Calculation of Ambient (H*(10)) and Personal (Hp(10)) Dose Equivalent from a 252Cf Neutron Source
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
The neutron emission rate from radioisotope neutron sources such as 252Cf sources can be calibrated by the National Institute of Standards and Technology (NIST) by the manganous sulfite bath method. This calibration method does not compute the dose or dose equivalent rate from the source. Because there is no accepted transfer standard for neutron dose measurements, secondary calibration facilities are responsible for determining their own neutron dose factors. This report describes a neutron source and irradiation apparatus in use at the Pacific Northwest National Laboratory Calibration Facility. The neutron source is a SR-Cf-3000 design 252Cf neutron source. The neutron source is contained in an aluminum transfer capsule that is used to transport the neutron source between its storage location and it’s irradiation location. During irradiations, the source is located in a transfer tube assembly that consists of two concentric aluminum tubes. When moderated neutrons are desired, the transfer tube assembly is surrounded by a sphere that is filled with D2O as a moderating medium. Ambient dose equivalent (H*(10)) and Personal dose equivalent (Hp(10)) dose rates and dose conversion factors were calculated for moderated and unmoderated neutron spectra based on the data provided in ICRP Publication 74. The neutron fluence-to-dose-equivalent conversion factors calculated for this report are summarized and compared to published values in Table 47. The calculated coefficients for the unmoderated 252Cf spectra agree very well with published reference values, within about 2%. The calculated coefficients for the D2O moderated 252Cf spectra, however, differ from published reference values by about 22%. The PNNL coefficients are higher than the published values which could be interpreted to mean that the PNNL D2O moderated spectrum is harder, i.e. higher average energy, than the spectrum published by the ISO (2000), which formed the basis for the published coefficients. The D2O moderating sphere in use at PNNL contains less D2O moderator than did the D2O moderating sphere that was used to calculate the ISO spectrum and this is the likely reason for much of the spectral differences. The exact location of the 252Cf activity in the source encapsulation is unknown. Preliminary measurements, not described in this report, indicate that the activity may be offset from the location that has been assumed in the past. Corrections for the offset are being proposed and will be the subject of another report. This report was written in a calculation package format to help meet various Quality Assurance requirements.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1050151
- Report Number(s):
- PNNL--19273; HU1003000
- Country of Publication:
- United States
- Language:
- English
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