scholarly journals Some experiments concerning the counting of scintillations produced by alpha particles.— Part I

1929 ◽  
Vol 122 (789) ◽  
pp. 304-319 ◽  
Keyword(s):  
Experimental Method ◽  
Atomic Structure ◽  
Alpha Particles ◽  
Γ Radiation ◽  
Modern Conception ◽  
Scintillation Method ◽  
Γ Rays ◽  
Α Particles

Among the various methods of detecting single a-particles, the scintillation method, because of its simplicity, is often the only one applicable. When the particles are to be counted in the presence of a strong β and γ radiation, the scintillation method is indispensable, for the scintillations produced by α-particles are easily detectable on the luminous background produced by the β and γ rays, while the electrical counter is seriously disturbed by these types of radiation. Though the counting of scintillations has been constantly used as an experimental method since 1908, and practically all the fundamental data on which the modern conception of atomic structure is based, were obtained by this method, very little systematic work has been done concerning the method itself and its limitations.

The interval between the departure of the disintegration particle and the emission of the gamma radiation

1932 ◽  
Vol 28 (1) ◽  
pp. 128-135 ◽  
Author(s):  
P. Wright
Keyword(s):  
Gamma Radiation ◽  
Γ Radiation ◽  
Γ Rays ◽  
Γ Ray ◽  
Recoil Atoms ◽  
Rough Calculation ◽  
Α Particles

Previous work on the existence and period of radium C′ is discussed with reference to an experiment of Jacobsen which provides evidence that a γ ray transformation of period comparable with that of radium C′ precedes the expulsion of α particles. It is shown that, from Jacobsen's results, part of the γ radiation from a source of recoil atoms should originate in the space surrounding the source.A rough calculation is made which shows that the γ rays above the source should be detectable by ordinary methods, and a description is given of an ionisation method capable of detecting the effect. The γ rays predicted by Jacobsen's experiment were tested for by using specially prepared sources of radium C. Phenomena associated with α recoil were also investigated for sources of radium (B + C) and thorium (B + C).No evidence of a γ ray emission from the space above any of the sources was obtained. The negative result indicates that the interval between the departure of the disintegration particle and the emission of the γ ray quantum is considerably less than 10−5second.

THE RANGE OF THE ALPHA-PARTICLES FROM URANIUM II

1931 ◽  
Vol 5 (5) ◽  
pp. 567-571 ◽  
Author(s):  
S. Bateson
Keyword(s):  
Direct Measurement ◽  
Alpha Particles ◽  
A Value ◽  
Scintillation Method ◽  
Good Agreement ◽  
Α Particles

The range of the α-particles from uranium II has been determined by a scintillation method to be 3.29 ± 0.08 cm. at 15 °C. and 760 mm. This is in good agreement with Laurence's value found with a Wilson chamber. From the Geiger-Nuttall relationship the period is calculated to be 28,000 years, a value considerably less than that found recently by direct measurement.

scholarly journals The association of γ-rays with the α-particle groups of thorium C

1932 ◽  
Vol 136 (829) ◽  
pp. 396-406 ◽  
Keyword(s):  
Long Range ◽  
Direct Evidence ◽  
Transition Probabilities ◽  
Essential Difference ◽  
Γ Radiation ◽  
Γ Rays ◽  
The One ◽  
Alternative Processes ◽  
Particle Group ◽  
Α Particles

As a result of the experiments of Rutherford, Ward and Lewis, it is now generally accepted that the emission of γ-rays from radioactive bodies is associated with the transitions of α-particles between stationary states in the nucleus. Direct evidence for the existence of these excited states in the case of radium C' is obtained from the several groups of long range α-particles which have been detected. Rosenblum has found that thorium C also emits several groups of α-particles, and the existence of a corresponding number of nuclear α-particle states can be safely inferred, which should also give rise to γ-radiation. This case was first discussed by Gamow, who pointed out that there was an essential difference here from radium C' In the latter body the extra α-particle states all have energy greater than the normal, and emission of the corresponding long range α-particles is a rare phenomenon, of the order of one long range particle for a million normal α-particles. The case of radium C' appears to be accounted for satisfactorily by the assumption of two alternative processes, either internal nuclear switch or α-emission from the excited state, the relative frequencies of occurrence depending on the ratio of the transition probabilities. With thorium C, however, the most intense α-particle group is not the one of lowest energy, and the groups only vary in intensity by a factor of one hundred instead of one million as with radium C' The assumption of alternative processes of γ-and α-emission would lead to values for the ratio of the transition probabilities for the two processes which are absolutely incompatible with what is known about the orders of magnitude of the probabilities of α-particle emission and radiation switch. Gamow therefore proposed that the thorium C nucleus is initially formed with its α-particles all in the gromid state and that disintegration could sometimes occur in such a way as to leave the product nucleus excited. Rosenblum gives the following data for the velocities and relative intensities of the groups from thorium C.

