Number Of Α-particles Research Articles

A Study on the Change in the Dielectric Properties of CR-39 Polymer Track Detector Due to α-Irradiation in the Frequency Range from 100 Hz to 100 kHz

The dielectric properties in the frequency range from 100 Hz to 100 kHz of polyallyldiglycol carbonate “CR-39” samples before and after irradiations have been investigated. The irradiations were verified with 4.84 MeV α-particles at different irradiation times. The dependence of the dielectric properties of unirradiated and irradiated samples at room temperature (25°C) and constant frequency (10 kHz) on the total number of α-particles have been studied. It was found that the CR-39 can be used as a detector for high α-particles fluxes.

Systematics of the 14N + 159Tb reaction between 6 and 22 MeV/u

Employing the results from inclusive and particle-KX-ray coincidence measurements for the 14N + 159Tb reaction between 6 and 22 MeV/u the cross sections of α-particles are decomposed into three components. These are (i) α-particles evaporated from the target-like nucleus, (ii) α-particles in coincidence with projectile-like fragments (PLF's) with Z ⩾ 3 and most likely resulting from sequential decay of excited primary fragments, and (iii) α-particles from processes in which only (fast) light particles with Z ⩽ 2 are emitted. The average number of α-particles emitted per collision increases with beam energy for each of the three components, whereas the total cross section tends to level off. The channels in which only light particles are emitted are found to be the major source of the large cross section of fast α-particles at forward angles. From γ-ray multiplicity data it is deduced that these channels involve a significantly larger excitation of the heavy residual nucleus (inelasticity) than the (quasi-elastic) channels in which a PLF with Z ⩾ 3 is emitted. However, from the near beam velocities of the α-particles it must be concluded that they are emitted prior to the attainment of full energy damping.

A method for determining doses in the inhalation of radon decay products

This article gives a new method for determining the absorbed energy in the inhalation of radon decay products from the number of α-particles emitted during the total decay of daughter products of radon separated from 1 liter of air. A method is proposed for determining the concentration of radon from the number of α-particles emitted due to total decay of the daughter products collected on a filter from a continuously purified volume.

The track density of a charged particle in a photographic emulsion

In the track formed by a charged particle passing through a photographic emulsion, the curve relating the number of grains per unit length dN/dR to the rate of energy loss dE/dR is important.R is the residual range, and dN/dR is commonly writteng. Hitherto based on experiment alone, this curve is shown to fit the equation of a photographic monolayer, (s dE/dR)p =g/(gs—g). Here gs is the linear saturation density,P the photon number ands the reaction cross-section of a silver halide crystal. Experiment shows thatP differs little from unity. The characteristic of a plate exposed to a large number of α-particles fits the Poisson equationD/Ds = 1 — exp [—sE]. This equation has been long accepted, but it is not easily explained.

The role of eddy diffusion in the distribution of ions in the atmosphere near the ground

On account of α-ray emission from rocks and other soil material the ionization within the first 10 cm above ground is more intense than further up. These ions are carried upward by eddy currents until they disappear by recombination. The theory of mass exchange by eddy currents was used to compute the average number of ions present at different levels above the ground assuming the validity of Schweidler’s linear recombination law for small ions. The number of α-particles emitted from the ground was determined by means of a scintillation counter (photomultiplier) for various rocks, soil materials and vegetation and it was found that the contribution of ions produced near the ground and carried upward to the 100 cm level is not negligible. It may amount to nearly 10 per cent of the total number of ions present at this level.

Range of Radiation from Samarium

In NATURE of December 3 we announced the discovery of radiation of α-ray type emitted by samarium. Recently we have determined the range of this radiation. The apparatus used, to which Prof. H. Geiger had kindly directed our attention, consisted of a perforated Geiger-Muller tube, surrounded by a cylindrical brass tube, the inside of which was coated with samarium oxide. The whole system could be evacuated, and the pressure could be varied until no more α-particles reached the counter. From the air pressure and the distance between the samarium oxide layer and the counter, the range of the particles could be determined. The value for the range of the samarium radiation in air at atmospheric pressure was found to be 1.13 cm. at 15° C. The reliability of the method was checked by determining the range of the α-rays of radium F and a value of 3.90 cm. was found. Making use of the known relation between range and velocity of α-particles, we can conclude that particles having the velocity of 1.05 × 109 cm. sec.1 are emitted by samarium. That samarium emits α-particles and not H-particles could be proved by comparing the magnitude of the electrometric deflections obtained when counting the number of α-particles emitted by samarium, and also the magnitude of the deflections which polonium radiation produced, when the range of the particles was cut down to 1.13 cms.

