B1 in Materials, Astronomy & MRI

Updated 3 July 2026

B1 is a multifunctional designation used across disciplines, representing the NaCl-type crystal structure, star-forming regions in Perseus, and the RF transmit field in MRI.
In crystallography, B1 denotes the rock salt structure with defined lattice properties and pressure-induced phase transitions, while in astronomy it marks dense, dynamic regions including candidate first hydrostatic cores.
In magnetic resonance, B1 (or B1⁺) refers to the oscillating RF field critical for imaging sensitivity and uniformity, with engineering innovations boosting efficiency and safety.

B1 is a designation that occurs in several scientific contexts, notably as a structural label in crystallography and materials science, as a designation for specific astronomical regions and objects, and as an indicator for the transmit radiofrequency field (B1⁺) in magnetic resonance applications. Below, the article is organized into critical research domains in which "B1" plays a technically significant role, emphasizing the detailed physicochemical and observational properties established in published literature.

1. B1 Structure in Solid-State Physics and Materials Science

In crystallography, "B1" refers to the rock salt (NaCl-type) structure, characterized by a face-centered cubic (fcc) lattice with the formula unit MX (where M is a cation such as an alkali, alkaline earth, or lanthanide metal, and X is an anion such as O or F). Space group Fm $\bar{3}$ m, Wyckoff positions M at (0,0,0) and X at (½,½,½), yields octahedral (six-fold) coordination for each species. The B1 structure is the ground state for many monoxides at ambient pressure, including MgO and all LnO (lanthanide oxides, Ln = La–Lu) (Ferrari et al., 13 Apr 2026, Cuong et al., 2021).

Key crystallographic properties for LnO B1 phases (from GGA-DFT calculations):

Compound	$a_0$ (Å)	$V_0$ (Å³)	$B_0$ (GPa)	$B_0'$	$P_{\rm tr}$ (GPa, B1→B2)
LaO	5.1643	137.7	125.1	4.51	102.6
CeO	5.1312	135.1	128.0	4.68	162.6
...	...	...	...	...	...
LuO	4.6566	101.0	131.1	3.01	209.0

Thermodynamic stability is pressure-dependent: all LnO remain in the B1 structure at low pressures, but undergo a reconstructive phase transition to the B2 (CsCl-type) structure at pressures $P_{\rm tr}$ ranging from as low as 29 GPa (YbO) to over 200 GPa (LuO), with an associated volume collapse of 7–8% (Ferrari et al., 13 Apr 2026).

For MgO, high-pressure melting at the B1 phase has been quantitatively captured by models that relate the melting temperature $T_m(P)$ to the isothermal bulk modulus $K_T(P)$ through moment-recurrence quantum statistical mechanics combined with work–heat equivalence considerations. For B1–MgO, $T_m$ spans from 3214 K at ambient pressure to $a_0$ 010,000 K at 370 GPa, with bulk moduli $a_0$ 1 typically in the range 160 GPa and pressure derivatives $a_0$ 2 (Cuong et al., 2021).

2. The Perseus B1 and B1-E Regions in Star Formation Studies

The "B1" and "B1-E" nomenclature is widely used in star formation to label dense clumps and subregions in the Perseus molecular cloud. B1-E is a $a_0$ 3100 M $a_0$ 4, $a_0$ 5 K clump characterized by a ring-like distribution of compact substructures ( $a_0$ 60.3–2 M $a_0$ 7; $a_0$ 85000–9000 AU), most of which are gravitationally unbound with virial parameters $a_0$ 9 and turbulent non-thermal motions (Mach 1–3); only B1-E2 appears bound ( $V_0$ 0) (Sadavoy et al., 2011).

