W.E. Burcham

The accurate determination of some (p, n) thresholds in the proton energy range 5 to 10 MeV

Abstract The thresholds for the reactions Al 27 (p, n)Si 27 , S 34 p, n)Cl 34 , Fe 54 (p, n)Co 54 and Ni 58 (p,n) Cu 58 have been measured with an accuracy of ±5 keV or better. The residual nucleus being in each case a position emitter with a half-life in the range 4 to 0.2 sec, it has been found convenient to measure the reaction yields by the activation method, positions being detected between short periods of proton irradiation. The proton energies at the thresholds were measured in terms of the accurately known energies of alpha particle from ThC and ThC′ sources, by comparison in a broad-range magnetic spectrograph. The values obtained for the (p, n) thresholds were 5802.9±3.8 keV in Al 27 ; 6451.1±4.5 keV in S 34 ; 9202.7±4.8 keV in Fe 54 ; 9512.9±5.0 keV in Ni 58 .

The elastic scattering of 33 MeV polarized 3He particles by beryllium and carbon

Abstract Angular distributions of 3 He polarization in elastic scattering from 9 Be and 12 C, and in inelastic scattering to the 4.44 MeV state of 12 C were measured using a 33 MeV polarized 3 He beam. The polarization and cross-section data were successfully analysed in terms of the standard optical model. Selectively of the 3 He elastic polarization for various potential sets was established in both optical model and coupled-channel analyses. While it is possible to determine unambiguously the geometry of the spin-orbit term, its strength is strongly correlated with other optical model parameters.

The ft value of the superallowed fermi beta decay 26mAl(β+)26Mg

Abstract The threshold for the reaction 26 Mg(p, n) 26m Al has been measured in terms of the accurately known energies of the α-particle groups from a ThC source. The result E th = 5208.5 ± 1.7 keV corresponds to a Q -value of −5013.5 ± 1.6 keV. The weighted mean of this and an earlier independent Q -value measurement gives for the end-point in the beta decay 26m Al( β + ) 26 Mg the result 3208.6±1.3 keV. The half-life for the beta decay has been measured as 6.346±0.005 sec. The ft value for the transition is thus found to be 3081±7 sec, including radiative corrections. This result is lower than those for other superallowed Fermi decays. It corresponds to a value for the vector coupling constant G β v = (1.4129±0.0016) x 10 −49 erg · cm 3 . The value inferred for the Cabibbo angle is cos θ β v = 0.985±0.001 , excluding uncertainties in the radiative corrections. This result appears to differ appreciably from the value inferred from the rate of K + → π 0 e + v decay.

The half-lives of Al26m, Cl34, Co54 and Cu58

Abstract The half-lives of Al26m, Cl34, Co54 and Cu58 have been measured with an accuracy of about 1 2 % . The activities were produced using (p,n) reactions on Mg26, S34, Fe54 and Ni58, respectively, at bombarding energies close to the reaction threshold. A beam chopping technique permitted a series of short irradiations of about one half-life interspersed with periods of several half-lives during which the activities were counted. The values of the half-lives obtained were 6.374±0.016 sec for Al26m, if1.565±0.007 sec for Cl34, 0.1937±0.0010 sec for Co54 and 3.204±0.007 sec for Cu58.

The beta end-point energy for the superallowed fermi decay 14O(β+) 14N

Abstract Accurate measurements of the threshold for the reaction 14 N(p,n) 14 O and of the energy of the first excited state of 14 N have provided a new value for the beta end-point energy in the Fermi decay of 14 O. The result is somewhat lower than the value currently used for ft calculations.

The half-life of 14O and the ft value of the superallowed Fermi decay

Abstract A series of experiments has been carried out to measure the half-life for 14 O decay, using different reactions and a variety of techniques, in two laboratories. Considerable care has been taken in the experiments, and in the data analyses, to reduce the possibility of systematic errors. The final result obtained is 70.588 ± 0.028 s, where the error is the statistical standard deviation (external error) of the weighted mean. This leads to an ft value for the 0 + → 0 + superallowed 14 O Fermi decay of 3050 ± 11 s, excluding electromagnetic radiative corrections; the corresponding “effective” ft value is 3090 ± 11 s, allowing for the first-order outer radiative correction. The error quoted for the ft value is determined very largely by the error in the f -value. This result for the 14 O Fermi decay is consistent with the ft values for the 26 mAl and 34 Cl decays.

Energy dependence of analysing power in elastic and inelastic scattering of 3He by 12C

Abstract Analysing powers for the elastic and 4.44 MeV state scattering of polarized 3He particles by 12C were measured between 20.5 and 33.0 MeV. The data show strong energy dependence of both magnitude and shape of the analysing power angular distribution. Main features of these variations can be explained by an energy-dependent optical-model potential with spin-orbit parameters similar to those established in previous studies. Phenomenological phase-shift analysis of the elastic scattering data provides no evidence for resonance effects in this energy region. Coupled-channels calculations assuming a rotational model and β2 = 0.30 can account for both elastic and inelastic data providing that the ratio of the spin-orbit and central deformation β s.o. β cent is energy dependent.

Superallowed Fermi decay of 14O and its relevance to weak interaction theory

Abstract A new measurement of the half-life for 14O decay has been made, giving the result 70.580 ± 0.035 s. This brings the ft value for the pure Fermi decay of 14O into agreement with the value for 26Alm, and gives support to the recent estimate of a lower limit to the mass of the intermediate vector boson.

A measurement of the half-life of the superallowed Fermi decay 46V(β+46Ti and a study of some systematic errors involved

Abstract The half-life for 46 V positon decay has been determined with high precision. Particular care has been taken to eliminate systematic effects introduced by inappropriate data analysis methods, by the presence of contaminant activities and by the occurrence of pulse pile-up in the electronic system. The final result obtained is 422.28 ± 0.23 ms, which is significantly lower than the presently accepted value.

The half-life for the superallowed fermi beta decay 50Mn(β+)50Cr

Abstract The half-life for the decay 50 Mn(β + ) 50 Cr has been measured to be 282.8 ± 0.3 ms. This result is ≈ 1% lower than the accepted value. It would bring the ft value for 50 Mn decay into agreement with recent measurements for other superallowed Fermi decays.