Gamma-ray Sensitivity Research Articles

Gamma-ray sensitivity during synchronous cell differentiation in Caulobacter crescentus.

Gamma-ray sensitivity of Caulobacter crescentus during its cell cycle was examined. Survival curves of the swarmer and stalked cells were similar and exponential in shape, whereas that of the predivisional cell was sigmoidal, with an extrapolation number of 1.8.

Innate metabolic differences and mutagen sensitivity of Drosophila melanogaster: I. Radiosensitivity of hyperkinetic mutant

The sensitivity to gamma-rays of a hyperkinetic mutant (HK 1), characterized by high metabolic activity, has been studied and compared with gamma-ray sensitivity of the wild-type Oregon-K. Radiation damage, as measured by the frequency of induced dominant lethals (DL) and sex-linked recessive lethals (SLRL), was more in HK 1 as compared with Or-K. The maximal sensitivity differences for these parameters were observed in the first brood. Translocations, on the contrary, were in general fewer in the HK 1 compared with Or-K. These results have been interpreted in terms of reduced repair of mutational lesions in the energy-stressed cells of HK 1.

Innate metabolic differences and mutagen sensitivity of Drosophila melanogaster I. Radiosensitivity of hyperkinetic mutant

The sensitivity to gamma-rays of a hyperkinetic mutant (HK 1 ), characterized by high metabolic activity, has been studied and compared with gamma-ray sensitivity of the wild-type Oregon-K. Radiation damage, as measured by the frequency of induced dominant lethals (DL) and sex-linked recessive lethals (SLRL), was more in HK 1 as compared with Or-K. The maximal sensitivity differences for these parameters were observed in the first brood. Translocations, on the contrary, were in general fewer in the HK 1 compared with Or-K. These results have been interpreted in terms of reduced repair of mutational lesions in the energy-stressed cells of HK 1 .

A comparison of thermal neutron and gamma ray sensitivities of common TLD materials

The thermal neutron responses in the range 1010 to 2*1012 n cm-2 and the gamma -ray sensitivities of common thermoluminescent materials (CaSO4:Dy, CaSO4:Tm, CaF2:Dy, CaF2:Mn, Li2B4O7:Mn, LiF (TLD-700, TLD-100, TLD-600), Mg2SiO4:Tb and BeO) have been studied in detail and the results compared with those published elsewhere.

Small back-to-back detector for precise comparison of fission and (n,α) reaction rates

A multiple wire proportional counter for simultaneous measurement and comparison of fission and (n,α) reaction rates in identical geometry is described. The active materials are plated in back-to-back geometry in a cylindrical housing less than 1.2 cm in diameter. Provision is made for assessment of gamma-ray sensitivity during in-core reactor measurements and for internal absolute calibration.

Two Active High-Intensity Neutron Detectors

Two neutron detectors were designed to have a high ratio of neutron to gamma ray sensitivity for time resolved measurements of intense neutron pulses. One detector utilized a thin aluminum foil sandwiched between two fission foils in an evacuated chamber. The foils were thick compared to the range of fission fragments. Fission fragments passing through the surfaces created secondary emission electrons, producing a large neutron induced signal compared to the gamma-ray induced response. The second detector utilized a pair of silicon fission fragment detectors exposed to a 235U foil at the opposite end of an evacuated tube. One silicon detector was exposed to both the gamma ray background and the neutron induced fission fragments from the foil, while the second silicon detector was shielded from the fission fragments by a thin aluminum shield, but otherwise was exposed to the same background radiation. Thus, the time resolved neutron signal could be recorded by observing the differential signal from the two silicon detectors with an oscilloscope and camera. The approximate neutron sensitivities of the two detectors were calculated and compared to the experimentally measured values obtained from exposures to thermal and fission spectrum neutrons.

Gamma-ray spectra and sensitivities for 2.8 MeV neutron activation analysis

The use of 2.8 MeV neutrons produced by the D(d, n)3He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·106 n·cm−2·sec−1 on the sample.

A scintillation type gamma-ray dosimeter with low neutron sensitivity

A scintillation type dosimeter with high gamma-ray sensitivity is described. Design considerations are neutron sensitivity, energy response, dynamic energy range and simplicity of the circuit. A method to measure the average energy is also described.