The interpretation of ionization measurements in gases at high pressures

1940 ◽  
Vol 36 (1) ◽  
pp. 101-126 ◽  
Author(s):  
Elizabeth Kara-Michailova ◽  
D. E. Lea
Keyword(s):  
Experimental Data ◽  
Systematic Error ◽  
High Pressures ◽  
Wave Length ◽  
Wall Effect ◽  
Γ Radiation ◽  
Fast Electrons ◽  
Γ Rays ◽  
Α Particles ◽  
Number Of Authors

When γ-radiation passes through a gas it ionizes by means of fast electrons which produce clusters of secondary ionization at intervals along their paths. At high pressures a considerable amount of recombination of ions takes place in these clusters; in the present paper a theory is described which enables the proportion of ions escaping recombination to be calculated as a function of the gas pressure and collecting field. A review of the available experimental data concerning the variation of ionization current with pressure and collecting field is given, and it is shown that the predictions of the cluster recombination theory are in satisfactory agreement with these experimental data.Jaffé has given a theory of initial recombination valid for a columnar distribution of ionization, and has shown that this theory is in agreement with experiments in which α-particles produce the ionization. A number of authors have applied Jaffé's equations to ionization produced by fast electrons regardless of the initial localization of the ions in clusters. It is shown in the present paper that such measure of agreement with experiment as is obtained by this procedure is only obtained at the expense of assigning incorrect values to certain known constants. Also in the case of X- and γ-rays the columnar theory predicts a variation of the proportion of recombination with the wave-length of the radiation which is much too rapid. It is further shown that the method based on Jaffé's equations which is used by Clay and his colleagues to extrapolate experimental ionization currents at finite collecting fields to saturation currents at infinite fields is liable to systematic error in a direction likely to lead to the deduction of a spurious wall effect or the exaggeration of an existing wall effect.

scholarly journals The artificial production of nuclear γ-radiation

1932 ◽  
Vol 136 (829) ◽  
pp. 428-453 ◽  
Keyword(s):  
Particle Bombardment ◽  
Rapid Growth ◽  
Absorption Coefficients ◽  
Γ Radiation ◽  
External Stimulation ◽  
Atomic Nuclei ◽  
Order Of Magnitude ◽  
Γ Rays ◽  
Stimulation Of ◽  
Α Particles

The study of the γ-radiations emitted by atomic nuclei has greatly increased in interest and importance in recent years owing to the theories connecting these radiations with the intimate structure of the nuclei. Many attempts have been made to excite atomic nuclei to radiation by external stimulation, mainly by bombardment with the α-, β-, γ-rays emitted by radioactive bodies. The first evidence of the artificial stimulation of nuclear γ-radiation was obtained by Slater in 1921, who found that a small amount of penetrating γ-radiation was produced when the elements tin and lead were bombarded by the α-particles emitted from radon. The experiments were very difficult on account of the rapid growth of radium B and C, but the consistency of the results, control experiments with paper substituted for lead, and the absorption coefficients of the radiations, all indicated that the results were trustworthy. Slater estimated that the fraction of the radon α-particles passing through the ead which produced γ-radiation was of the order 1 in 6000; in the case of tin this fraction was about 1 in 12000. Subsequent experiments by other investi­gators, including the present writer, using polonium α-particles instead of radon α-particles, showed definitely the absence of effects of this order of magnitude. Since polonium α-particles have only slightly less energy than radon α-particles, the observations are very difficult to reconcile. Later in this paper a possible explanation of this discrepancy will be suggested. Two years ago the writer obtained evidence, which will be mentioned later, of the production of penetrating y-radiations when aluminium was bombarded by polonium α-particles, and Bothe and Becker have definitely established the production of nuclear γ-radiation in several of the lighter elements by α-particle bombardment. The effects are, however, in every case of a much smaller intensity than those found by Slater. The amount of radiation observed is indeed so small that very strong sources of polonium are essential, and on this account the writer has only recently been able to make a detailed study of the radiations.

24.—The Origin of the Short-range Alpha Particles of Fission

1974 ◽  
Vol 71 (4) ◽  
pp. 285-292
Author(s):  
N. Feather
Keyword(s):  
Short Range ◽  
Mass Number ◽  
Neutron Emission ◽  
Neutron Number ◽  
Alpha Particles ◽  
Similar Process ◽  
Detailed Calculation ◽  
Γ Rays ◽  
Α Particles

SynopsisThe suggestion is made, and rendered plausible by detailed calculation, that the short-range α-particles of fission, identified by Kugler and Clarke [1], are emitted, in competition with ‘prompt’ γ-rays, from highly excited post-neutron-emission fragments of even neutron number N and, predominantly, of mass number A in the range 140 ≦ A ≧ 145. A similar process is energetically forbidden in relation to triton emission.

