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This paper describes a facility for producing variable energy neutron beams in the energy range 20 to 60 MeV using protons from the 76″ Isochronous Cyclotron at the University of California, Davis. The 7 Li(p, n) 7 Be reaction is used to produce nearly monoenergetic beams with approximately 60% of the neutrons in a well defined peak.

The angular distributions of 26.5 MeV neutrons scattered elastically by deuterons between 90° and 166° (C.M.) were measured by using charged particle telescopes. The absolute n-d cross section ( of ≈ 5% precision ) was obtained by normalizing to the precision n-p cross section. Within the errors, the magnitude of the minimum cross section was found to be in agreement with that of the proton-deuteron differential cross section at the same energy and in disagreement with some recent results.

Recent phase-shift fits to nucleon-nucleon scattering data have revealed that the phase parameter e1 is poorly determined for neutron-proton scattering near 50 MeV. Values of χ2, for the whole data set, show a nearly flat minimum when plotted against e1, apparently corresponding to solutions near e1 = −8° and 0° l). A measurement of the observable Ayy, would be valuable in determining the e1 parameter1). The only previous measurement of Ayy for neutron-proton scattering has been at 23 McV2).

Cross sections have been measured at 0° for the (p,n) reaction on 7Li and 9Be for 15, 20, and 30 MeV protons incident on thin targets. Results are presented as a function of neutron energy for neutrons above about 3 MeV.

Data have been obtained for the reaction D(p, 2p)n at E p = 14.45 MeV at θ 3 = θ 4 = 25°, 30°, 35° and 43°. The results are compared with calculations using the Amado model, the ordinary truncated multiple-scattering series and a modified truncated series, which includes the p-d initial state interaction.

Measurements are reported of pulse height distributions in Si(Li) detectors due to nuclear interactions of monoenergetic protons, deuterons, 3He and 4He beams in the range 15–80 MeV.

Charged particle proton, deuteron, triton, helium-3, and alpha particle spectra have been measured over a wide angular range for neutron energies of 27.4, 39.7, and 60.7 MeV, incident on Carbon, Nitrogen, and Oxygen. The main purpose of these measurements is to provide data for neutron dosimetry and for tests of nuclear models and their interpolation and extrapolation to other energies, particles, nuclei, etc. Good agreement is found in comparisons with charge symmetric proton-induced energy spectra, such as in (p,d) vs (n,d). Comparisons with models are being carried out. Kerma have been calculated at the three energies for each nucleus including elastic recoil contributions. The contributions from other reaction channels (6Li, etc.) have been estimated using sum rules and, where available, proton induced data. The total Kerma one obtains for C, N, and O appear to be considerably less than recent predictions of several authors.

The first spectra from the UC Davis cyclotron’s zero degree facility for (n,p) scattering have been obtained from 12C, 13C, 90Zr, and 209Bi at an incident neutron energy of 65 MeV. Cross sections for the ground state, the ∼4.4 MeV and the GDR are extracted for the carbon isotopes. Two broad resonances in 209Bi at ∼7.5 MeV and ∼15 MeV and a broad resonance in 90Zr at ∼22 MeV are compared with previous work done at Davis away from zero degrees.

The charge exchange reaction 40Ca(n,p)40K has been measured at 65.5 MeV. A strong enhancement is observed at energies corresponding to the analog of the 40Ca G.D.R. The angular distribution is partially consistent with a ΔL=1 transfer, but at forward angles deviates from it. Comparison with the (3He,t) and (p,n) reaction is presented.

The charge and transverse momentum distributions for the heavy−ion reactions with 1.2 GeV per nucleon 139−La incident on 12−C, 16−O, and 40−Ar targets are presented. Fragment momentum isotropy predicted in some models does not appear in these results.

