β-delayed proton emission means, a positron emitted firstly, then proton emit. so, a proton converted to a neutron and a positron, then a proton emit. as a result, the mass number reduced by 1 from lost 2 proton and gain 1 neutron. therefore, this process should be only happened in neutron-deficient nuclei.
Chromium-43 has atomic number 24, the neutron number is 19.
it was reported that a first time observation of β-delayed 3 proton decay in 45Fe. and the same decay was discovered in 43Cr in this paper. both process was recorded by an Imaging Time Projection Chamber.
the feature of this chamber is, it can capture the photos for decay process. in the paper, they shows a clear picture of 3-protons decay. and also, the measurement is very accurate. they can found 12 events of 3 protons decay among the total 12524 events of proton decay, which is about 1044 to 1. base on this precision, they deduced the relative branching ratio to be 91.8% for 1-proton case, 8.1% for 2 protons case, and 0.096% of 3 protons case.
by the chamber, they also recorded non-proton decay events, which may come from non-decay or β-deacy. the energy of β-decay is too small to detected.
However, they use the Maximum likelihood method to deduce the decay probability of β-decay. they found that it was 12%. since 2 β-decay has not been observed or either not possible, they deduced the absolute branching ratio.
a discussion on the extreme small branching ration of 3-protons decay was presented at the end of paper.