The total energy of the γ-radiation emitted from the active deposit of actinium

1938 ◽  
Vol 34 (3) ◽  
pp. 429-434 ◽  
Author(s):  
E. Kara-Michailova
Keyword(s):  
Fine Structure ◽  
Absorption Coefficient ◽  
Total Energy ◽  
Excellent Agreement ◽  
Experimental Error ◽  
Γ Radiation ◽  
Γ Rays ◽  
Γ Ray ◽  
Good Agreement ◽  
Α Particles

The disintegrations by which Ac B passes into the inactive AcPb are accompanied by a γ-radiation very weak compared with the intense γ-emission in the case of Ra or Th-active deposit. The analysis of the secondary β-ray spectrum of actinium-active deposit has revealed the existence of at least five γ-rays (1) (see Table I), of which the ray with energy 0·349 × 106 e.V. definitely belongs to the disintegration Ac C—C″ and is associated with the fine-structure of α-particles of Ac C. According to the measurements of Surugue the two rays of 0·4038 × 106 and 0·4257 × 106 e.V. energy are to be attributed to the disintegration AcB—C, whereas the origin of the 0·829 × 106 e.V. ray is less definite. The fit with experiments is best if this ray is assumed to be emitted from Ac B—C; but it may also (within experimental error) be attributed to the disintegration Ac C″—Pb. Experiments on the absorption coefficient of the γ-radiation of RaAc and its disintegration products prove that the 0·829 × 106 e.V. ray is the hardest γ-ray emitted by the active deposit of actinium(2). The value for the absorption coefficient between 4·6 and 10·6 cm. of lead was found to be μ/ρ = 0·76, in good agreement with the value found in previous experiments at smaller absorptions in aluminium (3). There is, on the whole, excellent agreement concerning the energies of the γ-components as measured according to different methods by different observers.

scholarly journals Valve methods of recording single alpha-particles in the presence of powerful ionising radiations

1931 ◽  
Vol 131 (817) ◽  
pp. 391-409 ◽  
Keyword(s):  
Solid Angle ◽  
Alpha Particles ◽  
Original Form ◽  
Γ Radiation ◽  
Simple Matter ◽  
The Mean ◽  
Ionising Radiations ◽  
Large Groups ◽  
Α Particles ◽  
Number Of Particles

In 1926, Greinacher showed that it was possible to detect single α-particles by linearly amplifying the ionisation current due to an α-ray by means of thermionic valves. Subsequently, he was also able to detect single H-particles by the same method. Other workers have since applied the method to various radio-active problems in which the counting would otherwise have had to be done by means of scintillation screens or Geiger counters, etc. The present writers, working in conjunction with H. M. Cave, also employed the method for determining the mean rate of emission of α-particles from radium C, by counting accurately the number of particles emitted within a defined solid angle. While the problem of encounting α- or H-particles can be a comparatively simple matter under certain conditions, there are many experiments necessarily carried out under conditions which render it utterly impossible to employ the Greinacher method in its original form. These experiments involve the counting of comparatively few particles in the presence of disturbances caused by powerful β- or γ- radiation, or by large groups of α-particles which it is not desired to count.

THE EFFECT OF INTERACTIONS ON THE ANGULAR DISTRIBUTION OF γ-RAYS FROM AN ASSEMBLY OF ORIENTED NUCLEI

1957 ◽  
Vol 35 (9) ◽  
pp. 1133-1145 ◽  
Author(s):  
J. M. Daniels
Keyword(s):  
Angular Distribution ◽  
Energy State ◽  
Nuclear Orientation ◽  
Γ Radiation ◽  
Orientation Experiment ◽  
High Temperature Approximation ◽  
Γ Rays ◽  
Matrix Formula ◽  
Paramagnetic Ions ◽  
Radioactive Ions

The angular distribution of γ-radiation from an assembly of nuclei oriented by the magnetic h.f.s. method can be very much modified by interactions between the radioactive ions and other paramagnetic ions in the crystal. In order to calculate the effect of these interactions, an operator Γ is derived which represents the angular distribution of γ-rays from a radioactive nucleus. The angular distribution at any temperature is given by Spur(Γρ), where ρ is the statistical matrix [Formula: see text], [Formula: see text] being the Hamiltonian for the whole crystal. For a high temperature approximation, ρ is expanded in powers of 1/T. It is found that, for alignment by the magnetic h.f.s. method, the first term which contains interaction parameters is that in 1/T4, and an expression is given for the contribution of interactions to this term.At very low temperatures, perturbation theory is used to estimate the effect of interactions on the lowest nuclear energy state, and hence on the angular distribution of γ-rays. It is found that, if an external magnetic field is applied along a principal axis of the g-tensor of the radioactive ions, interactions have no influence on the angular distribution of γ-rays in the limit of large fields. It is also shown that Bleaney's restriction, that for a successful nuclear orientation experiment the broadening of the levels should be less than the hyperfine splitting, is not necessary in this case.

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