Neutron Spectra, Fluence and Dose Rates from Bare and Moderated Cf-252 Sources

Radev, Radoslav

doi:10.2172/1252630

Cited by 3 publications

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The moderated spectrum ensures greater activation of most nuclides, which typically have larger thermal absorption cross sections. The spectrum shown in Figure 9 compares very favorably to recently reported measurements of a 252 Cf source shielded by various materials, including polyethylene [40]. Figure 9: Calculated neutron spectrum within the sample chamber with and without the pure and borated polyethylene present.…”

Section: Mcnp Modeling Of the Irradiatorsupporting

confidence: 77%

Design, Construction, and Modeling of a²⁵²Cf Neutron Irradiator

Anderson

Holbert

Bowler

2016

Science and Technology of Nuclear Installations

View full text Add to dashboard Cite

Neutron production methods are an integral part of research and analysis for an array of applications. This paper examines methods of neutron production, and the advantages of constructing a radioisotopic neutron irradiator assembly using252Cf. Characteristic neutron behavior and cost-benefit comparative analysis between alternative modes of neutron production are also examined. The irradiator is described from initial conception to the finished design. MCNP modeling shows a total neutron flux of 3 × 105 n/(cm2·s) in the irradiation chamber for a 25 μg source. Measurements of the gamma-ray and neutron dose rates near the external surface of the irradiator assembly are 120 μGy/h and 30 μSv/h, respectively, during irradiation. At completion of the project, total material, and labor costs remained below $50,000.

show abstract

Section: Mcnp Modeling Of the Irradiatorsupporting

confidence: 77%

Design, Construction, and Modeling of a²⁵²Cf Neutron Irradiator

Anderson

Holbert

Bowler

2016

Science and Technology of Nuclear Installations

View full text Add to dashboard Cite

show abstract

“…The facility values for 60 Co, 137 Cs, and 252 Cf in Table 2 are based on benchmark dose measurements for these sources and distances provided by RCL personnel and decayed to 4 December 2019. For 252 Cf, separate neutron and gamma-ray contributions to the dose rate were also provided by RCL personnel (Radev 2016) and decayed to 4 December 2019. Comparisons between the BPD results and the facility standard results show good agreement for the gamma-ray sources.…”

Section: Dosimetry Resultsmentioning

confidence: 99%

Testing the NASA BioSentinel Pixel Dosimeter Using Gamma-ray and Neutron Sources at the LLNL Calibration Lab

et al. 2022

View full text Add to dashboard Cite

The objective of this paper is to evaluate the accuracy of the NASA BioSentinel Pixel Dosimeter (BPD) using gamma-ray and neutron sources in a standard calibration lab. The dosimeter tested here is the ground-based version of the BPD that will be onboard the BioSentinel mission. The BPD was exposed to radiation from 60 Co, 137 Cs, and 252 Cf at selected distances (dose rates) at the Lawrence Livermore National Laboratory (LLNL) Radiation Calibration Laboratory (RCL), and the results were compared with NIST traceable benchmark values. It is recognized that these sources are not analogs for the space environment but do provide direct comparisons between BPD response and well characterized calibration lab values. For gamma rays, the BPD measured absorbed dose agrees to ≤ 3.8% compared with RCL benchmark values. For neutrons, the results show that the BPD is insensitive, i.e., the BPD detected only the gamma-ray dose component from 252 Cf. The LET spectra obtained for gamma rays from 60 Co and 252 Cf are consistent with expectations for these gamma-ray energies, but the LET spectrum from the 137 Cs gamma rays differs substantially. The potential causes for this difference are the high dose rate from 137 Cs and the lower secondary electron energy produced by 137 Cs gamma rays. However, neither of these results in errors in the absorbed dose. Based on comparisons with NIST-traceable standards, it is evident that the BPD can measure absorbed dose accurately from low LET charged particles. The sensor's insensitivity to neutrons is unlikely to be a limitation for the BioSentinel mission due to the expected low secondary neutron fluence.

show abstract

“…It is considered as an epithermal–fast neutron emitter with the most probable neutron energy in the range of 1–5 MeV, whereas thermal neutrons have a kinetic energy around 2.5 × 10 –8 MeV, i.e., 8 orders of magnitude lower. Moreover, several studies , have shown that even with the use of moderators, the neutron spectrum of 252 Cf can have a significant epithermal and fast flux component, as demonstrated by three D 2 O moderated spectra on Figure b. Thus, using only moderation is not sufficient to estimate the thermal neutron detection efficiency.…”

mentioning

confidence: 98%