 24 gamma transitions which could be accounted for by 21 excited levels in U235. The results are discussed within the framework of the unified model. The proposed level scheme exhibits a level density about twice as high as predicted by the Nilsson theory. This result is in fair agreement with the predictions of the superfluid model ofSolov'ev.

Excited States ofFe57Populated inCo57Decay

The gamma-ray spectrum emitted in the decay of ${\mathrm{Co}}^{57}$ has been measured with a high-resolution Ge(Li) detector. In addition to the well-known gamma transitions of 136.4, 122.0, and 14.4 keV, the following weak transitions with energies given in keV (intensity per ${10}^{5}$ ${\mathrm{Co}}^{57}$ decays) were observed: 229.8\ifmmode\pm\else\textpm\fi{}1.0 (0.5), 339.7\ifmmode\pm\else\textpm\fi{}0.4 (4.2), 352.5\ifmmode\pm\else\textpm\fi{}0.4 (3.2), 366.8\ifmmode\pm\else\textpm\fi{}0.5 (0.6), 570.0\ifmmode\pm\else\textpm\fi{}0.4 (13.2), 692.1\ifmmode\pm\else\textpm\fi{}0.3 (137), and 706.4\ifmmode\pm\else\textpm\fi{}0.4 (5.7). A unique decay scheme is established on the basis of these energy measurements and gamma-gamma coincidence measurements employing NaI(Tl) scintillation detectors. The excited states of ${\mathrm{Fe}}^{57}$ at 366.8 and 706.4 keV have spin and parity $\frac{3}{2}$- and $\frac{5}{2}$-, respectively. The total internal-conversion coefficient for the 14-keV transition was measured by two independent methods: (1) A gamma-gamma coincidence measurement in a calibrated geometry yielded a value of 9.0\ifmmode\pm\else\textpm\fi{}0.5. (2) A measurement of the M\ossbauer absorption cross section of 14-keV gamma rays in iron yielded a value of 8.9\ifmmode\pm\else\textpm\fi{}0.6. The good agreement between the results of these two independent methods resolves previously reported discrepancies. A more accurate determination of the half-life of the 14.4-keV first excited state by a gamma-gamma delayed-coincidence measurement gave a result of (9.8\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec.

Directional correlation of gamma rays in Rh 105

Gamma-gamma coincidence measurements on the decay of 4.4 h Ru 105 to Rh 105 form the basis for the decay scheme proposed. Directional correlation measurements have been made on the 315–470 keV, 485–470 keV and the 317–148 keV cascades. The respective correlation functions are: W = 1−(0.012)±0.010)P 2( cos θ) , W = 1+(0.079±0.019)P 2( cos θ)+(0.031)±0.022)P 4( cos θ) , W = 1+(0.161±0.020)P 2 cos θ)−(0.036±0.023)P 4( cos θ) . Spin assignments consistent with these measurements have been made to the levels involved.

Reinvestigation ofCs132Decay

There has been some disagreement in the literature as to the properties of the low-lying states in $^{132}\mathrm{Xe}$, and in particular as to the energy of the second excited state of this nucleus. The decay of $^{132}\mathrm{Cs}$ has been reinvestigated by use of $p\ensuremath{-}i\ensuremath{-}n$ lithium-drifted germanium detectors having high resolution, and it is found that the first and second excited states in $^{132}\mathrm{Xe}$ are depopulated by transitions with respective energies of 668.8\ifmmode\pm\else\textpm\fi{}1.0 and 630.7\ifmmode\pm\else\textpm\fi{}1.5 keV. In addition, gamma rays were also observed with the germanium detectors at energies of 464\ifmmode\pm\else\textpm\fi{}3, 507\ifmmode\pm\else\textpm\fi{}3, 511\ifmmode\pm\else\textpm\fi{}3, 773\ifmmode\pm\else\textpm\fi{}5, 1037\ifmmode\pm\else\textpm\fi{}3, 1140\ifmmode\pm\else\textpm\fi{}1.2, 1233\ifmmode\pm\else\textpm\fi{}3, 1300.0\ifmmode\pm\else\textpm\fi{}1.5, 1320.0\ifmmode\pm\else\textpm\fi{}1.5, and 1985\ifmmode\pm\else\textpm\fi{}5 keV. Gamma-gamma (NaI) coincidence measurements, made with a 100- by 200-channel multiparameter analyzer, revealed several new features of the decay. The excited levels observed in $^{132}\mathrm{Xe}$ are at 668.8\ifmmode\pm\else\textpm\fi{}1.0, 1299.5\ifmmode\pm\else\textpm\fi{}2.0, 1442\ifmmode\pm\else\textpm\fi{}3, 1808.3\ifmmode\pm\else\textpm\fi{}2.2, and 1988.8\ifmmode\pm\else\textpm\fi{}2.5 keV. Levels at 464\ifmmode\pm\else\textpm\fi{}3 and 1037\ifmmode\pm\else\textpm\fi{}3 keV in $^{132}\mathrm{Ba}$ are also populated.

