Most radiation safety guidelines in the nuclear industry are based on the data concerning the survivors of the nuclear explosions at Hiroshima and Nagasaki. Crucial to determining these guidelines is the radiation from the explosions. We have measured gamma-ray pulse-height distributions from an accurate replica of the Little Boy device used at Hiroshima, operated at low power levels near critical. The device was placed outdoors on a stand 4 m from the ground to minimize environmental effects. The power levels were based on a monitor detector calibrated very carefully in independent experiments. High-resolution pulse-height distributions were acquired with a germanium detector to identify the lines and to obtain line intensities. The 7631 to 7645 keV doublet from neutron capture in the heavy steel case was dominant. Low-resolution pulse-height distributions were acquired with bismuth-germanate detectors. We calculated flux spectra from these distributions using accurately measured detector response functions and efficiency curves. We then calculated dose-rate spectra from the flux spectra using a flux-to-dose-rate conversion procedure. The integral of each dose-rate spectrum gave an integral dose rate. The integral doses at 2 m ranged from 0.46 to 1.03 mrem per 10/sup 13/ fissions. The output of the Little Boy replica can bemore » calculated with Monte Carlo codes. Comparison of our experimental spectra, line intensities, and integral doses can be used to verify these calculations at low power levels and give increased confidence to the calculated values from the explosion at Hiroshima. These calculations then can be used to establish better radiation safety guidelines. 7 references, 7 figures, 2 tables.« less

Monte Carlo calculations of a bismuth-germanate scintillator's efficiency agree closely with experimental measurements. For this comparison, we studied the absolute gamma-ray photopeak efficiency of a scintillator (7.62 cm long by 7.62 cm in diameter) at several gamma-ray energies from 166 to 2615 keV at distances from 30.5 to 152.4 cm. Computer calculations were done in a three-dimensional cylind...

We present the experimentally determined intrinsic photopeak efficiencies for bismuth germanate scintillators 7.62 cm in diameter and 7.62 cm in length over the energy range 0.1–5.0 MeV. We studied eight detectors individually with point sources at 30.8, 61.3, 91.7, and 152.7 cm from the crystal; two additional detectors, for a total of 10, were studied with sources at 61.3 and 91.7 cm. We present intrinsic photopeak efficiency curves, determined by averaging the data from all detectors and fitting the results at each of the four distances.

The $^{12}\mathrm{C}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}\mathrm{p})$ reactions were studied at ${T}_{\ensuremath{\pi}}=220$ MeV. The final particles were detected both separately and in coincidence and their momenta were measured. Calculation of the excitation energy of the residual nucleus allowed clear separation of events where an outer proton was removed. The data provide detailed evidence confirming the quasielastic picture of pion knockout reactions. Evidence for this derives from the agreement between the peak energies found in the coincidence spectra and those found in inclusive spectra, from analysis of angular distributions, and from the location of peaks found in missing mass spectra. The coincidence cross section is found to account for about half of the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{+\ensuremath{'}}$) reaction, and about half of this in turn corresponds to quasifree knockout of the outer shell protons. Secondary processes in the (${\ensuremath{\pi}}^{\ensuremath{-}}$,${\ensuremath{\pi}}^{\ensuremath{-}}\mathrm{p}$) reaction are found to play a much more important role than in the (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{+}\mathrm{p}$) reaction.

We report a new procedure for unfolding gamma-ray pulse-height distributions acquired with bismuth-germanate detectors. The equipment used for acquiring the distributions consists of a LeCroy 3500 data acquisition and analysis system and eight bismuth-germanate scintillation detectors 7.62 cm in diameter and 7.62 cm long. The system was calibrated and characterized from 0.12 to 8.28 MeV by using gamma-ray spectra from a variety of radioactive sources and from the 14N(p,γ)15O reaction. By fitting these pulse-height distributions with a function containing 17 parameters, we determined theoretical response functions and used them to obtain the gamma-ray flux spectra at multiple space points from a variety of radioactive objects of interest to nuclear safeguards. We used two flux-spectrum-to-dose-rate conversion curves to obtain dose rates. For a composite source, consisting of several sources with accurately known strengths, the result of our procedure agreed with the expected value to within less than 10%. Direct use of measured spectra and the flux-spectrum-to-dose-rate curves to obtain dose rates avoids the errors that can arise because of spectrum dependence in simple gamma-ray dosimeter instruments.

Angular distributions for the reaction ${\ensuremath{\pi}}^{+}+d\ensuremath{\rightarrow}p+p$ have been measured for pion laboratory energies ranging from 20 to 65 MeV. Uncertainties in the total cross sections were less than 6% at all energies studied. The angle integrated cross sections were determined to be 4.31 \ifmmode\pm\else\textpm\fi{} 0.18, 4.84 \ifmmode\pm\else\textpm\fi{} 0.20, 4.26 \ifmmode\pm\else\textpm\fi{} 0.16, 5.19 \ifmmode\pm\else\textpm\fi{} 0.21, 5.30 \ifmmode\pm\else\textpm\fi{} 0.25, 5.20 \ifmmode\pm\else\textpm\fi{} 0.28, and 7.40 \ifmmode\pm\else\textpm\fi{} 0.30 mb for pion laboratory energies of 20, 25, 30, 35, 40, 45, and 65 MeV, respectively. These values confirmed the general trend observed for the total reaction cross section at energies below resonance. The angular distributions and integrated cross sections are compared with recent microscopic calculations. Though qualitative agreement is evident between the models used to describe the process and experimental results, quantitative agreement is still lacking.[NUCLEAR REACTIONS $d({\ensuremath{\pi}}^{+},p)p$, $E=20,25,30,35,40,45,65$ MeV; measured $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$, deduced total cross section for each energy; obtained fits to $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$ with polynomials linear and quadratic in ${cos}^{2}\ensuremath{\theta}$; compared with microscopic calculations for the reaction.]

We present measured angular distributions for ${\ensuremath{\pi}}^{+}$-elastic scattering at 30 and 50 MeV from selected targets with $A=12 \mathrm{to} 208$. These angular distributions were analyzed using a phenomenological optical potential of first-order form. The mass dependence of the potential strength parameters displays the isospin dependence expected from the free $\ensuremath{\pi}N$ interaction.NUCLEAR REACTIONS Elastic scattering of 30 and 50 MeV ${\ensuremath{\pi}}^{+}$ from $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, $^{208}\mathrm{Pb}$. Angular distributions: $25\ifmmode^\circ\else\textdegree\fi{}<{\ensuremath{\theta}}_{\mathrm{LAB}}<160\ifmmode^\circ\else\textdegree\fi{}$. Optical model analysis of cross-section data.

Two pronounced dips in the ${\mathrm{H}}^{\ensuremath{-}}$ photodetachment cross section have been observed at photon energies of 12.650\ifmmode\pm\else\textpm\fi{}0.004 and 12.837\ifmmode\pm\else\textpm\fi{}0.004 eV, just below the hydrogenic $n=3$ threshold. These energies were reached by crossing a uv laser beam with a relativistic ${\mathrm{H}}^{\ensuremath{-}}$ beam. The dips are interpreted as the first two members of a $^{1}P$ Feshbach resonance series, of the "+" type, converging on $n=3$. Fano line shapes have been fitted to these structures to extract their intrinsic widths and line profile indices.