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On the basis of recent experience, it is suggested that Ilford G-5 emulsion stacks should be refrigerated after exposure when they are to be shipped over large distances by public transport.

After he had listened to his voice on the wonderful wire recorder of the late 1930s, Dr. Vagtborg, director of Armour Research Foundation asked, “Why must the wire move so fast? Why can’t we record slower and longer on the same record?” In other words, why not increase the recording density?

In optical disk systems using push-pull tracking method, there have been problems of tracking offset errors caused by a disk skew and low signal-to-noise ratio due to a surface noise of the pregrooved area. In order to achieve higher track density recording, these problems have to be solved. We have developed a new type of on-land composite pregroove method for higher track density recording. In this method, the header data and the user data are recorded on the land area between two pregrooves on the disk. Each pregroove has 10-20 of tracking offset detection flags once per sector at each header area.

The results of some experiments and field application of Solid State Nuclear Track Detectors (SSNTD) for uranium exploration have been described in the present paper. The effect of position of the alpha sensitive plastic films and the mechanism of radon diffusion inside the film containing tubes on the ultimate track density has been studied. The effect of background radon levels in the exploration region has been considered and the results of some simulation experiments are reported. A comparison of the results of gamma surveymetric technique has been made with those obtained by using alpha sensitive plastic films. Finally, the results about an actual field application are reported.

For a convenient utilization of the track detectors, two techniques are investigated: standard optical system and spark counting. Results for the counting characteristics as a function of the irradiation parameters are given for the makrofol E and cellulose nitrate LR115 type II detectors for the experimental conditions used. The efficiency of detection is given.

We describe the design and construction of a large drift chamber of a novel design well adapted for operation in high magnetic fields and in the high track density environment of hadron colliders.

A double-beam Joyce-Loeble microdensitometer has been used (as well as a universal microdensitometer) in conjunction with the cellulose-nitrate based plastic, made by Kodak Pathe’ France, CA80-15, to investigate the adaptation for scanning of etched detectors, containing fast neutron induced recoil/knockon Traks. The background Track density, surface uniformity and response to light as well as heavy particles of different Z ≥ 1 of this detector, with a minimum threshold for registration for protons of Emin=70 keV, is superior to e.g. Makrofol-E and Lexan, having Emin~ 600 keV for protons.

Fission-track dating is one of the newest methods that geologists have to help them determine the ages of minerals and natural glasses. Fission tracks are stable over different temperature intervals in different minerals and glasses,and by dating several different minerals present in a rock it is possible to obtain a better understanding of its thermal history. This dating method, used in conjunction with other dating methods, is a powerful tool for the geologist as he tries to reconstruct the geologic history of a region.

The track diameter kinetics and variation of efficiency with etching time for 20°C and 30°C etching temperature were determined for cellulose nitrate detectors and explained theoretically. With planar 239 Pu sources and bone slices of varying thickness the efficiency as function of source-detector distance was measured and allowed the computation of a factor converting track density to dose rate for tissue sections with arbitrary thickness. Moreover, the dependence of selfabsorption on the thickness of the bone section and of the absorber was evaluated. The scan of a bone section from the femur of a rat injected with 241 Am demonstrates the application of the procedure for dose rate determinations with an image analysing system.

Analyses of the total alpha radioactivity distribution in 31 North Pacific manganese nodules yield an average growth rate of 6.8 (±2) mm/m.y. Samples from a single box core show almost identical total activity vs. depth profiles, regardless of nodule size or shape. A characteristic feature of many nodules examined is an apparent change (steepening) in slope of the alpha activity profile between depths of 0.5–1.5 mm. This feature may reflect a fundamental feature of nodule growth, possibly mobility of 230Th or its daughters in a regular way, interrupted growth, or nodule turnover. Near-surface decreases in total alpha activity probably result from 226Ra loss.

Distinctive tephra layers constitute important time-parallel markers, which if widespread, offer the potential for reliable correlation over long distances. Confident correlations require a multiple criterion approach to tephra characterisation and equivalence of samples should only be considered firmly established if their stratigraphic, palaeontologic, palaeomagnetic, and radiometric age relations are compatible, and the physicochemical properties of their glass shards and phenocrysts agree. The strong susceptibility of tephra to reworking further argues for use of several stratigraphic controls in order to safeguard against gross errors.

