A corporate bond that pays 4% per annum semi-annually has a yield of 3% p.a. with continuous compounding and a remaining life of 1.5 years (immediate after coupon payment). The yield on a similar risk-free bond is 2% p.a. with continuous compounding. The risk-free rates are 1% p.a. with continuous compounding for all maturities. Assume that the unconditional probability of default per every six months is a constant and that defaults can happen at the end of every six months (immediate before coupon payment). The recovery rate is 40%. Estimate the unconditional probability of default using the more exact calculation.