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The performance of nuclear reactors and other nuclear systems depends on a precise understanding of the neutron interaction cross sections for materials used in these systems. These cross sections exhibit resonant structure whose shape is determined in part by the angular momentum quantum numbers of the resonances. The correct assignment of the quantum numbers of neutron resonances is, therefore, paramount. In this project, we apply machine learning to automate the quantum number assignments using only the resonances' energies and widths and not relying on detailed transmission or capture measurements. The classifier used for quantum number assignment is trained using stochastically generated resonance sequences whose distributions mimic those of real data. We explore the use of several physics-motivated features for training our classifier. These features amount to out-of-distribution tests of a given resonance's widths and resonance-pair spacings. We pay special attention to situations where either capture widths cannot be trusted for classification purposes or where there is insufficient information to classify resonances by the total spin $J$. We demonstrate the efficacy of our classification approach using simulated and actual $^{52}$Cr resonance data., 22 pages, 5 tables, 13 figures. Version resubmitted to PRC after comments from referee (including bug fix) and accepted for publication

The production of radioactive isotopes by interactions of cosmic-ray particles with sodium iodide (NaI) crystals can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of NaI crystals with a neutron beam that matches the cosmic-ray neutron spectrum, followed by direct counting and fitting the resulting spectrum across a broad range of energies, we determined the integrated production rate of several long-lived radioisotopes. The measurements were then extrapolated to determine the sea-level cosmogenic neutron activation rate, including the first experimental determination of the tritium production rate: $(80 \pm 21)$ atoms/kg/day. These results will help constrain background estimates and determine the maximum time that NaI-based detectors can remain unshielded above ground before cosmogenic backgrounds impact the sensitivity of next-generation experiments., Comment: 20 pages, 15 figures, 7 tables

Twenty stations were established in a grass field of 8 acres, and twenty-nine soil samples were examined from each station in the course of 213 years. Wireworms (Agriotes sputator) were distributed among the twenty stations in a non-random manner. In this field, the wireworm distribution was correlated to a highly significant degree with nine factors (loss on ignition, organic carbon, nitrogen, Lolium, Agrostis, Chilopoda, staphylinid larvae, ants and Nematocera) and to a significant degree with three factors (altitude, pH of the soil and Diplopoda). Among these factors, three (the organic content of the soil as measured by loss on ignition, the prevalence of the grass Lolium, and the numbers of staphylinid larvae) were found by analysis to be most significantly correlated with the wireworm distribution. Sixteen stations were set up in a grass plot of 14 acre, and twenty-one soil samples were examined from each station during a period of 3 years. The distribution of wireworms at these stations was markedly non-random throughout the sampling period, some stations being consistently three or four times as heavily infested as others only 5 yd, away. Within this plot the distribution of wireworms was correlated to a highly significant degree with altitude, depth of loam and amount of soil moisture at 3 and at 9 in. depth. It was significantly correlated with the lime content of the soil. Ranunculus was prevalent on an area of low wireworm infestation. Among the factors studied in this plot, the amount of soil moisture at 3 in. depth was most important. It was negatively correlated with the distribution of wireworms. Within the plot, stations having high wireworm populations were infested almost exclusively by Agriotes sputator; those having low wireworm populations were infested about equally by A. sputator and A. ‘obscurus-lineatus’. Four square-yard samples were examined, each in eighty-one quadrats 4 in. square. Within each square yard, the wireworms were not distributed at random and independently, but were markedly aggregated. Separation of the wireworms collected from these samples into three size groups showed that the non-random distribution in square-yard samples was largely due to the small larvae, which were strongly aggregated. The medium-sized larvae were less markedly aggregated. The distribution of the large larvae under grass was not significantly different from a random distribution. To understand the factors controlling wireworm distribution it will be necessary to consider the distribution of the different larval age-groups. Two suggestions are made towards an explanation of the geographical distribution of wireworms in England. Study of the spatial distribution of wireworms raises some of the major problems of ecology and, in particular, illustrates the interdependence of spatial distribution and seasonal succession.

