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 γ-RAYS OF THORIUM CC′

1948 ◽  
Vol 26a (5) ◽  
pp. 313-325 ◽  
Author(s):  
S. C. Fultz ◽  
G. N. Harding
Keyword(s):  
Energy Level ◽  
Long Range ◽  
Level Scheme ◽  
Electric Quadrupole ◽  
Coincidence Rate ◽  
A Value ◽  
Γ Rays ◽  
Γ Ray ◽  
Particle Group ◽  
Α Particles

At least two energy level schemes have been proposed for the ThC′ nucleus, which is excited in the β-disintegration ThCC′. That of Ellis (1933) includes three γ-rays of energies 0.726, 1.62, and 1.80 Mev., the 1.62 Mev. ray being doubtful. The level scheme of Latyschev and Kulchitsky (1940) has eight γ-rays including one of energy 2.2 Mev., for which no corresponding long-range α-particle group has been observed. The two level schemes lead to widely differing values for the total γ-ray energy of ThCC′. In the present investigation a value for the total γ-ray energy of ThCC′ has been obtained by measuring coincidences between the γ-rays of ThCC′ and the subsequently emitted α-particles of ThC′. It is shown that this value (0.14 Mev.) favors the level scheme of Ellis, including only the γ-rays of energy 0.726 and 1.80 Mev., and taking the former as electric quadrupole. It was found that under certain conditions the external bremsstrahlung excited by the β-rays of ThCC′ in the source-holder contributed appreciably to the coincidence rate. Precautions were taken to minimize this effect.

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.

scholarly journals The γ-rays of radium (B + C) and of thorium (C + C')

1934 ◽  
Vol 143 (849) ◽  
pp. 350-357 ◽  
Keyword(s):  
Long Range ◽  
Published Data ◽  
Level System ◽  
The Past ◽  
Rigorous Test ◽  
Γ Rays ◽  
The Absolute ◽  
Relative Measurements ◽  
Α Particles

Reliable information about the γ-rays emitted by radium C' is particularly valuable since the main features of the nuclear level system are shown by the groups of long range α-particles and are hence accessible to direct investigation. These long range groups of α-particles have been measured recently by Rutherford, Lewis and Bowden by a greatly improved method which has not only brought to light several new groups, but in addition has given considerably greater accuracy in the determination of the energies of the groups than had been possible in the past. The energy of these groups in excess of that of the normal group is a measure of the excitation energy of the nucleus and the older measurements had indicated, as was to be expected, a close correspondence between these energies and the quantum energies of the γ-rays. The recent more accurate measurements of Rutherford, Lewis and Bowden provided the opportunity of a more rigorous test of this connection and showed the possibility, by the combination of the information from these two sources, of a direct experimental determination of the level system. However, the accuracy of the published data on the Ra C γ-rays deduced from the natural β-ray spectrum was subject to some doubts for the following reasons. The measurements dated from 1924 when the absolute energies of certain strong groups in the β-ray spectrum were measured and the energies of the remaining lines determined by relative measurements. The strong groups in question lay between 0.4 X 10 5 and 3.0 X 10 5 volts and the procedure of step-wise comparision up to energies of over 2 X 10 6 volts may have led to cumulative errors. More serious was that recent measurements on the Th (B + C) β-ray spectrum had thrown doubt on the correctness of the absolute values. Lastly, experiment gives values for H ρ , that is the momenta of the electrons in the groups, and the calculation of the energies involves e / m . The older data had been based on e / m = 1.769 X 10 7 , and while the change to the value 1.760 X 10 7 alters the energies proportionally far less, there was involved here an avoidable error which had to be removed.

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.

scholarly journals The ranges of the α-particles from the radioactive emanations and “A” products and from polonium

1932 ◽  
Vol 136 (829) ◽  
pp. 349-363 ◽  
Keyword(s):  
Long Range ◽  
Point Of View ◽  
Counting Methods ◽  
Γ Rays ◽  
The Mean ◽  
High Degree ◽  
Α Particles

The analysis of groups of α-particles by new counting methods has been described in previous papers, in which details have been given of the examination of the α-particles emitted by radium-C and -C' thorium-C and -C', and actinium-C and -C', including the long range particles. The methods have the advantage that any appreciable inhomogeneity of a group of α-particles is readily detected, and moreover, the mean range of a group may be directly measured with a high degree of precision. The experiments have now been extended to an examination of the α-particles emitted by the emanations and “A” products of the three radioactive series, and by polonium. The examination of these α-ray groups is not only of great interest from the point of view of the radioactive transformations, but also for the possible connection with the emission of γ-rays.

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.

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 Analysis of α-rays by an annular magnetic field

1933 ◽  
Vol 139 (839) ◽  
pp. 617-637 ◽  
Keyword(s):  
Magnetic Field ◽  
Long Range ◽  
Resolving Power ◽  
Counting Method ◽  
Range Measurements ◽  
Considerable Uncertainty ◽  
Radioactive Substances ◽  
Γ Rays ◽  
The Mean ◽  
Α Particles

In previous papers an account has been given of a new counting method for analysing the groups of α-rays emitted by radioactive substances, and for measuring directly their mean range in air. In the course of these experiments, we showed that the long range groups of α-particles from radium C' are very complex, consisting of at least nine groups, with mean ranges lying between 7·7 and 11·6 cm. of air. As it is believed that the energies of these long range groups are intimately connected with those of the γ-rays from radium C', it has become of great importance to determine the energies of these groups of particles with precision. As, however, the seven groups with ranges between 9·5 and 11·6 cm. differ so little in velocity that they can only be partially resolved in range measurements, it was very difficult in our experiments to determine the mean ranges with accuracy. Moreover, there has been considerable uncertainty as to the precise relation between the range and velocity of such long range particles. A much greater resolving power can be obtained by a direct velocity determination, using a magnet to bend the α-rays into a circle. The great Paris electromagnet has been used in this way by Rosenblum, who photographed the α-ray spectra produced by the well-known focussing method. He has demonstrated the complexity of a number of α-ray groups, and has measured their velocities with an accuracy of at least 1 in 1000.

scholarly journals Analysis of the α-particles emitted from thorium C and actinium C

1931 ◽  
Vol 133 (822) ◽  
pp. 351-366 ◽  
Keyword(s):  
Long Range ◽  
Special Interest ◽  
Differential Method ◽  
Automatic Method ◽  
Excited Nucleus ◽  
Γ Rays ◽  
Α Particles ◽  
Corresponding Analysis

In a recent paper, an account has been given of the analysis of the long range α-particles emitted by radium C. Nine distinct groups of α-particles were detected varying in range between 7·8 and 11·6 cm. in air. Evidence was given that the emission of γ-rays from radium C is intimately connected with the occurrence of these groups of long range α-particles, and it was concluded that the γ-rays arise from the transition of an α-particle in an excited nucleus between two levels of different energies. This question has been discussed in more detail by Rutherford and Ellis, who have advanced a tentative theory to account for the relation between the energies of the γ-rays emitted from radium C. In the present paper we give the results of a corresponding analysis of the long range α-particles from thorium C and an analysis of the groups of α-particles emitted from actinium C. In these experiments the differential method of analysis was used, as in the experiments with radium C. In the present experiments, however, instead of recording the α-particles photographically on a moving film, we have mainly employed the automatic method of counting, using thyratrons in place of the oscillograph. This method, which has been developed by one of us (C. E. Wynn-Williams), has been fully discussed in a recent paper. Here it suffices merely to refer to one or two points of special interest in connection with the present research.

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