Accelerated Proton Beams Research Articles

Use of high-sensitivity diamond detectors in DC mode for detailed beam-profile measurements in particle accelerators

Because of its high radiation hardness, diamond can be used better than other materials in the intense radiation field characterizing the interior region of a particle beam in an accelerator. In effect, the measurements reported here were carried out by placing diamond detectors under continuous irradiation in the 26-MeV proton beam of the 15-MV TANDEM accelerator of Southern National Laboratory (LNS) of INFN in Catania. The diamond detectors were built in the Rome Tor Vergata Laboratory. Diamond films were deposited by microwave plasma enhanced chemical vapor deposition on silicon substrates. A four-pixel beam monitor prototype was then realized by depositing four titanium gold contacts on the diamond surface. The signal was found to be stable and reproducible. The collected charge in DC mode was more than 20 000 electrons/protons for a diamond thickness of 65 μm, thus exhibiting a gain of approximately 10 4 with respect to the Faraday cup. For the measured samples, both response and release times of approximately 1 s were observed in the above experimental conditions. An analysis of the relative sensitivity between pixels was also performed. No differences of the detector current and Faraday cup current ratio were observed for different pixels, indicating the homogeneity of the beam monitor response.

Coupling of reactor power with accelerator current in ADS systems

In ADS systems, it is generally assumed that the electrical current feeding the accelerator proton beam originates from the grid. On the other hand, in an accidental event, the safety of these systems is largely based on current interruption, it being generally assumed for ADS that the required reactivity compensations during reactor operation and burn-up should be regulated through a current reserve rather than through a control rod adjustment (this avoiding inadvertent control rod removal accidents). In the case of a serious accident, if the current interruption fails, the consequences may be severe. In this work we consider an approach by which the probability of such an event is drastically reduced. Its principle is based on the coupling of the accelerator proton current, rather than with the external grid, to the electricity produced by the same reactor, except at start-up conditions, for which an external electrical current of a relatively low intensity would be used. A self-regulating mechanism, introducing an extra negative power feedback, for contributing to limiting temperature rise during transients, is also considered. The “balance of reactivity” method proposed by Wade is finally proposed for the analysis of accidental events. In an intercomparison analysis, the advantages of this approach with respect to ADS systems so far considered are discussed.

Radiation Effects in Chloride Molten Salt Compositions

Radiation effects on the composition of NaCl (70 mole %) and PbC12 (30 mole %) salts irradiated by a high energy accelerator proton beam were analyzed. In the temperature interval from ~50 to ~1200 °C this composition can be considered as radiation-resistant material, that can be recommended for use as target material for accelerator-driven transmutation systems.

The p + p → π+ + d reaction close to threshold at COSY

Differential and total cross sections of the p + p → π + + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π 0 + d and the π + + d → 2 p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.

The DISTO first level trigger at SATURNE

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multi-particle final states produced in pp scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the p/spl I.oarr/p/spl rarr/pK/sup +/Y/spl I.oarr/ (Y=/spl Lambda/, /spl Sigma//sup 0/ or Y*) reaction and vector meson production (/spl phi/, /spl omega/, and /spl rho/) in pp collisions. The common signature of such events is the multiplicity of four charged particles in the final state. A flexible 1st level trigger which uses topological information from fast detectors (scintillating fibers and hodoscope) has been built. It is completely software programmable through a menu-driven user interface and allows switching between production and monitor triggers on successive beam spills.

The HERA-B experiment: Physics programme and status

The HERA-B experiment aims to measure CP-violation in the B system, by exploiting the interaction of the proton beam of the HERA accelerator at DESY with a wire fixed target. Besides the main goal of measuring the β angle of the CKM unitarity triangle, a wide experimental program on B physics will be pursued.

