FIG. 2. Oscillogram of the spectrum excited by neutron capture in manganese.to the escape from the crystal of both annihilation quanta, and the weaker line at 3.94 Mev is due to the occasional capture of one such quantum by the crystal. The line at 4.45 Mev is too faint to show up in the reproduction. The lower energy group has been shown to correspond to the photoelectron lines produced by a trace of radium impurity in the polonium source, and to the polonium gamma-ray at approximately 790 kev. Figure 2 illustrates the spectrogram obtained with the manganese target in position. The oscillograph trigger level has been set fairly high to eliminate most of the intense low energy background pulses. It is apparent even from this reproduction that there are two intense bands, one at the end of the spectrum (consisting of three apparently associated pair lines), and the other at a somewhat lower energy (also consisting of three lines). Each of these bands has thus been identified with a homogeneous gamma-ray, the most prominent line in each group being the lowest energy pair line and corresponding to B and C in the differential discriminator distribution of Fig. 3. A is the Po-Be 3.43-Mev calibration line. The values of the two gamma-rays, as obtained from three photographs, are 5.27 Mev and 7.17 Mev, the corresponding differential discriminator values being 5.37 Mev and 7.15 Mev. We have, therefore, adopted values of 5.32±0.05 Mev and 7.16±0.05 Mev for the gamma-rays of neutron capture in Mn K , thus concluding that the latter figure represents the binding energy of the last neutron in Mn 56 and that there exists an excited level in the same nucleus of 1.84 Mev. The lower energy gamma-ray has not previously been reported, but recently Kinsey et al., 6 using a magnetic coincidence pair spectrometer in conjunction with the Chalk River reactor, have reported a gamma-ray of 7.25±0.03 Mev for manganese. However, manganese is classified by them as having a ground-state transition which predominates over that of all other radiation, a conclusion which does not follow from our own results which suggest a comparable intensity for the two radiations reported.It is recognized that an improvement in technique would probably be the use of a triple coincidence device to count only the main pair line for each gamma-ray, as discussed by Johanssen. 7 Such an arrangement would, however, require a much stronger neutron flux than was available. In conclusion we would emphasize that the photographic technique provides an excellent means for the rapid survey of neutron capture spectra, especially if microphotometer recording is available. A few homogeneous gammarays have been obtained with targets of Cd, CI, Ni, and W, superimposed on continuous backgrounds of unresolved radiation. 30 40 VOLTS FIG. 3. Differential pulse height distribution for the spectrum excited by neutron capture in manganese. (A) Po-Be calibration line at 3.43 Mev. (B) Main pair line of manganese gamma-ray of 5.37 Mev. (C) Main pair line of manganese gamma-ray of 7.15 ...

No abstract

Attenuation measurements in good geometry on polyethylene and graphite scatterers with transmissions from 0.30 to 0.65 have been made. A thin-walled gas target was used, producing forward d-d neutrons at a mean energy of 4.749=h0.009 Mev. Care was taken to minimize uncertainties arising from neutrons of other energies, from unshadowed background, and from impurities in the samples. The geometry was such that multiple scattering-in contributed no more than 0.12 percent to the total uncertainty. Checks against ratedependent sensitivity of the detector revealed no effects greater than 0.15 percent. The total n-p scattering cross section deduced from the measurements is 1.690=1=0.0066 barns, where the probable error has been increased from the statistical error of 0.002 4 barn to include the energy uncertainty and estimates of possible systematic effects. Values of ro s (n~p \ the singlet effective range of the n-p interaction, obtained from this result for several potential shapes, are compared with corresponding values of r^p~p\ The validity of the hypothesis of charge independence is found to depend on the potential shape assumed.

Nine elements are bombarded with 15-Mev deuterons from a cyclotron. The resulting angular distributions of 9.25-to 13.1-Mev neutrons are measured by means of a four-proportional counter telescope and also by threshold detectors. It is observed that all the measured angular distributions are peaked in the forward direction, some showing a peak at 0° and others peaks at 10°-15° with respect to the deuteron beam. Different methods of production of neutrons from (d,n) reactions are discussed, and it is shown that most of the observed neutrons are produced by a stripping process.