Add 'low dose radiation study' as study type

[kristenpeach]

Researchers use the threshold of <0.1 Gray to define "low dose" even though thats not an official (?) threshold according to Jack. Would be a valuable study type anyway. Probably as a child of external exposure study: http://purl.obolibrary.org/obo/RBO_00000091

https://science.osti.gov/ber/Research/bssd/Low-Dose-Radiation

[kristenpeach]

@svcostes mentioned this program is being resurrected. He may have some input on the definition.

[reality]

input needed on definition

[PaulNSchofield]

A study of the biological effects of low acute or protracted doses of ionising radiation defined as being below 500 mSv, less than 100mGy, or at dose rates less than 5mGy per hour. ( https://www.nationalacademies.org/our-work/developing-a-long-term-strategy-for-low-dose-radiation-research-in-the-united-states)

[DanBerrios]

Parent: radiobiology study type

Editor Note: These thresholds are based on the work described in https://www.nationalacademies.org/our-work/developing-a-long-term-strategy-for-low-dose-radiation-research-in-the-united-states