Chromosome Constitution and Gamma-Ray Sensitivity: A Possible Correlation in Hamster Cells Cultured in Vitro

Survival estimates were made for two sublines of Chinese hamster cells cultured in vitro, designated clones D and F, which had a preponderance of cells with 23 and 46 chromosomes, respectively. A digital computer was programmed to fit the best multitarget survival curves to the data by the method of least squares. The slopes of the survival curves for the two cell lines were similar, but the cell line with the largest number of chromosomes exhibited a larger extrapolation number; 8.5 for clone F, compared with 2.95 for clone D. Split-dose experiments were also performed. The recovery factor (defined to be the number of colonies formed on plates receiving the split dose, divided by the number of colonies formed on plates receiving the same total dose in a single exposure) was larger for cells of clone F than for cells of clone D-8.5, as opposed to 4.4. These results tend to confirm previous reports in the literature that radiation response varies with chromosome number, cells of higher ploidy being more re...

A Study of the Scintillation Properties of Various Hydrogenous and Non-Hydrogenous Solutes Dissolved in Hexafluorobenzene

To enhance the gamma-ray sensitivity relative to that of fast neutrons, haxafluorobenzene (C6F6), was substituted for the primary solvent in a standard hydrogenous scintillator solution. The solutes used included p-terphenyl, α-NPO, PPO, POPOP, DM-POPOP and decafluorobiphenyl. Optical absorption and emission spectra were measured. The sensitivity relative to NE-211 was determined for Co60 radiation, 14 MeV neutrons and 2.6 MeV neutrons as a function of solute concentration ranging between 0.03 g/liter and 3.0 g/liter. Sensitivity measurements were carried out by measuring the total integrated light output from the scintillators. For all samples studied, the relative sensitivity to Co60 gamma radiation was greater than that for fast neutrons by factors ranging between 5 and 15.

Neutron and Gamma-Ray Rate Sensitivities of Several Dynamic Detectors Used in Radiation Effects

The absolute rate-sensitivities of several burst sensors to neutrons and to gamma-rays in the mixed field of the Sandia pulsed reactor environment have been measured, using the shielding techniques of Coppage and Snyder(1) for variation of the neutron-to-gamma ray ratio over a factor of five to ten. The spectral changes effected by the shields are discussed. The sensors which were tested are: two reverse-biased preirradiated silicon diodes, MgO-RAD, phosphorphotodiode, and a fission (U238) detector. The ratio of the sensitivities of the detectors are 4. 8, 7.8, 9.1, 22, and 46 (x10-11 R-cm2/neutron (Pu)), respectively.

Gamma-ray sensitivity of oocytes of immature mice.

Sensitivity of oocytes of l0-day-old mice to radiationinduced cell death was estimated by counting surviving cells 72 hr after Co₆₀ gamma-ray exposures of 0, l, 3, 5, 7, l0, 15, and 25 r. An LD₅₀ of 8.4 r, with 95% confidence limits of 7.2 and 9.7 r has been estimated for stage I, and an LD₅₀ of 9.4 r, 95% confidence limits of 6.7 and l4.9 r, was obtained for stage 2 oocytes. Acute irradiation was more effective than chronic exposure in both young and adult females. After chronic exposure, survival is higher in the adult than for equivalent oocyte stages of young mice. This could result either from higher radiation sensitivity of oocytes of 7 to l4-day-old females, or from more efficient repair mechanisms in adult females. Oocytes in later stages of follicular development appeared to be more resistant in both immature and adult females. This result is in agreement with the fertility pattern of irradiated female mice and indicates highest resistance for more mature follicle stages. These data are discussed in relation to changes in fertility response of the mouse at different fetal and early postnatal oocyte stages. The possibility that radiation might have extremely severe effects onmore » the ovary at particularly sensitive periods of development in other species is emphasized. (auth)« less

Neutron-Insensitive Proportional Counter for Gamma-Ray Dosimetry

A gamma-ray dosimeter with low sensitivity to neutrons has been developed for radiation dosimetry in mixed fields of neutrons and gamma rays. Neutron sensitivity in a 2.5- to 3-Mev H2(d,n)He3 neutron field has been shown experimentally to be ≤1.2% on the basis of first collision dose in tissue. Gamma-ray sensitivity is independent of energy to within ±5% from 1.25 Mev (Co60) to 200 kev and to within ±20% down to 47 kev. The instrument is a proportional counter which may be used as a dosimeter for gamma rays in the presence of neutrons by pulse-height integration of the small pulses due to secondary electrons produced by gamma rays and rejection of the large pulses due to heavy particle recoils from neutrons.

