If your husband qualifies for a full pension then your survivors pension will be 50% of his Occupational Pension (which is not 50% of his pensionable salary).
Let's say John qualifies for a "full" pension on a salary of €100,000 pa. His Occupational Pension would be €36,200 (if he is over 66 his State Pension would currently be €13,800). His wife's Survivor's Pension would be 50% of €36,200. She should also be eligible for a Social Welfare Benefit (Widow's Pension based on her own or her spouses's PRSI record, or State Contributory Pension on her own record).
This relates to a full pension.
If your husband were to qualify for less than a full pension the calculation is somewhat different but the same principle applies.