As a preliminary step in the study of a system consisting of a flying insect and the air surrounding it, a comparison is made between the system under natural conditions of free flight and under experimental conditions (when the insect is held stationary), in order to ascertain under what conditions conclusions reached with the insect held stationary would hold for free flight. To avoid the difficulty of making this comparison directly in respect of each of the many factors involved, the resultant force which, acting continuously on the body of the insect, would most nearly replace those cyclicly changing forces that normally maintain or modify the state of motion in flight, is taken as an index of what is occurring in the system. When the insect is held stationary in ‘still air’ it is found in most cases that this resultant, though of sufficient magnitude to support the insect in flight, does not act through the centre of gravity: the line of action of the resultant intersects the body axis at some point behind the centre of gravity. The position of this point depends on the amplitude of wing beat. W hen the insect is exposed in a wind tunnel to a stream of air of appropriate speed and direction, however, the resultant acts through the centre of gravity, as in free flight. The forward displacement of the point of intersection between the line of action of the resultant and the body axis, when the insect is exposed to a stream of air, is analysed further, and it is found: (1) that the effect of the stream of air on the body of the insect is negligible in this connexion as compared with the effect on the wings; (2) that changes in amplitude of wing beat do not account for the forward displacement of the resultant; and (3) that when the insect is exposed to a stream of air the path travelled by the wing tip on its downward beat is displaced forwards along the body axis in a direction which would tend to produce the observed displacement of the resultant force. This forward displacement of the path travelled by the wing on its downward beat converts the elliptical course, characteristic of wing movements when the insect is held stationary in ‘still air’, into the figure of ‘8’ course commonly associated with insect flight, and is dependent on the movement or position of the third antennal joint relative to the second, which in turn is determined by the action of the stream of air on the third joint with its arista. The characteristic attitude of the legs in flight, and the continued vibration of the wings when air is blown at the insect from in front also depend on the sensory inflow from the antennae. The maintenance of the figure of ‘8’ path involves the interaction of the sensory inflow both from the antennae and from the halteres.

The number of wireworms in successive collections from five Cambridgeshire fields declined during the first year of cultivation to 25 % of the number present before the fields were ploughed from old grass. The decline in numbers was accompanied by a change in the composition of the wireworm population; the marked inverse correlation between number and size of larvae, which held for the wireworm populations under grass, progressively altered towards uniform numbers of the different size-groups. The incidence of natural control on the different sizes of larvae was obscured by their growth, and more medium-sized and large larvae were lost than would appear from the population-size histograms. Three groups of factors are considered as contributing to the decline in numbers after ploughing. Direct observation showed that many wireworms were destroyed in the actual process of cultivation. Evidence was insufficient to prove that the physical condition of cultivated soil adversely affects the number of wireworms. Comparison of the smaller size-groups in pasture and in the cultivated fields showed that the wireworm population failed to replenish itself under arable conditions.

A method has been developed, and is here briefly described, by means of which all the wireworm larvae of all stages can be collected from soil samples. By use of that method, complete wireworm populations have been obtained from soil samples of three types, two of which provide large homogeneous populations for detailed study while the third gives information about the seasonal and spatial infestation of fields. These collections show that the wireworm population of English pasture land is on the average about three times as large as has been commonly supposed. Populations have been found ranging up to ten millions per acre in the top 12 in. of soil. In two pastures studied intensively throughout the year, the wireworm population has been found to consist of large numbers of small larvae, decreasing numbers of larger larvae, and comparatively few of the very large larvae that have usually been allowed to represent the population. Such a composition is shown to be characteristic of wireworm populations under old grass at all seasons of the year and in several fields in different parts of the country. This result suggests that in research on the wireworm problem it is desirable to take into consideration the whole wireworm population throughout the year, not merely the large larvae during the cropping season.