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# birthRate

The number of particles spawned during each emission period. Animatable.

```
var birthRate: CGFloat { get set }
```

## Discussion

The system emits this number of particles at a constant rate through the duration of the period specified by the [`emissionDuration`](/documentation/SceneKit/SCNParticleSystem/emissionDuration) property. A value of zero prevents the system from emitting particles, unless you randomize the birth rate with the [`birthRateVariation`](/documentation/SceneKit/SCNParticleSystem/birthRateVariation) property.

The default value is `1`.

You can animate changes to this property’s value. See [Animating SceneKit Content](/documentation/SceneKit/animating-scenekit-content).

---

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