Key findings include:

Herschel continuum mapping (160–500 μm) reveals that structure on scales above the column threshold $V_0$ 1 cm $V_0$ 2 corresponds to the onset of “core formation.”
Spectroscopic surveys (NH $V_0$ 3, CCS, HC $V_0$ 4N) show supersonic linewidths and a spatial configuration of substructures with median separations $V_0$ 50.13 pc, smaller than the thermal Jeans length ( $V_0$ 6 pc), indicating local fragmentation post global collapse.
Optical polarization measurements indicate a strong, uniform magnetic field, inferred to regulate fragmentation and suppress active star formation relative to neighboring regions (Sadavoy et al., 2011).

Kinematic mapping with $V_0$ 7CO and C $V_0$ 8O lines displays a radial velocity gradient of $V_0$ 91 km s $B_0$ 0 pc $B_0$ 1 perpendicular to the main cloud gradient, while substructures display lower linewidths and are decoupled from the clump’s large-scale motions. The appearance of C $B_0$ 2O depletion is confined to the low-turbulence, near-transonic substructure (B1-E2), suggesting linkages between turbulence dissipation and grain-surface freeze-out chemistry in core evolution (Sadavoy et al., 2015).

3. B1-bS and B1-bN: Candidate First Hydrostatic Cores in Perseus

B1-bS and B1-bN are two dense condensations in the Perseus B1 region that exhibit spectral energy distributions (SEDs) inconsistent with simple, single-component greybody fits. Their SEDs are adequately reproduced only with a two-component model (compact warm center + cool envelope), with bolometric temperatures $B_0$ 3 of 18 K (B1-bS) and 14 K (B1-bN), substantial submillimeter luminosity fractions ( $B_0$ 4%), and no 24 μm emission, matching theoretical predictions for first hydrostatic cores (FHSCs). Their projected separation is $B_0$ 54700 AU ( $B_0$ 62 Jeans lengths), providing an opportunity to study interactions between proto-fragments at an extremely early evolutionary phase (Pezzuto et al., 2012).

4. B1 in Astrophysical Shock Chemistry: The L1157-B1 Proto-shock Laboratory

The B1 region in the L1157 outflow is a prototypical laboratory for molecular shock chemistry and the interplay of grain-surface and gas-phase reactions. High spatial resolution imaging, spectral-line surveys (CS, CH $B_0$ 7OH, HC $B_0$ 8N, H $B_0$ 9CO), and chemical modeling reveal:

Morphology: arch-shaped cavity walls and compact high-velocity “bullets” (sizes $B_0'$ 0750–1500 AU).
Kinematics: cavity-averaged gas at $B_0'$ 1 cm $B_0'$ 2, bullets at $B_0'$ 3– $B_0'$ 4 cm $B_0'$ 5; velocities from systemic +2.6 km s $B_0'$ 6 to $B_0'$ 716 km s $B_0'$ 8 (Benedettini et al., 2013).
Shock models: C-type shocks ( $B_0'$ 9 km s $P_{\rm tr}$ 0, $P_{\rm tr}$ 1 cm $P_{\rm tr}$ 2, $P_{\rm tr}$ 3 K) reproduce observed molecular abundances, line profiles, and the rapid transition from mantle-release to high-temperature gas-phase chemistry (Viti et al., 2011, Benedettini et al., 2013, Busquet et al., 2017, Mendoza et al., 2018).
Astrochemistry: Deuterated species (DCN), cyanopolyynes (HC $P_{\rm tr}$ 4N, HC $P_{\rm tr}$ 5N), and their spatial distributions provide diagnostics of the interplay between grain mantle sputtering and warm gas-phase reactions, validating models that require both a high peak shock temperature (for HC $P_{\rm tr}$ 6N and DCN in post-shock gas) and a transient mantle release (for enhanced DCN in jet-impacted zones) (Busquet et al., 2017, Mendoza et al., 2018).

