Inclusive Neutron Spectra Research Articles

Measurement of the neutron spectrum by the irradiation of a 2.04-GeV electron beam into thick targets

Inclusive neutron spectra produced by the irradiation of a 2.04-GeV electron beam into thick Al, Cu, Sn and Pb targets were measured by the TOF method. For such a high-energy region, it was the first experiment to measure the inclusive neutron spectra. A lead shield was placed at the middle point of the flight path to suppress any strong photon or electron background. The effects of the shield on the neutron spectra were calculated by the LAHET2.7 code with a small modification. The measured neutron energy in the experiments was from 10 to 200 MeV . The measured spectra were used for a benchmark test of our modified PICA95. It was found that the neutron spectra predicted by a combination of EGS4, our modified PICA95 and LAHET2.7 codes, tend to underestimate the measured ones.

Neutron spectra from the 156Er compound nucleus populated by 12C- and 64Ni-induced reactions.

Inclusive neutron spectra from the decay of [sup 156]Er compound nucleus populated at [ital E][sub [ital x]]=47 MeV excitation energy by the [sup 12]C+[sup 144]Sm and [sup 64]Ni+[sup 92]Zr reactions have been measured. The neutron spectra from the [sup 64]Ni-induced reaction are strongly contaminated by other reactions different from fusion evaporation so that inclusive spectra cannot be used to test nonstatistical or entrance channel effects in the compound nucleus decay.

Inclusive neutron cross sections at forward angles from Nb-Nb and Au-Au collisions at 800 MeV/nucleon.

Inclusive neutron spectra were measured at 0\ifmmode^\circ\else\textdegree\fi{}, 4\ifmmode^\circ\else\textdegree\fi{}, 8\ifmmode^\circ\else\textdegree\fi{}, 15\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, and 42\ifmmode^\circ\else\textdegree\fi{} from Nb-Nb and Au-Au collisions at 800 MeV/nucleon. A peak that originates from neutron evaporation from the projectile appears in the spectra at angles out to 8\ifmmode^\circ\else\textdegree\fi{}. The shapes and magnitudes of the spectra are compared with those calculated from models of nucleus-nucleus collisions. The differential cross sections for Au-Au collisions are about four times those for Nb-Nb collisions. The predictions of the Vlasov-Uehling-Uhlenbeck (VUU) and QMD theories agree with the angular distributions of the differential cross sections except at small angles; the VUU prediction overestimates the angular distributions from a few degrees to about 20\ifmmode^\circ\else\textdegree\fi{}, whereas the QMD prediction underestimates the angular distributions below 8\ifmmode^\circ\else\textdegree\fi{}. The Firestreak model overestimates the angular distribution for Nb-Nb collisions and underestimates it for Au-Au collisions. Also, the VUU and QMD models agree with the measured double-differential cross sections in more angular and energy regions than the Firestreak and intranuclear cascade models; however, none of the models can account for the peaks at small angles (\ensuremath{\theta}\ensuremath{\le}15\ifmmode^\circ\else\textdegree\fi{}).

Inclusive neutron spectra at 0 degrees from Nb-Nb and Au-Au collisions at 800 MeV/nucleon.

Inclusive neutron spectra were measured at 0\ifmmode^\circ\else\textdegree\fi{} from Nb-Nb and Au-Au collisions at 800 MeV/nucleon. The spectra in the rest frame of the projectile were decomposed into three Gaussians with standard deviations of 55\ifmmode\pm\else\textpm\fi{}4, 114\ifmmode\pm\else\textpm\fi{}12, and 259\ifmmode\pm\else\textpm\fi{}22 MeV/c for Nb-Nb collisions, and 56\ifmmode\pm\else\textpm\fi{}4, 110\ifmmode\pm\else\textpm\fi{}10, and 279\ifmmode\pm\else\textpm\fi{}15 MeV/c for Au-Au collisions. Physical processes associated with each Gaussian are discussed. The dependence of the parameters of the three Gaussians on the impact parameter indicates that the temperature of the spectators excited by peripheral collisions is lower than that excited by nonperipheral collisions, that projectile neutrons involved in nonperipheral collisions have a broader momentum distribution than those involved in peripheral collisions, and that an observed high-energy tail has its origin primarily in nonperipheral collisions. The high-energy tail is explained well by collective backscattering of neutrons in the target from nucleon clusters in the projectile with a mean cluster size of about 1.3 in both Nb and Au.

