D.F. Measday

A study of the reaction π+d→pp for pion energies between 142 and 262 MeV

The differential cross section for the reaction π+d→pp has been measured at pion laboratory energies of 142, 165, 187, 230 and 262 MeV. The angular distribution in the c.m. has been expressed in the form K(A+cos2θ−B cos4θ). For the first time in this energy region the results are sufficiently precise to require the cos4θ term. Low energy measurements (η ⩽ 2.0) of this reaction and the time reverse reaction have been re-analyzed and we find that the total cross section in mb for the reaction pp→π+d can be expressed as (0.18±0.02)η + (0.95±0.15)η3 where η is the pion momentum in the c.m. system in units of mπc.

Reaction cross sections for protons in the energy range 220–570 MeV

Abstract Proton reaction cross sections have been measured for targets of natural isotopic abundance of the following elements and compounds: H, Be, C, Al, Fe, Cu, Ge, Sn, Pb, H 2 O, B 4 C and NaI. Data for proton energies between 220 and 570 MeV have been obtained with two types of transmission-counter assembly. The total errors are of the order of ± 3 %, which is a factor of three better than existing measurements in this energy region. A slight increase of the reaction cross sections with energy is observed for most of the elements studied. The results interpreted in terms of the semi-classical theory of reaction cross section as function of energy clearly demonstrate the onset of pion-production above 250 MeV.

The loss of protons by nuclear inelastic interactions in various materials

Abstract The number of nuclear inelastic interactions of stopping protons in various materials has been calculated using the latest reaction cross-sections. The results are compared with experimental measurements of this effect in silicon, sodium iodide and plastic scintillator and an excellent agreement is found. The calculations are used to determine the loss of counts in proton telescoped due to the presence of absorbers, but the agreement with experimental measurements is satisfactory only for absorbers which are fairly thick (> 50% of the range of the protons).

A remeasurement of the Panofsky ratio

Abstract By stopping π − in a liquid hydrogen target, we have measured the Panofsky ratio to be P =1.546±0.009. The measurement was carried out by using a large 46 cm φ × 51 cm NaI crystal to detect the high energy photons from the π − p→ π o n and π − p→ γ n reactions. Our value of the Panofsky ratio represents a factor of two increase in precision over the previous best value of P =1.533 ±0.021.

Proton total cross sections on 1H, 2H, 4He, 9Be, C and O in the energy range 180 to 560 MeV

Abstract Proton total cross sections have been measured for the nuclei 1 H, 2 H, 4 He, 9 Be, C and O from 180 to 560 MeV (610 to 1170 MeV/c). The standard transmission technique was used with a resulting total error of 1 % to 2 %. Statistical errors were small ( 4 He, 9 Be, 12 C. and 16 O this experiment also gives new information on the real part of the spin-independent forward scattering amplitude for proton-nucleus elastic scattering. Total cross sections have been calculated using a Glauber model approach and poor agreement with the data is obtained, even for deuterium.

The 12C(p, γ) reaction from 10 to 50 MeV

Abstract The excitation functions for radiative proton capture reactions leading to the 13N ground state ( 12 C ( p , γ 0 ) 13 N ) and to a state at 3.5 MeV in 13 N ( 12 C ( p , γ 2 ) 13 N ∗ ) have been measured with incident proton energies from 10 to 48.5 MeV. The excitation function for the ground state reaction shows strong peaks at excitations in 13N of 13, 20 and 32.5 MeV. If these are interpreted as the regions of strong E1 radiative strength the results are in good agreement with the T = 1 2 dipole states predicted in the shell model calculations of Easlea. The excitation function for radiative capture to the excited state has a peak at an excitation of 24.5 MeV in 13N and above that energy falls slowly with increasing energy, being still detectable at the maximum proton energy of 48.5 MeV.

A new NaI gamma-ray spectrometer

Abstract An improved NaI gamma-ray spectrometer has been developed for the detection of 10–40 MeV gamma rays. It consists of a 25.4 cm diameter × 25.4 cm long NaI cylinder surrounded by a plastic scintillator anticoincidence shield which is 10.8 cm thick. An energy resolution of 3.2% fwhm has been achieved for 15 MeV gamma rays. It has also been observed that the uniformity of pulse-height response in large plastic scintillators with polished surfaces is far superior to that of scintillators with surfaces which are painted white.

Neutron total cross sections for neutrons, protons and deuterons in the energy range of 90 to 150 MeV

Abstract The neutron total cross section for scattering by protons and deuterons has been measured to an accuracy of 2% in the energy range of 90 to 150 MeV. Monokinetic neutron beams were used and the results are therefore free of the systematic errors associated with many earlier measurements. The n–p cross sections agree with an earlier measurement of Taylor, but below 100 MeV they are several per cent larger than the results of Bowen et al . The difference between the neutron cross sections for deuterium and hydrogen are consistent with the results of Riddle et al. below 120 MeV. The neutron-neutron cross sections have been inferred, and they agree with the results of Riddle et al.

The electric dipole resonance of 13C and 13N

Abstract The available experimental information about the electric dipole resonance of 13C and 13N is analysed, showing the difference between the dipole resonance in these (4n + 1) nuclei and those in the 4n nuclei which have been studied more frequently. Comparison of (γ, n) and γ, p) cross-sections should determine the isobaric spins of the components of the resonance. The measurements fit most simply with all three components having T = 1 2 . However, simple considerations about the structure of 13C and 13N show that an important part of the resonance should have T = 3 2 . We show that it is possible that the 26 MeV resonance can be basically T = 3 2 with a not too large admixture of a T = 1 2 state with particular properties. We investigate a simple weak-coupling model in which the ground states of 13C and 13N are made by coupling a nucleon to the ground state of 12C and show how cross-sections deduced for the 13N(γ, p0) reaction are consistent with being due to the excitation of the extra nucleon in such a model. A more general shell-model calculation, due to Easlea, is discussed, showing that its conclusions probably do not agree with our conclusions about the 13N(γ, p0) measurements. We indicate approximations in this calculation which could perhaps be the cause of this discrepancy. We show how this weak-coupling model makes further predictions about the modes of breakup of the 13C, 13N dipole resonance.

Neutron-induced peaks in Ge detectors from evaporation neutrons

Abstract We have studied the peak shapes at 596 and 691 keV resulting from fast neutron interactions inside germanium detectors. We have used neutrons from a 252 Cf source, as well as from the 28 Si(μ − , nv), and 209 Bi(π − , xn) reactions to compare the peaks and to check for a dependence of peak shape on the incoming neutron energy. In our investigation, no difference between these three measurements has been observed. In a comparison of these peak shapes with other studies, we found similar results to ours except for those measurements using monoenergetic neutrons in which a significant variation with neutron energy has been observed.