Reception device (1) for the separation of a mixture (2), especially blood, in a lighter phase (3) of lower density and a heavier phase (4) of higher density, with - a receiving container (5 ) having a first end (7) and a second end (8) located at a distance from each other in the direction of a longitudinal axis (6), where the first end (7) is open and the second end (8) it is closed with a bottom (9) and between the first end (7) and the second end (8) a side wall (10) with an inner surface (11) and an outer surface (12) extends, and in an area of transition (27) the inner surface (11) of the side wall (10) becomes a bottom surface (28) formed by the bottom (9) delimiting the side wall (10) and the bottom (9) a space of reception (13), - a separation element (14) which is arranged in the reception space (13) and is completely and continuously formed from an elastically deformable material, the density of the separation element (14) being located between those of the phases (3, 4) to be separated, - a removable closure unit (15) that closes the first open end (7) of the receiving container (5), - presenting the separating element (14) in its non-deformed starting form a three-dimensional shape made predominantly spherical, being arranged before filling the reception space (13) with the mixture (2) to be separated, in the area of the second end (8) closed with the bottom (9), and being in at least one contact plane (23) oriented perpendicularly with respect to the longitudinal axis (6) in contact with the inner surface (11) of the side wall (10), - an outer diameter (24) of the separation element (14) being in its non-deformed starting form greater than a cross-sectional dimension (25) of the receiving space (13) in the contact plane (23), mant the separation element (14) being positioned in a position of prestressed availability on the inner surface (11) of the side wall (10), - and a first partial section (29) of the inner surface (11) being made. , which is direc