Inclusive neutron spectra from the break-up of3He in peripheral collisions with27Al,63Cu,93Nb,197Au

The break-up contribution to the continuous neutron spectra measured with3He projectiles of 34.4MeV for targets with masses 27≦A≦197 shows a broad peak centering the more belowE3He/3 the heavier the target is. The DWBA theory of elastic and inelastic break-up underestimates the inclusive spectra, but gives the correct shapes. Both, calculated and experimental peak positions, are indicative of a peripheral collision.

The neutron exit channel in 3He-induced break-up reactions

Inclusive neutron spectra of 3He-induced reactions with 27A1, 63Cu, 93Nb and 197Au were measured for 26.0, 34.4 and 43.1 MeV projectile energy at laboratory angles from 3° to 177° using time-of-flight techniques. The component remaining after incoherent subtraction of compound and precompound contributions from the inclusive spectra shows a broad continuous bump and is assigned to the direct projectile break-up. Due to Coulomb effects, the position of the bump is shifted from 1 3 E 3 He c.m. to lower and higher energies in neutron- and proton-spectra, respectively. Experimental and theoretical results characterize the projectile break-up as a peripheral process. Break-up neutron yields increase with incident energy and target mass. Experimental spectra are the more underestimated by DWBA model calculations the less the incident energy exceeds the Coulomb barrier of the target nucleus. These discrepancies are attributed to the neglect of reaction mechanisms, e.g. a sequential break-up involving a singlet deuteron as intermediate state or an excitation of the projectile into the continuum followed by an immediate decay.

Inclusive neutron, proton and deuteron energy spectra from stopped π− absorption in 6Li, 9Be, 16O and 27Al

Inclusive energy spectra ( E ⩾ 20MeV) of neutrons, protons, and deuterons emitted after stopped π − absorption in 6Li, 9Be, 16O and 27Al (neutrons only) were measured. Single-neutron emission rates of the order of 10 −2 and 10 −3 per stopped pion were obtained for 6Li, 9Be, 16O and for 27Al respectively. The experimental data indicate a predominant contribution of two-nucleon absorption mechanism to the neutron and proton spectra for all the studied nuclei, and presence of direct deuterons from cluster-absorption for 6Li. Values of R np are deduced, which are consistent with predictions based on the absorption mechanism by a correlated pair of nucleons with pion rescattering.

Inclusive neutron spectra at 0 degrees from the reactions Pb(Ne,n)X and NaF(Ne,n)X at 390 and 790 MeV per nucleon.

Inclusive neutron spectra at 0\ifmmode^\circ\else\textdegree\fi{} were measured from both 390- and 790-MeV/u Ne ions on targets of Pb and NaF. A striking peak at a neutron energy slightly below the beam energy per nucleon has a width (in the projectile rest frame) of \ensuremath{\sim}58 MeV/c, which is essentially the same for these two energies and these two targets. We suggest that this narrow peak is projectile evaporation and that it is superimposed on the broader fragmentation process predicted by statistical models. The high-momentum region of the cross section may reflect collective behavior.

Inclusive neutron and proton energy spectra following the negative pion absorption at rest in 12C

The results of a measurement of the inclusive energy spectra of the neutrons and protons emitted following the absorption at rest of negative pions on 12C are presented. The spectra have been measured with the time-of-flight method with an overall resolution of 650 psec. From the neutron spectrum the rate of 1.7 × 10 −2 neutrons per stopped pion has been deduced for the single-neutron emission reaction 12C( π −, n) 11 B. Comparisons are made with calculated spectra and other experimental spectra.

