M. A. Paciotti

Computed tomography using proton energy loss

An experiment has been performed to demonstrate the feasibility of proton computed tomography. The proton energy loss was used to measure the projections of the relative stopping power of the phantom. High quality reconstructions were obtained from scans of 19 cm and 30 cm diameter performance phantoms. Comparison with reconstructions from an EMI CT-5005 X-ray scanner showed the proton technique is more dose efficient by a large factor.

Proton computed tomography of human specimens

The experimental procedure and results of a comparative study of the imaging characteristics of proton and X-ray CT scans are presented. Scans of a human brain and heart are discussed. The proton produced images are found to be similar in information content while providing a decided dose advantage.

The Relative Efficiency of Soft-Error Induction in 4K Static RAMS by Muons and Pions

Soft-error rates in a 4K static RAM have been obtained for 164 MeV/c pions and 109 MeV/c muons. The pion beams were found to be at least 10000 times more effective than were the muon beams, with the implication that effects of pions in cosmic rays at sea level may not be negligible.

Meson Interactions in NMOS and CMOS Static RAMs

Nuclear interactions of heavy particles, such as neutrons, protons, and heavy ions are one of the primary causes of errors in memory chips exposed to radiation in the environment. Pions, the quanta associated with the nuclear force, and muons are produced in large quantities in such reactions and can be responsible for a portion of those errors attributed to primary particles. Pions and muons also are important constituents of cosmic rays at lower elevations. The rate of error induction in 4K static RAMs from high-energy pion and muon beams has been measured at three energies and as a function of depth in plastic. Preliminary data for 16K NMOS and 64K CMOS static RAMs were also obtained. Only two errors were observed from muon beams incident upon 4K chips for 1.4 × 1010 particles/cm2 . In contrast, energetic pion beams produced errors in the same chips at the rate of typically 5 × 10-8 errors per incident particle per cm2 . In the pion beams the rate decreased slowly with decreasing energy until the particles approached the end of their range. In the stopping region, the error rate continued to decrease for positively charged pions but increased about a factor of seven for negatively charged pions. Monte Carlo programs have been run both to simulate the production of pions in the atmosphere as a function of elevation and to simulate the inteactions of pions in the 4K chip.

An estimate of error rates in integrated circuits at aircraft altitudes and at sea level

Abstract Negative muons nearing the end of their range can undergo capture in the nucleus, disintegrate, and damage microelectronics. Although there are large numbers of muons produced in the atmosphere by cosmic rays, there have been no experimental data evaluating the vulnerability of integrated circuits to stopping muons. Changes in bit states (errors) in 4K NMOS static RAMs have been obtained with accelerator beams of positive and negative muons nearing the end of their range, along with the corresponding microdosimetric spectra. These data and earlier results are used to estimate both absolute error rates and the relative contributions of different particle types at 10 km (a nominal aircraft altitude) and at sea level. The calculation indicates that typical error rates at 10 km would be about 10 errors per megabit per year, only slightly less than the estimated rate for satellite altitudes.

Tuning of the First Section of the Biomedical Channel at LAMPF

Results are presented from the tuning of the first section of the Biomedical Channel at LAMPF; the work centers about the use of the third bending magnet as a magnetic spectrometer. The momentum resolution at the intermediate focus is given in detail. The performance of a wedge degrader that compresses the wide momentum acceptance of the first section is discussed. The output ¿- rate is also given.

Dosimetry of pion therapy beams.

Cellular, animal, and human radiobiology studies are in progress at the Los Alamos Meson Physics Facility as part of a joint University of New Mexico and Los Alamos Scientific Laboratory pion therapy project. To support these activities, dosimetry has been performed on many different pion beam configurations. The effect of both static and dynamic momentum spreaders and of collimators on beam profiles, depth-dose distributions, and peak-to-plateau ratios have been studied. The absorbed dose is obtained by the application of Bragg-Gray cavity theory to ionization chamber measurements. Calculations have been made for the effective W values and average mass-stopping-power ratios needed for the Bragg-Gray equation. Kerma corrections are applied to transform the dose from the chamber wall to dose in muscle.

Microdosimetry: Measured Probabilities for Energy Deposited by Mesons in One-Micron Sites in Silicon

Probabilities of ionizing events and probability distributions for energy deposited by positive and negative pi mesons and positive mu mesons have been measured in one-micron equivalent sites in silicon. A new low-noise silicon proportional counter was developed to measure complete distributions beginning at a few electron-volts per micrometer. The data show that 140-MeV/c pions when compared with 80-MeV muons are more likely to initiate processes with thresholds greater than about 50 MeV/kg/m2. These results support our earlier hypothesis that, at lower altitudes, pions are more likely to induce errors in memory chips than muons. It is proposed that error rates from pions at lower elevations may be comparable in number to those from neutrons.

Dose outside the treatment volume for irradiation with negative pions

Irradiation of humans with negative pions requires a knowledge of the absorbed dose and radiation quality outside the primary pion beam. In conjunction with early clinical trials at LAMPF, experimental data have been obtained with microdosimetric techniques and multiwire proportional counters. Theoretical calculations have been made for the neutron contribution to the dose and are consistent with these data. Measurements were made with in 40 cm x 51 cm x 76 cm water phantom for a negative pion beam of initial momentum of 170 MeV/c, deltap = +/- 3MeV/c. The absorbed dose outside the treatment volume is the result of: (1) neutrons and photons from the pion interactions,(2) treatment room background and (3) peripheral muons, electrons and pions in the primary beam. The first two components are nearly isotropic and are congruent to 0.02% of the peak dose at a distance of 24 cm from the treatment volume; the third component is anisotropic and varies from 0.01 to 0.1% of the peak dose. Collimation of the bean increases the dose outside the treatment volume typically by 50%.

Treatment planning for negative pi-meson radiation therapy: UNM-LASL experience

Abstract Human radiobiological studies using negative pi-mesons have recently been conducted at the Los Alamos Meson Physics Facility; metastatic tumor nodules in the skin and superficial tumors have been treated. Large tumors of the head and neck, cervix and rectum will be treated later this year to evaluate mucosal reactions. The dosimetry and treatment planning for these clinical studies is presented. Comparisons of measurements and calculations of the effect of inhomogeneities on pion dose distributions are shown. The pion treatment code, PIPLAN, and the Oak Ridge National Laboratory Monte Carlo code have been compared and an example of their respective dose distribution calculations is given.