The DISTO data acquisition system at SATURNE

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multiparticle final states produced in pp scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the p/spl I.oarr/p/spl rarr/pK/sup +/Y/spl I.oarr/ (Y=/spl Lambda/,/spl Sigma//sup 0/ or Y*) reaction and vector meson production (/spl phi/,/spl omega/ and /spl rho/) in pp collisions. The data acquisition system is based on a VME 68030 CPU running the OS/9 operating system, housed in a single VME crate together with the CAMAC interface, the triple port ECL memories, and four RISC R3000 CPU. The digitization of signals from the detectors is made by PCOS III and FERA front-end electronics. Data of several events belonging to a single Saturne extraction are stored in VME triple-port ECL memories using a hardwired fast sequencer. The buffer, optionally filtered by the RISC R3000 CPU, is recorded on a DLT cassette by DAQ CPU using the on-board SCSI interface during the acceleration cycle. Two UNIX workstations are connected to the VME CPUs through a fast parallel bus and the Local Area Network. They analyze a subset of events for on-line monitoring. The data acquisition system is able to read and record 3500 eV/burst in the present configuration with a dead time of 15%.

Characterization of metal complexes of pharmaceutical interest by capillary electrophoresis with element sensitive detection

The application of capillary electrophoresis to the separation and detection of compounds of medical interest is described. A proton-induced X-ray emission (PIXE) detector was used for metal-specific and sensitive detection. The detected X-rays are generated inside the capillary by an accelerated proton beam. The application of this novel detection mode in addition to common UV detectors is demonstrated for different complexes of gadolinium with polyaminopolyacetic acids. Using the PIXE detector lower limits of detection have been achieved which could be convincingly demonstrated by a comparison with UV detection in the direct and indirect detection mode. Furthermore, kinetic experiments investigating the decomposition of the Re(III)-HEDP (1-hydroxyethylidene diphosphonic acid) boon seeking agent were discussed. Finally, metallothioneins (MTs) from rabbit liver and horse kidney have been separated and up to six isoforms were completely or partially resolved. Copper, zinc and cadmium, attached to the isoforms, have been detected simultaneously.

Secondary particle contribution to LET spectra on LDEF

Four experiments utilizing passive detectors (P0006, P0004, A0015, M0004) were flown on LDEF to study the radiation environment. These experiments have been summarized in a companion paper (Benton et al., 1996). One of the experimental goals was to measure LET spectra at different locations and shielding depths with plastic nuclear track detectors (PNTD). It was found that the LET spectra extended well above the LET cutoff imposed by the geomagnetic field on GCR particle penetration into LEO. The high LET particles detected were mostly short-range (range < 2000 μm), indicating that they were secondaries produced locally within the PNTD. The presence of these high LET particle fluences is important for the determination of dose equivalent because of the high Quality Factors (Q) involved. A relatively small fraction of particle fluence can contribute a large fraction of dose equivalent. Short-range, inelastic secondary particles produced by trapped protons in the South Atlantic Anomaly (SAA) were found to be a major contributor to the LET spectra above 100 keV/μm. The LET spectra were found to extend beyond the ∼ 137 keV/ μm relativistic GCR Fe peak to over 1000 keV/μm. The high LET tail of the LET spectra was measured in CR-39 and polycarbonate PNTDs using different techniques. GCR made a relatively modest contribution to the LET spectra as compared to the contributions from short-range secondary particles and stopping protons. LET spectra intercomparisons were made between LDEF measurements and exposures to 154 MeV accelerated proton beams. The similarities support the role of nuclear interactions by trapped protons as the major source of secondary particles in the PNTDs. Also techniques were employed to reduce the range cutoff for detection of the short-range secondaries to ∼ 1 μm, so that essentially all secondary particles were included in the LET spectra. This has allowed a more realistic assessment of secondary contribution to dose equivalent. Comparisons of measured and calculated LET spectra have been made that demonstrate the need for more accurate modeling of secondary particles in radiation transport codes. Comparisons include preliminary calculations in which attempts have been made to include secondary particles.

Contribution de la biomicroscopie ultrasonore au traitement conservateur des mélanomes de l'uvŽe antérieure

Ultrasound Biomicroscopy (UBM) is a new ophthalmological imaging technique essentially designed for the study of the anterior eye segment. Over the last 10 months, we've evaluated its contribution to the conservative treatment of anterior uveal melanoma's by means of accelerated proton beam irradiation. Using UBM, we have examined 55 cases of uveal melanoma's, whose anterior border was situated at 6 mm or less from the limbus and that were consequently treated by proton beam irradiation. The presumed tumoral origin was the ciliary body's pars plicata in 13 cases and the pars plana or the choroid in 42 cases, 17 of which presented a tumoral invasion of the pars plicata. A pars plana detachment anterior to or surrounding the anterior tumoral border, was present in 22 cases. The height of the tumor could only be measured by UBM if it was less than 2.5 mm. Information gathered using UBM have contributed to an improvement of the therapy plan in 32 cases. Because of the strong attenuation of the high frequency ultrasound signal, UBM can only be used for the examination of intra-ocular structures situated in direct neighbourhood to the global wall. Despite this technical limitation, ist contribution to the planning of the conservative treatment of anterior uveal melanoma's by proton beam irradiation has appeared to be considerable.