Kodak-Pathe LR 115 II cellulose nitrate detectors and medical radium sources (tubes and needles) were placed in a vessel. After exposition track density was measured on etched detectors for leakage testing. If track density was high, autoradiograms were also made with cellulose nitrate. To determine the concentration of Rn-222 and its alpha active daughter products as a function of track densities, calibration was performed. The sensitivity of this method for leakage testing is higher than 1 nCi Rn-222 per 24 h.

Heavy cosmic-ray track densities in surface samples from the different physical faces of fragments A, B and F of the St. Severin amphoterite (80% of the recovered weight) have been measured and are used, after identification (i.e. ablated external surfaces, or internal surfaces due to disruption in flight), to estimate the ablation rate. Assuming a negligible space erosion, an upper limit 23.5% ≤ τ ≤ 33.4% on the ablation rate is found. An upper limit on space erosion rate (0.3 cm/10 6 years) was based on the assumption that the sample with the highest track density was the less ablated (0.25 cm). Assuming such a space erosion, a lower limit 16.5% ≤ τ ≤ 18.4% on the ablation rate was found.

We have studied by combined high voltage and scanning electron microscopies both the latent and etched track distributions in lunar fragmental rocks as well as in solar type gas-rich meteorites. We have used a new experimental approach for studying gas-rich meteorites to avoid problems with the interpretation of the results. Some implications of the present results concerning the ancient solar flare cosmic rays and the origin of the track distributions in gas-rich meteorite crystals will be discussed.

In the current optical data storage, binary coding is used, in which mark and null states correspond to high and low levels of reflected light. In the binary coding, the capacity of recording information can be increased by minimizing the pit size and maximizing the track density. However, the minimization of pit size will reach a limit even if near-field optics are used. To overcome this limitation, we have proposed and demonstrated multilevel optical data storage by changing the pit depths of a birefringent film. In this method, the volume of stored information can be increased without increasing the pit density. Multilevel pits with the width of 1 µm and with various depths were formed on a liquid crystalline polymer film with the birefringence of 0.20, and the phase difference between orthogonal polarizations was confirmed to be proportional to the depth of the pits.

THE number density of fission tracks in solids is reduced if the sample is heated before chemical etching, and the effect of annealing must be accounted for before an age date can be assigned to the sample1–3. The extent of the annealing can be observed by a measurement of the reduction in the track parameters (diameter and/or length) and subsequent comparison to unannealed tracks. Correct ages can be obtained by careful calibration studies of track density reduction against track diameter or length reduction at different annealing temperatures and times4,5. For crystalline minerals, however, these correction techniques are not generally valid6. In this study, glass samples were partially annealed and then immersed in liquid nitrogen for various periods and we show that the properties of the glass and/or the track parameters can be altered so as to observe tracks that would normally be erased by annealing.

Integrated thin-film heads were developed for operation at a track density of 16/mm (405/in) and a linear density of 1200 fc/mm. Because relatively low velocity was used (300 r.p.m.), magnetoresistive sensors were incorporated directly inside the writing poles. Read amplitudes usually exceeding 20 mV/mm of track width were measured and were stable to within +or-2% over hundreds of write/read cycles. >

This year a new low-cost ($7000) semi-automatic counting system has become available from Image Technology, Inc. of Deer Park, New York. Tracks in CR-39 from proton recoils, either chemically etched or electro-chemically etched, can easily be counted when the system's video camera is coupled to an optical microscope with a low-power objective. An area of one square millimeter can be counted in less than three seconds.

Fission track density in sphene from syenite using three different etchants (NaOH, HCl and acidic mixture) is found statistically consistent. Therefore it is impossible to obtain three different age values.

In the spark counting technique of fission fragment tracks in thin plastic detectors, the upper limit on the track density is shown to be increased considerably by a simple modification in the technique. The track detector used was Makrofol.

THE method of dating by fission tracks1 has been used by several workers to date rock minerals and baked relics2. The method depends on the spontaneous fission of 238U atoms in mineral or glass taking place at a constant rate, and leaving fission tracks. Once formed, the fission tracks disappear if the material is heated above a critical temperature. The fission track age, T (yr), can be represented by the following equation3 where ρs is the fossil fission track density (cm−2), ρi is the induced track density by bombardment with thermal neutrons (cm−2), λ, is the total decay constant for uranium (yr−1), λf is the fission decay constant for 238U (we use 6.85 × 10−17 yr−1 (ref. 4), Φ is the thermal neutron dose (cm−2), σ is the thermal neutron cross section for fission 235U (cm−2), η) is the isotope ratio 235U/238U, and Rs and Rt are the mean values of the etchable length of the fragments produced by a spontaneous fission and that produced by the induced fission (cm).