Induced Conductivity of CdS by β- and γ-rays

Properties of CdS crystais were investigated under irradiation by BETA rays from 10 mc of Sr/sup 90/ or from an accelerator of the Van de Granff type and gamma rays from 1 c of Cs/sup 137/ or from 200 c of Co/sup 60/. The ohmic contact of electrodes and the crystal uniformity were first inspected, and some properties concerning the induced conductivity of CdS crystals by BETA and gamma rays were discussed in comparison with those observed when the crystals were irradiated by visible light. It was concluded that the sample crystals grown are uniform and that they have low trap density and high sensitivity for BETA or gamma rays. It was also shown that the elemertary phenomema of the induced conductivity in the case of BETA or gamma ray irradiation were quite simliar to those in the case of visible-light irradiation, and that the number of electrons excited into the conduction band by a BETA particle was about one hundred times larger than that by a gamma particle of 1.3 to 1.5 Mev. (auth)

Thiacrystal scintillation counter.

The preoperative detection and identification of many types of lesions such as mediastinal tumors (1) have depended upon the use of the Geiger-Muller counter. The conventional scintillation counter has been generally inapplicable due to its size and weight. The necessity for collimation with a thick crystal has required increased distance which more than offsets the scintillation counter's greater sensitivity for gamma rays (usually by a factor of 2 or more), and until recently (2, 3) this instrument has had no significant sensitivity to the soft x-rays from a lesion activated with P32. For these reasons experiments were begun about eighteen months ago using thin NaI and CsI crystals of various diameters. In counting for the purpose of detecting, locating, and outlining a lesion (in contrast to pulse-height analysis, for example) only the first few millimeters of the crystal are necessary. A thin crystal requires a negligible shielding weight and has an inherent spatial sensitivity similar to a good, properly shielded G-M tube with many times the sensitivity of the tube. Detailed theoretical and practical considerations will be given elsewhere (4), and further work is in progress. It appears that a crystal about 3 mm. in thickness and 25 mm. in diameter is optimum. A beryllium window has not proved helpful. For the past six months a practical thin-crystal counter has been in use and has proved highly advantageous for many types of diagnostic procedures such as the preoperative localization of malignant brain tumors. The present counter is shown in Figure 1. It has a conventional PM-PA chassis, a 3 × 25-mm. NaI (T1) crystal, with an 0.10-mm. Al window. Shielding consists of a Pb ring 12.5 mm. thick surrounding the crystal and extending 15 mm. behind it around the magnetic shield. The entire instrument weighs 1,180 gm. (2.6 lb.). Response curves (Fig. 2) of this counter to two phantom “lesions,” each under a slab of Lucite 25 mm. thick are reproduced in Figure 2: (a) 0.35 μc I131, 5 mm. in diameter; (b) 6.0 μc P32, 2.0 cm. in diameter. The G-M tube is still the reference instrument, but the thin-crystal counter has equal versatility and as much as fifty times the sensitivity. As in the surgical probe counter (5), the relative sensitivity and background can be varied to suit the problem by varying the operating voltage. Student physicians are currently learning to use the new instrument.

Correction for the gamma-ray sensitivity of the beta-counter in the standardization of cobalt-60 by the beta-gamma coincidence method.

Correction for the gamma-ray sensitivity of the beta-counter in the standardization of cobalt-60 by the beta-gamma coincidence method.

