Semen cryopreservation or sperm banking is the process of preserving sperm cells. The preserved sperm can be used indefinitely after the process. Semen samples are slowly frozen in liquid nitrogen vapours. Once the samples have been frozen, they are placed in special containers where they are stored in the liquid nitrogen until they are needed. It can be used for sperm donation where the recipient wants the treatment in a different time or place, or as a means of preserving fertility for men undergoing vasectomy or treatments that may compromise their fertility, such as chemotherapy, radiation therapy or surgery.