High track density multitrack magnetic heads are batch-fabricated from a stack of wafers which are photolithographically processed to provide lands and grooves on the wafers. Thin magnetic films are deposited in the grooves; and coils respectively inductively cooperative with the films are photolithographically formed about the films, the lands serving both to provide track-to-track spacing and to protect the magnetic films from magnetostriction-producing stress.

A magnetic head (31) for writing and/or reading information in mutually parallel tracks of a magnetic recording medium (32) with high track density. By causing the transducing gap (34) of the head (31) to be bevelled in the depth, the lateral cross-talk in particular is reduced, at least in a given wavelength range where the wavelength is of the same order of magnitude as the gap depth (d). The transducing gap bevel makes an angle which is not greater than 45° with the face of the head facing the recording medium during operation.

Digital magnetic recording on flexible media has grown from ½ in tape in 1959 to include mass storage systems, digital cassettes, data cartridges and flexible disks in 1980. The properties of greatest interest are the capacity of the removable unit, the access time to the data and the rate at which data can be communicated to another device. To the customer the price he must pay per bit of data stored is very important but he must also consider the price of the drive unit and not just the price of the removable unit. The characteristic by which different storage devices are most commonly compared is their storage capacity. To increase this continuously in response to the ever-increasing amount of information that must be stored in machine-accessible form requires a steady improvement in the amount of data that can be packed into each unit of area. The problems encountered in increasing this areal storage density are discussed in detail. Three kinds of limit to bit and track density are considered: the fundamental limit, the technological limit and the economic limit. No estimate is attempted for the economic limit which is strongly machine-dependent but the fundamental limit to bit and track density is given as 20 000 bits or tracks per mm (500 000/in). The technological limit for bit density is given as 4000–8000 b/mm (100 000–200 000 bpi) and for track density 600 t/mm (15 000 tpi).

Narrow track recording heads suffer from wavelength dependent side fringing effects. During writing these manifest themselves in track widening and erasing of neighboring tracks, and during reading in side fringing response and crosstalk. Side fringing fields have been analyzed theoretically but experimental verification of this phenomena is scarce. Measured values of actual track width, erasing width and crosstalk are reported. The measurements have been performed with specially manufactured disk heads with widths ranging from 10-50 μm. One set of heads was constructed similar to the 3330-II heads. Another set was constructed such that they resemble as closely as possible the shape of the theoretical head that is used as a model. Some heads were locally narrowed by laser machining. Actual track width was measured as a function of write current amplitude at low recording density (no pulse crowding) and as a function of wavelength at optimum write current amplitude. The measured track widening agrees with theory and can be as high as 5 μm at either side of the head at optimum write current and low pulse density. Track widening decreases with decreasing wavelength. The distance from the head side at which the head still effectively erases can be as high as 15μm. In a disk drive this will be the factor that limits the track density. Inter track read crosstalk is determined by measuring the displacement curve (i.e., the curve representing the read signal versus position as the head is shifted across its own track at different wavelengths). The curves agree with theory except for the presence of "side lobes."

A new technique of quantitative track counting, the Buffon needle method, is advanced. It is based on random sampling of the solid state track recorder (SSTR) surface. This new method extends quantitative track scanning to track densities well up into the track pile-up regime. It is shown that the Buffon needle method possesses a reduced dependence upon both track density nonuniformity and track size distribution. Sources of experimental error arising in the Buffon needle method are assessed. The validity of the Buffon needle method is demonstrated down to at least the 10% uncertainty level (1sigma) by manual sampling of high fission track density mica SSTR observed with scanning electron microscopy.

Discrete-track recording is a magnetic-recording method which employs a single-gap head and a discrete-track medium to increase the head-repositioning tolerance in saturation digital recording. A head with a conventional ring structure may be used. The recording medium consists of discrete magnetic tracks separated by nonmagnetic lands. Width of the magnetic tracks depends largely on the desired track density and maximum tolerable head-repositioning error. Test results indicate excellent track performance; consequently, satisfactory and reliable operation can be expected under actual machine conditions. Major advantages of discrete-track recording are economy, reliability, and increased head-repositioning tolerances.