ß decay of (38)Ca: sensitive test of isospin symmetry-breaking corrections from mirror superallowed 0+ → 0+ transitions.

We report the first branching-ratio measurement of the superallowed 0+→0+ß transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68) s with a relative precision of ±0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed ß decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

Experimental validation of the largest calculated isospin-symmetry-breaking effect in a superallowed Fermi decay.

A precision measurement of the γ yields following the ß decay of (32)Cl has determined its isobaric-analogue branch to be (22.47(-0.18)(+0.21))%. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to 0+ → 0 + transitions for tests of the standard model.

A novel approach to medical radioisotope production using inverse kinematics: A successful production test of the theranostic radionuclide 67Cu.

A novel method for the production of important medical radioisotopes has been developed. The approach is based on performing the nuclear reaction in inverse kinematics, namely sending a heavy-ion beam of appropriate energy on a light target (e.g. H, d, He) and collecting the isotope of interest. In this work, as a proof-of-concept, we studied the production of the theranostic radionuclide 67Cu (T1/2 = 62 h) via the reaction of a 70Zn beam at 15 MeV/nucleon with a hydrogen gas target. The 67Cu radionuclide alongside other coproduced isotopes, was collected after the gas target on an aluminum catcher foil and their radioactivity was measured by off-line γ-ray analysis. After 36 h post irradiation, apart from the product of interest 67Cu, the main radioimpurity coming from the 70Zn + p reaction was 69mZn (T1/2 = 13.8 h), which can be reduced by further radio-cooling. Moreover, along with the radionuclide of interest produced in inverse kinematics, the production of additional radioisotopes is possible by making use of the forward-focused neutrons from the reaction and allowing them to interact with a secondary target. A preliminary successful test of this concept was realized in the present study. The main requirement to obtain activities appropriate for preclinical studies is the development of high-intensity heavy-ion primary beams.

Precise tests of internal-conversion theory.

Using the 165.9-keV M1 transition in (139)La as a calibrant, we have determined the K-shell internal conversion coefficients (ICCs) for the 127.5-keV E3 transition in (134)Cs and the 661.7-keV M4 transition in (137)Ba to 0.6% precision. Unlike previous less-precise measurements of these ICCs, which differed significantly from calculated values, our results agree well with calculations that include the atomic K-shell vacancy and disagree with those that exclude it. These results, which are consistent with what we also found for (193)Ir, confirm our earlier conclusions but for different energies, multipolarities and atomic numbers.

Precise test of internal-conversion theory: αK measurements for transitions in nine nuclei spanning 45 ≤ Z ≤ 78.

We have been testing the theory used to calculate internal-conversion coefficients (ICCs) by making a series of measurements of αK values with precision better than ±2%. So far we have measured E3 transitions in three nuclei, 103Rh, 111Cd and 134Cs; and M4 transitions in six nuclei, 119Sn, 125Te, 127Te, 137Ba, 193Ir and 197Pt. Together, these span a wide range of A and Z values. In all cases, the results strongly favor Dirac-Fock calculations in which the final-state electron wave function has been computed in an atomic field that includes the vacancy created by the internal-conversion process.

Effort as Person-Focused Praise: "Hard Worker" Has Negative Effects for Adults After a Failure.

Although work with children demonstrates a benefit of process-focused praise relative to person-focused praise on post-failure motivation, few studies have examined this result in adults. We tested the effect of three types of praise on adults' post-failure outcomes: person-focused intelligence ("high intelligence"), person-focused effort ("hard worker"), and process-focused effort ("worked hard") in a sample of 156 adults recruited from Amazon's MTurk. Participants completed a set of easy visual pattern recognition problems and were told that they performed better than most adults and were given one of the three types of feedback. They then completed more difficult problems and were told that they had not performed well. Participants in the "hard worker" condition (compared to "worked hard") were more likely to endorse intelligence as a reason for failure. They also reported lower perceived success and less enjoyment than participants in other conditions. Participants in the "high intelligence" condition were more likely to attribute their failure to intelligence than participants in the "worked hard" condition. The results suggest that the benefit of process-focused praise typically found in children (worked hard compared to intelligent) was mostly not replicated in adults, and person-focused effort praise was detrimental in a non-college student adult sample.

Test of internal-conversion theory with precise gamma- and X-ray spectroscopy.

Precise measurements of K-shell internal conversion coefficients (ICCs) are being used to determine the best method for calculating these coefficients. A recent result for the M4 transition from 193Irm has been refined, demonstrating conclusively that the atomic vacancy created by the ejected electron must be properly accounted for in the calculation of ICCs. Measurements of additional cases are discussed.

Precise efficiency calibration of an HPGe detector up to 3.5 MeV, with measurements and Monte Carlo calculations.

Previously we used relative and absolute efficiency measurements combined with Monte Carlo calculations to define the efficiency of an HPGe gamma-ray detector with 0.2% accuracy from 50 to 1400 keV. This work has been extended to 4.8 MeV with measurements of relative efficiencies from 24Na, 56Co, and 66Ga sources. The combined results of experiment and calculation yield an efficiency curve up to 3.5 MeV with 0.4% accuracy. Single- and double-escape peak contributions also agree with calculation if positron annihilation-in-flight is incorporated.

Precise test of internal-conversion theory: transitions measured in five nuclei spanning 50≤Z≤78.

In a research program aimed at testing calculated internal-conversion coefficients (ICCs), we have made precise measurements of αK values for transitions in five nuclei, (197)Pt, (193)Ir, (137)Ba, (134)Cs and (119)Sn, which span a wide range of A and Z values. In all cases, the results strongly favor calculations in which the final-state electron wave function has been computed using a potential that includes the atomic vacancy created by the internal-conversion process.

FT values measured to ±0.1% for superallowed beta transitions: metrology at sub-second time scales.

Because of angular-momentum conservation, superallowed ß decay between 0(+) analog states involves only the vector part of the weak interaction, so its measured ft value can be used to determine the vector coupling constant, G(V). If many such transitions are measured, then the constancy of G(V) can be established and several important tests made on fundamentals of the electroweak Standard Model. We have developed apparatus that allows us to measure half-lives to ±0.03% and branching ratios to ±0.1% or better, for cyclotron-produced activities with half-lives as short as 100 ms. We present an overview of the equipment and a summary of more than 10 years of results.