Inclusive neutron spectra from the absorption of stopped negative pions in heavy nuclei

Energy spectra of neutrons emitted after the absorption of stopped negative pions in heavy nuclei from 165Ho to 238U have been measured and interpreted in terms of models for pion absorption on a peripheral nucleon pair and subsequent secondary reactions. The mean number of evaporation, direct and total neutrons, their mean energies and nuclear temperature parameters have been deduced from the inclusive neutron spectra. The extracted nuclear temperatures and level density parameters for heavy nuclei show no shell effects in the energy region excited by the stopped pion reaction. For 238U the ratio of pre- to post-fission neutron yields has been deduced from the experimental data.

Inclusive neutron and charged particle spectra from the absorption of stopped negative pions in nickel isotopes

Energy spectra of neutrons and charged particles emitted after the absorption of stopped negative pions in the Ni isotopes 58Ni, 60Ni, 62Ni and 64Ni have been measured. The data are compared with model calculations for pion absorption on a peripheral nucleon pair and subsequent secondary reactions. The sum of the mean number of emitted neutrons and protons 〈 n〉 + 〈 p〉 is 7.2 ± 1.2, independent of the neutron number N, whereas the difference 〈 n〉 — 〈 p〉 increases linearly with N from 1.6 ± 0.8 for 58Ni to 5.0 ± 1.1 m for 64 Ni . The experimental results are compared with measurements of residual nuclei from stopped π −- and p-induced reactions in the above-mentioned Ni isotopes.

Proton and Neutron Inclusive Spectra and the Importance of the Single Nucleon-Nucleon Scattering Process

Comparison of inclusive neutron and proton spectra from 90-MeV protons on /sup 27/Al, /sup 58/Ni, /sup 90/Zr, and /sup 209/Bi indicates that single nucleon-nucleon scattering dominates the high-energy regions of forward-angle continuum spectra. The ratios of cross sections observed agree with ratios expected for scattering of the incident proton by a bound target nucleon. For /sup 27/Al, a plane-wave impulse-approximation quasifree scattering calculation fits forward-angle proton and neutron spectra simultaneously with the same normalization.

Measurement of inclusive zero-angle neutron spectra at the CERN ISR

With a total absorption spectrometer, inclusive neutron spectra have been measured at four ISR energies at zero degrees. The invariant cross sections show scaling behaviour in x with an important contribution of pion exchange at large x. At √ s = 52.8 GeV the spectrum of photons is given for x ⩽ 0.375.

Inclusive neutron spectra in electroproduction above the resonance region

Inclusive neutron spectra in electroproduction above the resonance region

Inclusive neutron spectra in electroproduction above the resonance region

In electroproduction on hydrogen at momentum transfers −0.3, −0.6, −0.9 (GeV/ c) 2 and W = 2.3 GeV we have measured, over a range of backward centre-of-mass angles, the yield of neutrons with momenta between 0.4 and 1.2 GeV/ c, and in addition, protons over a limited range with momenta greater than 0.8 GeV/ c. We compare the neutron yields with those of the protons and also with previous experiments. We find that the yield of neutrons is significantly greater than that of protons.

Measurement of the inclusive forward neutron spectrum produced in proton-copper interactions at 24 GeV/ c

We present data on the inclusive neutron spectra produced in the forward direction by the interactions of 23.85 GeV/ c protons in a copper target. The results are in good agreement with the predictions of the triple-Regge model.

Measurement of inclusive neutron spectra at the ISR

With a total absorption counter, inclusive neutron spectra have been measured at four ISR energies and at angles of 20, 66 and 119 mrad. The spectra show scaling behavior in the variables x and p⊥. Pion exchange is found to be important at large x values.

Measurement of inclusive neutron spectra from p-Be up to 24 GeV/c incident momentum

We present data on inclusive neutron spectra produced in an internal Be target of the CERN PS, for incident proton momenta between 8 and 24 GeV/ c at 0°, and for an incident proton momentum of 19 GeV/ c at 50 mrad.