Decay of 99Mo- 99mTc

The decay parameters of 99Mo 99mTc have been determined using liquid-liquid extractions, 4π β-γ and γ-γ coincidence counting and absolute gamma-spectroscopy measurements. Gamma-ray energies and intensities were obtained with a 7.6 cm × 7.6 cm NaI(Tl) spectrometer. The relative intensities of the 0.74 and 0.78 MeV gamma rays were measured using a lithium ion-drifted germanium detector (these peaks were unresolved in the NaI(Tl) spectra). The observed number of gamma photons per 99Mo disintegration with energies of 0.93, 0.780, 0.740, 0.372, 0.181 and 0.142 MeV was found to be 0.004, 0.044, 0.124, 0.013, 0.068 and 0.076, respectively. Gamma-gamma coincidence measurements confirmed the 0.93 MeV gamma ray in the 99Mo decay. A quantitative separation of 99mTc followed by X- and gamma-ray emission rate determinations gave the sum of the internal conversions of the 0.142 and 0.140 MeV gamma rays as α T = 0.099±0.015. At equilibrium the 99mTc daughter activity was determined to be 0.964 that of the 99Mo activity.

Level Structure inAu197from the Decay ofHg197m,Hg197, andPt197

Gamma-ray spectra of ${\mathrm{Hg}}^{197}$, ${\mathrm{Hg}}^{197m}$, ${\mathrm{Pt}}^{197}$ were measured with a NaI(Tl) scintillation spectrometer. Electron spectra were obtained with a silicon detector and permanent-magnet spectrographs. Gamma-gamma coincidence measurements were also made. The $K$ internal-conversion coefficient of the 191-keV transition was found to be 0.77\ifmmode\pm\else\textpm\fi{}0.2 and 0.93\ifmmode\pm\else\textpm\fi{}0.2 by two different techniques. This result is consistent with an $M1$ transition and does not necessitate any $E0$ contribution. The energy of the 279-keV transition from ${\mathrm{Hg}}^{197m}$ was found to be (279.5\ifmmode\pm\else\textpm\fi{}0.6) keV. The experiments indicate the existence of a 269-keV transition depopulating the 269-keV level in the decay of both ${\mathrm{Pt}}^{197}$ and ${\mathrm{Hg}}^{197}$.

A re-investigation of the decay of Eu 147 to Sm 147

A re-investigation of the decay of Eu 147 has been undertaken; gamma-ray intensity measurements and gamma-gamma directional correlations have been performed using an isotopically and chemically pure source. Gamma-gamma directional correlations were measured for the 680-122 and 957-122 keV cascades; the data were consistent with the predominantly M1 assignment for the 680 keV transition based on internal conversion data. Evidence has been found for seven new gamma-ray transitions with energies of 1122, 1195, 1250, 1320, 1326, 1423 and 1448 keV. Gamma-gamma coincidence measurements performed on a chemically but not isotopically pure source of Eu 147 showed that the 1122 and 1250 keV transitions are in coincidence with the 198 keV transition and that the 1195, 1326 and 1423 keV transitions are in coincidence with the 122 keV transition. The energy of the previously reported 881 keV transition was measured and found to be 862 keV. This transition is shown to proceed from a level of 1060 keV; internal conversion coefficient data and gamma-gamma directional correlations indicate that the spin and parity of this level would be 3 2 + assuming a spin sequence for the three lowest levels of 7 2 −, 5 2 − and 3 2 − . The total positon feeding was determined to be (0.54±0.08)% of the total decay. The experimental results are compared with the theoretical results obtained by Schima employing quasi-particle states to account for the short-range forces and zero, one and two phonon states for the collective effects.

