New measurement of the beta decay rate of the16N(0?)-16O(0+) transition

Abstract

The beta decay rate of the ~6N(0-;120keV)-,~oo(0+,G.S.) transition has been remeasured. Our result (A~=0.48+0.024s-1) is in excellent agreement with a previous measurement but strongly disagrees with another experimental value. The two agreeing results provide an experimental verification of the importance of meson exchange currents in 0 + -0-weak transitions. A value of gp/ga~ll-12 can be inferred from the corresponding A, rate. PACS : 23.40. HcThe fl-decay rate Ap of the 0-(120 keV, ta/2 = 5.25/is) level of 16N to the ground state of 160, and the inverse muon capture rate A,, have generate d considerable interest [1][2][3][4][5][6][7][8][9][10], following a suggestion [1] that the AJAp ratio was essentially nuclear structure independent. It was thought possible to extract from this ratio the induced pseudoscalar coupling constant g/gA" Later calculations [3][4][5][6] have shown that mesonic exchange currents (MEC's) account for about 75 ~ of the fl-decay rate and 35 % of the muon-capture rate. These transitions can therefore be considered an ideal case for testing our understanding of MEC's. Several measurements of A~ have been reported [7][8][9][10]. Gagliardi and Garvey [8] confirmed with much better statistics (,--5 %) the experiment of Palffy etal. [7], using the same experimental technique. Our group had reported a value of A s [9], in agreement with those of [7] and [8] with a different setup. Since then, another value has been published [10], obtained with a method similar to ours, but differing by 35 % from the previous measurements. We report here our final measurement of the 0---+0 + decay. The principle of the measurement is the following:

Radiative muon capture on carbon, oxygen, and calcium

“…For the purposes of comparison, the value of g p /g a extracted using this procedure is also given in Table 5.7. The much larger error on g p /g a than those determined using the other It is suggestive, however, that the value of g p /g a found using the MIA theory of Gmitro et al [73] is consistent with the values of g p /g a (~ 11 -12) determined from OMC and /9-decay measurements in 16 0 [131,132,46]. It is perhaps relevant that the explicit effects of meson-exchange corrections have been included (to some degree) in both the MIA calculations and the calculations used to extract g p /g a from the OMC and /9-decay data.…”

“…J> 12 C 5) )) [43] [44] [38] 9.4 ± 1.7 7.2 ± 1.7 9.1 ± l.S Guichon et al [45]; Hamel et al [46] 16Q [47] 11-12 Miller et al [48] 28 SI V -7 [35,36] [ 49] 12.9 ± 3.9 -1.9 ± 3.1 possible renormalization effects.…”

Measurement of the beta spectrum of the 0? (120 keV) state of16N

“…Indeed, the populations No of the 0-first excited level and N2 of the 2-ground state evolve in the following manner [4,7] :…”

“…Thus the beta spectrum evolution can be followed and various time components can be extracted. As described elsewhere [4,5], the photomultipliers had to be pulsed during irradiation to ensure a rapid gain recovery after irradiation. Nevertheless, the gain did not recover immediately after irradiation and we decided to monitor the time evolution of the gain with a second parallel biparametric system, using a fast (5 ns) pulsed LED illuminating the photocathode of the E-counter.…”

“…The spectrum was measured with a plastic scintillator telescope consisting of an E detector preceded by two thin AE detectors. More detailed informations on the experimental arrangement can be found in [4] and [-5].…”