Flux Of Primary Particles Research Articles

TU‐A‐BRB‐04: Fragmentation Analysis in Heavy Ion Therapy: A Novel Experimental Approach to Measure Lateral Distributions of Secondary Charged Particles

Purpose: In carbon ion beam radiotherapy, nuclear fragmentation in tissue leads to an attenuation of the primary particle flux and the build‐up of lighter projectile fragments. The radio‐biological effectiveness of these secondary particles differs from the primary ions. Therefore, fragmentation has to be considered in physical models used for therapy planning. While until now large apparatus have been used for ion spectroscopic measurements, we developed an experimental technique to measure lateral distributions of charged particles directly within or closely behind phantoms, using a small pixelated detector. Methods: Experiments were performed at the Heidelberg Ion‐Beam Therapy Center. A carbon ion pencil beam (∼5mm nominal width, E initial=271MeV/u) was directed towards a 12.7cm thick PMMA phantom. Secondary particles leaving the phantom were detected with the Timepix detector, placed perpendicular to the beam 5cm behind the phantom. The Timepix detector consists of a 300μm thick silicon sensor and a read‐out chip with 256×256 square pixels (55μm pitch). The high spatial resolution and the pixel‐wise energy calibration enable to determine the energy‐loss of individual particles in the sensitive layer. Together with pattern recognition analysis of characteristic particle traces in the detector, we are able to distinguish types of particles and discriminate the ion species. Results: Lateral distributions of events identified as being induced by hydrogen, helium and boron ions were determined. They show approximately Gaussian shaped profiles with FWHM values of 3.2mm (boron), 6.3mm (helium) and 13.1mm (hydrogen). These results are consistent with the expectation, that lighter fragments show wider distributions. Conclusions: We present a novel method to determine secondary charged particle distributions in heavy ion therapy directly within phantoms. The main advantage lies in the flexibility of the set‐up. The performance of the method is promising to enable fragment distributions measurements in a wide phase space in the future. Research carried out in frame of the Medipix Collaboration

Study of the primary spectrum and composition around the knee at the Andyrchy-BUST experiment

The experimental data of the Andyrchy-BUST experiment are presented. The three types of experimental data, taken in our experiment, have been analyzed: high en- ergy muon number spectrum, EAS size spectrum and depen- dence of the mean number of high energy muons on EAS size. Joint analysis of these experimental data have been used for both studying the primary composition and testing inter- action models. In the range of primary energies of 10 14 10 15 eV per nu- cleus, direct methods for studying the energy spectrum and nuclear composition of primary cosmic rays become ineffi- cient because of a decrease in the flux of primary particles with an increase in their energy. Therefore, at these and, of course, higher energies, indirect methods based on simulta- neous measurement of the characteristics of different com- ponents of extensive air showers (EASs), initiated by the pri- mary particle in the atmosphere, are used. The interpretation of these measurements requires their comparison with EAS simulations in the atmosphere. In turn, the calculation re- sults depend on the hadronic interaction models. But it is widely known that none of the present interaction models can completely describe a full set of experimental data for cosmic rays. Joint analysis of the various characteristics of different EAS components measured in the same experiment can be used for both studying the primary composition and testing interaction models (Apel et al., 2007; Garyaka et al., 2008). At the Andyrchy-BUST experiment the electromag- netic and high energy muon components are measured. The electromagnetic component in our experiment is measured

Depth distribution of vacancies generated by irradiating a solid surface with a flux of accelerated ions

Kinetic transport theory is used to find analytical expressions for the absorbed doses of the primary-particle flux and primary-particle energy as functions of distance into a solid with finite or semi-infinite thickness when the surface of the latter is irradiated by a flux of accelerated ions (atoms) in the direction normal to the surface. The theory was compared with experiments in which solid silicon films with thicknesses 50, 100, and 400 nm were irradiated by a flux of accelerated boron atoms with energies from 10 to 20 keV. These expressions were used to calculate the depth distribution of vacancies generated in a solid whose surface is irradiated by a flux of accelerated ions. The method developed can be used to determine the depth distribution of vacancies created by fluxes of accelerated electrons, neutrons, or photons.