Recalculation of Mass Defects

THE well-known mass defect curve of the old nuclear scheme calculated with regard to α-particles and protons presented a difficulty with its minimum of binding energy for tin and an increasing portion between tin and lead. On the other hand, the mass defect values against protons give a rather smoothly decreasing curve.1 As has already been pointed out,2 the number of α-particles must be considerably reduced from the point of view of the new scheme, which does not admit any electrons in nuclei, but only neutrons and protons (presumably joined as α-particles). The curve of mass defect against protons and neutrons (perhaps with a single ‘central’ α-particle) is very similar to the old curve against protons, but decreases less rapidly. Clearly the new mass defect values relatively to α-particles, neutrons and protons must lie somewhere between the old values computed relative to protons and α-particles respectively (because the number of α-particles is decreased). We may emphasise that this new mass defect curve shows no increasing portion between tin and lead. For illustration we give two typical values: Old: 50Sn124 = 31α + 12ɛ; mass defect = 0.158 (in mass units); 82Pb208 = 52α + 22ɛ; mass defect = 0.035. New: 50Sn124= 25α + 24w (w = neutron); mass defect = 0.304; 82Pb208 = 41α + 44w; mass defect = 0.366.

Fine Structure of α-Rays

IT is usually assumed that the long range α-particles observed in C'-products of radioactive series correspond to different quantum levels of the α-particle in the nucleus. If after the preceding β-disintegration the nucleus is left in an excited state with the α-particle on one of the levels of higher energy, one of the two following processes can take place: either the α-particle will cross the potential barrier surrounding the nucleus and will fly away with the total energy of the excited level (long range α-particle), or it will fall down to the lowest level, emitting the rest of its energy in the form of electromagnetic radiation (γ-rays), and will later fly away as an ordinary α-particle of the element in question. Thus there must exist a correspondence between the different long range α-particles and the γ-rays of the preceding radioactive body. If p is the relative number of nuclei in the excited state, γ the corresponding decay constant, and θ the probability of transition of the nucleus from the excited state to one of the states of lower energy with emission of energy (in form of γ-quanta or an electron from the electronic shells of the atom), the relative number of long range α-particles must be N = pλ/θ. Knowing the number of α-particles in each long range group and calculating, from the wave mechanical theory of radioactive disintegration, the corresponding values of λ, we can estimate for each group the value θ/p, giving a lower limit for the probability of γ-emission. For example, for thorium-C' possessing besides the ordinary α-particles also two groups of long range α-particles, we have for transition probabilities from two excited states to the normal state θ1<0.4 × 1012 sec.−1 and θ2<2 × 1012 sec.−1, which is the right order of magnitude for the emission of light quanta of these energies. With decreasing energy λ decreases much more rapidly (exponentially) than θ, so that the number of long range α-particles from the lower excited levels will be very small. (From this point of view we can also easily understand why the long range α-particles were observed only for C'-products for which the energy of normal α-particles is already much greater than for any other known radioactive element.)

The number of α-particles emitted by thorium C + C′

The number of α-particles emitted per second by thorium (C + C′) has been determined by an ionisation method. The number obtained is 4·26 ± ·08 × 1010 α-particles per second per curie equivalent γ-ray activity when in equilibrium with radio-thorium and when measured by the γ-rays of thorium C″ through 18 mm of lead. The result agrees within 1 per cent, with that extrapolated from Shenstone and Schlundt's values.The same apparatus was used to determine the slope of the Bragg curve over the first three centimetres of the range. The data fit the curve as given by I. Curie and Behounek within the accuracy of experiment. The curve given by G. H. Henderson falls too rapidly as it approaches the axis of ordinates.

CXI. A determination of the number of α-particles per second emitted by thorium C of known γ-ray actvity

CXI. <i>A determination of the number of α-particles per second emitted by thorium C of known γ-ray actvity</i>

Number of α-Particles Emitted by Radium

Number of α-Particles Emitted by Radium

An investigation of the spectrum of ionium

The preparation of ionium described by Prof. Rutherford in the footnote consisted of a mixture of the oxides of ionium and thorium. The percentage of ionium oxide in the preparation is not known. It can be calculated, however, provided we know both the period of ionium and the number of α -particles emitted by 1 grm. of the substance per second. The latter has been determined by Dr. H. Geiger, who found that 1 grm. expelled 10 8 α -particles per second. The period, however, is not known with certainty. Soddy has found that, on certain assumptions, it is at least 100,000 years, and this is the only experimental result that we have at present.

Rate of emission of α-particles from uranium and its products

The object of this investigation was to find directly how many α -particles are emitted per second per gramme of uranium in equilibrium with all its products. The number can be calculated from the rate of emission of the particles from radium, determined by Rutherford, but no direct experiment has previously been performed with uranium as it occurs in Nature. To estimate the number of α -particles emitted, their well-known property of producing scintillations when they strike a zinc sulphide screen (each α -particle producing one scintillation) was employed. The scintillations were observed through a microscope provided with a special objective.

The photographic action of the α-particles emitted from radio-active substances

It has been shown by Rutherford that the photographic action of α -particles stops suddenly when the thickness of an interposed aluminium screen is increased beyond a certain value. It is noticeable that the thickness of the screen required to completely stop photographic action is identical with that required to stop ionisation in gases and scintillations of a phosphorescent screen caused by α -particles. The first object of the present experiments was to investigate the manner in which the photographic action of α -particles varies along their path, and to see if there is any connection between this and the well-known variation of the ionisation produced in gases. This having been accomplished, a relation was found between the photometric density of the film produced on development and the number of α -particles incident upon it. Experiments were then made to see whether a single α -particle produced a detectable photographic effect.