Study of the Decay ofTm168to Levels inEr168Using Coincidence and Directional Correlation Techniques

The levels in Er/sup 168/ populated by electron capture of Tm/sup 168/ were studied using scintillation spectrometers, gamma-gamma and electron-gamma coincidence measurements, and directional correlation techniques. The following conclusions were reached: the spin and parity of the 1543-kev level are 3-; the 1280-kev transition is El(<0.08% M2); the 721-kev transition is E1(<0.05% M2); and the 743kev transition is E2(<2.4% M1). The attenuation coefficient G/sub 2/ for the 1280 kev-80 kev correlation was determined to be 0.77 plus or minus 0.19 for a source consisting of a dilute aqueous solution of TmCl/sub 3/. The amalysis of the results of the Tm/sup 168/ decay is compared with the predictions using various models. The ratios of reduced transition probabilities for transitions from the gamma vibrational band in Er/sup 168/ are analyzed and a band-mixing parameter z = 0.055 is found. (auth)

Decay of Ce144

Level structure of Pr 144 was investigated by gamma-gamma coincidence measurements and the spins of the levels were determined using the gamma-gamma directional correlation method. The 166 keV level proposed by Freeman has been confirmed. A new 92 keV gamma ray coincident with the 41 keV gamma ray has been found. A decay scheme containing the new level is proposed. Interpretations of the levels are discussed in terms of the shell model.

Decay ofTm173

The mass assignment of ${\mathrm{Tm}}^{173}$ has been confirmed by cross bombardments involving the reactions ${\mathrm{Er}}^{170}(\ensuremath{\alpha}, p){\mathrm{Tm}}^{173}$, ${\mathrm{Yb}}^{173}(n, p){\mathrm{Tm}}^{173}$, and ${\mathrm{Yb}}^{174}(\ensuremath{\gamma}, p){\mathrm{Tm}}^{173}$ with isotopically enriched targets, and its decay has been studied by $\ensuremath{\beta}$-ray and $\ensuremath{\gamma}$-ray scintillation spectrometry. The half-life of ${\mathrm{Tm}}^{173}$ is 8.24\ifmmode\pm\else\textpm\fi{}0.08 h. Three gamma rays, with energies (and relative intensities) of 66 (0.01), 399 (1.0), and 465 (0.09) keV, were observed. Analysis of the $\ensuremath{\beta}$-ray spectrum indicates the presence of two major groups with end-point energies of 1.32\ifmmode\pm\else\textpm\fi{}0.03 MeV (2%) and 0.89\ifmmode\pm\else\textpm\fi{}0.04 MeV (98%). Gamma-gamma coincidence measurements and the $\ensuremath{\gamma}$-ray intensity data show that the 0.89-MeV $\ensuremath{\beta}$-ray group is composed of two components which differ in energy by 66 keV. The proposed decay scheme for ${\mathrm{Tm}}^{173}$ involves excited levels in ${\mathrm{Yb}}^{173}$ at 399 and 465 keV. The 399-keV level is an isomeric state with a 3.5\ifmmode\pm\else\textpm\fi{}0.3 \ensuremath{\mu}sec half-life, and it de-excites by a pure $E2$ transition which is hindered by a factor of \ensuremath{\approx}1.6\ifmmode\times\else\texttimes\fi{}${10}^{3}$ compared to the single-particle estimate. This hindrance is attributed to violation of the asymptotic selection rules for deformed nuclei.

Beta Decay ofB12

The 3.23-MeV gamma-ray transition between the 7.66- and 4.43-MeV states of ${\mathrm{C}}^{12}$ has been observed in the beta decay of ${\mathrm{B}}^{12}$ by means of scintillation detectors and coincidence techniques. The ${\mathrm{B}}^{12}$ activity was made by the ${\mathrm{B}}^{11}(d, p){\mathrm{B}}^{12}$ reaction using a Van de Graaff accelerator and a beam-chopping system for irradiation and delayed counting. All parts of the target-collimator assembly were constructed of beryllium in order to minimize bremsstrahlung production. Beta rays were detected in an 8-in.-diam by \textonequarter{}-in.-thick Pilot-B scintillator and gamma rays were detected in two 5-in.\ifmmode\times\else\texttimes\fi{}5-in. NaI counters placed on opposite sides of the source. Gamma-gamma coincidence measurements were made by displaying the output of each NaI detector in coincidence with a channel centered on the full-energy-loss peak of 4.43-MeV gamma rays in the opposite NaI detector. The additional requirement of a coincidence with the beta-ray detector was imposed for beta-gamma-gamma coincidence experiments. In both types of measurements the full-energy-loss and one-escape peaks of the 3.23-MeV gamma rays were observed. Based on the average result of two previous nuclear reaction measurements of the fractional decay of the 7.66-MeV state by the emission of 3.23-MeV gamma rays the present observation of these gamma rays leads to a value of (1.7\ifmmode\pm\else\textpm\fi{}0.5)% for the beta-ray branching of ${\mathrm{B}}^{12}$ to the 7.66-MeV state of ${\mathrm{C}}^{12}$.