Thick-target Data Research Articles

INCL Intra-Nuclear Cascade and ABLA De-Excitation Models in Geant4

We present INCL intra-nuclear cascade and ABLA de-excitation (evaporation/fission) models that can be used to calculate collisions between projectile particles and nuclei at energies from 0.2 to 3 GeV. Supported projectiles are proton, neutron, pions and light ions up to alpha. The optimal target materials range from carbon to uranium. We have extended the INCL model light ion projectile support up to carbon-ions and compared the results against thin and thick target data and Geant4 Binary cascade model. Both thin and first thick target results of the INCL model are in good agreement with experimental data.

Production of cosmogenic nuclides in meteoroids: accelerator experiments and model calculations to decipher the cosmic ray record in extraterrestrial matter

Accelerator experiments at low and medium energies provide a basis for the development of models describing the production of cosmogenic nuclides by solar and galactic cosmic ray particles. Here, recent efforts to understand cosmogenic nuclide production are outlined taking their production in meteoroids as an example. Thin-target and thick-target experiments are described, by which the relevant cross sections are measured and in which the isotropic irradiation of meteoroids in space is simulated under completely controlled conditions. Thin-target and thick-target data are combined to develop and to validate model calculations of cosmogenic nuclide production rates by solar and galactic cosmic ray particles. The model calculations provide the basis to interpret the observed abundances of cosmogenic nuclides with respect to the exposure history of the irradiated matter and to the history of the cosmic radiation itself.

Micro-particle impact flux on the timeband capture cell experiment of the Eureca spacecraft

Measurements of hypervelocity impact fluxes (in both thick and thin targets) detected by the University of Kent at Canterbury's Timeband Capture Cell Experiment (TiCCE) (flown on ESA's Eureca spacecraft) are presented. The foil perforations are used to derive the ballistic limit values, or the maximum thickness of Al perforated, for the impacting particles. This data is then combined with the thick target data to derive a unified ballistic limit flux. A significant enhancement in the observed large particle flux compared with LDEF is found, possibly due to the pointing history of Eureca compared to the Earth's orbital direction. Comparisons are also made to predictions from ESABASE modelling. Preliminary results of a study of perforation morphology are also presented, providing insight into particle shape, density and directionality.

The near Earth space impact environment — An LDEF overview

Impact data from craters on finite targets and thin foil perforations are used to establish impact distributions for key pointing directions on the returned spacecraft LDEF over sizes ranging from sub-micron to millimetres. Using thin and thick target data corresponding to the same average impactor fluxes, equivalences are established. From such merged distributions and from variations in flux with pointing direction, average flux distributions at constant crater size are established for LDEF's principal pointing directions and, incorporating LDEF's offset angle, further models for the flux distribution relative to LDEF's orbit vector. Though natural meteoroids dominate at medium dimensions, orbital particulates and space debris are evident at micron and millimetre crater dimensions. For the natural particulates a mean velocity ranging between 16.7 and 22kms −1 (depending on particle size) and a density of 1.0±0.3gcm −3 is indicated. For the microdebris, crater morphology shows that a higher density is required. Asymmetries in the North and South fluxes point to a non-uniform meteoroid population; this natural component on LDEF is shown to agree very well with that calculated for the interplanetary meteoroid flux. The model fluxes are available (electronic and hard copy) through the Meteoroid and Debris Special Investigation Group Database.

The new Schonland PIXE microprobe and applications to geological and archaeological samples

The new positive ion microprobe at the Schonland Centre is described and details are given of its configuration, its imaging system and software. In a unique configuration, the microprobe has access to two accelerators, a 6 MV EN tandem and a 2.5 MV single-ended machine. The imaging system uses a CAMAC based system and runs on a personal computer under OS/2. The implementation of PIXE and treatment of thick-target data are presented. Applications discussed are analysis of tin artifacts from the prehistory of metallurgy in South Africa; a diamond-containing rock; carbonado, gold contained in pyrite and cogenetic minerals included in diamond.

The 12C(p, g)13N Cross Section near the Ep = 0·46 MeV Peak

The I2C(p,'Y?3N cross section in the neighbourhood of the Ep = 0�46 MeV peak has been measured using thin and thick targets, and fitted using R-matrix formulae. The best value for the radiation width of the first excited state of I3N is 0�53�0�05 eV. eanalysis of earlier thick-target data gives values consistent with this result.