Distribution of energetic particles and secondary radiation according to orbital station “MIR” data obtained in 1991

A set of instruments for measuring energetic particle fluxes, containing two neutron detectors under different plexiglas shielding thicknesses, a scintillation detector, measuring energy release >0. I MeV and 0.5 MeV and a Geiger counter were launched onboard OS ‘MIR’. The latitude dependencies of the cosmic ray measurements were obtained and studied. The distributions of primary particle fluxes (protons and electrons) as well as secondary particle fluxes (bremsstrahlung gamma-rays and neutrons) produced in interactions of radiation belt particles with the station materials were obtained. The electron belt, generated during the storm of March 24 1991, is studied.

Auroral spectroscopy and its application to the characterization of primary particle fluxes.

The main features of the ultraviolet, visible and infrared spectra of aurora are described. Excitation processes by auroral primary particles are summarized. A simple approach is followed to provide an understanding of the main factors influencing the dependence of the relative intensity of features of the auroral spectrum on incident particle energy and atmospheric parameters. The status of the use of various optical measurements to infer average particle energies and total energy fluxes is reviewed including comments on precautions to be observed and limitations to be considered in the application and interpretation of optical measurements.

Plasma measurements in pulsating auroras

Plasma probe experiments consisting of a Langmuir probe and a hemispherical gridded analyzer were flown on each of two Black Brant rockets during the pulsating aurora campaign in Canada in February, 1980. Electron temperature, suprathermal electron flux, and electron density profiles were obtained up to altitudes of approximately 150 km. The peak electron densities at 120 km of about 2 × 105 cm−3 are consistent with primary particle fluxes having Maxwellian distributions with a characteristic energy of about 2 keV. The integral flux of secondary electrons, with energies greater than 4 eV, increased with altitude and reached fluxes of 3.0 × 107 and 1.7 × 109 cm−2 s−1 sr−1 on the two flights. A close correlation was found between the optical pulsations and pulsations in the suprathermal flux which were 3 times the background flux. Pulsations in the electron density were barely detectable (< 20%) on only one flight. The observations support a magnetospheric flux limiting mechanism for these pulsating auroras rather than an ionospheric feedback model.

Cosmic Rays in the Energy Range 1014?1017 eV

It is possible to explain the gross features of extensive air showers using very different alternative assumptions about the character of particle interactions, provided that different assumptions are made about the primary particle flux and composition. From this fact it is first shown that a very consistent set of fairly direct measurements on primary flux now exists (subject to the acceptance of a systematic bias in one set of data), together with constraints on the composition. (Protons and other nuclei however turn out not to have the same rigidity spectrum.) The gross features of showers mostly fit a scaling model with rising cross sections, but there are contrary indications (particularly from y-ray flux, particle spread and core structure at the higher energies) that a change in the nature of interactions occurs above 10'5 eV, and this puzzle has not been solved.

Characteristics of high frequency auroral pulsations

The power spectrum of pulsating aurora has been measured in the frequency range 1–20 c/s. It shows consistently an exponential fall off with increasing frequency above about 1–2 c/s. It is shown that this is consistent with an assumption that the modulation mechanism in the flux of primary particles takes place at some distance from the atmosphere, the dispersion in energy smearing out pulsations at higher frequencies.

Cosmic ray measurements in the U.K. Scout I satellite

The main purpose of this experiment is to make accurate measurements of the primary cosmic ray energy spectrum and of the way in which this spectrum changes as a result of modulation by the inter-planetary magnetic field. The cosmic ray intensity will be measured as a function of latitude and longitude using Geiger-Muller counters, which respond to the total flux of primary particles, and a Cerenkov counter, which responds only to the heavy primaries with a charge of six or greater. An outline of the physical background to the experiment is given, together with a description of the sensor and its associated electronics.