5. B1 as the RF Magnetic Field in Magnetic Resonance

In MR physics, "B1" (and B1⁺, the transmit component) denotes the oscillating magnetic field generated by the RF coil for excitation or spatial encoding of nuclear spins. Technical advancements in B1⁺ engineering have a direct impact on sensitivity, homogeneity, and safety in advanced MRI and MRS protocols:

Dual-tuned multimodal surface coils, constructed from concentric stacks of coupled loops (e.g., three for $P_{\rm tr}$ 7H and three for $P_{\rm tr}$ 8P), utilize eigenmode selection principles to enhance B1⁺ efficiency. In such designs, the lowest-frequency in-phase eigenmodes reinforce the central field, yielding $P_{\rm tr}$ 9 (for $P_{\rm tr}$ 0P) and $P_{\rm tr}$ 1 (for $P_{\rm tr}$ 2H) B1⁺ gains over single-tuned reference coils of the same size, with negligible SAR penalty ( $P_{\rm tr}$ 3) and strong inter-nuclear decoupling (>20 dB isolation) (Zhao et al., 31 Dec 2025).
In multinuclear and high-field applications, such as 7 T $P_{\rm tr}$ 4H/ $P_{\rm tr}$ 5P MRSI, B1⁺ inhomogeneity and RF losses limit sensitivity for "X-nuclei." Engineering solutions based on coupling matrices and eigenmode decomposition circumvent the efficiency penalties common in standard dual-tuned platforms.
Parallel transmit (pTx) and high-permittivity material (HPM) approaches further enable B1⁺ homogenization. For example, conformal barium-titanate HPM shells at 7 T act as dielectric potential wells, flattening B1⁺ distribution and reducing slice-by-slice coefficient of variation (CV) by 54% and peak SAR by 42% (Hwang et al., 2019). Multi-channel mapping and phase-only shims optimized from large-dynamic-range B1⁺ maps boost target ROI B1⁺ by 37–42% with concomitant improvements in homogeneity and SAR efficiency (Buck et al., 2022).
Dedicated B1⁺ mapping methods using optimized pulse sequences (e.g., adiabatic Bloch-Siegert, multi-angle TSE for metal environments, joint T1/B1⁺ estimation in cardiac mapping) are indispensable for robust quantitative imaging and sequence calibration in challenging conditions (Khodarahmi et al., 10 Jan 2025, Khalighi et al., 2024, Han et al., 2021, Helms et al., 2021).

"B1" labels have also been applied to a broad spectrum of astrophysical phenomena:

In cometary science, C/2014 B1 (Schwartz) is a long-period comet exhibiting a stable, discus-shaped dust coma due to equatorial ejection of $P_{\rm tr}$ 6 mm grains, a morphology possible only when ejection velocities ( $P_{\rm tr}$ 71–10 m s $P_{\rm tr}$ 8) are comparable to nucleus escape velocities and dominated by gravitational, not radiation pressure, dynamics (Jewitt et al., 2019).
In galactic center studies, "Sgr B1" refers to an evolved H II region in the central molecular zone whose ionization structure, mapped via SOFIA [O III] 52/88 μm, shows excitation by late-O stars augmented with fast-shock X-rays; SED fitting constrains electron densities to $P_{\rm tr}$ 9– $T_m(P)$ 0 cm $T_m(P)$ 1 (Simpson et al., 2018).

7. Conclusion

"B1" is a multifaceted symbol whose meaning is sharply context-dependent but invariably denotes a critical structural, field, or regional property in both physical and observational sciences. Its precise technical definition—as a crystallographic ground state (NaCl-type), a key protostellar region (Perseus B1 and subregions), an RF magnetic field essential for MR, or a label for unique cometary morphology—anchors it as a keystone in contemporary research, methodologies, and instrument design across disciplines (Zhao et al., 31 Dec 2025, Ferrari et al., 13 Apr 2026, Cuong et al., 2021, Sadavoy et al., 2011, Pezzuto et al., 2012, Benedettini et al., 2013, Busquet et al., 2017, Mendoza et al., 2018, Hwang et al., 2019, Jewitt et al., 2019, Simpson et al., 2018).