On the depth dependence of spallation reactions in a spherical thick diorite target homogeneously irradiated by 600 MeV protons: Simulation of production of cosmogenic nuclides in small meteorites

An artificial meteorite made out of diorite with a radius of 5 cm was irradiated isotropically with 600 MeV protons in order to simulate the production of cosmogenic nuclides in small meteorites by galactic cosmic ray protons. The primary proton dose of 4.82 × 10 15 cm −2 is equivalent to a some 50 Ma of cosmic ray exposure. The depth dependent production of a wide range of radionuclides from target elements O, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Ba, and Lu was measured. Furthermore, the production of He and Ne isotopes from Al, Mg, Si, as well as from glass and meteoritic material was determined. Thick-target data are compared with thin-target production rates measured simultaneously, thus allowing to separate the contribution of secondary protons and neutrons. The results demonstrate that, in contrast to present presumptions, even in small meteorites secondary particles have to be considered and that the depth profiles show differences in production of up to 30% between surface and center. The experimental data are discussed with respect to cosmic irradiation conditions of real meteorites. Using Monte Carlo techniques depth dependent nucleon spectra were calculated. On the basis of these spectra and of thin-target excitation functions theoretical production rates were derived and compared with the experimental ones. This comparison shows that it is possible to reproduce the experimental depth profiles quite well by thin-target calculations provided reliable excitation functions are at hand. The thick-target measurements and the thin-target calculations provide a basis for an advanced modelling of the production of cosmogenic nuclides in small meteorites, which strictly differentiates between all contributing production modes.

Measurements and calculations of neutron spectra from 35 MeV deuterons on thick lithium for the FMIT facility

Neutron yields and energy spectra were measured for 35 MeV deuterons on a thick target of natural lithium. Data were obtained using the time-of-flight technique over an angular range of 0° to 150° and for neutron energies from about 1 to 50 MeV. A simple nuclear model that describes the differential cross sections of neutron production was adjusted to agree with these new thick target data. Different model parameters were obtained when the model was adjusted to agree with previous ORNL thick target data for 40 MeV deuterons. Our experimental data are in good agreement with model predictions based upon the ORNL time-of-flight data but are somewhat lower than predictions based upon the ORNL dosimetry data. Finally the model was used to predict the neutron spectrum at the position of highest flux in the FMIT test cell.

The 7Li( p, n) 7Be reaction as a therapy neutron source, especially for smaller cyclotrons

Accelerator experiments at low and medium energies provide a basis for the development of models describing the production of cosmogenic nuclides by solar and galactic cosmic ray particles. Here, recent efforts to understand cosmogenic nuclide production are outlined taking their production in meteoroids as an example. Thin-target and thick-target experiments are described, by which the relevant cross sections are measured and in which the isotropic irradiation of meteoroids in space is simulated under completely controlled conditions. Thin-target and thick-target data are combined to develop and to validate model calculations of cosmogenic nuclide production rates by solar and galactic cosmic ray particles. The model calculations provide the basis to interpret the observed abundances of cosmogenic nuclides with respect to the exposure history of the irradiated matter and to the history of the cosmic radiation itself.

X-Ray Line Intensities and Cathode-Ray Retardation in Thick Targets of Silver

$K$-line intensities from thick silver targets have been measured in arbitrary units for voltages up to 180 kv, with emergence angles from 1 to 25\ifmmode^\circ\else\textdegree\fi{}. A practical use of these data is the determination of the voltage which will give the maximum efficiency of line emission at any emergence angle. At 1\ifmmode^\circ\else\textdegree\fi{} the best voltage is 70 kv but at 25\ifmmode^\circ\else\textdegree\fi{} it is well above 180 kv. These data are also used in conjunction with data on thin targets to get information as to the retardation of cathode rays in silver. For this purpose the thick-target data are corrected to eliminate the effects of target absorption, indirect production of line rays through fluorescence and loss of cathode rays by rediffusion. The loss of energy per unit distance along the path of a cathode ray varies as the -1.4 power of the speed, just as it does in light elements according to more direct evidence collected by E. J. Williams.