Heavy primary interactions in water loaded emulsions

Water loaded emulsions have been used to study cut-off energy, spectrum and flux of primary particles at geomagnetic latitude and longitude 47 ℴS, 135 ℴW. Results agree with Stormer cut-off energy for the latitude. Most interactions in the water loaded emulsions were shown to occur in light nuclei.

41. The solar daily variation of the cosmic ray intensity

Some recent measurements of the solar daily variation for cosmic rays incident from the east and west directions at 45° to the vertical in London are described. The results do not agree with those to be expected if the variation was due to a non-isotropic flux of primary particles entering the earth's magnetic field. This result is discussed in relation to other evidence and it is concluded that the daily variation is probably due to a modulation of the primary cosmic ray intensity in the earth's magnetic field.

LXVH. The solar daily variation of the cosmic ray intensity

Abstract Some recent measurements of the solar daily variation for cosmic rays incident from the east and west directions at 45° to the vertical in London are described. The results do not agree with those to be expected if the variation was due to a non-isotropic flux of primary particles entering the earth's magnetic field. This result is discussed in relation to other evidence and it is concluded that the daily variation is probably due to a modulation of the primary cosmic ray intensity in the earth's magnetic field.

LXI. The penetrating component of cosmic radiation in the upper atmosphere

Summary The vertical intensity of the hard component of cosmic radiation has been measured in geomagnetic latitude 56°, to a minimum atmospheric depth of 4 g/cm2. The intensity, determined with a precision of 2·5%, shows no maximum. This agrees closely with the results of Pomerantz. The primary particle flux at this latitude, capable of penetrating 90 g/cm2 of lead is found to be 0 ·164±0·003 particles cm−2 sec−2 ster−1. The flux of μ-mesons in the upper atmosphere has been derived, and shows a maximum of 0.039 particles cm−2 sec−1 ster−1 at a depth of 150 g/cm2. Penetrating showers produced in lead have also been measured to a minimum atmospheric depth of 7 g/cm2, the primaries being found to have an absorption length of 120 g/cm2 of air.

Analysis of the Nucleonic Component Based on Neutron Latitude Variations

A "specific yield" function ${S}_{A}(E,x)$ is defined which gives the production rate of disintegration neutrons at atmospheric depth $x$ arising from a unit flux of vertically incident cosmic-ray primaries of atomic weight $A$ and energy-per-nucleon $E$. The functions are obtained by comparing the latitude variations for the primary particle fluxes with the latitude variations for neutron production at various depths in the atmosphere. For atmospheric depths between at least 200 and 600 g/${\mathrm{cm}}^{2}$, it is found that the specific yields increase rapidly with energy up to about 4-Bev/nucleon and then become insensitive to energy up to at least 12.7-Bev/nucleon. It is also shown that this insensitivity probably extends up to considerably larger energies. The theoretical implications of these results are qualitatively discussed.

The theory of counting experiments using pulsed sources: chance coincidences and counting-rate losses

The use of artificially pulsed sources of particles in experiments in nuclear physics has already given rise to powerful methods of investigating short-period phenomena and of studying the effects of ‘slow’ neutrons of different energies. On the other hand, the use of such sources introduces complications in counting experiments which are not present when steady sources are employed and it is possible to assume that the time distribution of ionizing events in any counter is a strictly random one. Again, sources which are effectively steady in respect of one counting arrangement are not necessarily so in respect of all. Ordinary cyclotron sources (i.e. cyclotron sources which are not ‘artificially’ pulsed) belong to this class; they have justifiably been considered as steady in the majority of experiments hitherto performed, but the flux of primary particles reaching the target is definitely periodic in time (with the period of the R.F. Voltage applied to the dees), thus a cyclotron will appear as ‘naturally’ pulsed whenever it is used with a counting system for which the effective resolving time is sufficiently short (say < 10−7 sec.).