Delta Rays Research Articles

Calorimetric measurement of electron stopping power of aluminum and copper between 11 and 127 keV

The stopping powers of aluminum and copper have been measured for electrons between 11 and 127 keV. Evaporated foils of about 200-nm thickness were stretched across rings and inserted into a short cylinder which was supported by thermocouple wires. Peltier heating and cooling by one thermopile were used to control foil temperature, while another thermopile measured its temperature. Calibration was accomplished by reducing beam energy until complete absorption was obtained. Delta rays produced in the foil were returned to it by repelling electrodes. Corrections were made for increased path length in the foil due to multiple elastic small-angle scattering and for spurious heating by scattered electrons striking the ring holding the foil. After correcting for these effects, good agreement with the Bethe-Bloch formula was found.

A core plasma model of charged particle track formation in insulators

In a new model of track structure in insulators, delta ray electrons are assumed to return to the core to form a two-component plasma. Track formation results from expansion and cooling of this plasma.

Emission of δ electrons from inner-shell excitation in heavy-ion-atom collisions

The authors have measured double-differential cross sections d2 sigma /dEed Omega e for delta electrons emitted in energetic ion-atom collisions with energies between about 15 and approximately 100 keV. Various incident ions (p,O,S) with energies from 1.8 to 10 MeV amu-1 and thin-foil targets (Cu,Ag,Au) were investigated. Comparison of the authors' results with theory shows that the semiclassical approximation (SCA) describes the data in the entire range whereas the binary-encounter approximation (BEA) often fails. Angular distributions, recoil- and combined-atom effects are discussed in some detail.

Characteristics of submicron pores obtained by chemical etching of nuclear tracks in polycarbonate films

Calibrated pores in the range 102–2×103 Å have been obtained by chemical etching of polycarbonate thin films irradiated with high energy krypton ions (500 MeV, Kr25+). Both the amorphous and the crystalline forms of polycarbonate (Makrofol, Bayer), further designated by their respective trade names N and KG, have been investigated up to thicknesses of 60 μm, close to the theoretical ion range of 77 μm. From conductivity studies, three different domains have been separated around the ion track: A highly damaged core of radius ?50 Å with a fast etching rate vT ≊104 Å/min, an intermediate zone of radius ?500 Å with an etching rate vI = 0.9 Å/min, an outer region with an etching rate equal to that of the undamaged material, vG = 0.47 Å/min. These observations are compatible with the delta ray model for track formation in plastic materials. Scanning electron microscope investigations have revealed that the pores formed in the N material are straight cylinders with a narrow distribution of the pore entrance diameters. On the other hand, the pores for the KG type are much less uniform and appear to be tapered, the difference between the two sides of the membrane being as much as 50%. These characteristics could be related to inhomogeneities in the morphological structure due to (i) the finite size of the crystalline domains and (ii) an asymetric manufacturer’s processing of the film surfaces.

Modified energy-deposition model, for the computation of the stopping-power ratio for small cavity sizes

This paper presents a modification to the Spencer-Attix theory, which allows application of the theory to larger cavity sizes. The modified theory is in better agreement with the actual process of energy deposition by delta rays. In the first part of the paper it is recalled how the Spencer-Attix theory can be derived from basic principles, which allows a physical interpretation of the theory in terms of a function describing the space and direction average of the deposited energy. A realistic model for the computation of this function is described and the resulting expression for the stopping-power ratio is calculated. For the comparison between the Spencer-Attix theory and this modified expression a correction factor to the ''Bragg-Gray inhomogeneous term'' has been defined. This factor has been computed as a function of cavity size for different source energies and mean excitation energies; thus, general properties of this factor have been elucidated. The computations have been extended to include the density effect. It has been shown that the computation of the inhomogeneous term can be performed for any expression describing the energy loss per unit distance of the electrons as a function of their energy. Thus an expression has been calculated whichmore » is in agreement with a quadratic range-energy relationship. In conclusion, the concrete procedure for computing the stopping-power ratio is reviewed.« less

A study of the bubble formation mechanism in a hydrogen bubble chamber using electron and positron tracks

The mechanism of bubble formation in liquid hydrogen was studied by measuring the difference in bubble density on electron versus positron tracks. The measured difference is consistent with the Seitz-heat spike theory and suggests that it is secondary delta rays with energies well above the ionization potential that participate in bubble formation. These data are also consistent with the observation of no relativistic rise in bubble density for liquid hydrogen.