A large Multiple Sampling Ionization Chamber (MUSIC) has been developed as a part of the Heavy Ion Spectrometer System (HISS). This facility is being used for the study of relativistic nuclear collisions at the Bevalac of Lawrence Berkeley Laboratory. We have measured for MUSIC a single event resolution of 15% for Fe beam and a charge resolution better than 0.5 units of charge for a Ne beam. These results indicate that a charge resolution of one unit from Z = 7 to Z = 100 should be achieved with the present detector.

The study of giant resonances in nuclei via inelastic electron and hadron scattering is currently of great interest.1,2 These resonances are outstanding manifestations of nuclear vibrational motion in which an appreciable number of nucleons participate. Charge exchange reactions such as (p,n) and (n,p) offer powerful options for studying isovector excitations without interference from isoscalars. In general, if the target has isospin T then an isovector transition leaves the residual nucleus with isospin T-1, T, or T+1. (Refer to fig. 1.) The T-1 excitation requires charge exchange, as in (p,n), so that the 3-component T3=T (the charge-component) of isospin is also changed to T-1. Only for N=Z (T=0) nuclei are all isovector transitions to states of isospin T+l. In such reactions as (p,p’) and (e,e’) the isoscalar mode can also be excited and, indeed, these tend to be the strongest transitions at medium energies (≲ 100 MeV).

A new type of neutron flux and energy-measuring detector, which uses large-area ΔE and E detectors, and multiwire chambers (MWC) is being developed. The purpose is to allow one to measure neutron elastic and inelastic scattering and in particular to measure (n,xn) neutron continuum over a wide energy range. The detector offers many distinct advantages over the conventional neutron time-of-flight (TOF) method. The system was tested using a large area CH2 converter to produce recoil protons, which are tracked in the two MWC’s and registered in the AE and E detectors. A 7Li(p,n) spectrum from 62 MeV protons was measured and a 40Ca(n,n′) spectrum from 65 MeV neutrons was also measured.

We report on our measurements of n‐p scattering observables at 50 MeV, most notably the recent measurement of the spin‐correlation parameter, Ayy. This measurement is sensitive to the phase shift parameters ?1 and δ (1P1), for which early phase shift analyses gave poorly determined or ’’unphysical’’ values. The results of our measurements are incorporated in a phase shift analysis to determine or ’’unphysical’’ values. The results of our measurements are incorporated in a phase shift analysis to determine current best‐fit values of 50 MeV n‐p phase shifts.

Double-differential cross sections for the neutron-induced production of p, d, t, $^{3}\mathrm{He}$, and alpha particles from oxygen and nitrogen have been measured using an unpolarized neutron facility. Neutron beam energies of 27.4, 39.7, and 60.7 MeV were used. The charged particle energy spectra, at six forward laboratory angles, 15, 20, 35, 40, 45, and 65, and, where feasible, at three backward angles, 90, 130, and 150 deg, range up to the kinematic maximum, from a typical low-energy cutoff of 4 MeV for p, d, t, and alpha particles, and 8 MeV for $^{3}\mathrm{He}$. Intranuclear cascade plus deexcitation calculations were carried out. The data are compared with these calculations and with available proton-induced (charge-symmetric) reaction spectra for oxygen.

The inclusive light fragment (Z ≤ 7) yield data in Au+Au reactions, measured by the EOS Collaboration at the LBNL Bevalac, are presented and discussed. For peripheral collisions the measured charge distributions develop progressively according to a power law which can be fitted by a single r exponent independently of the bombarding energy in the range 250-1200 A MeV. In addition to this universal feature, we observe that the location of the maximum in the individual yields of different charged fragments shift towards lower multiplicity as the fragment charge increases from Z = 3 to Z = 7. This trend is common to all six measured beam energies. Finally, a monotonic increase is observed in the THe,DT thermometer, built from double yield ratios. We find that our data bring additional experimental evidence of a liquid - gas phase transitions in nuclei, already reported by the EOS Collaboration for the Au -t C reaction.

Energy measurements of a 20–60 MeV neutron beam to an absolute precision of 0.1% are easily achieved using a simple time-of-flight method.