Study of coherent diffractive production reactions ofp+C→[Y 0 K +]+C type and observation of narrow structures in ∑ (1385)0 K + and ∑0 K + effective mass spectra

In the experiments at the SPHINX facility in 70 GeV proton beam of the IHEP accelerator the coherent diffractive production reactions on carbon nucleip+C→ [∑(1385)0K++C andp+C→[Σ0K+]+C were investigated. The evidences for new baryon states were obtained in the study of hyperon-kaon effective mass spectra in these two reactions:X (2050) with massM=(2052±6) MeV and width Γ=(35−35+22) MeV inM[∑(1385)0K+] andX(2000) withM=1999±6 MeV and Γ=91±17 MeV inM[Σ0K+]. The unusual features of these massive states (small enough decay widths, anomalously large branching ratios for decays with strange particles emission) make them very serious candidates for cryptoexotic pentaquark baryons with hidden strangeness.

Les mélanomes familiaux de l'uvée

Familial uveal melanoma are rare and a few number of cases has been described in literature until now. An autosomal dominant inheritance was proposed. From the 2169 patients examined and/or treated in the Jules Gonin Hospital for an uveal melanoma from 1969, we identified 11 patients from 9 families in which at least two members were affected. We compared the clinical data of the familial melanoma with those of the sporadic cases of our collective with the Kruskal-Wallis Tests. The following parameters were studied: age and sex of patients, largest and smallest tumor diameter, height and volume of tumor, distance between tumor and optic nerve and macula, distance of tumor to the equator. Age and sex were also compared with literature. Among the 11 patients, nine were treated with an accelerated proton beam, one with Cobalt60 applicator and one has been enucleated. The median age was 58 years among the probands and 54.6 years among the sporadic cases of the collective. Sex ratio is superposable between both groups: male 45.5%, female 54.5% among the probands and male 48.6%, female 51.4% among the sporadic cases. The comparison between both groups with the Kruskal-Wallis Tests did not show any significant statistical difference. An uveal melanoma occurring at least in two members of the same family is not due to chance alone. Genetic factors associated to external factors are probably responsable.

Search forN ? (1960) baryon

In the experiments at the SPHINX facility in the 70 GeV proton beam of the IHEP accelerator the diffractive production reactionsp+N→[Σ(1385)0K+] +N andp+N→[Σ(1385)0K+]+N+ (neutral particles) were studied. In the effective mass spectra of the [Σ(1385)0K+] system in these processes there were no signals from the anomalously narrow baryon stateNϕ (1960) which had been observed earlier in the measurement at the BIS-2 setup.

On increasing the bent crystal extraction efficiency by using a thin internal target

The results of new tuning regime are reported. The efficiency estimations for different distributions of the particles on a bent crystal input for a concrete scheme of the IHEP accelerator proton beam were made.

Measurements of mass attenuation coefficients of yttrium with characteristic lines from elements excited by energetic protons

The characteristic X-rays from elemental or compound targets excited by a proton beam of tandem accelerator is a quasimonochromatic X-ray source. The mass attenuation coefficients of yttrium have been systematically measured in the region 3.3 keV to 29.1 keV by using this kind of X-ray source. The experimental uncertainties of mass attenuation coefficients have been reduced to ±1%. The coherent scattering cross sections have been calculated in accordance with the present experimental condition. The total photoelectric cross sections have been obtained by subtracting scattering cross section from the measured total cross sections.