Neutron-Insensitive Gamma-Ray Dosimeter

A gamma-ray dosimeter for mixed radiation dosimetry with a neutron sensitivity of ≤ 2 per cent (on the basis of absorbed dose in tissue) has been developed. This instrument consists of a graphite-wall, helium-CO2-filled proportional counter operated at pressures of the order of 5–40 cm. Hg. Large pulses due to heavy particle recoils produced by neutrons, such as carbon recoils from the walls and helium recoils in the gas, are discarded. Small pulses due to secondary electrons produced by gamma rays are recorded and are weighted according to height (i.e., according to the amount of current represented by each pulse) (1). The counter acts as a Bragg-Gray cavity, the “current” serving as a measure of the gamma-ray dose. Gamma-ray sensitivity is independent of energy to within ±20 per cent from 1.25 Mev (Co60) to 47 kev. Some indication of the incident gamma-ray spectrum may be obtained from the gamma-ray pulse height distribution. The counter container (outside the graphite lining) is made of thin aluminum to minimize production of gamma rays in the walls by inelastic scattering of the incident neutrons. Detection of these gamma rays by the counter represents neutron sensitivity, since the initiating particles are neutrons. Tests were made with 2.5 Mev H2(d,n)He3 neutrons. The counter indicated an absorbed dose which was 2 per cent of the measured fast-neutron dose. This value is the sum of two contributions: (a) the gamma-ray contamination of the neutron radiation (the true gamma-ray dose) and (b) the neutron sensitivity of the dosimeter. Since we do not know the gamma-ray contamination of the neutron field, we obtain only an upper limit on the neutron sensitivity of the counter. Efforts are being made to decrease the gamma-ray contamination of the neutrons by redesigning the target assembly to minimize gamma-ray production by inelastic scattering. This instrument operates at low dose rates (≤200 mrad/hr.), below the useful range of the gamma-ray dosimeter of Sigoloff (2), which has been estimated to have comparably low neutron sensitivity. The instrument could be adapted for survey meter use by including a “single-window” pulse-height analyzer to accept pulses in a fixed range of pulse heights. This instrument is being used at the National Bureau of Standards in connection with an experiment to measure the neutron sensitivity of photographic film.

Influence of Static Pressure on Gamma-ray Sensitivity of Photographic Emulsions

Influence of Static Pressure on Gamma-ray Sensitivity of Photographic Emulsions

Gold Sensitization of X-Ray Films*

Sensitization of non-screen type x-ray emulsions with aqueous solutions of ammonium or alkali aurous thiocyanates leads to a wave-length dependent increase of their x-ray and gamma-ray sensitivities. For a particular fine-grain emulsion the gain in photographic speed is shown to increase from a factor of 1.5 at 1.3A to a factor of 10 at 0.011A. This wave-length dependence of the sensitizing effect is governed by the range—energy relationship of electrons, by the shape of the energy loss curve of electrons, and the threshold sensitivity of the average grain. The sensitivity of the average grain in an unsensitized and a gold-sensitized emulsion was derived from the number of quanta required to produce the same photographic effects at different wave-lengths. Gold sensitization caused an increase in threshold sensitivity from (6 kev)−1 to (1.2 kev)−1 for the average grain of the emulsion under investigation. A comparison of the quantities of latent image silver formed by light exposure on one hand, and by electrons on the other, indicates that gold sensitization increases the effective radius of action of the sensitivity centers and also the number of active centers at the grain surface.

Present status of the theory of the effect of the Earth's magnetic field on cosmic rays by M. S. Vallarta, Sc.D., Ph.D.

Air-shower measurements in the primary energy range beyond 10 TeV can be used to address important questions of astroparticle and particle physics. The most prominent among these questions are the search for the origin of charged Galactic cosmic rays and the so-far little understood transition from Galactic to extra-galactic cosmic rays. A very promising avenue towards answering these fundamental questions is the construction of an air-shower detector with sufficient sensitivity for gamma-rays to identify the accelerators and large exposure to achieve accurate spectroscopy of local cosmic rays. With the new ground-based large-area (up to 100 km2) wide-angle (Ω∼ 0.6–0.85 sr) air-shower detector concept HiSCORE (Hundred∗i Square-km Cosmic ORigin Explorer), we aim at exploring the cosmic ray and gamma-ray sky (accelerator-sky) in the energy range from few 10 s of TeV to 1 EeV using the non-imaging air-Cherenkov detection technique. The full detector simulation is presented here. The resulting sensitivity of a HiSCORE-type detector to gamma-rays will extend the energy range so far accessed by other experiments beyond energies of 50–100 TeV, thereby opening up the ultra high energy gamma-ray (UHE gamma-rays, E > 10 TeV) observation window.