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A review of recent studies using the nuclear resonance photon scattering (NRPS) from 15N occurring in several gases is presented. In particular, new results on the adsorption and molecular orientation of N2, N2O and NO2 on graphite are given and compared with theoretical calculations using molecular dynamics simulations (MDS). In another application, we studied the scattering of photons from NO2 occurring in solid NaNO2. The results were compared with those of adsorbed NO2 on graphite. A huge difference in the scattering cross section of the two systems was observed and explained.

Resonant photon scattering from /sup 39/K has been studied with bremsstrahlung produced by electrons with end-point energies of 6.6, 8.5, and 9.4 MeV. Values of gGAMMA/sub 0//sup 2/GAMMA for 24 levels below 9 MeV were measured and the gGAMMA/sub 0/ values of 17 levels were deduced. The widths of some levels above 4 MeV were found to be much larger (on the average, more than a factor of 10) than those reported from experiments using the Doppler shift attenuation method. Three of these levels are known from studies of the (d,/sup 3/He) reaction to carry most of the d/sub 5/2/sup -1/ proton strength in /sup 39/K. The B(M1up-arrow) strength of J = (52/sup +/ levels below 7 MeV is compared with predictions based on simple single-particle shell-model wave functions coupled with free-nucleon and empirically renormalized M1 operators and weighted by single-proton pickup spectroscopic factors.

The widths of nine energy levels in $^{11}\mathrm{B}$ at 2.125, 4.445, 5.021, 6.743, 6.793, 7.286, 7.978, 8.559, and 8.920 MeV were determined by carrying out self-absorption and photon scattering measurements. The temperature variation of the scattering cross section was measured at $T=298$ K and $T=730$ K to study in some detail the effective temperature ${T}_{e}$ of $^{11}\mathrm{B}$ in ${\mathrm{B}}_{4}$C, BN, and elemental B. The influence of ${T}_{e}$ on the deduced values of the radiative widths of $^{11}\mathrm{B}$ is discussed.

Nuclear resonance fluorescence from energy levels in /sup 27/Al lying between 2 and 10 MeV excitation energy has been measured with bremsstrahlung beams of end-point energies of 7.66 and 10.37 MeV. Values of gGAMMA/sub 0/ and gGAMMA/sub 0/GAMMA/sub ..gamma..//GAMMA for 39 levels below 10 MeV were obtained from scattering cross section and self-absorption measurements. The measurements give an upper bound of total B(M1up-arrow) below 7.7 MeV excitation which is about 25% less than the predictions of a large-scale shell model calculation based on the free-nucleon M1 operator. The same shell model wave functions combined with an effective M1 operator based on moments and transitions between low-lying states is in good agreement with the present experimental results.

A bremsstrahlung photon beam from electrons with end-point energies of 7.66 and 10.37 MeV was used for photoexciting levels in /sup 23/Na. Values of gGAMMA/sub 0//sup 2//GAMMA and gGAMMA/sub 0/ of 22 levels below 10 MeV were obtained using scattering and self-absorption measurements. The values for 7 levels are reported for the first time. The temperature variation of the scattering cross section was measured at T = 300 K and T = 78 K to study in some detail the effective temperature T/sub e/ of metallic /sup 23/Na. The results of the total B(M1up-arrow) strength of T = 1/2 levels below 9 MeV were found to be in excellent agreement with the large-scale shell-model calculations.

Strong correlations between the measured strengths of excitations in the (γ, γ′) and (d, τ) reactions to the d 5 2 −1 proton states in 39K and to the p 3 2 −1 proton states in 15N were observed. The results are discussed in terms of the analogies between the two reactions.

The ground-state radiative widths of nine levels below 10.2 MeV in /sup 15/N were measured using resonance fluorescence. The results are compared with various theoretical predictions and are found to best agree with very recent unpublished calculations in which the full 1h..omega.. configurational basis is included in constructing the wave functions of the /sup 15/N levels.

The elastic scattering cross section of 7.9 MeV photons by U and Th was measured in the angular range 25°–140°. It is shown that at this energy the forward elastic scattering is due almost entirely to Delbruck scattering. The results are systematically lower by > 50% than the calculated values. A good agreement with theory was obtained only after excluding the contribution of the real part of the Delbruck scattering amplitude.

Elastic and inelastic nuclear resonant scattering of monochromatic photons from $^{75}\mathrm{As}$ have been studied using a 47-cc Ge (Li) detector. The $\ensuremath{\gamma}$ source was provided by thermal-neutron capture in iron. The energy of the resonance level in $^{75}\mathrm{As}$ was found to be 7.646 MeV. Assuming the high-energy lines to be primary transitions deexciting the resonance level, 25 energy levels were found from the ground state up to 2.6 MeV, seven of which may be identified with recently reported levels. By measuring the angular distribution of the scattered radiation, the spin of the scattering level was determined to be \textonehalf{} and the spins of 14 low-lying levels were thus found to be either \textonehalf{} or $\frac{3}{2}$. The total radiative width of the resonance level was determined and was found to be $\ensuremath{\Gamma}=0.36\ifmmode\pm\else\textpm\fi{}0.10$ eV and $\frac{{\ensuremath{\Gamma}}_{0}}{\ensuremath{\Gamma}}=0.11$. The $^{75}\mathrm{As}$ levels are compared with the predictions of the Coriolis coupling model.

Quasi-monochromatic photons in the range E γ = 14.4−16.6 MeV have been used to study inelastic scattering to the 2 + , γ -vibrational band head in 166 Er. The results for transitions to this branch are drastically smaller (by a factor ≈3–5) than the predictions of the dynamic collective model (DCM).

The elastic scattering cross section of 9 MeV photons from lead and uranium targets was measured at forward angles between 7° and 20dg with a Ge(Li) detector. The contribution of Delbruck scattering was found to be dominant while that of Rayleigh scattering is probably negligible.

Recent studies at the IRR‐2 reactor using monoenergetic neutron capture γ‐rays fall into three categories: 1) study the low energy GDR tail using the (γ, γ) and (γ, n) reactions; 2) study of interference effects between nuclear resonance fluorescence, Rayleigh and Delbruck scattering at small angles; 3) testing the 2D absorption structure of simple molecules on graphite using nuclear resonance scattering technique.