Secondary Electron Emission from Ionization of Water Vapor by 0.3- to 2.0-MeV He + and He 2+ Ions

Yields of secondary electrons (delta rays), differential in ejected electron energy and emission angle, are reported for 0.075 to 0.5 MeV/amu helium ions, both singly and doubly charged (..cap alpha.. particles) arising from single collisions with water molecules in vapor phase. Results are compared with similar data reported previously for protons with the same velocity. We found that the bound electron of the He/sup +/ ion effectively screens the nuclear charge for collisions at large impact distances, thereby suppressing the yield of low-energy secondaries while contributing directly to the yield of high-energy secondaries. This results in a secondary electron spectrum of higher mean energy and lower total yield for He/sup +/ than the bare He/sup 2 +/ produces. Comparison of the yields for He/sup 2 +/ with similar data for protons indicates deviations from Z/sup 2/ scaling which occur primarily for secondary electrons ejected at small angles, and hence, close to the path of the primary ion and for electron velocities similar to the ion velocity. These results imply that the detailed structure of helium ion tracks is somewhat different from what would be predicted from a simple Z/sup 2/ scaling of proton track structure.

Delta-Electron Emission in Deep-Inelastic Heavy-Ion Collisions

This paper reports calculations of the influence of a reactin time T>10/sup -21/ s in deep inelastic Xe-Pb collisions on the energy spectrum of delta electrons ejected in the same collision. It is shown that the lifetime of the superheavy composite system causes pronounced oscillations of width epsilon=h/T in the electron distribution, which survive the inclusion of multistep excitations and the folding with a lifetime distribution function. This effect may serve as an atomic clock for deep inelastic collisions.

Heavy-Ion Track Structure in Silicon

The energy deposition in the vicinity of a heavy ion path in silicon has been investigated by a Monte Carlo transport analysis of the delta rays produced along the track. The dose as a function of radial distance is presented for C, A1, and Fe ions with energies between 10 and 10,000 MeV. The average dose in cylinders of radii between 10-3 and 1 μm as a function of the distance of the cylinder from the path is also presented.

Identification of relativistic charged particles by means of ionisation energy loss in proportional counters — A new approach

The proportional counter is now finding widespread application as a relativistic particle identifier in high energy physics. The multiple sampling technique is used with a suitable bias to combat the small magnitude of the relativistic rise in the ionisation energy loss and the wide (and skewed) pulse height distributions obtained in thin gas counters. The numbers of samples required for useful discrimination is high (∼10 2)imposing something of an economic penalty on the technique. In this paper we report a development which, by suppressing the delta ray contribution to the total charge pulse from the anode wire, reduces the number of samples required to achieve a given degree of separation. A Monte Carlo model convoluting the ‘delta ray suppressed’ data from a one sample detector shows that when it is required to separate pions and electrons at 1 GeV/ c with a detection efficiency for the electron of 90%, a ‘suppressor’ circuit can achieve a pion rejection ratio of 250:1 with 82 samples, whereas the truncated mean approach (lowest 70% of samples) requires 100 samples. Given the simple circuitry employed there is every reason to anticipate that the basic technique should be capable of further improvement and also economic to implement.

Optical Čerenkov radiation from microscopic BaSO4grains

In the analysis of an experiment to determine the response of scintillators to relativistic heavy ions, we have discovered that the BaS${\mathrm{O}}_{4}$ grains (radius \ensuremath{\sim}0.5 \ensuremath{\mu}m), which constitute the highly reflective interior surface of our light-integration box, emit \ifmmode \check{C}\else \v{C}\fi{}erenkov radiation with an index of refraction intermediate to that of crystalline BaS${\mathrm{O}}_{4}$ and to that of the air-crystal volume-averaged reflective coating. The small amount of radiation emitted below threshold (\ensuremath{\sim} 2% of the $\ensuremath{\beta}=1$ signal) is consistent with the expected level due to \ifmmode \check{C}\else \v{C}\fi{}erenkov emitting delta rays and/or to diffraction radiation with no residual scintillation.

Photodensitometry of tracks of highly ionizing particles in the cosmic rays

Photodensitometric measurements with instruments in two different laboratories show that the optical density as a function of lateral distance around a track in emulsion is highly reproducible. For tracks of particles with zenith angle 8° to 65°, charge 40 to 83 and velocity 0.36 to 0.98 c , we have compared the density distribution with a simple model of track structure. At lateral distances ≥ 10 μ m this distribution correlates well with ( Z/β ) 2 , is independent of β for 0.6 ⩽ β ≲ 0.98 and decreases at low β as expected owing to kinematic cutoff of knock-on electrons.

