The Collective Radioactive Decay of Atomic Nuclei Initiated by an External Mechanical Impact: Science Fiction or a New Class of Physical Processes

Abnormally high pressure or temperature can significantly reduce the lifetime of atomic nuclei including stable. A hypothesis on stable nuclei decays caused by mechanical collision of macro-objects containing these nuclei is put forward. Mechanisms of such decays are presented. At the same time the distance between interacting nuclei can be significantly higher than the range of nuclear interaction (as manifestations of strong interaction). In decays initiated by external impact, the mean lifetime with respect to particular decay can change depending on these factors. The hypothesis is verified experimentally. When a bismuth bullet collides with a steel flat target, we see different types of stable bismuth isotope decay including cluster one, which is not found in nature (if there is no external impacts). This new class of physical processes can be related to the collective radioactive decay of atomic nuclei initiated by an external mechanical impact.

Cyclotrons as Drivers for Precision Neutrino Measurements

As we enter the age of precision measurement in neutrino physics, improved flux sources are required. These must have a well defined flavor content with energies in ranges where backgrounds are low and cross-section knowledge is high. Very few sources of neutrinos can meet these requirements. However, pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for decay-at-rest sources are cyclotron accelerators, which are compact and relatively inexpensive. This paper describes a scheme to produce decay-at-rest sources driven by such cyclotrons, developed within the DAEδALUS program. Examples of the value of the high precision beams for pursuing Beyond Standard Model interactions are reviewed. New results on a combined DAEδALUS—Hyper-K search for CP violation that achieve errors on the mixing matrix parameter of 4° to 12° are presented.

Longevity of Plutonium 238 Heat Sources

ABSTRACTPlutonium oxide heat sources are used to power space missions. The heat produced by alpha decay of the 238 isotope of Pu is converted to electricity in a thermopile, providing electricity during a substantial fraction of the 88 year half-life of the isotope. Decay of the Pu produces helium and uranium, and a fraction of the evolved helium is captured in the oxide matrix. All of the helium produced in decay can in principle be contained in the oxide lattice, where it occupies the tetrahedral sites. Some helium diffuses out at a rate that is somewhat dependent on the form and morphology of the fuel. Rates have previously been measured for oxide aged about 1 year. Current measurements on sealed heat sources as old as 34 years indicate that the rate of diffusion has changed only slightly over time. Possible mechanisms for helium release include bubble diffusion, point defect migration, agglomeration and movement of He at grain boundaries, and volume diffusion through the lattice sites. We observe primarily diffusion from site to site within the lattice, with an activation energy of 18.7 kcal/mole, independent of point defect movement, despite the rising concentration of helium in the lattice over time and the accumulation of radiation damage within the lattice. Because of the slow diffusion of helium from the fuel to the headspace, heat sources are anticipated to be stable over a long lifetime.

Lithium as a Potential Adjuvant to 131I Therapy of Metastatic, Well Differentiated Thyroid Carcinoma1

As lithium inhibits the release of iodine from the thyroid but does not change iodine uptake, it may potentiate 131I therapy of thyroid cancer. The effects of lithium on the accumulation and retention of 131I in metastatic lesions and thyroid remnants were evaluated in 15 patients with differentiated thyroid carcinoma. Two 131I turnover studies were performed while the patients were hypothyroid. One was performed while the patient received lithium; the second served as a control study. From a series of γ-camera images, it was found that lithium increased 131I retention in 24 of 31 metastatic lesions and in 6 of 7 thyroid remnants. A comparison of 131I retention during lithium with that during the control period showed that the mean increase in the biological or retention half-life was 50% in tumors and 90% in remnants. This increase occurred in at least 1 lesion in each patient and was proportionally greater in lesions with poor 131I retention. When the control biological half life was less than 3 days, lithium prolonged the effective half-life, which combines both biological turnover and isotope decay, in responding metastases by more than 50%. More 131I also accumulated during lithium therapy, probably as a consequence of its effect on iodine release. The increase in the accumulated 131I and the lengthening of the effective half-life combined to increase the estimated 131I radiation dose in metastatic tumor by 2.29 ± 0.58 (mean ± sem) times. These studies suggest that lithium may be a useful adjuvant for 131I therapy of thyroid cancer, augmenting both the accumulation and retention of 131I in lesions.

Isotope decay range distribution curves for use in the analysis of electron microscope autoradiographs.

Analysis of autoradiographs at the electron microscope level requires special procedures, since the size of the radioactive structures visualized are comparable to the range of the radioactive decay particles emitted. Quantitative analysis in these circumstances requires that the sizes, shapes, and juxtaposition of the various structures be taken into account in relation to the range distribution of silver grains, produced by the decays, from a point source for the particular isotope and autoradiographic conditions employed. We present the distribution of silver grains about a point source for the four electron capture isotopes 51Cr, 55Fe, 111In, and 125I. Thin radioactive line sources were constructed and the distribution of autoradiographic grains measured. The grain distributions are discussed in relation to the number of particles per disintegration and their energy and range. A simple calculation enables these line source distributions to be converted into point source distributions, which can then be used for whichever method of quantitative analysis is considered appropriate for a particular problem. An outline is given of some of the more important aspects of various methods of analysis.