Treatment of eye tumors by accelerated proton beams. 7 years experience

The therapeutic results of 1070 cases of intraocular tumors treated with an accelerated proton beam at the University Eye Clinic of Lausanne and at the Paul Scherrer Institute of Villigen are analysed. This total is composed of 981 cases of uveal melanomas treated by proton beam as first treatment modality, 42 cases of recurrent choroidal melanomas, 16 cases of conjunctival melanomas, 8 cases of choroidal hemangiomas, 18 cases of uveal metastases and of 5 other ocular tumors. The mortality rate at 5 years for tumors treated with an accelerated proton beam as first treatment modality was 13%, and the mortality rate of recurrent melanomas was 23%. The risk factor for life expectancy analysed with the Cox model pointed out that the largest tumor diameter, the width of the tumor, the presence of an extrocular extension and the age of the patient were the most significant parameters. The conclusions of this study are compared with those found in available literature.

Treatment of exterior extension of choroid melanomas by accelerated proton beams

Among the 934 patients with a choroidal melanoma treated in first intention with an accelerated proton beam since 1984, 41 (4.4%) presented an extrascleral extension, of which 11 were located anteriorly and 30 posteriorly. For these 30 cases, the diagnosis was made by B ultrasonography only when the volume of the extension was important, between 20 and 2280 mm3. The Cox model multi-variant analysis was used to study the statistically significant parameters in the development of an extrascleral extension. It appears that the maximal diameter of the intraocular tumor (p = 0.0012), the localisation of the anterior margin (p = 0.0304) and the age of the patients (p = 0.0097) are statistically meaningful. The 4 years' survival, studied with the Kaplan-Meier curves, is estimated at 60% for the patients with extrascleral extension and at 85% for the patients without. These results are similar to those of literature, whatever treatment is chosen (enucleation and radiotherapy, exenteration).

A time projection chamber for double-beta-decay experiments

A large-volume time projection chamber (TPC) designed for double-beta-decay experiments with solid samples of 2.5 m 2 total surface is described. The TPC will operate in a weak magnetic field of ≲ 0.05 T with He+20% CH 4 gas filling at atmospheric pressure. A prototype TPC operating in the 10 GeV proton beam of the IHEP Serpukhov accelerator had shown ≈100% efficiency and a spatial resolution of ≲ 0.45 mm in the direction of the drift of electrons and ≈ 1.6 mm along the delay lines. A limit on half-life of ∼ 10 24 years should be reached with the large TPC operating in the deep underground laboratory.

ULTRA-HIGH-TECH CANCER THERAPY

Last month, scientists at the Fermi National Accelerator Laboratory here unveiled the first proton beam accelerator built for hospital use. When the machine is ready for operation next year at Loma Linda University Medical Center near Los Angeles, many believe it will prove itself a major breakthrough in the wan on cancer. Others, however, think the proton accelerator is a white elephant. They complain that its untested medical benefits and enormous price make it the ultimate example of medical technology run amok. Some doctors say proton therapy will prove useless in the treatment of most cancers. It is unquestionably the most expensive piece of medical equipment ever built. The cost—$40 million, including the special building needed to house the machine—dwarfs the cost of the next most expensive medical device: the Positron Emitting Tomography scanner, which shows metabolic activity within the brain and can cost about $5 million. Protons were first suggested as a potential cancer therapy in 1946 by Robert Rathbun Wilson, who established the Fermi National Accelerator Laboratory. But it wasn't until the 1970s that patients were first exposed to protons in physics labs at Harvard University, the University of California at Berkeley, at Fermi and at several institutions abroad. In physics labs cluttered with cable and oscilloscopes, physicists have seen some spectacular results using physics research machines moonlighting to treat cancer patients. At Harvard, where 174 patients with malignant tumors at the base of the brain have been treated, the therapy has had an 85% cure rate, compared with 35% cure rate for conventional therapies. (Patients in remission or cancer-free for five years are considered cured.) The beam is virtually useless in cancers that have spread beyond the original site. Such metastacized (sic) cancers account for more [than] two thirds of all malignancies says [one] radiation oncologist. "There's some usefulness, no doubt about it. But the candidates for proton therapy are limited. . . . It won't make a major impact on the cure rates for all cancers. It will make a little dent, but it will cost a lot to make that dent.

Acceleration of intense proton beam with split coaxial four-rod RFQ

The 50 MHz four-rod split coaxial resonator (SCR) with continuous modulated electrodes which was developed at our institute is well suited as a high-cu