Delta electrons as a probe of strong magnetic fields in heavy ion collisions

We propose that the spin polarization of delta electrons should be used as a measure of the strong magnetic fields ( B∼10 17 G) induced by the nuclear motion in collisions of very heavy ions. The polarization is typically of the order of 10–20 percent in Pb-Pb and U-U collisions. We also discuss the bombarding energy dependence up to E 1ab = 200MeV/ u, where 500 keV level splitting between spin up and down states is obtained.

Dose Distribution Due to Low-Energy Electrons and Delta Rays Produced along the Path of a Heavy Charged Particle in Water

Spatial distributions of dose in water have been calculated for plane perpendicular and point isotropic sources of low-energy electrons (0.5 to 10 keV). Also calculated were dose distributions from delta rays produced along the path of a 1-MeV proton. In these dose calculations, a partial wave analysis was used to compute the elastic scattering cross sections, and a moments method was used to solve the transport equations. Doses from the plane perpendicular and point isotropic sources agree well with Monte Carlo results. However, doses calculated for delta rays differ considerably from earlier theoretical and experimental results.

Chemical effects of fission recoils. 3. Relaxation times of processes leading to ethyl radicals

The formation of n-butane in the fission-recoil induced radiolysis of gaseous ethylene in the presence of small quantities of oxygen is interpreted by competition between radical combination in the track, radial diffusion, and radical removal by oxygen. The differential equations describing these reactions are solved and fitted to experiment by adjusting the initial mean track radius, r/sub i/, until calculations and observations agree. r/sub i/ is found to be substantially larger than the radius for physical energy deposition by primary interaction of the recoiling fission fragment or the radius within which secondary electrons (delta rays) deposit their energy. It is proposed that this is largely the result of diffusive spread of precursors to ethyl radical formation. These must survive for approximately 10/sup -9/ s before competition for second-order disappearance sets in. The functional form of the dependence of r/sub i/ on the reciprocal square root of the density is consistent with this postulate. 2 figures, 1 table.

Further measurements and reassessment of the magnetic-monopole candidate

Within the stack, consisting of 35 Lexan detectors and three nuclear emulsions, in which the unusual event was found, we have measured tracks of \ensuremath{\sim} 200 cosmic-ray nuclei with $26\ensuremath{\le}Z\ensuremath{\le}83$ which provide an internal calibration of the response of the detectors. Our measurements in Lexan and in emulsion together show that the unusual particle produced a knockon-electron energy distribution incompatible with any known nucleus. The track etch rate and its gradient in Lexan give the quantity $\frac{|Z|}{\ensuremath{\beta}}$ and, if the particle was a nucleus, a lower limit on its velocity. We found $\frac{|Z|}{\ensuremath{\beta}}\ensuremath{\approx}114$ at each of 66 positions in the Lexan stack extending over a range of \ensuremath{\sim} 1.4 g/${\mathrm{cm}}^{2}$. The best fit to the Lexan data alone would be for a hypothetical superheavy element with $Z\ensuremath{\approx}108$ to 114 and $\ensuremath{\beta}$ such that $\frac{Z}{\ensuremath{\beta}}\ensuremath{\approx}114$. A known nucleus with $90\ensuremath{\le}Z\ensuremath{\le}96$ would also give an acceptable fit to the Lexan data if it fragmented once in the stack with a loss of about 2 units of charge, keeping $\frac{Z}{\ensuremath{\beta}}\ensuremath{\approx}114$. A nucleus with $Z<90$ could maintain $\frac{Z}{\ensuremath{\beta}}\ensuremath{\approx}114$ only by a properly spaced set of fragmentations. A nucleus with $\ensuremath{\beta}$ as low as 0.6 could fit the Lexan data only if it fragmented at least eight times in succession, with a probability \ensuremath{\sim} ${10}^{\ensuremath{-}17}$. In the 200-\ensuremath{\mu}m G-5 emulsion, visual measurements of the track "cores" produced by relatively-low-energy electrons $\ensuremath{\lesssim}10$ keV) are consistent with the Lexan result that the unusual particle had $\frac{|Z|}{\ensuremath{\beta}}\ensuremath{\approx}114$. However, measurements of the density of silver grains at radial distances greater than \ensuremath{\sim} 10 \ensuremath{\mu}m show that the particle produced far fewer high-energy $\ensuremath{\gtrsim}50$ keV) knockon electrons in each of the three emulsions than would a known nucleus with $\frac{Z}{\ensuremath{\beta}}\ensuremath{\approx}114$. If it were a known, long-lived nucleus with $Z<96$ and therefore having $0.84>~\ensuremath{\beta}$ 0.6 in order to fit the Lexan data, its signals in the three emulsions would imply a very low $\frac{Z}{\ensuremath{\beta}}$ of only \ensuremath{\sim} 85 instead of 114. The abnormally small production rate of long-range electrons observed in all three emulsions is the essential evidence that we have found a unique particle. A monopole does not provide an acceptable fit to all of the data. A slow particle ($\ensuremath{\beta}\ensuremath{\approx}0.4$) could fit all of the observations, provided its mass were so great (${10}^{3}$ amu) that it did not slow appreciably in the 1.4-g/${\mathrm{cm}}^{2}$ stack. A fast ($0.7\ensuremath{\lesssim}\ensuremath{\beta}\ensuremath{\lesssim}0.9$) antinucleus with $\frac{Z}{\ensuremath{\beta}}\ensuremath{\approx}\ensuremath{-}114$, because of its low Mott cross section for production of high-energy knockon electrons, could fit the data, especially if it fragmented once with loss of 1 or 2 units of charge. An ultra-relativistic ($\ensuremath{\beta}\ensuremath{\gtrsim}0.99$) superheavy element with $Z\ensuremath{\approx}+110$ to +114 can also account for the data and is not in conflict with any negative searches. Our knowledge of the $Z$ and $\ensuremath{\beta}$ dependence of the response of Lexan appears sufficient to preclude values of $|\frac{Z}{\ensuremath{\beta}}|$ less than \ensuremath{\sim} 110. An explanation of the weak distant energy deposition in terms of fluctuations by a normal nucleus or locally insensitive emulsion regions appears to be unlikely. Freak occurrences such as a ${10}^{20}$-eV jet or an upward moving nucleus do not fit the data. Having achieved only an incomplete characterization of a single example of what appears to be a new particle, we emphasize the obvious-that further examples of such particles must be found before its identity can be established.

