Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou , the masses of ^ { 82 } Zr and ^ { 84 } Nb were measured for the first time with an uncertainty of \sim 10 keV , and the masses of ^ { 79 } Y , ^ { 81 } Zr , and ^ { 83 } Nb were re-determined with a higher precision .
The latter are significantly less bound than their literature values .
Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart .
Our results do not support the predicted island of pronounced low \alpha separation energies for neutron-deficient Mo and Tc isotopes , making the formation of Zr-Nb cycle in the rp -process unlikely .
The new proton separation energy of ^ { 83 } Nb was determined to be 490 ( 400 ) keV smaller than that in the Atomic Mass Evaluation 2012 .
This partly removes the overproduction of the p -nucleus ^ { 84 } Sr relative to the neutron-deficient molybdenum isotopes in the previous \nu p -process simulations .