Iodine‑131 (i131) is a radioactive isotope that is used in the treatment of cancer of the thyroid. The natural tendency of the thyroid to take up iodine creates a pathway for which radiation (β − and γ) emitted from this unstable nucleus can be directed onto the cancerous tumor with very little collateral damage to surrounding healthy tissue. Another advantage of the isotope is its relatively short half‑life of 8 days. Calculate the binding energy b of iodine‑131. The mass of i131 is 130. 906124 u.