Return to unsaturated response of polymeric scintillators excited by relativistic heavy ions

From the response of two scintillators to relativistic 20Ne ions obtained at the Lawrence Berkeley Bevalac, to cosmic-ray iron ions, and to atmospheric muons, it is shown that plastic scintillators provide a very nearly linear response in d E/dx at high charge and relativistic energies, i.e., scintillators become “unsaturated” in this regime. Scintillators operated in this regime are found to be “halo” detectors, sensitive almost solely to delta rays with energies above 1.5 keV. A simple algebraic expression 13) is given which permits rapid calculation of scintillator response.

δRays fromK-Shell Ionization Induced by Heavy Ions

The spectrum of high-energy $\ensuremath{\delta}$ rays emitted in an 83-MeV ($^{16}\mathrm{O}$, $^{197}\mathrm{Au}$) collision is measured. The data are compared with the scaled Born approximation and the adiabatic monopole model.

Have We Seen a Heavy Antinucleus?

The hypothesis of the first observed heavy antinucleus is proposed for the event of Price et al. This hypothesis demands depletion of the high-energy knock-on electrons, which should be clearly evident in the nuclear emulsion. This hypothesis does not directly contradict any previous antimatter search; and conflict with extrapolations from previous searches is of small statistical significance.

Development of a large, low-mass, water Cherenkov counter

The development of a large water Cherenkov counter for use in triggering over a large side aperture of the Brookhaven National Laboratory Multi-Particle Spectrometer is described. Design considerations, prototype-testing, and testing and utilization of the full-scale counter are discussed. The water radiator occupied a volume of 7.6 × 102 × 229 cm 3; the large walls of the radiator box were constructed of PVC foam with aluminum skins, and were supported only at the periphery. Light was collected vertically along the 102 cm dimension, with one 2″ photomultiplier (RCA 4507) employed for each of the eight cells. The major inside reflectors were aluminized mylar sealed within a glass envelope for reasons of durability and also of total internal reflection within the glass. With highly relativistic particles, efficiencies of 99.2% or greater were obtained at midplane from all cells; efficiencies decreased one percent or less near the bottom of the cells. Light produced by knock-on electrons from low-momentum protons was found to increase slowly with radiator thickness. This light was discriminated against with high efficiency. The Cherenkov counter was used as a major trigger element to distinguish side-pion from proton-recoil events in a recent MPS experimental run at the Brookhaven Alternating Gradient Synchrotron.