Small-Order Effects in Beta Spectra

Abstract

An intermediate-image spectrometer and a thin-lens spectrometer were used to examine carefully the beta spectra of P 32 , K 42 , and As 76 . The P 32 beta spectrum was examined for a Fierz-type deviation, and within the experimental error none was found. The value of the parameter r, describing the magnitude of the Fierz deviation as defined by Davidson and Peaslee, was found to be 0.00±0.03. The first forbidden transitions with A/ = 0, "yes" of K 42 and As 76 were examined for deviations from a linear Kurie plot. Within experimental error no deviations were found. From the shape factors calculated by Mahmoud and Konopinski on the basis of an STP combination, one would expect deviations for these first-forbidden transitions if the best previous estimate of certain parameters are correct. A deviation of the K 42 Kurie plot below 500 kev was attributed to an additional beta group.

Branching Ratio in the Decay of K42

“…The beta spectrum with endpoint energy of 1.985 MeV is known to have an allowed shape (7,9). A possible small deviation is of no importance in this work; a Kurie plot with the assumption that the spectrum has an allowed shape is shown in Fig.…”

“…The beta disintegration with endpoint energy of 3.545 MeV is known to be first order unique forbidden (7,9) (1'::] = 2, yes). It is necessary to apply the shape factor C/2) (the notation of MAHMOUD and KONOPINSKI) to obtain Fig.…”

Branching Ratio in the Decay of K42

“…The beta disintegration with endpoint energy of 3.545 MeV is known to be first order unique forbidden (7,9) (A J = 2, yes). I t is necessary to apply the shape factor Cl(Z) (the notation of MAHMOUD and KONOPINSKI) to obtain BORJE PERSSON Pulse height distribution in the anthracene detector, not corrected for photon contribution, a t low energies where this distribution is not identical with the experimentally determined beta spectrum.…”

“…Beta spectra from other disintegration modes, e. g. corresponding to endpoint energies of 0.5 and 1.7 MeV, cannot be identified in the diagram. The amount to which they contribute is uncertain but has been reported to be about 0.2 per cent (9).…”

Small order shape factors in beta spectra

“…It is almost constant for low Z isotopes, decreasing by 0.7$ for P 32 over the energy range from 250 to 1600 kev. P 32 and Y 9 ® were examined by Pohm, et al (25), in a thin-lens spectrometer and in an Intermediate-image spectrom-90 eter. The Y shape-factor plots obtained from both instru-•zp ments gave no indication of deviation from theory.…”